Alterations of CYP3A4 and P-glycoprotein activity in vivo with time in renal graft recipients

Prescribing Pattern and Safety of Immunosuppressants in Renal Transplant Patients: An Observational Study

BACKGROUND

Renal transplantation is a life-saving procedure and contributes to a better quality of life in patients with end-stage renal disease. The discovery and use of immunosuppressants to prevent and treat allograft rejection are responsible for the improved outcome after the transplant. Long-term usage of these drugs warrants special monitoring and follow-up of the adverse drug reactions developed during the post-transplant period. This study analyzes the prescribing pattern and severity and outcome of adverse drug reactions of immunosuppressants in renal transplant patients.

MATERIALS AND METHODS

A cross-sectional, observational study was done in patients more than 18 years of age who have undergone renal transplantation and receiving immunosuppressants in the Department of Nephrology in a tertiary care hospital.

RESULTS

During the two-month study period, 150 post-transplant patients were screened for adverse drug reactions, and the prescription pattern was also studied. Immunosuppressive therapy was given as induction and maintenance therapy. The short-term induction therapy regimen was based on the type of donor (injection basiliximab or anti-thymocyte globulin). The long-term maintenance therapy comprises triple therapy of tacrolimus, mycophenolate mofetil, and prednisolone in 102 (68%) patients and cyclosporine, mycophenolate mofetil, prednisolone in 37 (25%) patients. A total of 116 adverse drug reactions were reported in 82 patients. The pattern of the adverse drug reactions showed urinary tract infections in 26 (17.3%) patients on tacrolimus-based regimen and hypertension in 20 (13.3%) patients on tacrolimus and cyclosporine-based regimen. Causality assessment using the World Health Organization causality assessment scale showed that the observed reactions were of probable 42 (36%) and possible 74 (64%) categories.

CONCLUSIONS

Long-term intake of immunosuppressive drugs is essential to improve the quality of life in renal transplant individuals and it is essential to monitor adverse drug reactions of these drugs through vigilant self-reporting and pharmacovigilance practices.

Potential drug-drug interactions in hospitalised haematological patients

Background Frequently, haematological patients undergo highly complex and intensive treatment protocols, so a high risk of drug-drug interactions could be expected. Objectives To determine prevalence of clinically relevant drug-drug interactions, to identify the most frequent drug-drug interactions and associated risk factors. Methods A prospective, observational and descriptive study was carried out from November 2012 to February 2013. Twice a week, every patient's treatment sheet was collected. Each medication list was screened through two databases: Thomson MicromedexTM and Drug Interaction FactsTM. All identified potential drug-drug interactions with a moderate or higher severity rating were recorded. Summary statistics were used to describe patient and disease characteristics, most often prescribed drugs, and frequency, types and classification of drug-drug interactions. Multiple logistic regression models were used to identify risk factors associated with drug-drug interactions. Results A total of 2061 drug-drug interactions were detected in 317 treatment sheets from 58 patients. The prevalence of treatment sheets with drug-drug interactions by Micromedex and Drug Interaction Facts databases were 74.1% and 56.8%, respectively. Azole antifungals, immunosuppressive drugs, antiemetics, antidepressants, acid suppressants and corticosteroids were the most frequent involved drugs. In multivariate analysis, the main risk factor associated with increased odds for drug-drug interactions was a higher number of non-antineoplastic drugs. Conclusions The prevalence of drug-drug interactions was common, with immunosuppressant and azole antifungal agents being the most commonly involved drugs. The factor having the greatest influence on drug-drug interactions was a higher number of non-antineoplastic drugs.

Bioavailability, Efficacy and Safety of Generic Immunosuppressive Drugs for Kidney Transplantation: A Systematic Review and Meta-Analysis

BACKGROUND

Concerns exist over the extrapolation of bioavailability studies of generic immunosuppressive drugs in healthy volunteers, regarding their efficacy and safety in kidney transplant recipients. We conducted a meta-analysis of trials examining the bioavailability of generic (test) immunosuppressive drugs relative to their brand (reference) counterparts in healthy volunteers, based on the US Food and Drug Administration requirements for approval of generics, and their efficacy and safety in kidney transplant recipients.

METHODS

Eligible studies were identified in PubMed, Cochrane Central Register of Controlled Trials, Scopus, ClinicalTrials.gov, and conference abstracts.

RESULTS

Twenty crossover trials of healthy volunteers (n = 641) and 6 parallel-arm randomized controlled trials of kidney transplant recipients (n = 594) were identified. The 90% CI of the pooled test-to-reference drug ratio for maximum or peak plasma concentration (Cmax) and area under the plasma concentration time-curve from time 0 to time of last determinable concentration (AUC(0-t)) fell within the required range (0.80-1.25) for cyclosporine (Cmax 0.91; 90% CI 0.86-0.95; and AUC(0-t) 0.97; 90% CI 0.94-1.00), tacrolimus (Cmax 1.17; 90% CI 1.09-1.24; and AUC(0-t) 1.00; 90% CI 0.97-1.03) and mycophenolate mofetil (Cmax 0.98; 90% CI 0.96-1.01; and AUC(0-t) 1.00; 90% CI 0.99-1.01). In subgroup analyses, some generic cyclosporine formulations did not meet criteria for bioequivalence. No significant differences were observed in the time to maximum plasma concentration and terminal plasma half-life between generic and brand drugs. In parallel-arm trials, generic cyclosporine was non-inferior to brand counterpart in terms of acute allograft rejection, infections, and death.

CONCLUSIONS

Not all generic immunosuppressive drugs have similar relative bioavailability to their brand name counterparts. Evidence on their efficacy and safety is inconclusive. Tighter regulatory requirement for approval of generic drugs with narrow therapeutic index is needed.

Effect of CYP3A5 genotype, steroids, and azoles on tacrolimus in a pediatric renal transplant population

BACKGROUND

Numerous studies have described the impact of cytochrome P450 3A5 (CYP3A5) genotype on Tacrolimus (TAC) exposure. The purpose of this study was to conduct a comprehensive analysis of genetic and non-genetic factors affecting the TAC dose-exposure relationship over the first year post pediatric renal transplant.

METHODS

Data were collected retrospectively for the first year post-transplant in pediatric renal transplant patients receiving TAC maintenance immunosuppression. The effect of CYP3A5 genotype (CYP3A5*3 and *6 alleles), age, azoles, and corticosteroids on TAC trough concentration normalized for dose (TAC Co/D ng/ml/mg/kg/day) was assessed using a linear mixed model.

RESULTS

Over time, TAC Co/D was lower in recipients with CYP3A5*1/*3 genotype compared to those with CYP3A5*3/*3 genotype (44.5 ± 14.4 vs. 107.6 ± 6.4, p = 0.03), increased in patients >12 years of age compared to < 12 years (93.9 ± 8.7 vs. 53.1 ± 12.9, p = 0.007), and decreased by concomitant corticosteroids (69.5 ± 12.7 vs. 89.9 ± 20.0, p = 0.04). The observed increased TAC Co/D in the presence of azoles (271 ± 41 vs. 111 ± 91, p = 0.016) could be attributed to clotrimazole.

CONCLUSIONS

Multiple factors, including CYP3A5 genotype, and age, influence TAC Co/D in pediatric kidney transplant recipients. Clotrimazole administered as troches also contribute to TAC Co/D variability.

Donor ABCB1 variant associates with increased risk for kidney allograft failure

The impact of variation within genes responsible for the disposition and metabolism of calcineurin inhibitors (CNIs) on clinical outcomes in kidney transplantation is not well understood. Furthermore, the potential influence of donor, rather than recipient, genotypes on clinical endpoints is unknown. Here, we investigated the associations between donor and recipient gene variants with outcome among 4471 white, CNI-treated kidney transplant recipients. We tested for 52 single-nucleotide polymorphisms (SNPs) across five genes: CYP3A4, CYP3A5, ABCB1 (MDR1; encoding P-glycoprotein), NR1I2 (encoding the pregnane X receptor), and PPIA (encoding cyclophilin). In a discovery cohort of 811 patients from Birmingham, United Kingdom, kidney donor CC genotype at C3435T (rs1045642) within ABCB1, a variant known to alter protein expression, was associated with an increased risk for long-term graft failure compared with non-CC genotype (hazard ratio [HR], 1.69; 95% confidence interval [CI], 1.20-2.40; P=0.003). No other donor or recipient SNPs were associated with graft survival or mortality. We validated this association in 675 donors from Belfast, United Kingdom (HR, 1.68; 95% CI, 1.21-2.32; P=0.002), and in 2985 donors from the Collaborative Transplant Study (HR, 1.84; 95% CI, 1.08-3.13; P=0.006). In conclusion, these data suggest that an ABCB1 variant known to alter protein expression represents an attractive candidate for future study and risk stratification in kidney transplantation.

Change of Cyclosporine Absorption over the Time after Kidney Transplantation

Background

Although the immunosuppressant cyclosporine (CsA) is widely used after kidney transplantation over the long term, there is still no firm consensus on the best way to monitor of CsA blood levels.

Objectives

Cyclosporine (CsA) assay is critical for the management of renal transplant recipients due to inter– and intra–patient variation in CsA absorption and metabolism. Patients and Methods: In a retrospective cross sectional study, blood levels of CsA (through and 2 hours post dose) measured at least 5 times during 3 years post transplantation, in 7702 kidney transplant recipients from different transplant center of Tehran, IR Iran between 2008 and 2012. Cyclosporine absorption (CA) calculated C2/C0 ratio.

Results

CA had a significant correlation with allograft function (P = 0.000, r =.0.285), this correlation was stronger than its relationship with C0 and C2 blood levels (P = 0.000 and P = 0.000 as well as r = 0.033 and r = 0.090, respectively). In univariate analysis during different times after transplantation, C0 and C2 blood levels significantly decreased over three years follow up (P = 0.000), (P = 0.000); While, CA reversely increases over the time (P = 0.000). In linear regression model overall CA levels had correlation with lower age of recipient (P = 0.02), hypokalemia (P = 0.001), higher level of creatinine (P = 0.02) and triglyceride (P = 0.001).

Conclusions

The present study shows that CsA absorption changes trough the post-transplant time and appears to increases over time in long–term period after kidney transplantation.

ABCB1 single-nucleotide polymorphisms determine tacrolimus response in patients with ulcerative colitis

Tacrolimus (Tac) is effective in the treatment of steroid-refractory ulcerative colitis (UC); however, nonresponse and unpredictable side effects are major limitations. Because Tac response in patients who have undergone solid-organ transplantation has been associated with the presence of variants in CYP3A and ABCB1, we elucidated the contributions of CYP3A4*1B and CYP3A5*3 and of ABCB1 1236C>T, 2677G>T,A, and 3435C>T polymorphisms to Tac response in 89 patients with UC. Short-term remission and response were achieved in 61 and 14% of the patients, respectively, and were associated with colectomy-free survival. In a linear logistic regression model, patients with homozygous variants for one of the three ABCB1 alleles showed significantly higher short-term remission rates as compared with those of other genotypes. The effects held true after multivariate analysis including multiple comparisons and were more pronounced after correction for dose-adjusted Tac blood trough levels. We suggest that ABCB1, but not CYP3A5, may predict short-term remission of Tac in steroid-refractory UC.

Effect of CYP3A and ABCB1 single nucleotide polymorphisms on the pharmacokinetics and pharmacodynamics of calcineurin inhibitors: Part I

The calcineurin inhibitors ciclosporin (cyclosporine) and tacrolimus are immunosuppressant drugs used for the prevention of organ rejection following transplantation. Both agents are metabolic substrates for cytochrome P450 (CYP) 3A enzymes--in particular, CYP3A4 and CYP3A5--and are transported out of cells via P-glycoprotein (ABCB1). Several single nucleotide polymorphisms (SNPs) have been identified in the genes encoding for CYP3A4, CYP3A5 and P-glycoprotein, including CYP3A4 -392A>G (rs2740574), CYP3A5 6986A>G (rs776746), ABCB1 3435C>T (rs1045642), ABCB1 1236C>T (rs1128503) and ABCB1 2677G>T/A (rs2032582). The aim of this review is to provide the clinician with an extensive overview of the recent literature on the known effects of these SNPs on the pharmacokinetics of ciclosporin and tacrolimus in solid-organ transplant recipients. Literature searches were performed, and all relevant primary research articles were critiqued and summarized. Influence of the CYP3A4 -392A>G SNP on the pharmacokinetics of either ciclosporin or tacrolimus appears limited. Variability in CYP3A4 expression due to environmental factors is likely to be more important than patient genotype. Influence of the CYP3A5 6986A>G SNP on the pharmacokinetics of ciclosporin is also uncertain and likely to be small. CYP3A4 may play a more dominant role than CYP3A5 in the metabolism of ciclosporin. The CYP3A5 6986A>G SNP has a well established influence on the pharmacokinetics of tacrolimus. Several studies in kidney, heart and liver transplant recipients have reported an approximate halving of tacrolimus dose-adjusted trough concentrations and doubling of tacrolimus dose requirements in heterozygous or homozygous carriers of a CYP3A5*1 wild-type allele compared with homozygous carriers of a CYP3A5*3 variant allele. Carriers of a CYP3A5*1 allele take a longer time to reach target blood tacrolimus concentrations. Influence of ABCB1 3435C>T, 1236C>T and 2677G>T/A SNPs on the pharmacokinetics of ciclosporin and tacrolimus remains uncertain, with inconsistent results. Genetic linkage between the three variant genotypes suggests that the pharmacokinetic effects are complex and not related to any one ABCB1 SNP. It is likely that these polymorphisms exert a small but combined effect, which is additive to the effects of the CYP3A5 6986A>G SNP. In liver transplant patients, recipient and donor liver genotypes may act together in determining overall drug disposition, hence the importance of assessing both. Studies with low patient numbers may account for many inconsistent results to date. Meta-analyses of the current data should help resolve some discrepancies. The majority of studies have only evaluated the effects of individual SNPs; however, multiple polymorphisms may interact to produce a combined effect. Further haplotype analyses are likely to be useful. It is not yet clear whether pharmacogenetic profiling of calcineurin inhibitors will be a useful clinical tool for personalizing immunosuppressant therapy.

Different evolution of trough and dose levels during the first year after transplantation for tacrolimus versus cyclosporine

At present, the two calcineurin inhibitors-cyclosporine (CsA) and tacrolimus (FK506)-are among the most frequently used immunosuppressants in clinical transplantation. Both drugs share variable oral bioavailability, which necessitates intense drug monitoring. This variability is attributed to large interindividual differences in drug catabolism by cytochrome P450 3A4/5 (CYP3A4/5) and drug efflux by P-glycoprotein (PGP). In addition, the activity of both CYP3A4 and PGP can vary substantially within the same individual due to environmental factors such as concomitant intake of inducing/inhibiting medications (eg, rifampicin/sporanox) or food substances (eg, grapefruit juice). More recently, an inducing effect of methylprednisolone on intestinal and hepatic CYP3A4 has been shown. Also, an influence of gender on CYP3A4 activity (being higher in women) has been reported. Once CsA and FK506 are absorbed and reach the bloodstream, both drugs are avidly bound to erythrocytes (up to 95% for FK506 and 50% for CsA) and plasma proteins, leaving only a small fraction of circulating active drug. This phenomenon also limits further hepatic catabolism and hence clearance of drug, which is influenced by hematocrit and levels of plasma proteins such as albumin. The aim of the present study was to compare the influence of changing steroid doses, hematocrit, and albumin on trough and dose levels of FK506 versus CsA during the first year after transplantation. In addition, the evolution of trough and dose levels of FK506 versus CsA was stratified according to gender.

Evolution of the absorption profile of cyclosporine A in renal transplant recipients: a longitudinal study of the de novo and maintenance phases

BACKGROUND

Therapeutic drug monitoring for cyclosporine microemulsion (CsA-ME) is often performed using either trough levels (C0) or levels at 2 h post-dose (C2). This analysis assessed changes in C0 and C2 and their relationship to CsA-ME dose over time post-transplant in renal transplant patients.

METHODS

Data were obtained from MO2ART, a prospective multicentre trial in which CsA-ME dose was adjusted based on C2 level. All 98 patients in whom C0 and C2 were available at day 5, month 3 and month 12 were included, out of 234 who completed the 12 month study. Normalized dose (ND) of CsA-ME, defined as dose per kilogram body weight, was calculated, together with C0/ND, C2/ND and C2/C0.

RESULTS

C0/ND and C2/ND both increased between day 5 and month 3: C0/ND from 33+/-15 to 53+/-24 (ng/ml)/(mg/kg) and C2/ND from 161+/-64 to 248+/-80 (ng/ml)/(mg/kg). Between month 3 and month 12, C2/ND remained stable but C0/ND decreased to 42+/-20 (ng/ml)/(mg/kg) while the C2/C0 ratio increased from 5.2+/-1.9 to 6.5+/-2.3, indicating an acceleration of drug elimination. The inter-individual coefficient of variation was higher for C0/ND than for C2/ND at 3 months (45 vs 32%, P<0.05) and at 12 months (48 vs 31%, P<0.01).

CONCLUSIONS

CsA clearance accelerates between months 3 and 12 post-transplant, resulting in lower C0 levels for a given exposure (as measured by C2). As a consequence, C0 monitoring may progressively underestimate CsA exposure during the first year post-transplant. C2 monitoring contributes to improved individualized CsA-ME treatment in both the de novo phase and beyond month 3.

In Vivo Effects of Cyclosporin A and Ketoconazole on the Pharmacokinetics of Representative Substrates for P-Glycoprotein and Cytochrome P450 (CYP) 3A in Rats

In this study, the in vivo effects of cyclosporin A (CsA) and ketoconazole (KCZ), which are used as inhibitors of P-glycoprotein (Pgp) and cytochrome P450 (CYP) 3A, respectively, on the pharmacokinetics of rhodamine 123 (Rho123), nelfinavir (NFV) and erythromycin (EM) were evaluated in rats. The biliary excretion clearance (Clbile) of a known Pgp substrate, Rho123, after intravenous pretreatment with CsA or KCZ (0-20 mg/kg after i.v. administration) showed maximum reduction by 85.6 or 54.1%, respectively, suggesting that the inhibitory potency of KCZ is about half that of Pgp in the liver. Without pretreatment with CsA or KCZ, the clearance ratio of Clbile relative to the total body clearances of Rho123, NFV and EM was 10.5, 0.07 and 31.1%, respectively. After CsA pretreatment, these ratios decreased markedly in a manner dependent on the dose of CsA, while after CZ pretreatment the clearance ratios of NFV and EM increased significantly in a manner dependent on the dose of KCZ. However, in the liver, the contribution of Pgp to the changes in the pharmacokinetic parameters of Rho123, NFV and EM after intravenous administration was much less than that of CYP3A. The portal levels of Rho123 and EM but not NFV after intra-loop administration in the presence of 10 microM CsA in the jejunal loop increased significantly, while in the presence of 25 microM KCZ in the jejunal loop, the portal levels of those substrates showed no notable change as compared to the control levels. In conclusion, KCZ had dual potency to inhibit CYP3A and Pgp, and its inhibitory potency for Pgp was half that of CsA in the rat liver. In addition, metabolism via CYP3A contributed more significantly to the clearance of these substrates that did excretion via Pgp in the liver. In the small intestine, the contribution of Pgp is a more important factor in determining the oral bioavailability of EM than metabolism via CYP enzymes. The elimination of NFV is mainly dependent on liver metabolism via CYP3A, and the Pgp efflux mechanism in the liver and intestine did not contribute as importantly to the oral bioavailability of NFV under in vivo conditions, although NFV has been demonstrated to be a substrate of Pgp under in vitro conditions.