Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation

IL-21R-Targeted Nano-immunosuppressant Prevents Acute Rejection in Allogeneic Transplantation by Blocking Maturation of T Follicular Helper Cells

During organ transplantation, immune rejection is a primary cause of graft failure. In the underlying pathophysiology of rejection, T follicular helper (Tfh) cells and interleukin-21 (IL-21) play pivotal roles. Tfh cells exacerbate the humoral immune response by promoting B cell differentiation and antibody production, which leads to damage of the transplanted tissue. IL-21, a key pro-inflammatory cytokine, binds to its receptor (IL-21R) to enhance both the growth and function of Tfh cells, while also further driving B cell activation and differentiation into plasma cells. Building on this knowledge, we have developed a tacrolimus-based nano-inhibitor designed to target Tfh cells. This nano-inhibitor is constructed using a mPEG-PLGA-PLL (PEAL) scaffold, with IL-21R monoclonal antibodies conjugated to its surface, and tacrolimus encapsulated within the structure. In vitro experiments demonstrated that this nano-inhibitor effectively targets Tfh cells, inhibiting the differentiation of naive CD4+ T cells into Tfh cells. In co-culture systems of T and B cells, it significantly suppresses the activation of both cell types, leading to a reduction in IgG antibody production. In vivo, the nano-inhibitor selectively targets secondary lymphoid organs, reduces systemic inflammation, minimizes lymphocyte infiltration into the graft, and induces immune tolerance toward the transplanted tissue. In addition, no significant toxicity was observed in vitro or in vivo. As a therapeutic agent that simultaneously modulates both T and B cell responses, we believe it holds significant promise for broader applications in transplantation immunotherapy. STATEMENT OF SIGNIFICANCE: This study presents a groundbreaking nano-immunosuppressant designed to target both T and B cells, addressing the critical challenge of acute rejection in allogeneic transplantation. By combining tacrolimus nanoparticles with IL-21 receptor antibodies, this immunosuppressant effectively suppresses Tfh cell proliferation and B cell activation, significantly reducing IgG generation. The formulation enhances tacrolimus's bioavailability, minimizes off-target toxicity, and overcomes its narrow therapeutic window. In vitro and in vivo studies show reduced lymphocyte infiltration, lower inflammatory markers, and decreased nephrotoxicity compared to conventional tacrolimus.

Exploring the comprehensive factors influencing tacrolimus pharmacokinetics in early renal transplant recipients: A population pharmacokinetic analysis

PURPOSE

To establish a population pharmacokinetic (PopPK) model of tacrolimus in the early stages after renal transplantation and evaluate the model's predictive performance with external data.

METHODS

Intravenous and oral tacrolimus were administered to 302 renal transplant recipients in the early posttransplantation stages. Related data were obtained from the electronic medical records. Single nucleotide polymorphisms in genes associated with tacrolimus pharmacokinetics were tested. The data were analyzed by NONMEM. The external data from 153 patients were subsequently used to evaluate model extrapolation.

RESULTS

A one-compartment model was used to determine tacrolimus pharmacokinetics. The estimated clearance (CL), volume of distribution (V) and bioavailability (F) of tacrolimus were 4.91 L/h, 77 L and 26.5%, respectively. CL and V decreased with increasing hematocrit. CL and F decreased with increasing operation time. Diltiazem and Wuzhi capsule resulted in 28.4% and 43.9% decreases in the CL, respectively. Omeprazole or esomeprazole resulted in a 9% increase in F. The value of F for patients expressing CYP3A5 was 36.6% lower than that for the patients who did not express CYP3A5. The evaluation of external data revealed that the proportion of individual prediction error within 20% of the observed tacrolimus concentration was greater than 77.3%.

CONCLUSIONS

A PopPK model for tacrolimus was established for early renal transplantation. CYP3A5 was a significant covariate for F. Fat-free mass was the best predictor of the influence of body size on CL and V. The model could be extrapolated to stable renal transplant recipients.

An immunomodulatory encapsulation system to deliver human iPSC-derived dopaminergic neuron progenitors for Parkinson's disease treatment

Parkinson's disease is a neurodegenerative condition associated with the progressive loss of dopaminergic neurons. This leads to neurological impairments with heightening severity and is globally increasing in prevalence due to population ageing. Cell transplantation has demonstrated significant promise in altering the disease course in the clinic, and stem cell-derived grafts are being investigated. Current clinical protocols involve systemic immunosuppression to prevent graft rejection, which could potentially be avoided by encapsulating the therapeutic cells in a locally immunosuppressive biomaterial matrix before delivery. Here we report the progression of an immunomodulatory encapsulation system employing ultrapure alginate hydrogel beads alongside tacrolimus-loaded microparticles in the encapsulation of dopaminergic neuron progenitors derived from human induced pluripotent stem cells (hiPSCs). The hiPSC-derived progenitors were characterised and displayed robust viability after encapsulation within alginate beads, producing dopamine as they matured in vitro. The encapsulation system effectively reduced T cell activation (3-fold) and protected progenitors from cytotoxicity in vitro. The alginate bead diameter was optimised using microfluidics to yield spherical and monodisperse hydrogels with a median size of 215.6 ± 0.5 μm, suitable for delivery to the brain through a surgical cannula. This technology has the potential to advance cell transplantation by locally protecting grafts from the host immune system.

Model-Informed Dosing Optimization of Tacrolimus for Concomitant Administration With Itraconazole to Japanese Lung Transplant Recipients

BACKGROUND

Tacrolimus is an immunosuppressant administered to patients undergoing lung transplantation. Itraconazole is often concomitantly used with tacrolimus to prevent fungal infections and increase tacrolimus concentration. However, the pharmacokinetics of tacrolimus in Japanese lung transplant recipients and the effect of itraconazole on its pharmacokinetics have not been adequately evaluated. Population pharmacokinetic analysis was conducted to develop an optimal dose adjustment method for use upon itraconazole initiation in Japanese lung transplant recipients.

METHODS

This study comprised Japanese lung transplant recipients whose blood tacrolimus and itraconazole concentrations were measured between January 2017 and December 2019. A nonlinear mixed-effects modeling program was used to explore the covariates of tacrolimus pharmacokinetics and effects of concomitant itraconazole use. Using the model, the optimal initial tacrolimus dose was calculated and a dose adjustment method comprising concomitant itraconazole use was developed.

RESULTS

A total of 1693 tacrolimus trough blood concentrations and 85 itraconazole trough plasma concentrations were obtained from 43 patients. Postoperative day, albumin level, and administration route were extracted as covariates for tacrolimus pharmacokinetics. The drug-drug interaction between tacrolimus and itraconazole could be predicted more accurately by considering the concentration-dependent inhibition of itraconazole. The optimal initial tacrolimus dose was 2.0 mg twice daily for tube and 1.5 mg twice daily for oral administration. To maintain the target concentration, the tacrolimus dose was reduced by 60% upon itraconazole initiation.

CONCLUSIONS

This study is the first to use population pharmacokinetic analysis to assess the interaction between tacrolimus and itraconazole in patients who underwent lung transplantation. These results provide useful insights for optimizing the initial tacrolimus dose for concomitant itraconazole use.

Tacrolimus and diabetic rodent models

Tacrolimus (TAC) is an immunosuppressant widely utilized in organ transplantation. One of its primary adverse effects is glucose metabolism disorder, which significantly increases the risk of diabetes. Investigating the molecular mechanisms underlying TAC-induced diabetes is essential for developing effective prevention and treatment strategies for these adverse effects. In addition, TAC can induce cost-effective, non-obese animal models of diabetes, where the metabolic parameter changes closely resemble those observed during the onset and progression of type 2 diabetes (T2DM), post-transplantation diabetes mellitus (PTDM), and associated complications. This review, based on articles indexed in PubMed up to August 19, 2024, identified 48 studies focusing on TAC-induced diabetic rodent models and 22 studies exploring the effects of TAC on diabetic or obese rodent models. These studies were systematically summarized based on TAC dosage, route of administration, duration of administration, and glucose metabolism indices used for evaluation. Additionally, the impact of TAC dose reduction or discontinuation on glucose metabolism was assessed, along with pharmacological agents that modulate TAC-induced diabetes, including anti-diabetic medications, anti-inflammatory and antioxidant compounds, biologics, and antibiotics. Key signaling pathways implicated in TAC-induced diabetes include CaN/NFAT, PI3K/AKT/mTOR, and TGF-β/Smad, all of which impair islet β-cell function, thereby contributing to diabetes development. This review provides a concise summary of the characteristics of relevant murine models, offering valuable guidance for selecting appropriate and economical animal models for future research.

Intrapatient tacrolimus variability is associated with medical nonadherence among pediatric kidney transplant recipients

Background

Long-term survival of kidney allografts is limited by multiple factors, including nonadherence. High intrapatient variability in tacrolimus levels (≥30%) is associated with de novo donor-specific antibody (dnDSA) formation, increased risk of rejection and graft loss.

Methods

We prospectively analyzed the association between tacrolimus intrapatient variability and nonadherence in pediatric kidney transplant recipients. We derived a composite adherence score from 0 to 3 points based on (1) Basel Assessment of Adherence to Immunosuppressive Medical Scale©; (2) healthcare team score; and (3) intentionally missed laboratory or clinic visits. A score of 1 or more was considered nonadherent. Tacrolimus 12 h trough levels, patient characteristics and clinical outcomes were collected. Tacrolimus IPV was calculated as the coefficient of variation.

Results

The nonadherent group had a significantly higher median tacrolimus intrapatient variability (31%) as compared to the adherent cohort (20%) (p < 0.001.) Tac IPV demonstrated strong predictive performance for adherence (AUC 0.772), with a particularly high sensitivity of 90% at thresholds up to 20%, offering a practical and actionable framework for assessing adherence-related risks in clinical practice.

Conclusions

Tacrolimus intrapatient variability may be a useful biomarker to identify nonadherence and high-risk patients, allowing for early interventions to prevent adverse graft outcomes.

Effect of isavuconazole on the concentration of tacrolimus in a patient with genotype CYP3A5*1/*3: a case report

BACKGROUND

Azole antifungals are the standard treatment for pulmonary mycosis, which may develop during long-term immunotherapy for kidney transplant. Isavuconazole (ISCZ) is a cytochrome P450 (CYP) 3 A inhibitor that has a risk of interacting with the immunosuppressive drug tacrolimus (TAC). We report a case of simple pulmonary aspergilloma with renal dysfunction due to increased trough levels of TAC after ISCZ coadministration.

CASE PRESENTATION

A male in his 60s was treated with TAC 3.0 mg/day orally to prevent graft rejection after kidney transplantation. He received a loading dose of ISCZ 600 mg/day orally for two days, followed by a maintenance dose of 200 mg/day for simple pulmonary aspergilloma. The TAC trough concentration increased markedly from 2.4 to 9.9 ng/mL on day 6 after coadministration. The creatinine level increased from 0.70 to 1.08 mg/dL, suggesting renal dysfunction due to TAC. Subsequently, the TAC dosage was reduced, leading to a decreased blood TAC concentration and improved renal function. The patient's genotype was CYP3A5*1/*3.

CONCLUSIONS

In the early stages of ISCZ treatment, the blood TAC concentration is higher, and CYP3A5 polymorphisms may partially explain the extent of this interaction. We recommend more careful monitoring of TAC and serum creatinine levels for approximately one week after ISCZ administration.

Sublingual Administration of Tacrolimus is Safe and Provides Similar Drug Exposure to Per-oral Route in Liver Transplant Recipients During Early Postoperative Period-A Large, Retrospective, Observational Study

Background/Aims

Per-oral (PO) administration of tacrolimus (TAC) results in inadequate trough levels in the early postoperative period in liver-transplant (LT) recipients who undergo Roux-en-Y hepaticojejunostomy for biliary reconstruction. Sublingual administration (SL) of tacrolimus provides an alternative route in such patients.The objectives of this study were to assess the feasibility and safety of SL tacrolimus in adult LT-recipients in the early postoperative period and to compare therapeutic efficacy of SL administration of tacrolimus versus PO route.

Methods

single-center, retrospective, observational study carried out in adult living donor liver transplant (LDLT) recipients between January 2022 and December 2022. Recipients who underwent Roux-en-Y hepaticojejunostomy for biliary reconstruction received tacrolimus through the SL route till postoperative day (POD) 5 as they were kept nil per oral constituted the study group while recipients who underwent duct-to-duct (D-D) anastomosis for biliary reconstruction were allowed orally from POD1 and received PO-tacrolimus were chosen as controls. The feasibility and safety of SL-tacrolimus were assessed in terms of patient acceptance, need to discontinue SL-tacrolimus, incidence of local adverse effects, and systemic adverse events like neurotoxicity and nephrotoxicity. Therapeutic efficacy was evaluated by comparing median trough levels (TAC level) achieved and incidence of graft rejection between two groups.

Results

Two hundred twelve patients underwent LT during the study period, of which 125 were included (58 in the SL-group and 67 in PO-group). Both groups had comparable baseline characteristics. In the SL-group, all patients tolerated SL-Tacrolimus well and no local adverse events were observed. Patients with SL-Tacrolimus administration achieved a higher median TAC level (ng/ml) vs. PO route (5.85 vs. 5 (P = 0.06)) despite receiving similar median cumulative tacrolimus dose before assessing TAC-level. Fifty percent of patients achieved TAC level ≥6 ng/ml in SL-group vs. 35.8% in PO-group (P = 0.14). The incidence of neurotoxicity, nephrotoxicity, and graft rejection during hospital stay were similar in both the groups (P = 0.56, 0.82, and 0.28, respectively).

Conclusion

SL-tacrolimus is safe and provides similar trough levels to PO-tacrolimus and may be considered as a viable alternative whenever inadequate TAC levels are anticipated through the per-oral route.

FK506 Enhancement of Neuromuscular Junction Recovery After Nerve Injury Is Macrophage-Dependent

INTRODUCTION

Motor recovery following nerve injury is dependent on time required for muscle reinnervation. This process is imperfect, however, and recovery is often incomplete. At the neuromuscular junction (NMJ), macrophage signaling aids muscle reinnervation. Tacrolimus (FK506) treatment speeds functional recovery through unknown mechanisms. This study investigated whether macrophages were required for FK506 neuroenhancing effects.

METHODS

Wildtype (WT) mice and mice with impaired macrophage recruitment to injury sites (Ccr2 -/- ) were injected subcutaneously with either saline or FK506 for 3 days prior to sciatic nerve transection and immediate repair and then daily for 4 weeks. Functional recovery was assessed by grid walk and muscle force. Morphometric NMJ and macrophage analyses were conducted in extensor digitorum longus muscles.

RESULTS

FK506-injected WT mice showed increased proportions of fully reinnervated NMJs and terminal Schwann cells/NMJ (p < 0.05), improved recovery of tetanic muscle force (p < 0.05), and improved grid walking (p < 0.05) relative to controls. Ccr2 -/- mice showed no enhancements in recovery; Ccr2 -/- mice treated with FK506 did not differ from controls on any tested metric. We also observed at the NMJ of WT mice increased macrophage numbers with FK506 treatment and increased macrophages expressing FK506 binding protein, FKBP52, after nerve injury.

DISCUSSION

These results show that macrophages are required for FK506-mediated improvements in NMJ reinnervation and muscle function. These data implicate macrophages in the mechanism underlying FK506-mediated enhancement of motor recovery after nerve injury. Enhanced knowledge of the neuroenhancing mechanism of FK506 may identify new clinically relevant therapeutic targets.

Evaluation of Effective Half-Life and Its Impact on Time to Steady State for Oral MeltDose Tacrolimus (LCPT) in De Novo Kidney Transplant Recipients

BACKGROUND

For extended-release drug formulations, effective half-life (t 1/2eff ) is a relevant pharmacokinetic parameter to inform dosing strategies and time to reach steady state. Tacrolimus, an immunosuppressant commonly used for the prophylaxis of organ rejection in transplant patients, is available as both immediate- and extended-release formulations. To the best of our knowledge, the t 1/2eff of tacrolimus from these different formulations has not yet been assessed. The objective of this study was to characterize the t 1/2eff and terminal half-life (t 1/2z ) of an extended-release once-daily tacrolimus formulation (LCPT) and twice-daily immediate-release tacrolimus (IR-Tac).

METHODS

A noncompartmental analysis of pharmacokinetic data obtained from a phase 2 study in de novo kidney transplant recipients receiving either LCPT or IR-Tac was conducted. Intensive blood sampling was performed on days 1, 7, and 14, and tacrolimus whole blood concentrations were measured using a validated liquid chromatography with tandem mass spectrometry method. T 1/2eff was estimated using within-participant accumulation ratios. T 1/2z was estimated by linear regression of the terminal phase of the concentration versus time profile.

RESULTS

The median accumulation ratios of LCPT and IR-Tac on day 14 were 3.18 and 2.06, respectively.The median (interquartile range; IQR) t 1/2eff for LCPT at day 14 of dosing was 48.4 (37.4-77.9) hours, whereas the t 1/2z was 20.3 (17.6-22.9) hours. For IR-Tac, the median (IQR) t 1/2eff and t 1/2z on day 14 were 12.5 (8.8-23.0) hours and 12.2 (9.2-15.7) hours, respectively.

CONCLUSIONS

Consistent with its prolonged release of tacrolimus, LCPT demonstrated a higher accumulation ratio and a longer t 1/2eff compared with IR-Tac. These findings underscore the pharmacokinetic differences between different drug formulations of the same moiety and may help inform dose adjustments for LCPT in kidney transplantation.

Pharmacokinetic Boosting of Calcineurin Inhibitors in Transplantation: Pros, Cons, and Perspectives

ABSTRACT

The concept of pharmacokinetic (PK) boosting of calcineurin inhibitors (CNI) emerged after the FDA approval of cyclosporine-A. Several studies followed, and the proof of concept was well established by the late 1990s. This also continued for the next blockbuster immunosuppressant, tacrolimus. The driver for such research was an endeavor to save costs, as both drugs were expensive due to patent protection. Two CYP inhibitors, ketoconazole and diltiazem, have been extensively studied in this context and continue to be prescribed off-label along with the CNI. It has been observed that using ketoconazole reduces the dose requirement of tacrolimus by about 50% and 30% with diltiazem, which is in conformity with their pharmacological actions. Off-label co-prescription of these drugs with CNI is often encountered in low and middle-income countries. The foremost reason cited is economic. This article collates the evidence from the clinical studies that evaluate the PK-boosting effects of CNI and also reviews the gaps in the current evidence base. The current knowledge prevents the transplant community from making meaningful inferences about the risks and benefits of such strategies. Although the PK-boosting strategy can lead to serious adverse events, emerging evidence suggests that it may be advantageous for individuals with high CNI dose requirements. Hence, PK boosting may be an unmet need in the therapeutics of CNI. Nevertheless, there are several unanswered questions surrounding such use, and therefore, this merits testing in well-designed clinical studies. Moreover, drugs with better safer profiles and a history of successful PK boosting may be considered for evaluation with CNI.

Customizing Tacrolimus Dosing in Kidney Transplantation: Focus on Pharmacogenetics

ABSTRACT

Different polymorphisms in genes encoding metabolizing enzymes and drug transporters have been associated with tacrolimus pharmacokinetics. In particular, studies on CYP3A4 and CYP3A5, and their combined cluster have demonstrated their significance in adjusting tacrolimus dosing to minimize under- and overexposure thereby increasing the proportion of patients who achieve tacrolimus therapeutic target. Many factors influence the pharmacokinetics of tacrolimus, contributing to inter-patient variability affecting individual dosing requirements. On the other hand, the growing use of population pharmacokinetic models in solid organ transplantation, including different tacrolimus formulations, has facilitated the integration of pharmacogenetic data and other variables into algorithms to easier implement the personalized dose adjustment in transplant centers. The future of personalized medicine in transplantation lies in implementing these models in clinical practice, with pharmacogenetics as a key factor to account for the high inter-patient variability in tacrolimus exposure. To date, three clinical trials have validated the clinical application of these approaches. The aim of this review is to provide an overview of the current studies regarding the different population pharmacokinetic including pharmacogenetics and those translated to the clinical practice for individualizing tacrolimus dose adjustment in kidney transplantation.

Examining Whole Blood, Total and Free Plasma Tacrolimus in Elderly Kidney Transplant Recipients

BACKGROUND

Therapeutic monitoring is routinely performed to ensure tacrolimus whole-blood concentrations fall within a predefined target. Despite this, patients still experience inefficacy and toxicity that could be related to variability in free (unbound) tacrolimus exposure. Therefore, the aim of this study was to compare tacrolimus-free plasma (C u ), total plasma (C p ), and whole-blood (C wb ) concentrations in adult kidney transplant recipients and to characterize tacrolimus disposition across different matrices.

METHODS

Twelve-hour concentration-time profiling was performed in 15 recipients, allowing simultaneous measurement of C u , C p , and C wb . Pharmacokinetic parameters were estimated using noncompartmental analysis. The relationship between C wb and C p were examined using a capacity-limited binding model, incorporating the hematocrit fraction ( fHCT ) to estimate maximum binding concentration ( Bmax ) and dissociation constant ( Kd ). The relationship between C p and C u was evaluated using a linear binding model to estimate the nonspecific binding parameter ( Nplasma ). Nonlinear regression analysis was used to obtain estimates of Bmax , Kd , and Nplasma .

RESULTS

A total of 195 paired C wb , C p , and C u values were collected. The median ratios of C wb :C p , C p :C u , and C wb :C u were 9:1, 20:1, and 138:1, respectively. Variability in free plasma exposure was large; free trough values ranged from 8 to 51 ng/L and free area-under-the-concentration-time-curve values ranged from 424 to 7160 ng·h/L. Median (range) estimates of Bmax , Kd , and Nplasma were 90.4 µg/L (22.4-752.5 µg/L), 2.36 µg/L (0-69.2 µg/L), and 0.05 (0.035-0.085), respectively. The interindividual variability (CV%) in binding parameters was considerable ( Bmax 117.2%; Nplasma 32.5%).

CONCLUSIONS

Large variability was observed in tacrolimus-free plasma exposure and binding parameters. Future research to characterize the relationship between tacrolimus C u and patient outcomes may be of benefit.

Cannabidiol and Δ9-tetrahydrocannabinol induce drug-metabolizing enzymes, but not transporters, in human hepatocytes: Implications for predicting complex cannabinoid-drug interactions

Cannabidiol (CBD) or delta-9-tetrahydrocannabinol (THC) can inhibit multiple CYPs and UGTs in vivo and/or in vitro. CBD, but not THC, is also a time-dependent inhibitor of CYP3A, CYP1A2, and CYP2C19. We showed that a single 640 mg oral dose of CBD inhibits oral midazolam plasma clearance by 56%, whereas others found no interaction of chronic CBD with midazolam. These data can be explained if chronic CBD induces CYP3A enzymes. To investigate if CBD or THC induces CYP enzymes or transporters, we treated 4 lots of human hepatocytes for 72 hours with in vivo relevant concentrations of CBD (42 nM, 420 nM) or THC (250 nM, 700 nM). Then, mRNA expression and CYP activity were measured using quantitative polymerase chain reaction and liquid chromatography-tandem mass spectrometry, respectively. CYP3A4 mRNA was significantly induced to 7.3-, 11.1-, and 3.3-fold by CBD (420 nM) and 14.8-, 5.9-, and 3.1-fold by THC (700 nM) in 3 of the 4 lots. CYP3A activity was significantly induced 3.39- and 3.28-fold by low (42 nM) and 2.4- and 2.3-fold by high (420 nM) CBD concentrations, respectively, in 2 lots, and 2.3-fold by THC (700 nM) in 1 lot. Rifampin (10 μM) significantly induced CYP3A mRNA and activity across all lots. CBD (420 nM) significantly induced CYP1A2 and CYP2B6 mRNA (but not activity) in 2 lots. No significant induction of other CYPs, UGTs, or transporters was observed. Incorporation of CBD Emax and EC50 of CYP3A4 mRNA induction (without scaling by rifampin mRNA induction) into a CBD physiologically-based pharmacokinetic model successfully captured the lack of the observed chronic CBD-midazolam drug interaction. SIGNIFICANCE STATEMENT: Time-dependent inhibition and induction of CYP3A enzymes by cannabidiol (CBD) is a plausible explanation for the significant CBD-midazolam pharmacokinetic interaction after single-dose CBD administration and the absence of such an interaction after multiple-dose CBD administration.

Drug-drug interaction between ensitrelvir and tacrolimus in a patient undergoing treatment for COVID-19: a case report

BACKGROUND

Ensitrelvir is a novel SARS-CoV-2 3-chymotrypsin-like protease inhibitor, similar to nirmatrelvir/ritonavir. Several case reports have demonstrated the efficacy of 3-chymotrypsin-like protease inhibitors in treating prolonged coronavirus disease 2019 (COVID-19) in immunocompromised patients. Tacrolimus (TAC) is a widely used immunosuppressive agent whose blood level can increase significantly due to the inhibition of cytochrome P450 3A (CYP3A) and P-glycoprotein by nirmatrelvir/ritonavir. Since ensitrelvir also inhibits CYP3A and P-gp, similar elevations in TAC levels are expected. A prior case report observed an increase in TAC trough levels with concurrent administration of ensitrelvir. However, no studies have quantitatively described the changes in TAC blood levels and clearances before and after ensitrelvir administration when TAC administration was discontinued to mitigate the drug-drug interaction (DDI) risk; data on safe dosing protocols to avoid the DDI during co-administration of ensitrelvir and TAC remain lacking. Here, we report a case in which TAC levels were successfully managed in a patient with rheumatoid arthritis (RA) who received ensitrelvir for persistent COVID-19 by preemptive discontinuation of TAC and close monitoring of TAC blood levels following ensitrelvir administration.

CASE PRESENTATION

An 81-year-old Japanese woman who had been administered TAC (1.5 mg once daily) for RA received two courses of remdesivir for moderate COVID-19. However, her viral load remained high and her respiratory status deteriorated. Considering persistent COVID-19, we initiated combination therapy with remdesivir and ensitrelvir (day 0). TAC was discontinued, and the TAC blood levels decreased from 3.6 ng/mL to 1.1 ng/mL over five days. Subsequently, we re-administered TAC (0.2 mg), observing a level of 1.0 ng/mL by day 7. The TAC dose was adjusted to 1.0 mg daily, and TAC levels on day 12 and 14 were 6.5 and 3.7 ng/mL, respectively. TAC (1.5 mg daily) was resumed on day 15. The calculated t1/2 of TAC were 33.7, 71.9, and 114.6 h from day -1 to 0, day 0 to 2, and day 2 to 5, respectively. The t1/2 of TAC was extended to 3.4-fold its original duration under ensitrelvir treatment.

CONCLUSIONS

This DDI extended the half-life of TAC by approximately 3.4-fold, an effect that gradually diminished over 7 to 10 days. When patients receiving TAC treatment start ensitrelvir therapy, a dose reduction of TAC by approximately one-third to one-fourth is considered appropriate.

Prediction of the Intra-T Lymphocyte Tacrolimus Concentration after Kidney Transplantation with Population Pharmacokinetic Modeling

The intracellular tacrolimus concentration in CD3+ T lymphocytes is proposed to be a better representative of the active component of tacrolimus than the whole blood concentration. However, intracellular measurements are complicated. Therefore, the aim of this study was to describe the relationship between intracellular and whole blood tacrolimus concentrations in a population pharmacokinetic model. Twenty-eight de novo kidney transplant recipients, treated with a once-daily oral extended-release tacrolimus formulation, were followed during the first-month post-transplantation. Additional whole blood and intracellular tacrolimus concentrations were measured at day 6 ± 1 (pre-dose, 4 and 8 hours post-dose) and day 14 ± 3 (pre-dose) post-transplantation. Pharmacokinetic analysis was performed using nonlinear mixed effects modeling software (NONMEM). The ratio between intracellular (n = 109) and whole blood (n = 248) concentrations was best described by a two-compartment whole blood model with an additional intracellular compartment without mass transfer from the central compartment. The ratio remained stable over time. Prednisolone dose influenced the absorption rate of tacrolimus, while hemoglobin, CYP3A4*22 allele carrier, and CYP3A5 expresser status were associated with the oral clearance of tacrolimus (P-value < 0.001). Furthermore, the intracellular tacrolimus concentrations were correlated with the intracellular production of interleukin-2 (P-value 0.015). The intracellular tacrolimus concentration can be predicted from a measured whole blood concentration using this model, without the need for repeated intracellular measurements. This knowledge is particularly important when the intracellular concentration is ready to be implemented into clinical practice, to overcome the complexities of cell isolation and analytical methods.

The tradeoff between the efficacy of calcineurin inhibitors: prevention of allograft rejection vs. post-transplant renal and cardiovascular complications

Solid organ transplantation has emerged as a crucial intervention in the field of medicine. During transplantation, our human body perceives the organ as an exogenous entity or graft, initiating an immune reaction to eliminate it. This immune response ultimately culminates in the rejection of the graft. So, to mitigate the possibility of graft rejection, implementing immune suppression is imperative. In this context, the utilization of calcineurin inhibitors (CNIs) assumes a pivotal role. Calcineurin inhibitors significantly preserve immunosuppression following solid organ transplantation. Calcineurin inhibitors have considerably improved short-term results in renal transplantation by reducing acute rejection rates. Concerning the limited therapeutic window of these medications, careful monitoring of pharmacological treatment and individual doses is required. However, a significant number of patients do experience CNI toxicity. Side effects of CNIs include renal failure, hypertension, respiratory disorders, gastrointestinal damage, gingivitis, and so on. Higher trough level of the drug causes acute nephrotoxicity, which is of three types: functional toxicity, tubular toxicity, and vascular toxicity. Acute nephrotoxicity, if untreated, leads to irreversible, progressive deterioration of allograft function, leading to chronic nephrotoxicity. Cardiovascular toxicity of CNIs includes atrial hypertension caused by vasoconstriction of the afferent arteriole, vascular remodeling, hypertrophy, dyslipidemia, and also the onset of diabetes. Such clinical complications further affect the patient's survivability and subjective well-being, possibly leading to graft loss. This review focuses on the most severe side effects of CNIs: renal and cardiovascular toxicity.

External evaluation of tacrolimus population pharmacokinetic models in adult lung transplant patients: How to enhance the predictive ability of the model?

PURPOSE

Tacrolimus is the cornerstone of current immunosuppressive strategies after lung transplantation. However, its narrow therapeutic range and considerable pharmacokinetic variability pose challenges for individualized treatment. Several tacrolimus population pharmacokinetic (popPK) models have been developed for precision dosing in adult lung transplant patients. However, their applicability across different clinical settings remains uncertain. The aim of this study was to evaluate the external predictability of these models and identify influential factors.

METHODS

Published models were systematically retrieved and assessed based on an external dataset of 39 patients (1240 tacrolimus trough concentrations) using three approaches: (1) prediction-based diagnosis using dosing records and patient characteristics; (2) simulation-based diagnosis, with prediction- and variability-corrected visual predictive checks (pvcVPC) and normalized prediction distribution error tests (NPDE); and (3) Bayesian forecasting using one to four observations for posterior predictions. We also investigated the impact of model structure and covariates on predictability.

RESULTS

The predictive performance of six published models was externally evaluated, but none demonstrated satisfactory accuracy in prediction- and simulation-based diagnosis. Bayesian forecasting yielded satisfactory results with only one prior observation and optimal predictive performance with 2-3 priors for all included models. The structural model parameterized on plasma tacrolimus concentration outperformed others. Significant correlations were observed between prediction-error and daily tacrolimus dose, postoperative day, and voriconazole co-administration.

CONCLUSIONS

The overall predictive performance of all published models was unsatisfactory, making direct extrapolation inappropriate. However, Bayesian forecasting significantly improves predictive performance. Utilizing plasma tacrolimus concentration for parameter estimation can improve the predictive ability of tacrolimus popPK models.

Efficacy of tacrolimus versus cyclosporine after lung transplantation: an updated systematic review, meta-analysis, and trial sequential analysis of randomized controlled trials

BACKGROUND

Little data supports using tacrolimus versus cyclosporin for immunosuppression concerning acute rejection and bronchiolitis obliterans syndrome/Chronic Lung Allograft Dysfunction CLAD complications following lung transplantation (LTx). Our goal was to evaluate the use of tacrolimus versus cyclosporine in preventing these complications after LTx.

METHODS

We included randomized controlled trials (RCTs) by searching PubMed, Web of Science, SCOPUS, and Cochrane through January 10th, 2024. We pooled dichotomous data using the risk ratio (RR) and continuous data using the mean difference (MD) with a 95% confidence interval (CI).

RESULTS

We included Four RCTs with a total of 677 patients. Tacrolimus was significantly associated with decreased risk of acute rejection (RR: 1.21, 95% CI [1.03, 1.42], I2 = 25%, P = 0.02) compared with cyclosporine, bronchiolitis obliterans syndrome/CLAD (RR: 1.87, 95% CI [1.26, 2.77], I2 = 52%, P = 0.002), and treatment withdrawal (RR: 3.11, 95% CI [2.06, 4.70], I2 = 0%, P =  < 0.00001). However, tacrolimus significantly increased the risk of new-onset diabetes (RR: 0.33, 95% CI [0.12, 0.91], I2 = 0%, P = 0.03), and kidney dysfunction (RR: 0.79, 95% CI [0.66, 0.93], I2 = 0%, P = 0.006). In contrast, there was no difference in the incidence of all-cause mortality (RR: 91, 95% CI [0.68, 1.22], I2 = 0%, P = 0.53), arterial hypertension (RR: 2.40, 95% CI [0.41, 14.21], I2 = 92%, P = 0.33), and new cancer (RR: 1.57, 95% CI [0.79, 3.10], I2 = 4%, P = 0.20).

CONCLUSION

Tacrolimus has decreased acute rejection episodes and CLAD rate than cyclosporine, but it increased the risk of new-onset diabetes and kidney dysfunction.

Patiromer Does Not Alter Tacrolimus Pharmacokinetics in Kidney Transplant Recipients When Administered Three Hours Post-Tacrolimus

Background

Hyperkalemia is common in kidney transplant (KTx) recipients. Patiromer, a potassium-binding polymer used to treat acute and chronic hyperkalemia, has the potential to bind charged particles in the gastrointestinal tract and thereby potentially affect the absorption of coadministered drugs. The immunosuppressive drug tacrolimus (Tac) has a narrow therapeutic window, is susceptible to drug-drug interactions (DDIs), and a potential gastrointestinal interaction with patiromer could elevate the risk of allograft rejection. We aimed to investigate the potential DDI between patiromer and Tac pharmacokinetics in KTx with hyperkalemia by sampling capillary blood using volumetric absorptive microsampling (VAMS).

Methods

Thirteen KTx recipients on Tac twice daily (BID) with plasma potassium levels of >4.6 mmol/L were included. Two 12 h Tac pharmacokinetic investigations were performed with and without 8.4 mg patiromer/d for 1 wk. Oral Tac dose remained unchanged and patiromer was administered 3 h after Tac dose. Tac sampling was self-conducted using VAMS after mastering the technique.

Results

Ten patients provided 2 evaluable pharmacokinetic profiles. The Tac area under the curve (AUC)0-12 ratio (AUCTac+patiromer/AUCTac) was 0.99 (90% confidence interval [CI], 0.86-1.14), and the Cmax ratio was 1.01 (90% CI, 0.86-1.19). Tac C0 and C12 fulfilled the bioequivalence criteria with a ratio of 0.98 (90% CI, 0.90-1.07) and 0.93 (90% CI, 0.83-1.04), respectively.

Conclusions

When administered 3 h after the Tac morning dose, patiromer has no clinically relevant impact on Tac pharmacokinetics. We demonstrate that VAMS is a well-suited sampling method to simplify the execution of DDI studies.

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

A retrospective analysis of tacrolimus pharmacokinetic in Saudi paediatric patients in early post-liver transplantation period

BACKGROUND

Tacrolimus is an essential immunosuppressive medication in paediatric patients' post-liver transplantation. Achieving tacrolimus target concentration in early post-transplantation is crucial to minimise the risk of acute rejection; however, this is challenging due to inter- and intra-patient variability in tacrolimus metabolism and clearance. Therefore, our study aims to describe tacrolimus trough concentration variability and pharmacokinetics in paediatric post-liver transplantation during the first two weeks post-transplantation.

METHOD

This retrospective multicentre observational study included paediatric patients post-liver transplantation. Post-operative data was collected within the initial 14 days using electronic health records, including daily tacrolimus doses, measured trough concentrations, graft data, surgical data, and documented acute rejection. Pharmacokinetic analysis was completed using the Monolix software. We used the empirical Bayesian estimates of clearance and volume of distribution for covariate testing to assess possible correlations. We performed a stepwise regression analysis (alpha = 0.05).

RESULTS

Ninety-one paediatric patients were included in the study, with a mean age of 4.1 years (SD = 4.6). The mean graft-to-recipient weight ratio (GRWR) was 3% (SD = 6). The vast majority of the patients received the liver from living donors (n = 84, 92.3%). The average time needed to reach therapeutic concentration was 4.6 (SD = 2.8) days. The initial clearance (Clini) was very low at baseline (0.012 L/h), then increased dramatically to 9.84 L/h at 14 days post-transplantation. The clearance appeared to be time-dependent, and the time needed to reach 50% of maximum clearance was five days post-transplantation. The covariates that significantly affected clearance included bodyweight and aspartate transaminase, while the only significant covariate for volume of distribution was bodyweight.

CONCLUSION

Tacrolimus is a drug with high intra- and interindividual variability, making dosing challenging in the paediatric liver transplantation population. Prospective studies with more intensive sampling are needed to address the time-dependent changes in clearance, which will aid in establishing the optimal dosing regimens in this population.

Factors influencing intrapatient variability of tacrolimus and its association with 1-year post-transplant outcomes in pediatric liver transplant recipients

Objective

This study aims to explore the factors influencing tacrolimus intrapatient variability (TAC-IPV) and its association with 1-year post-transplant outcomes in pediatric liver transplant recipients.

Methods

Clinical and biological data of pediatric patients after liver transplantation were collected. The patients were divided into high- and low-IPV groups according to the median TAC-IPV for statistical comparisons. Factors with p < 0.05 in univariate analysis were introduced into binomial logistic regression analysis. Correlation analysis was used to test the connections between the Tac-IPV and outcomes within 1 year after liver transplantation (LT), and Kaplan-Meier was used to draw the survival curves.

Results

A total of 116 children underwent 746 measurements of TAC trough concentrations. The median TAC-IPV was 32.31% (20.81%, 46.77%). Hematocrit (p = 0.017) and concomitant medications (p = 0.001) were identified as independent influencing factors for TAC-IPV. The incidence of transplant rejection (p = 0.008), CMV infection (p < 0.001), and hospital admission due to infection (p = 0.003) were significantly higher in the high-IPV group than in the low-IPV group. Kaplan-Meier survival analysis suggests that after considering the time factor, high IPV (IPV > 32.31%) was still significantly associated with transplant rejection (HR = 3.17 and p = 0.005) and CMV infection (HR = 2.3 and p < 0.001) within 1 year after LT.

Conclusion

The study highlights the significant variation in TAC-IPV among children post-liver transplantation, emphasizing the impact of hematocrit levels and concomitant medications on TAC-IPV. Elevated TAC-IPV is associated with increased risks of transplant rejection, CMV infection, and readmission due to infection in the first year after liver transplantation. Close monitoring of patients with high TAC-IPV is recommended to promptly detect adverse reactions and provide timely intervention and treatment.

Beyond Borders: International Immunosuppression Practices in Pediatric Lung Transplantation

INTRODUCTION

Current recommendations for lung transplantation immunosuppression do not explicitly target children, and many pharmacotherapies used in pediatrics are extrapolated from adults.

METHODS

Data were collected from an anonymous survey distributed to International Pediatric Lung Transplant Collaborative (IPLTC) members from November 2023 to February 2024. Eligible participants included pediatric lung transplant physicians, pharmacists, or others with expertise in their lung transplant center's protocols. Participant and program demographics were surveyed, including location and transplant volume. Seventeen multiple-choice questions, text responses, and Likert scale statements covered the following: induction immunosuppression, maintenance immunosuppression, drug monitoring, dose optimization, and expert guidance available in current literature.

RESULTS

Among the 23 pediatric lung transplant healthcare professionals who responded, 13 respondents (57%) preferred using basiliximab as their standard induction immunosuppression. 3 (13%) prefer rabbit anti-thymocyte globulin (rATG), while 7 (30%) consider either rATG or basiliximab for induction. Of 22 responses with 100% completion, 21 of 22 (95.2%) respondents reported a combination of tacrolimus, mycophenolate mofetil (MMF), and corticosteroids (CCS) as their preferred maintenance immunosuppression regimen, reflecting the suggested preferred regimen for pediatric lung transplantation. Feedback on the perception of available evidence-based or established guidelines revealed the majority (90.0%) of respondents found them to be insufficient for pediatrics.

CONCLUSION

This international survey highlights the variability in immunosuppression practices across pediatric lung transplant programs around the world. The findings underscore a gap in unified, evidence-based practice guidelines. With strong consensus among respondents on the lack of established guidelines, there is a clear directive for future research to establish standardized practices in pediatric lung transplantation.

Development and validation of an LC-MS/MS method for highly concentrated tacrolimus and cyclosporine samples prepared from pharmaceutical products to assess drug loss from feeding tubes

Introduction

Tacrolimus and cyclosporine are common immunosuppressants utilized post-organ transplantation to manage allograft rejection. Both have narrow therapeutic indices and are frequently measured to support dose adjustments. Although nasogastric tubes are commonly used to provide nutritional support and serve as a route for immunosuppressant administration, they were never validated for such purposes.

Objective

To develop and validate a liquid chromatography - tandem mass spectrometry (LC-MS/MS) method for highly concentrated tacrolimus and cyclosporine samples prepared from pharmaceutical products to support the validation of feeding tube administration of these immunosuppressants.

Methods

The method involved stepwise dilutions with dimethyl sulfoxide before analysis using online sample preparation and LC-MS/MS. It was validated in a CLIA-certified clinical laboratory that measures immunosuppressants by LC-MS/MS and is designed to support clinical studies evaluating drug loss from feeding tubes.

Results

The method was linear between 6.8 µg/mL and 75 µg/mL for tacrolimus, and between 0.9 mg/mL and 10 mg/mL for cyclosporine, with r2 > 0.99 and total precision <5 % at all QC levels. The method demonstrated good recovery using cyclosporine Certified Reference Material, tacrolimus European Pharmacopeia Reference Standard, and prepared pharmaceutical products. Minimal matrix effects were observed.

Conclusion

An analytical method was developed and validated for in vitro studies with simulated administration of tacrolimus or cyclosporine to assess loss during drug administration using feeding tubes.

Association between salivary microbiota and tacrolimus pharmacokinetic variability in kidney transplant

Kidney transplantation (KT) serves as a highly effective treatment for end-stage renal disease (ESRD). Nonetheless, the administration of tacrolimus, a commonly used immunosuppressant in KT, faces challenges due to the lack of dependable biomarkers for its efficacy and the considerable variability in tacrolimus pharmacokinetics (TacIPV). In this study, 183 saliva samples from 48 KT recipients under tacrolimus therapy, alongside 9 healthy control samples, were subjected to 16S rRNA sequencing. The analysis revealed significant differences in the composition of salivary microbiota among KT recipients, patients with ESRD, and healthy controls. Moreover, trough blood concentrations (C0) of tacrolimus were associated with alterations in microbiota composition. Notably, Capnocytophage consistently exhibited a negative correlation in both group-level and individual trends. Furthermore, distinct taxa were identified that effectively distinguished recipients with varying TacIPV, as demonstrated by a cross-validation random forest model (mean AUC = 0.7560), with Anaerolinea emerging as a prominent contributor to the classifier. These findings suggest that salivary microbiota is closely linked to tacrolimus C0 levels and could aid clinicians in differentiating KT recipients based on TacIPV.

Potential influence of interleukin-6 -174G/C gene polymorphism on kidney graft function and tacrolimus dose requirements: five-year follow-up

1. INTRODUCTION

The study aimed to investigate the influence of interleukin (IL)-6 -174 G/C gene polymorphism on graft function (defined as estimated glomerular filtration rate, eGFR), as well as on the tacrolimus (Tac) pharmacokinetics during the five years after kidney transplantation.

2. METHODS

The study included 115 Caucasian kidney transplant recipients on Tac-based immunosuppression. The patients were followed between 6 and 60 post-transplantation months. Interleukin-6 and CYP3A5 genotyping were performed.

3. RESULTS

Patients carrying the IL-6 -174GG genotype had lower eGFR values compared to the patients with the IL-6 -174GC and -174CC genotypes at the 12th, 48th and 60th post-transplantation months. The linear regression analysis indicated that eGFR at the 6th post-transplantation month and IL-6 -174 G/C polymorphism are independent predictors of eGFR values in the late post-transplantation period. The IL-6 -174GG genotype carriers had lower dose-adjusted trough concentration (C0/D) of Tac compared to the IL-6 C allele carriers during the entire observation period (except at the 24th month), while this effect was independent of the CYP3A5 genotype within three years post-transplantation.

4. CONCLUSION

Interleukin-6 genotyping could be an additional tool to categorise patients towards the risk of graft deterioration in the long-term post-transplantation period. The IL-6 genotyping could be supportive in genotype-guided dosing of Tac.

Model-Informed Precision Dosing of Tacrolimus: A Systematic Review of Population Pharmacokinetic Models and a Benchmark Study of Software Tools

BACKGROUND AND OBJECTIVE

Tacrolimus is an immunosuppressant commonly administered after solid organ transplantation. It is characterized by a narrow therapeutic window and high variability in exposure, demanding personalized dosing. In recent years, population pharmacokinetic models have been suggested to guide model-informed precision dosing of tacrolimus. We aimed to provide a comprehensive overview of population pharmacokinetic models and model-informed precision dosing software modules of tacrolimus in all solid organ transplant settings, including a simulation-based investigation of the impact of covariates on exposure and target attainment.

METHODS

We performed a systematic literature search to identify population pharmacokinetic models of tacrolimus in solid organ transplant recipients. We integrated selected population pharmacokinetic models into an interactive software tool that allows dosing simulations, Bayesian forecasting, and investigation of the impact of covariates on exposure and target attainment. We conducted a web survey amongst model-informed precision dosing software tool providers and benchmarked publicly available tools in terms of models, target populations, and clinical integration.

RESULTS

We identified 80 population pharmacokinetic models, including 44 one-compartment and 36 two-compartment models. The most frequently retained covariates on clearance and distribution parameters were cytochrome P450 3A5 polymorphisms and body weight, respectively. Our simulation tool, hosted at https://lpmx.shinyapps.io/tacrolimus/ , allows thorough investigation of the impact of covariates on exposure and target attainment. We identified 15 model-informed precision dosing software tool providers, of which ten offer a tacrolimus solution and nine completed the survey.

CONCLUSIONS

Our work provides a comprehensive overview of the landscape of available tacrolimus population pharmacokinetic models and model-informed precision dosing software modules. Our simulation tool allows an interactive thorough exploration of covariates on exposure and target attainment.

Physiologically-based pharmacokinetic modelling to investigate the effect of CYP3A4/3A5 maturation on tacrolimus pharmacokinetics in paediatric HSCT patients

Tacrolimus (FK506) is a cornerstone of GVHD-prophylaxis treatment in paediatrics undergoing haematopoietic stem cell transplantation (HSCT). However, due to concerns about highly inter/intra-individual variability, precision dosing of FK506 is crucial. Cytochrome P450 (CYP) 3A4 and 3A5 are considered important sources of FK506 pharmacokinetic variability. Nevertheless, the impact of age-related maturation in hepatic and intestinal CYP3A4/3A5 enzymes remains unknown in paediatric HSCT patients. Physiologically-based pharmacokinetic (PBPK) models were developed and verified in adult volunteers and adult HSCT patients using GastroPlus™ (version 9.0), and then extrapolated to paediatric HSCT patients, taking into account the maturation of CYP3A4 and CYP3A5. Default CYP3A4 and CYP3A5 ontogeny profiles were updated based on the latest reports. The paediatric PBPK model was evaluated with independent data collected from Sun Yat-sen Memorial Hospital (86 paediatric HSCT patients, 1 to 16 -year-old). Simulations were performed to evaluate a reported FK506 dosing regimen in infants and children with different CYP3A5 genotypes. Extensive PBPK model validation indicated good predictability, with the predicted/observed (P/O) ratios within the range of 0.80-fold to 1.25-fold. Blood tacrolimus concentration-time curves were comparable between the real and virtual patients. Simulations showed that the higher levels of tacrolimus in 9-month-old to 3-year-old infants were mainly attributed to the CYP3A4/3A5 ontogeny profiles, which resulted in lower clearance and higher exposure relative to dose. The oral dosage of 0.1 mg/kg/day (q12 h) is considered appropriate for paediatric HSCT patients 9 months to 15 years of age with CYP3A5 *1/*1 genotypes. Lower doses were required for paediatric HSCT patients with CYP3A5 *1/*3 (0.08 mg/kg/day, q12h) or CYP3A5 *3/*3 genotypes (0.07 mg/kg/day, q12h), and analyses demonstrated 12.5-20 % decreases in ≤3-year-old patients. The study highlights the feasibility of PBPK modelling to explore age-related enzyme maturation in infants and children (≤3-year-old) undergoing HSCT and emphasizes the need to include hepatic and gut CYP3A4/3A5 maturation parameters.

Optimizing tacrolimus dosing in Hispanic renal transplant patients: insights from real-world data

Aim

Tacrolimus, an immunosuppressant used to prevent organ rejection in renal transplant patients, exhibits high inter-patient variability, necessitating therapeutic drug monitoring. Early post-transplant tacrolimus exposure in Hispanics is understudied. Although genotypic information is linked to pharmacokinetic differences, its clinical application remains limited. This study aimed to use a real-world data-driven, pharmacokinetic model-based approach for tacrolimus in Hispanics to determine a suitable initial dose and design an optimal dose titration strategy by simulations to achieve plasma trough concentration target levels of 10-12 ng/mL at the earliest.

Methods

Sparse concentration-time data of tacrolimus were obtained from electronic medical records for self-identified Hispanic subjects following renal transplant. Rich pharmacokinetic literature data was leveraged to estimate structural pharmacokinetic model parameters, which were then fixed in the current analysis. Only apparent clearance was estimated with the sparse tacrolimus data and potential covariates were identified. Simulations of various starting doses and different dose titration strategies were then evaluated.

Results

The analysis included 121 renal transplant patients with 2,215 trough tacrolimus concentrations. A two-compartment transit absorption model with allometrically scaled body weight and time-varying hematocrit on apparent clearance adequately described the data. The estimated apparent clearance was 13.7 L/h for a typical patient weighing 70 kg and at 30% hematocrit, demonstrating a 40% decrease in clearance compared to other patient populations. Model based simulations indicated the best initial dose for the Hispanic population is 0.1 mg/kg/day. The proposed titration strategy, with three dose adjustments based on trough levels of tacrolimus, increased the proportion of patients within the target range (10-12 ng/mL) more than 2.5-fold and decreased the proportion of patients outside the therapeutic window by 50% after the first week of treatment.

Conclusion

Hispanic renal transplant population showed an estimated 40% decrease of apparent clearance in the typical patient compared to other populations with similar characteristics. The proposed dose adjustment attained the target range rapidly and safely. This study advocates for tailored tacrolimus dosing regimens based on population pharmacokinetics to optimize therapy in Hispanic renal transplant recipients.

Guiding the starting dose of the once-daily formulation of tacrolimus in "de novo" adult renal transplant patients: a population approach

Aims

The once-daily extended-release tacrolimus formulation (ER-Tac) has demonstrated similar efficacy and safety to the twice-daily immediate-release formulation (IR-Tac), but few population-based pharmacokinetic models have been developed in de novo kidney transplant patients to optimize doses. Therefore, this study aimed i) at developing a population pharmacokinetic model for ER-Tac in de novo adult kidney transplant patients ii) and identifying genetic factors and time-varying covariates predictive of pharmacokinetic variability to guide tacrolimus dosage during the early post-transplant period.

Methods

A total of 1,067 blood tacrolimus concentrations from 138 kidney transplant patients were analyzed. A total of 29 out of 138 patients were intensively sampled for 24 h on the day 5 post-transplantation; meanwhile, for the remaining patients, concentrations were collected on days 5, 10, and 15 after transplantation. Tacrolimus daily doses and genetic and demographic characteristics were retrieved from the medical files. Biochemistry time-varying covariates were obtained on different days over the pharmacokinetic (PK) study. A simultaneous PK analysis of all concentrations was carried out using the non-linear mixed-effects approach with NONMEM 7.5.

Results

A two-compartment model with linear elimination and delayed absorption best described the tacrolimus pharmacokinetics. Between-patient variability was associated with oral blood clearance (CL/F) and the central compartment distribution volume (Vc/F). Tacrolimus concentrations standardized to a hematocrit value of 45% significantly improved the model (p < 0.001). This method outperformed the standard covariate modeling of the hematocrit-blood clearance relationship. The effect of the CYP3A5 genotype was statistically (p < 0.001) and clinically significant on CL/F. The CL/F of patients who were CYP3A5*1 carriers was 51% higher than that of CYP3A5*1 non-carriers. Age also influenced CL/F variability (p < 0.001). Specifically, CL/F declined by 0.0562 units per each increased year from the value estimated in patients who were 60 years and younger.

Conclusion

The 36% between-patient variability in CL/F was explained by CYP3A5 genotype, age, and hematocrit. Hematocrit standardization to 45% explained the variability of tacrolimus whole-blood concentrations, and this was of utmost importance in order to better interpret whole-blood tacrolimus concentrations during therapeutic drug monitoring. The dose requirements of CYP3A5*/1 carriers in patients aged 60 years or younger would be highest, while CYP3A5*/1 non-carriers older than 60 years would require the lowest doses.

Individualized dosing parameters for tacrolimus in the presence of voriconazole: a real-world PopPK study

Objectives

Significant increase in tacrolimus exposure was observed during co-administration with voriconazole, and no population pharmacokinetic model exists for tacrolimus in renal transplant recipients receiving voriconazole. To achieve target tacrolimus concentrations, an optimal dosage regimen is required. This study aims to develop individualized dosing parameters through population pharmacokinetic analysis and simulate tacrolimus concentrations under different dosage regimens.

Methods

We conducted a retrospective study of renal transplant recipients who were hospitalized at the Second Xiangya Hospital of Central South University between January 2016 and March 2021. Subsequently, pharmacokinetic analysis and Monte Carlo simulation were employed for further analysis.

Results

Nineteen eligible patients receiving tacrolimus and voriconazole co-therapy were included in the study. We collected 167 blood samples and developed a one-compartment model with first-order absorption and elimination to describe the pharmacokinetic properties of tacrolimus. The final typical values for tacrolimus elimination rate constant (Ka), apparent volume of distribution (V/F), and apparent oral clearance (CL/F) were 8.39 h-1, 2690 L, and 42.87 L/h, respectively. Key covariates in the final model included voriconazole concentration and serum creatinine. Patients with higher voriconazole concentration had lower tacrolimus CL/F and V/F. In addition, higher serum creatinine levels were associated with lower tacrolimus CL/F.

Conclusion

Our findings suggest that clinicians can predict tacrolimus concentration and estimate optimal tacrolimus dosage based on voriconazole concentration and serum creatinine. The effect of voriconazole concentration on tacrolimus concentration was more significant than serum creatinine. These findings may inform clinical decision-making in the management of tacrolimus and voriconazole therapy in solid organ transplant recipients.

Pharmacokinetics and Pharmacodynamics of Systemic Corticosteroids in Autoimmune and Inflammatory Diseases: A Review of Current Evidence

BACKGROUND AND OBJECTIVE

Systemic corticosteroids have a long history of use in the treatment of autoimmune and inflammatory diseases. Both efficacy and safety show large interindividual variability (IIV), suggesting that corticosteroids may have the potential for individualised dosing strategies to optimise therapy. This systematic review aims to provide an overview of current evidence on the pharmacokinetic (PK) and pharmacodynamic (PD) relationships of systemic corticosteroids in patients with autoimmune and inflammatory diseases.

METHODS

A systematic literature search was conducted in PubMed and Embase for PK/PD studies of systemic corticosteroids in autoimmune and inflammatory diseases in humans published until December 2023. Studies were scored from 1 to 5 according to criteria for the levels of evidence, as inspired by the Oxford Centre for Evidence-Based Medicine.

RESULTS

Twelve studies (1981-2016) were included. The majority of these studies had a small sample size. The corticosteroids involved were prednisone, prednisolone, methylprednisolone and budesonide. Substantial IIV of corticosteroid PK was described in all studies. Evidence for a relationship between the PK of corticosteroids and efficacy was inconclusive and limited. However, there was some evidence for a relationship between the PK of prednisolone and the severity of Cushingoid features.

CONCLUSION

There is insufficient evidence to draw firm conclusions on the potential associations between PK and clinical outcome of systemic corticosteroid treatment in autoimmune and inflammatory diseases. This is remarkable given the many decades that steroid drugs have been used in clinical care. Prospective research is recommended with robust and well-defined cohorts to fully quantify the PK/PD associations of corticosteroids.

A joint population pharmacokinetic model to assess the high variability of whole-blood and intracellular tacrolimus in early adult renal transplant recipients

Tacrolimus (TAC) has high pharmacokinetic (PK) variability during the early transplantation period. The relationships between whole-blood and intracellular TAC concentrations and clinical outcomes remain controversial. This study identifies the factors affecting the PK variability of TAC and characterizes the relationships between whole-blood and intracellular TAC concentrations. Data regarding whole-blood TAC concentrations of 1,787 samples from 215 renal transplant recipients (<90 days postoperative) across two centers and intracellular TAC concentrations (648 samples) digitized from previous studies were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were screened, and the distribution of whole-blood to intracellular TAC concentration ratios (RWB:IC) was estimated. The final model was evaluated using bootstrap, goodness of fit, and prediction-corrected visual predictive checks. The optimal dosing regimens and target ranges for each type of immune cell subsets were determined using Monte Carlo simulations. A two-compartment model adequately described the data, and the estimated mean TAC CL/F was 23.6 L·h-1 (relative standard error: 11.5 %). The hematocrit level, CYP3A5*3 carrier status, co-administration with Wuzhi capsules, and tapering prednisolone dose may contribute to the high variability of TAC PK variability during the early post-transplant period. The estimated RWB:IC of all TAC concentrations in peripheral blood mononuclear cells (PBMCs) was 4940, and inter-center variability of PBMCs was observed. The simulated TAC target range in PBMCs was 20.2-85.9 pg·million cells-1. Inter-center variability in intracellular concentrations should be taken into account in further analyses. TAC dosage adjustments can be guided based on PK/PD variability and simulated intracellular concentrations.

Pharmacogenetics of Calcineurin inhibitors in kidney transplant recipients: the African gap. A narrative review

Calcineurin inhibitors (CNIs) are the mainstay of immunosuppression in kidney transplantation. Interpatient variability in the disposition of calcineurin inhibitors is a well-researched phenomenon and has a well-established genetic contribution. There is great diversity in the makeup of African genomes, but very little is known about the pharmacogenetics of CNIs and transplant outcomes. This review focuses on genetic variants of calcineurin inhibitors' metabolizing enzymes (CYP3A4, CYP3A5), related molecules (POR, PPARA) and membrane transporters involved in the metabolism of calcineurin inhibitors. Given the genetic diversity across the African continent, it is imperative to generate pharmacogenetic data, especially in the era of personalized medicine and emphasizes the need for studies specific to African populations. The study of allelic variants in populations where they have greater frequencies will help answer questions regarding their impact. We aim to fill the knowledge gaps by reviewing existing research and highlighting areas where African research can contribute.

Influence of Tacrolimus Intrapatient Variability on Allograft Rejection Frequency and Survival Following Liver Transplantation

BACKGROUND

Tacrolimus is the primary calcineurin inhibitor used in immunosuppressive regimens to prevent allograft rejection (AR) after organ transplantation. Recent studies have linked intrapatient variability (IPV) of tacrolimus with AR occurrence and reduced survival, especially in kidney transplant recipients. However, limited data are available on the impact of tacrolimus IPV on adverse outcomes after liver transplantation (LT).

AIMS

The aim of this study was to assess the association between tacrolimus IPV using various methodologies with acute AR and long-term patient survival after LT.

METHODS

All patients who underwent LT from January 2010 to July 2021 were retrospectively evaluated. Tacrolimus IPV was calculated for each patient using the mean and SD, mean absolute deviation (MAD), coefficient of variation (CV), and time in therapeutic range (TTR). These measures were then compared with AR within the first 24 months after LT and to long-term survival.

RESULTS

Out of 234 patients, 32 (13.7%) developed AR and 183 (78.2%) survived, with a mean follow-up of 101 ± 43 months. Tacrolimus IPV, assessed by mean, SD, MAD, and CV, was 8.3 ± 2.1, 2.7 ± 1.3, 32.0% ± 11.7%, and 39.4% ± 15.4%, respectively. There was no statistically significant correlation between Tacrolimus IPV and AR or survival post-LT.

CONCLUSIONS

In a large cohort of patients from diverse racial backgrounds, tacrolimus IPV was not associated with clinically relevant outcomes such as AR and survival after LT.

A descriptive study of the single-nucleotide polymorphisms known to affect the Tacrolimus trough concentration per dose, among a population of kidney failure patients in a tertiary hospital in Ghana

BACKGROUND

The burden of chronic kidney disease (CKD) and kidney failure in Ghana is on the ascendency, with the prevalence of CKD estimated at 13.3%. Patients with CKD who progress to kidney failure require life sustaining kidney replacement therapy (KRT) which is almost exclusively available in Ghana as haemodialysis. Kidney transplantation is considered the best KRT option for patients with irreversible kidney failure due to its relative cost efficiency as well as its superiority in terms of survival and quality of life. However, because transplants may trigger an immune response with potential organ rejection, immunosuppressants such as tacrolimus dosing are required.

OBJECTIVE

This study sought to determine single nucleotide polymorphisms in CYP3A5, CYP3A4 and MDR1 genes that affect the pharmacokinetics of Tacrolimus in a population of Ghanaian patients with kidney failure.

METHOD

This cross-sectional study comprised of 82 kidney failure patients undergoing maintenance haemodialysis at the Renal and Dialysis unit of Korle-Bu Teaching Hospital (KBTH). Clinical and demographic data were collected and genomic DNA isolated. Samples were genotyped for specific SNPs using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

Participants, 58/82 (70.73%) harbored the wildtype CYP3A5*1/*1 AA genotype, 20/82 (24.39%) carried the heterozygous CYP3A5*1/*3 AG genotype, and 4/82 (4.88%) had the homozygous mutant CYP3A5*3/*3 GG genotype. Also, 6/82 (7.32%) carried the wildtype AA genotype, 11/82 (13.41%) had the heterozygous AG genotype, and 65/82 (79.27%) harbored the homozygous mutant GG genotype of CYP3A4*1B (-290 A>G). For MDR1_Ex21 (2677 G>T), 81/82 (98.78%) carried the wildtype GG genotype, while 1/82 (1.22%) had the heterozygous GT genotype. For MDR1_Ex26 (3435 C>T), 63/82 (76.83%) had the wildtype CC genotype, while 18/82 (21.95%) carried the heterozygous CT genotype, and 1/82 (1.22%) harbored the mutant TT genotype.

CONCLUSION

SNPs in CYP3A4, CYP3A5, and MDR1 genes in a population of Ghanaian kidney failure patients were described. The varying SNPs of the featured genes suggest the need to consider the genetic status of Ghanaians kidney failure patients prior to transplantation and tacrolimus therapy.

Chronological alterations in de novo malignancies after living-donor liver transplantation: A cohort study of 1781 recipients using annual comparisons of standardized incidence ratios

BACKGROUND

De novo malignancies (DNMs) are a major adverse event after solid organ transplantation; however, their characteristics and recent trends after living-donor liver transplantation (LDLT) remain unclear.

METHODS

We retrospectively reviewed 1781 primary LDLT recipients (1990-2020) and annually calculated standardized incidence ratios (SIRs) of DNMs compared to the age-adjusted Japanese general population.

RESULTS

After 21 845 person-years follow-up, 153 DNM lesions (8.6%) were identified in 131 patients (7.4%). The incidence was 0.007 person-years. DNMs included 81 post-transplant lymphoproliferative disorders (PTLDs), 14 colorectal, 12 lung, and 12 gastric cancers, and so on. Comorbid DNMs significantly worsened recipient survival than those without (p < .001). The 5- and 10-year recipient survival after DNM diagnosis were 65% and 58%, respectively. Notably, SIR1993-1995: 8.12 (95% CI: 3.71-15.4, p < .001) and SIR1996-1998: 3.11 (1.34-6.12, p = .01) were significantly high, but had decreased time-dependently to SIR2005-2007: 1.31 (0.68-2.29, p = .42) and SIR2008-2010: 1.34 (0.75-2.20, p = .33), indicating no longer significant difference in DNMs development. Currently, however, SIR2014-2016: 2.27 (1.54-3.22, p < .001) and SIR2017-2019: 2.07 (1.40-2.96, p < .001) have become significantly higher again, reflecting recent aging of recipients (>50 years) and resultant increases in non-PTLD DNMs. Furthermore, characteristically in LDLT, the fewer the donor-recipient HLA-mismatches, the less the post-transplant DNMs development.

CONCLUSION

DNM development after LDLT was significantly higher than in the general population due to higher PTLD incidence (1993-1998), but once became equivalent (2005-2013), then significantly increased again (2014-2019) due to recent recipient aging and resultant increase in solid cancers.

Successful Treatment of Intractable Tuberculous Peritonitis in a Woman with Chronic Kidney Allograft Dysfunction Using Contezolid Containing Regimen

Tuberculosis(TB) is a serious infection that affects transplant recipients, particularly in high TB burden countries. Clinical presentation of these patients is atypical, and the care and management are frequently tricky as multi-drug interaction and intolerable adverse effects. Contezolid, a novel oxazolidinone antibacterial agent, had been demonstrated to be effective for TB in vitro and had been shown in some clinical cases with a more favorable safety profile than linezolid, the first-generation oxazolidinone, which had a commonly seen myelosuppression and neuropathy. Additionally, Contezolid has a unique metabolic mechanism that leads to less drug interaction. Here, we report a case of multi-system TB in a transplant recipient with chronic kidney allograft dysfunction. She was intolerant to most first and second-line anti-TB drugs and repeatedly developed ascites and nocturnal low-grade fever. She finally achieved good efficacy and safety results after enhanced anti-TB treatment with the addition of contezolid. Given the increased risk of TB in patients with organ transplantation and multi-drug interaction in patients with severe comorbidities, further clinical studies are needed to investigate the application and appropriate dosage of contezolid in patients with active TB.

Overexpressed FKBP5 mediates colorectal cancer progression and sensitivity to FK506 treatment via the NF-κB signaling pathway

Colorectal cancer (CRC) is a common and deadly tumor. FK506-binding protein 5 (FKBP5) is associated with some cancers, but the role of FKBP5 in CRC is not clear. The present study aimed to reveal the relationship between FKBP5 and CRC and to uncover the roles of FK506 in CRC. In total, 96 CRC patients were recruited. Survival analysis was conducted using the Kaplan-Meier method and COX regression analyses. Bioinformatics analyses were performed to explore the functions of FKBP5. The mechanisms of FKBP5 and the roles of FK506 in CRC progression were clarified by immunohistochemistry, MTS, scratch assay, transwell and flow cytometric analyses via in vitro and in vivo experiments. FKBP5 was overexpressed in 77 cancer tissues compared to that in matched normal tissues, and the overall survival rate of these patients was relatively shorter. Bioinformatics analyses showed that FKBP5 regulates proliferation, invasion, migration, epithelial-mesenchymal transition and nuclear factor-kappa B (NF-κB) signaling. The upregulation or downregulation of FKBP5 dramatically increases or decreases the proliferation, invasion and migration abilities of CRC cells. The expression of NF-κB, inhibitor B kinase α, matrix metalloproteinase-2 and metalloproteinase-9 positively correlated with FKBP5. FK506 inhibits the progression of CRC via the FKBP5/NF-κB signaling pathway. Our study identified a regulatory role for FKBP5 in CRC progression. Therefore, targeting FKBP5 may provide a novel treatment approach for CRC. FK506 can inhibit the progression of CRC by restraining the FKBP5/NF-κB signaling pathway and is expected to become a new drug for the treatment of CRC.

Phenytoin enzyme induction for management of supratherapeutic tacrolimus levels due to drug-drug interaction with nirmatrelvir/ritonavir: Case series and discussion

PURPOSE

Nirmatrelvir/ritonavir is one of few options for outpatient treatment of COVID-19, but its use has been limited in transplant recipients due to significant drug interactions with immunosuppressants. Tacrolimus toxicity is possible when the drug is coadministered with nirmatrelvir/ritonavir and may require urgent reduction of tacrolimus levels. This case series describes the use of phenytoin for enzyme induction in 5 adult solid organ transplant recipients with supratherapeutic tacrolimus levels resulting from coadministration with nirmatrelvir/ritonavir.

SUMMARY

Solid organ transplant recipients are at high risk for complications related to COVID-19. Outpatient treatment options are limited, and therapeutic drug monitoring is complex in patients requiring quarantine. The 5 solid organ transplant recipients described herein were initiated on nirmatrelvir/ritonavir in the outpatient setting and subsequently presented with supratherapeutic tacrolimus concentrations greater than 59 ng/mL and developed signs and symptoms of tacrolimus toxicity. In all patients, nirmatrelvir/ritonavir and tacrolimus were discontinued, and oral phenytoin (200-400 mg/day) was given for 2 to 4 days. Tacrolimus was resumed once tacrolimus levels decreased to appropriate levels.

CONCLUSION

These observations demonstrate that metabolism induction using phenytoin may be a useful strategy in the setting of supratherapeutic tacrolimus levels resulting from concomitant administration with nirmatrelvir/ritonavir.

Genotype-Guided Model for Prediction of Tacrolimus Initial Dosing After Lung Transplantation

The determination of the appropriate initial dose for tacrolimus is crucial in achieving the target concentration promptly and avoiding adverse effects and poor prognosis. However, the trial-and-error approach is still common practice. This study aimed to establish a prediction model for an initial dosing algorithm of tacrolimus in patients receiving a lung transplant. A total of 210 lung transplant recipients were enrolled, and 26 single nucleotide polymorphisms (SNP) from 18 genes that could potentially affect tacrolimus pharmacokinetics were genotyped. Associations between SNPs and tacrolimus concentration/dose ratio were analyzed. SNPs that remained significant in pharmacogenomic analysis were further combined with clinical factors to construct a prediction model for tacrolimus initial dose. The dose needed to reach steady state tacrolimus concentrations and achieve the target range was used to validate model prediction efficiency. Our final model consisted of 7 predictors-CYP3A5 rs776746, SLCO1B3 rs4149117, SLC2A2 rs1499821, NFATc4 rs1955915, alanine aminotransferase, direct bilirubin, and hematocrit-and explained 41.4% variance in the tacrolimus concentration/dose ratio. It achieved an area under the receiver operating characteristic curve of 0.804 (95% confidence interval, 0.746-0.861). The Hosmer-Lemeshow test yielded a nonsignificant P value of .790, suggesting good fit of the model. The predicted dose exhibited good correlation with the observed dose in the early postoperative period (r = 0.748, P less than .001). Our study provided a genotype-guided prediction model for tacrolimus initial dose, which may help to guide individualized dosing of tacrolimus in the lung transplant population in clinical practice.

Population pharmacokinetics of everolimus in renal transplant recipients receiving long-term multiple immunosuppressive therapy

Everolimus is used for immunosuppression after renal transplantation. This study aimed to develop a population pharmacokinetic (PopPK) model of everolimus using therapeutic drug monitoring (TDM) data of patients under long-term multiple immunosuppressive therapy, including tacrolimus. To develop the model, 185 renal transplant recipients with 3358 everolimus blood concentrations during a median postoperative period of 35.3 months were included. The PopPK model is described as a one-compartment model with first-order absorption. The population mean of apparent clearance is 8.92 L/h (relative standard error = 3.6%), and this negatively correlated with the dose-normalized concentration (C/D) of tacrolimus and hematocrit value, and positively correlated with a daily dose of everolimus (i.e. TDM effect). The usefulness of dose adjustment using the final popPK model was assessed by a simulation study. The ratio of the first trough measurement within the therapeutic range of 3-8 ng/mL increased from 69.8% in the original dose to 87.9% in the individual dose calculated by the final PopPK model. The tacrolimus C/D ratio before initiating everolimus therapy and the hematocrit value were useful to estimate the initial dose of everolimus and can improve the safety and effectiveness of immunosuppressive therapy involving everolimus.

Recurrent rejections after liver transplantation for hepatocellular carcinoma with stem cell features in an adult patient

Patients with hepatoblastoma featuring carcinoma characteristics have better outcomes after liver transplantation, than after chemotherapy and resection. Possibly this should be extrapolated to aggressive subtypes of hepatocellular carcinomas in non-cirrhotic livers, where early liver transplantation might also be indicated. However, the risks associated with liver transplantation and immunosuppressive treatment after liver transplantation are once again demonstrated by this case of a 32-year-old women with a negative personal and familial history of liver diseases. She underwent transplantation (DBD) for a hepatocellular carcinoma with stem cell features (HCC-HS; an aggressive 'hepatoblast subtype' of hepatocellular carcinoma) after chemotherapeutical downstaging techniques failed to sufficiently downstage the tumor. Despite being on conventional immunosuppressive regimens (tacrolimus and mycophenolate mofetil with initial corticosteroids tapered), this patient still developed two severe rejection episodes, one of which necessitated retransplantation (DCD). Both episodes were preceded by alterations in tacrolimus trough levels, either intentionally, when tacrolimus was reduced within a nephroprotective regimen, or unintentionally, when rifampicin, a CYP3A4 inducer, significantly lowered the trough levels. Together, these episodes stress the importance of therapeutic drug monitoring of tacrolimus. Furthermore, the patient experienced an everolimus-linked drug-induced thrombotic microangiopathy, underwent multiple ERCPs for an anastomotic stricture and only one and a half year after the first liver transplantation she already suffers from long-term immunosuppressive-related side effects such as impaired glucose tolerance, hypertension and a potential cardiomyopathy. At present, she is still alive and experienced no recurrence of her primary tumor. Her case underscores the significant challenges in post-liver transplantation care.

Pharmacokinetic assessment of tacrolimus in combination with deoxyschizandrin in rats

Background

Tacrolimus (Tac) is commonly used for postoperative immunosuppressive therapy in transplant patients. However, problems, for example, low bioavailability and unstable plasma concentration, persist for a long time, Studies have reported that the deoxyschizandrin could effectively improve these problems, but the pharmacokinetic parameters (PKs) of Tac combined with deoxyschizandrin are still unknown.

Method

In this study, an UHPLC-MS/MS method has been established for simultaneous quantitation of Tac and deoxyschizandrin. The PKs of Tac influenced by different doses of deoxyschizandrin after single and multiple administrations were analyzed, and the different impact of deoxyschizandrin and Wuzhi capsule on PKs of Tac were compared.

Result

The modified UHPLC-MS/MS method could rapid quantification of Tac and deoxyschizandrin within 2 min using bifendatatum as the internal standard (IS). All items were successfully validated. The C max of deoxyschizandrin increased from 148.27 ± 23.20 to 229.13 ± 54.77 ng/mL in rats after multiple administrations for 12 days. After co-administration of 150 mg/mL deoxyschizandrin, Tac had an earlier T max and greater C max and AUC0-t, and the C max and AUC0-t of Tac increased from 14.26 ± 4.73 to 54.48 ± 14.37 ng/mL and from 95.10 ± 32.61 to 315.23 ± 92.22 h/ng/mL, respectively; this relationship was positively proportional to the dosage of deoxyschizandrin. In addition, compared with Wuzhi capsule, the same dose of deoxyschizandrin has a better effective on Tac along with more stable overall PKs.

Conclusion

An UHPLC-MS/MS method was established and validated for simultaneous detection of deoxyschizandrin and Tac. Deoxyschizandrin could improve the in vivo exposure level and stability of Tac, besides, this effect is better than Wuzhi capsule in same dose.

Tacrolimus's Time Below Therapeutic Range Is Associated With Acute Pancreatic Graft Rejection and the Development of De Novo Donor-specific Antibodies

Tacrolimus is pivotal in pancreas transplants but poses challenges in maintaining optimal levels due to recipient differences. This study aimed to explore the utility of time spent below the therapeutic range and intrapatient variability in predicting rejection and de novo donor-specific antibody (dnDSA) development in pancreas graft recipients. This retrospective unicentric study included adult pancreas transplant recipients between January 2006 and July 2020. Recorded variables included demographics, immunosuppression details, HLA matching, biopsy results, dnDSA development, and clinical parameters. Statistical analysis included ROC curves, sensitivity, specificity, and predictive values. A total of 131 patients were included. Those with biopsy-proven acute rejection (BPAR, 12.2%) had more time (39.9% ± 24% vs. 25.72% ± 21.57%, p = 0.016) and tests (41.95% ± 13.57% vs. 29.96% ± 17.33%, p = 0.009) below therapeutic range. Specific cutoffs of 31.5% for time and 34% for tests below the therapeutic range showed a high negative predictive value for BPAR (93.98% and 93.1%, respectively). Similarly, patients with more than 34% of tests below the therapeutic range were associated with dnDSA appearance (38.9% vs. 9.4%, p = 0.012; OR 6.135, 1.346-27.78). In pancreas transplantation, maintaining optimal tacrolimus levels is crucial. Suboptimal test percentages below the therapeutic range prove valuable in identifying acute graft rejection risk.

Association of CYP3A4-392A/G, CYP3A5-6986A/G, and ABCB1-3435C/T Polymorphisms with Tacrolimus Dose, Serum Concentration, and Biochemical Parameters in Mexican Patients with Kidney Transplant

Tacrolimus (TAC) is an immunosuppressant drug that prevents organ rejection after transplantation. This drug is transported from cells via P-glycoprotein (ABCB1) and is a metabolic substrate for cytochrome P450 (CYP) 3A enzymes, particularly CYP3A4 and CYP3A5. Several single-nucleotide polymorphisms (SNPs) have been identified in the genes encoding CYP3A4, CYP3A5, and ABCB1, including CYP3A4-392A/G (rs2740574), CYP3A5 6986A/G (rs776746), and ABCB1 3435C/T (rs1045642). This study aims to evaluate the association among CYP3A4-392A/G, CYP3A5-6986A/G, and ABCB1-3435C/T polymorphisms and TAC, serum concentration, and biochemical parameters that may affect TAC pharmacokinetics in Mexican kidney transplant (KT) patients.

METHODS

Forty-six kidney transplant recipients (KTR) receiving immunosuppressive treatment with TAC in different combinations were included. CYP3A4, CYP3A5, and ABCB1 gene polymorphisms were genotyped using qPCR TaqMan. Serum TAC concentration (as measured) and intervening variables were assessed. Logistic regression analyses were performed at baseline and after one month to assess the extent of the association between the polymorphisms, intervening variables, and TAC concentration.

RESULTS

The GG genotype of CYP3A5-6986 A/G polymorphism is associated with TAC pharmacokinetic variability OR 4.35 (95%CI: 1.13-21.9; p = 0.0458) at one month of evolution; in multivariate logistic regression, CYP3A5-6986GG genotype OR 9.32 (95%CI: 1.54-93.08; p = 0.028) and the use of medications or drugs that increase serum TAC concentration OR 9.52 (95%CI: 1.79-88.23; p = 0.018) were strongly associated with TAC pharmacokinetic variability.

CONCLUSION

The findings of this study of the Mexican population showed that CYP3A5-6986 A/G GG genotype is associated with a four-fold increase in the likelihood of encountering a TAC concentration of more than 15 ng/dL. The co-occurrence of the CYP3A5-6986GG genotype and the use of drugs that increase TAC concentration correlates with a nine-fold increased risk of experiencing a TAC at a level above 15 ng/mL. Therefore, these patients have an increased susceptibility to TAC-associated toxicity.