Evaluation of Limited Sampling Strategies for Mycophenolic Acid After Mycophenolate Mofetil Intake in Adult Kidney Transplant Recipients

Limited Sampling Strategies Fail to Accurately Predict Mycophenolic Acid Area Under the Curve in Kidney Transplant Recipients and the Impact of Enterohepatic Recirculation

BACKGROUND

Therapeutic drug monitoring for mycophenolic acid (MPA) is challenging due to difficulties in measuring the area under the curve (AUC). Limited sampling strategies (LSSs) have been developed for MPA therapeutic drug monitoring but come with risk of unacceptable performance. The authors hypothesized that the poor predictive performance of LSSs were due to the variability in MPA enterohepatic recirculation (EHR). This study is the first to evaluate LSSs models performance in the context of EHR.

METHODS

Adult kidney transplant recipients (n = 84) receiving oral mycophenolate mofetil underwent intensive MPA pharmacokinetic sampling. MPA AUC 0-12hr and EHR were determined. Published MPA LSSs in kidney transplant recipients receiving tacrolimus were evaluated for their predictive performance in estimating AUC 0-12hr in our full cohort and separately in individuals with high and low EHR.

RESULTS

None of the evaluated LSS models (n = 12) showed good precision or accuracy in predicting MPA AUC 0-12hr in the full cohort. In the high EHR group, models with late timepoints had better accuracy but low precision, except for 1 model with late timepoints at 6 and 10 hours postdose, which had marginally acceptable precision. For all models, the good guess of predicted AUC 0-12hr (±15% of observed AUC 0-12hr ) was highly variable (range, full cohort = 19%-61.9%; high EHR = 4.5%-65.9%; low EHR = 27.5%-62.5%).

CONCLUSIONS

The predictive performance of the LSS models varied according to EHR status. Timepoints ≥5 hours postdose in LSS models are essential to capture EHR. Models and strategies that incorporate EHR during development are required to accurately ascertain MPA exposure.

Clinical Evidence on the Purported Pharmacokinetic Interactions between Corticosteroids and Mycophenolic Acid

Corticosteroids (steroids) are commonly used concurrently with mycophenolic acid (MPA) as the first-line immunosuppression therapy for the prevention of rejection in solid organ transplantations. Steroids are also commonly administered with MPA in various autoimmune disorders such as systemic lupus erythematosus and idiopathic nephrotic syndrome. Despite various review articles having suggested the presence of pharmacokinetic interactions between MPA and steroids, definitive data have not yet been demonstrated. The aim of this Current Opinion is to critically evaluate the available clinical data and propose the optimal study design for characterising the MPA-steroid pharmacokinetic interactions. The PubMed and Embase databases were searched for relevant clinical articles in English as of September 29, 2022, where a total of 8 papers have been identified as supporting and 22 as non-supporting the purported drug interaction. To objectively evaluate the data, novel assessment criteria to effectively diagnose the interaction based on known MPA pharmacology were formulated, including the availability of independent control groups, prednisolone concentrations, MPA metabolite data, unbound MPA concentrations, and the characterisations of entero-hepatic recirculation and MPA renal clearance. Overall, the majority of the identified corticosteroid data were pertaining to prednisone or prednisolone. Our assessment indicated that no conclusive mechanistic data supporting the interaction are available in the current clinical literature, and further studies are required to quantify the effects/mechanisms of steroid-tapering or withdrawal on MPA pharmacokinetics. This current opinion provides justification for further translational investigations, as this particular drug interaction has the potential to exert significant adverse outcomes in patients prescribed MPA.

Effect of Meal Timings and Meal Content on the AUC0-12h of Mycophenolic Acid: A Simulation Study

Meal timings and content related to gallbladder emptying in the enterohepatic circulation are important for explaining the high variability in mycophenolic acid exposure. The limited sampling strategy (LSS) was established to estimate the area under the plasma concentration-time curve from time 0 to 12 hours (AUC_0-12h ) of mycophenolic acid in therapeutic drug monitoring. The aim of this study is to investigate the effect of meal timings and content on the AUC_0-12h of mycophenolic acid and to assess the influence of meals on LSS. A mycophenolic acid pharmacokinetic model with a mechanism-based enterohepatic circulation process was employed to perform simulations under various assumed meal scenarios. The simulations were compared to evaluate the effect of meal timings and meal content on mycophenolic acid AUC_0-12h . Monte Carlo simulations were performed using the meal parameter with the greatest impact on mycophenolic acid AUC_0-12h as a variable. The corresponding LSS equations were established, and the predictive performance was assessed. Both the meal timings and meal content affected the mycophenolic acid AUC_0-12h , and the postdose fasting period had the greatest impact. The predictive performance of the LSS is sensitive to the postdose fasting period. Therefore, meal timings may improve the estimation of mycophenolic acid AUC_0-12h and the efficacy of therapeutic drug monitoring.

Evaluation and Validation of the Limited Sampling Strategy of Polymyxin B in Patients with Multidrug-Resistant Gram-Negative Infection

Polymyxin B (PMB) is the final option for treating multidrug-resistant Gram-negative bacterial infections. The acceptable pharmacokinetic/pharmacodynamic target is an area under the concentration–time curve across 24 h at a steady state (AUC_ss,24h) of 50–100 mg·h/L. The limited sampling strategy (LSS) is useful for predicting AUC values. However, establishing an LSS is a time-consuming process requiring a relatively dense sampling of patients. Further, given the variability among different centers, the predictability of LSSs is frequently questioned when it is extrapolated to other clinical centers. Currently, limited data are available on a reliable PMB LSS for estimating AUC_ss,24h. This study assessed and validated the practicability of LSSs established in the literature based on data from our center to provide reliable and ready-made PMB LSSs for laboratories performing therapeutic drug monitoring (TDM) of PMB. The influence of infusion and sampling time errors on predictability was also explored to obtain the optimal time points for routine PMB TDM. Using multiple regression analysis, PMB LSSs were generated from a model group of 20 patients. A validation group (10 patients) was used to validate the established LSSs. PMB LSSs from two published studies were validated using a dataset of 30 patients from our center. A population pharmacokinetic model was established to simulate the individual plasma concentration profiles for each infusion and sampling time error regimen. Pharmacokinetic data obtained from the 30 patients were fitted to a two-compartment model. Infusion and sampling time errors observed in real-world clinical practice could considerably affect the predictability of PMB LSSs. Moreover, we identified specific LSSs to be superior in predicting PMB AUC_ss,24h based on different infusion times. We also discovered that sampling time error should be controlled within −10 to 15 min to obtain better predictability. The present study provides validated PMB LSSs that can more accurately predict PMB AUC_ss,24h in routine clinical practice, facilitating PMB TDM in other laboratories and pharmacokinetics/pharmacodynamics-based clinical studies in the future.

The Evaluation of Multiple Linear Regression-Based Limited Sampling Strategies for Mycophenolic Acid in Children with Nephrotic Syndrome

We evaluated mycophenolic acid (MPA) limited sampling strategies (LSSs) established using multiple linear regression (MLR) in children with nephrotic syndrome treated with mycophenolate mofetil (MMF). MLR-LSS is an easy-to-determine approach of therapeutic drug monitoring (TDM). We assessed the practicability of different LSSs for the estimation of MPA exposure as well as the optimal time points for MPA TDM. The literature search returned 29 studies dated 1998–2020. We applied 53 LSSs (n = 48 for MPA, n = 5 for free MPA [fMPA]) to predict the area under the time-concentration curve (AUC_pred) in 24 children with nephrotic syndrome, for whom we previously determined MPA and fMPA concentrations, and compare the results with the determined AUC (AUC_total). Nine equations met the requirements for bias and precision ±15%. The MPA AUC in children with nephrotic syndrome was predicted the best by four time-point LSSs developed for renal transplant recipients. Out of five LSSs evaluated for fMPA, none fulfilled the ±15% criteria for bias and precision probably due to very high percentage of bound MPA (99.64%). MPA LSS for children with nephrotic syndrome should include blood samples collected 1 h, 2 h and near the second MPA maximum concentration. MPA concentrations determined with the high performance liquid chromatography after multiplying by 1.175 may be used in LSSs based on MPA concentrations determined with the immunoassay technique. MPA LSS may facilitate TDM in the case of MMF, however, more studies on fMPA LSS are required for children with nephrotic syndrome.

Therapeutic drug monitoring of mycophenolate mofetil in pediatric patients: novel techniques and current opinion

Introduction: Mycophenolate mofetil (MMF) is an ester prodrug of the immunosuppressant mycophenolic acid (MPA) and is recommended and widely used for maintenance immunosuppressive therapy in solid organ and stem-cell transplantation as well as in immunological kidney diseases. MPA is a potent, reversible, noncompetitive inhibitor of the inosine monophosphate dehydrogenase (IMPDH), a crucial enzyme in the de novo purine synthesis in T- and B-lymphocytes, thereby inhibiting cell-mediated immunity and antibody formation. The use of therapeutic drug monitoring (TDM) of MMF is still controversial as outcome data of clinical trials are equivocal. Areas covered: This review covers in great depth the existing literature on TDM of MMF in the field of pediatric (kidney) transplantation. In addition, the relevance of TDM in immunological kidney diseases, in particular childhood nephrotic syndrome is highlighted. Expert opinion: TDM of MMF has the potential to optimize therapy in pediatric transplantation as well as in nephrotic syndrome. Limited sampling strategies to estimate MPA exposure increase its feasibility. Future perspectives rather encompass approaches reflecting total immunosuppressive load than single drug TDM.

A new model to determine Optimal Exposure to Tacrolimus and Mycophenolate Mofetil after renal transplantation

BACKGROUND

Drug dosing for Tacrolimus (TAC) and Mycophenolate Mofetil (MMF) after kidney transplantation remains challenging. Therapeutic drug monitoring (TDM) offers a means to individualize drug dosing and improve outcomes.

METHODS

In this observational study, patients having mycophenolic acid (MPA) exposure assessed by limited sampling strategy (LSS) within the first 6 months were included and followed for 1 year.

RESULTS

A total of 113 clinical events occurring in 110 patients were classified into 3 groups: Group 1 Stable (n = 34), Group 2 Over drug exposed (n = 64) having infections or drug toxicity and Group 3 Under drug exposed (n = 15) developing rejection or de novo donor-specific alloantibodies. Although TAC levels, MMF dose, MPA, and MPA Glucuronide (MPAG) exposure, expressed as area under curve (AUC), individually failed to predict outcomes, a scoring model incorporating all 3 drug levels TAC TDM × (MPA AUC + MPAG/10 AUC) correctly classified outcomes. A score over 1071 had a sensitivity and specificity of 0.94 (95% CI 0.56-0.83) and 0.84 (95% CI 0.69-0.89) for over exposure. A score below 625 had a sensitivity and specificity of 0.76 (95% CI 0.53-0.93) and 0.80 (95% CI 0.41-0.70) for under exposure.

CONCLUSIONS

This integrated model of assessing TAC and MMF exposure may facilitate individualized therapy.

Optimizing Mycophenolic Acid Exposure in Kidney Transplant Recipients: Time for Target Concentration Intervention

The immunosuppressive agent mycophenolate is used extensively in kidney transplantation, yet dosing strategy applied varies markedly from fixed dosing ("one-dose-fits-all"), to mycophenolic acid (MPA) trough concentration monitoring, to dose optimization to an MPA exposure target (as area under the concentration-time curve [MPA AUC0-12]). This relates in part to inconsistent results in prospective trials of concentration-controlled dosing (CCD). In this review, the totality of evidence supporting mycophenolate CCD is examined: pharmacological characteristics, observational data linking exposure to efficacy and toxicities, and randomized controlled trials of CCD, with attention to dose optimization method and exposure achieved. Fixed dosing of mycophenolate consistently leads to underexposure associated with rejection, as well as overexposure associated with toxicities. When CCD is driven by pharmacokinetic calculation to a target concentration (target concentration intervention), MPA exposure is successfully controlled and clinical benefits are seen. There remains a need for consensus on practical aspects of mycophenolate target concentration intervention in contemporary tacrolimus-containing regimens and future research to define maintenance phase exposure targets. However, given ongoing consequences of both overimmunosuppression and underimmunosuppression in kidney transplantation, impacting short- and long-term outcomes, these should be a priority. The imprecise "one-dose-fits-all" approach should be replaced by the clinically proven MPA target concentration strategy.

Pharmacokinetic Comparison of Two Mycophenolate Mofetil Formulations in Kidney Transplant Recipients

BACKGROUND

The aim of this study was to investigate and compare the pharmacokinetic (PK) characteristics of mycophenolate mofetil (MMF) capsule and MMF dispersible tablet by detecting the active metabolite of mycophenolic acid (MPA) in Chinese kidney transplant recipients.

METHODS

In the prospective, randomized, open-label study, the renal transplant patients were given a multiple dose of either the MMF capsule or MMF dispersible tablet combination with tacrolimus (Tac). For each patient, 11 serial blood samples were collected over 12 hours (h). Parameters including predose concentration (C0), postdose minimum and maximum concentration (Cmin and Cmax), time to Cmax (Tmax), total body clearance (CL), and area under the concentration-time curve for the 12-hour exposure (AUC0-12h) were determined. Patient interviews were conducted to assess the occurrence of adverse events.

RESULTS

Baseline characteristics were comparable between both groups. The C0, Cmin, Cmax, Tmax, CL, and AUC0-12h values were not significantly different after multiple doses of MMF capsule or MMF dispersible tablet (P > 0.05). The median values of AUC0-12h were 43.98 and 41.95 mcg·h/mL for MMF capsule and MMF dispersible tablet, respectively. Interindividual variability in Cmax, Cmin, and C0 were considerable in both groups. No serious adverse events were reported by patients or found on analysis of laboratory tests.

CONCLUSIONS

PK parameters of the 2 MPA drugs were comparable in early renal transplant patients in this study. The 2 formulations were well tolerated in Chinese kidney transplant patients.

Pharmacokinetics of Mycophenolate Mofetil and Development of Limited Sampling Strategy in Early Kidney Transplant Recipients

The mycophenolate mofetil (MMF) dose management for optimization of post-transplant treatment especially the early postoperative phase has been well recognized. MMF is a pro-drug of mycophenolic acid (MPA) and is widely used in Chinese renal transplant patients. Until now, the pharmacokinetic (PK) characteristics and model for the area under the concentration–time curve for the 12-h (h) of exposure (AUC_0-12h) of MPA (MPA-AUC_0-12h) estimation were lacking for the new formulation of MMF dispersible tablet in renal transplant patients. The aims of the study were to investigate the PK characteristics of MMF dispersible tablet by detecting the active metabolite of MPA and to establish an accuracy and precision equation for calculating MPA-AUC_0-12h by limited sampling strategy (LSS) in Chinese kidney transplant patients. A total of 60 postoperative kidney transplant recipients were given a multiple-dose of MMF dispersible tablet twice daily combination with tacrolimus (Tac) and steroids. On the 5th day post-transplantation, blood specimens were collected before drug administration and up to 12 h after MMF dispersible tablet administration. Non-compartmental PK analysis was used to determine the data obtained from individual patients. Multivariate stepwise regression analysis was used to develop models for predicting MPA-AUC_0-12h. The 3- and 4-point sampling models using 2 h, 4 h, 8 h and 1 h, 2 h, 4 h and 8 h, respectively, allowed accurate estimation of MPA-AUC_0-12h. PK parameters of MMF dispersible tablet were obtained and the 4-point LSS is the best model for accurate and precise estimation of MPA-AUC_0-12h.

Limited Sampling Strategy for Estimating Mycophenolic Acid Exposure on Day 7 Post-Transplant for Two Mycophenolate Mofetil Formulations Derived From 20 Chinese Renal Transplant Recipients

PURPOSE

To assess the pharmacokinetic properties of mycophenolate mofetil (MMF) dispersible tablets and capsules by the enzyme multiplied immunoassay technique (EMIT) in Chinese kidney transplant recipients in the early post-transplantation phase and to develop the equations to predict mycophenolic acid (MPA) area under the 12-hour concentration-time curve (AUC_0-12h) using a limited sampling strategy (LSS).

METHODS

Forty patients who underwent renal transplantation from brain-dead donors were randomly divided into dispersible tablets (Sai KE Ping; Hangzhou Zhongmei Huadong Pharma) and capsules (Cellcept; Roche Pharma, Why, NSW, Australia) groups, and treated with MMF combined with combination tacrolimus and prednisone as a basic immunosuppressive regimen. Blood samples were collected before treatment (0) and at 0.5,1, 1.5, 2, 4, 6, 8, 10, and 12 hours post-treatment and 7 days after renal transplantation. Plasma MPA concentrations were measured using EMIT. LSS equations were identified using multiple stepwise linear regression analysis.

RESULTS

The peak concentration (C_max) in the MMF dispersible tablets (MMFdt) group (7.0 ± 2.8) mg/L was reduced compared with that in the MMF capsules (MMFc) group (10.8 ± 6.2 mg/L; P = .012); time to peak concentration in the MMFdt group was 3.2 ± 2.3 hours, which was nonsignificantly elevated compared with that of the MMFc group (2.2 ± 1.7 hours). Three-point estimation formulas were generated by multiple linear regression for both groups: MPA-AUC_MMFdt = 3.542 + 3.332C_0.5h + 1.117C_1.5h + 3.946C_4h (adjusted r² = 0.90, P < .001); MPA-AUC_MMFc = 8.149 + 1.442C_2h + 1.056C_4h + 7.133C_6h (adjusted r² = 0.88, P < .001). Both predicted and measured AUCs showed good consistency.

CONCLUSIONS

After treatment with MMF dispersible tables or MMF capsules, the C_max of MPA for the MMFdt group was significantly lower than that of the MMFc group; there was no significant difference in other pharmacokinetic parameters. Three-time point equations can be used as a predictable measure of the AUC_0-12h of MPA.

Pharmacokinetics and target attainment of mycophenolate in pediatric renal transplant patients

MPA is an immunosuppressive agent used to prevent graft rejection after renal transplantation. MPA shows considerable inter- and intraindividual variability in exposure in children and has a defined therapeutic window, and TDM is applied to individualize therapy. We aimed to study the exposure to MPA measured as the AUC in pediatric renal transplant patients, to identify factors influencing exposure and to assess target attainment. Children transplanted between 1998 and 2014 in a single center were included. Two groups were identified: Group 1 (AUC <3 wk post-transplantation) and Group 2 (AUC >18 months post-transplantation). Therapeutic targets were set at: AUC0-12h of 30-60 mg h/L. A total of 39 children were included in Group 1 (median age 13.3 yr) vs. 14 in Group 2 (median age 13.4 yr). AUC0-12h was 29.7 mg h/L in Group 1 and 56.6 mg h/L in Group 2, despite a lower dosage in Group 2 (584 and 426 mg/m(2) , respectively). About 46% of patients reached the target AUC0-12h in Group 1. Time since transplantation and serum creatinine were significantly associated with MPA exposure (p < 0.001), explaining 36% of the variability. Individualization of the mycophenolate dose by more intense and more early TDM could improve target attainment.

How accurate and precise are limited sampling strategies in estimating exposure to mycophenolic acid in people with autoimmune disease?

Mycophenolic acid (MPA) is a potent immunosuppressant agent, which is increasingly being used in the treatment of patients with various autoimmune diseases. Dosing to achieve a specific target MPA area under the concentration-time curve from 0 to 12 h post-dose (AUC12) is likely to lead to better treatment outcomes in patients with autoimmune disease than a standard fixed-dose strategy. This review summarizes the available published data around concentration monitoring strategies for MPA in patients with autoimmune disease and examines the accuracy and precision of methods reported to date using limited concentration-time points to estimate MPA AUC12. A total of 13 studies were identified that assessed the correlation between single time points and MPA AUC12 and/or examined the predictive performance of limited sampling strategies in estimating MPA AUC12. The majority of studies investigated mycophenolate mofetil (MMF) rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation of MPA. Correlations between MPA trough concentrations and MPA AUC12 estimated by full concentration-time profiling ranged from 0.13 to 0.94 across ten studies, with the highest associations (r (2) = 0.90-0.94) observed in lupus nephritis patients. Correlations were generally higher in autoimmune disease patients compared with renal allograft recipients and higher after MMF compared with EC-MPS intake. Four studies investigated use of a limited sampling strategy to predict MPA AUC12 determined by full concentration-time profiling. Three studies used a limited sampling strategy consisting of a maximum combination of three sampling time points with the latest sample drawn 3-6 h after MMF intake, whereas the remaining study tested all combinations of sampling times. MPA AUC12 was best predicted when three samples were taken at pre-dose and at 1 and 3 h post-dose with a mean bias and imprecision of 0.8 and 22.6 % for multiple linear regression analysis and of -5.5 and 23.0 % for maximum a posteriori (MAP) Bayesian analysis. Although mean bias was less when data were analysed using multiple linear regression, MAP Bayesian analysis is preferable because of its flexibility with respect to sample timing. Estimation of MPA AUC12 following EC-MPS administration using a limited sampling strategy with samples drawn within 3 h post-dose resulted in biased and imprecise results, likely due to a longer time to reach a peak MPA concentration (t max) with this formulation and more variable pharmacokinetic profiles. Inclusion of later sampling time points that capture enterohepatic recirculation and t max improved the predictive performance of strategies to predict EC-MPS exposure. Given the considerable pharmacokinetic variability associated with mycophenolate therapy, limited sampling strategies may potentially help in individualizing patient dosing. However, a compromise needs to be made between the predictive performance of the strategy and its clinical feasibility. An opportunity exists to combine research efforts globally to create an open-source database for MPA (AUC, concentrations and outcomes) that can be used and prospectively evaluated for AUC target-controlled dosing of MPA in autoimmune diseases.

Safety of reduced dose of mycophenolate mofetil combined with tacrolimus in living-donor liver transplantation

Background/Aims

The dose of mycophenolate mofetil (MMF) has been reduced in Asia due to side effects associated with the conventional fixed dose of 2-3 g/day. We aimed to determine the pharmacokinetics of a reduced dose of MMF and to validate its feasibility in combination with tacrolimus in living-donor liver transplantation (LDLT).

Methods

Two sequential studies were performed in adult LDLT between October 2009 and 2011. First, we performed a prospective pharmacokinetic study in 15 recipients. We measured the area under the curve from 0 to 12 hours (AUC_0-12) for mycophenolic acid at postoperative days 7 and 14, and we performed a protocol biopsy before discharge. Second, among 215 recipients, we reviewed 74 patients who were initially administered a reduced dose of MMF (1.0 g/day) with tacrolimus (trough, 8-12 ng/mL during the first month, and 5-8 ng/mL thereafter), with a 1-year follow-up. We performed protocol biopsies at 2 weeks and 1 year post-LDLT.

Results

In the first part of study, AUC_0-12 was less than 30 mgh/L in 93.3% of cases. In the second, validating study, 41.9% of the recipients needed dose reduction or cessation due to side effects within the first year after LDLT. At 12 months post-LDLT, 17.6% of the recipients were administered a lower dose of MMF (0.5 g/day), and 16.2% needed permanent cessation due to side effects. The 1- and 12-month rejection-free survival rates were 98.6% and 97.3%, respectively.

Conclusions

A reduced dose of MMF was associated with low blood levels compared to the existing recommended therapeutic range. However, reducing the dose of MMF combined with a low level of tacrolimus was feasible clinically, with an excellent short-term outcome in LDLT.

Mycophenolate mofetil in patients with anti-neutrophil cytoplasmic antibody-associated vasculitis: a prospective pharmacokinetics and clinical study

Anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV) treatment strategy is based on immunosuppressive agents. Little information is available concerning mycophenolic acid (MPA) and the area under the curve (AUC) in patients treated for AAV. We evaluated the variations in pharmacokinetics for MPA in patients with AAV and the relationship between MPA-AUC and markers of the disease. MPA blood concentrations were measured through the enzyme-multiplied immunotechnique (C(0), C(30), C(1), C(2), C(3), C(4), C(6) and C(9)) to determine the AUC. Eighteen patients were included in the study. The median (range) MPA AUC(0-12) was 50·55 (30·9-105·4) mg/h/l. The highest coefficient of determination between MPA AUC and single concentrations was observed with C(3) (P < 0·0001) and C(2) (P < 0·0001) and with C(4) (P < 0·0005) or C(0) (P < 0·001). Using linear regression, the best estimation of MPA AUC was provided by a model including C(30), C(2) and C(4): AUC = 8·5 + 0·77 C(30) + 4·0 C(2) + 1·7 C(4) (P < 0·0001). Moreover, there was a significant relationship between MPA AUC(0-12) and lymphocyte count (P < 0·01), especially CD19 (P < 0·005), CD8 (P < 0·05) and CD56 (P < 0·05). Our results confirm the interindividual variability of MPA AUC in patients treated with MMF in AAV and support a personalized therapy according to blood levels of MPA.

Limited sampling strategy of mycophenolic acid in adult kidney transplant recipients: influence of the post-transplant period and the pharmacokinetic profile

We aimed to develop an accurate and convenient LSS for predicting MPA-AUC(0-12 hours) in Tunisian adult kidney transplant recipients whose immunosuppressive regimen consisted of MMF and tacrolimus combination with regards to the post-transplant period and the pharmacokinetic profile. Each pharmacokinetic profile consisted of eight blood samples collected during the 12-hour dosing interval. The AUC(0-12 hours) was calculated according to the linear trapezoidal rule. The MPA concentrations at each sampling time were correlated by a linear regression analysis with the measured AUC(0-12). We analyzed all the developed models for their ability to estimate the MPA-AUC(0-12 hours). The best multilinear regression model for predicting the full MPA-AUC(0-12 hours) was found to be the combination of C1, C4, and C6. All the best correlated models and the most convenient ones were verified to be also applicable before 5 months after transplantation and thereafter. These models were also verified to be applicable for patients having or not the second peak in their pharmacokinetic profiles. For practical reasons we recommend a LSS using C0, C1, and C4 that provides a reasonable MPA-AUC(0-12 hours) estimation.

Evaluation of limited sampling models for prediction of oral midazolam AUC for CYP3A phenotyping and drug interaction studies

BACKGROUND

The area under the concentration-time curve (AUC) after oral midazolam administration is commonly used for cytochrome P450 (CYP) 3A phenotyping studies. The aim of this investigation was to evaluate a limited sampling strategy for the prediction of AUC with oral midazolam.

METHODS

A total of 288 concentration-time profiles from 123 healthy volunteers who participated in four previously performed drug interaction studies with intense sampling after a single oral dose of 7.5 mg midazolam were available for evaluation. Of these, 45 profiles served for model building, which was performed by stepwise multiple linear regression, and the remaining 243 datasets served for validation. Mean prediction error (MPE), mean absolute error (MAE) and root mean squared error (RMSE) were calculated to determine bias and precision

RESULTS

The one- to four-sampling point models with the best coefficient of correlation were the one-sampling point model (8 h; r (2) = 0.84), the two-sampling point model (0.5 and 8 h; r (2) = 0.93), the three-sampling point model (0.5, 2, and 8 h; r (2) = 0.96), and the four-sampling point model (0.5,1, 2, and 8 h; r (2) = 0.97). However, the one- and two-sampling point models were unable to predict the midazolam AUC due to unacceptable bias and precision. Only the four-sampling point model predicted the very low and very high midazolam AUC of the validation dataset with acceptable precision and bias. The four-sampling point model was also able to predict the geometric mean ratio of the treatment phase over the baseline (with 90 % confidence interval) results of three drug interaction studies in the categories of strong, moderate, and mild induction, as well as no interaction.

CONCLUSION

A four-sampling point limited sampling strategy to predict the oral midazolam AUC for CYP3A phenotyping is proposed. The one-, two- and three-sampling point models were not able to predict midazolam AUC accurately.

Maximum a posteriori Bayesian estimation of mycophenolic Acid area under the concentration-time curve: is this clinically useful for dosage prediction yet?

This review seeks to summarize the available data about Bayesian estimation of area under the plasma concentration-time curve (AUC) and dosage prediction for mycophenolic acid (MPA) and evaluate whether sufficient evidence is available for routine use of Bayesian dosage prediction in clinical practice. A literature search identified 14 studies that assessed the predictive performance of maximum a posteriori Bayesian estimation of MPA AUC and one report that retrospectively evaluated how closely dosage recommendations based on Bayesian forecasting achieved targeted MPA exposure. Studies to date have mostly been undertaken in renal transplant recipients, with limited investigation in patients treated with MPA for autoimmune disease or haematopoietic stem cell transplantation. All of these studies have involved use of the mycophenolate mofetil (MMF) formulation of MPA, rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation. Bias associated with estimation of MPA AUC using Bayesian forecasting was generally less than 10%. However some difficulties with imprecision was evident, with values ranging from 4% to 34% (based on estimation involving two or more concentration measurements). Evaluation of whether MPA dosing decisions based on Bayesian forecasting (by the free website service https://pharmaco.chu-limoges.fr) achieved target drug exposure has only been undertaken once. When MMF dosage recommendations were applied by clinicians, a higher proportion (72-80%) of subsequent estimated MPA AUC values were within the 30-60 mg · h/L target range, compared with when dosage recommendations were not followed (only 39-57% within target range). Such findings provide evidence that Bayesian dosage prediction is clinically useful for achieving target MPA AUC. This study, however, was retrospective and focussed only on adult renal transplant recipients. Furthermore, in this study, Bayesian-generated AUC estimations and dosage predictions were not compared with a later full measured AUC but rather with a further AUC estimate based on a second Bayesian analysis. This study also provided some evidence that a useful monitoring schedule for MPA AUC following adult renal transplant would be every 2 weeks during the first month post-transplant, every 1-3 months between months 1 and 12, and each year thereafter. It will be interesting to see further validations in different patient groups using the free website service. In summary, the predictive performance of Bayesian estimation of MPA, comparing estimated with measured AUC values, has been reported in several studies. However, the next step of predicting dosages based on these Bayesian-estimated AUCs, and prospectively determining how closely these predicted dosages give drug exposure matching targeted AUCs, remains largely unaddressed. Further prospective studies are required, particularly in non-renal transplant patients and with the EC-MPS formulation. Other important questions remain to be answered, such as: do Bayesian forecasting methods devised to date use the best population pharmacokinetic models or most accurate algorithms; are the methods simple to use for routine clinical practice; do the algorithms actually improve dosage estimations beyond empirical recommendations in all groups that receive MPA therapy; and, importantly, do the dosage predictions, when followed, improve patient health outcomes?

Omeprazole impairs the absorption of mycophenolate mofetil but not of enteric-coated mycophenolate sodium in healthy volunteers

In 2 crossover studies, 12 healthy volunteers (6 male/6 female) received a single oral dose of mycophenolate mofetil (MMF) 1000 mg or an equimolar dose of enteric-coated mycophenolate sodium (EC-MPS) 720 mg fasting with and without coadministered omeprazole 20 mg bid. The plasma concentrations of mycophenolic acid (MPA) and of the inactive metabolite mycophenolic acid glucuronide (MPA-G) were measured by high-performance liquid chromatography (HPLC). In addition, dissolution of MMF 500 mg or EC-MPS 360 mg tablets was determined using an USP paddle apparatus in aqueous buffer of pH 1 to 7. The bioavailability of MPA following administration of MMF or EC-MPS was similar except for the time to peak concentration, which was longer in the EC-MPS group. Concomitant treatment with omeprazole lowered significantly C(max) and AUC(12h) of MPA following administration of MMF. The pharmacokinetics of EC-MPS was not affected. Dissolution of MMF in aqueous buffer decreased dramatically at pH above 4.5. The EC-MPS tablet was stable up to pH 5. Above, EC-MPS was quantitatively disintegrated and MPS quantitatively dissolved. There is strong evidence that impaired absorption of MMF with concomitant proton pump inhibitors is due to incomplete dissolution of MMF in the stomach at elevated pH.