Gender-dependent racial difference in disposition of cyclosporine among healthy African American and white volunteers

Atopic dermatitis in skin of colour. Part 2: considerations in clinical presentation and treatment options

Recent advances in atopic dermatitis (AD) present the condition as a heterogeneous disease of distinct endotypes across ethnic groups. AD in people with skin of colour may appear psoriasiform, lichenoid, scaly or papular, with a violaceous colour and there is a higher prevalence of post-inflammatory dyspigmentation compared with affected individuals of White ethnicity. These differences in clinical presentation may limit the use of AD assessment tools in people with skin of colour, leading to the potential for misdiagnosis and underestimation of severity, particularly in relation to assessment of erythema. Recent targeted therapies for AD have been studied in multiple ethnic groups; however, ethnicity-based subgroup analysis is often not performed. Further research is required to understand whether treatment responses or safety may differ among ethnic groups.

Harnessing Clinical Trial and Real-World Data Towards an Understanding of Sex Effects on Drug Pharmacokinetics, Pharmacodynamics and Efficacy

Increasing clinical data on sex-related differences in drug efficacy and toxicity has highlighted the importance of understanding the impact of sex on drug pharmacokinetics and pharmacodynamics. Intrinsic differences between males and females, such as different CYP enzyme activity, drug transporter expression or levels of sex hormones can all contribute to different responses to medications. However, most studies do not include sex-specific investigations, leading to lack of sex-disaggregated pharmacokinetic and pharmacodynamic data. Based available literature, the potential influence of sex on exposure-response relationship has not been fully explored for many drugs used in clinical practice, though population-based pharmacokinetic/pharmacodynamic modelling is well-placed to explore this effect. The aim of this review is to highlight existing knowledge gaps regarding the effect of sex on clinical outcomes, thereby proposing future research direction for the drugs with significant sex differences. Based on evaluated drugs encompassing all therapeutic areas, 25 drugs demonstrated a clinically meaningful sex differences in drug exposure (characterised by ≥ 50% change in drug exposure) and this altered PK was correlated with differential response.

Comparing Predictions of a PBPK Model for Cyclosporine With Drug Levels From Therapeutic Drug Monitoring

This study compared simulations of a physiologically based pharmacokinetic (PBPK) model implemented for cyclosporine with drug levels from therapeutic drug monitoring to evaluate the predictive performance of a PBPK model in a clinical population. Based on a literature search model parameters were determined. After calibrating the model using the pharmacokinetic profiles of healthy volunteers, 356 cyclosporine trough levels of 32 renal transplant outpatients were predicted based on their biometric parameters. Model performance was assessed by calculating absolute and relative deviations of predicted and observed trough levels. The median absolute deviation was 6 ng/ml (interquartile range: 30 to 31 ng/ml, minimum = -379 ng/ml, maximum = 139 ng/ml). 86% of predicted cyclosporine trough levels deviated less than twofold from observed values. The high intra-individual variability of observed cyclosporine levels was not fully covered by the PBPK model. Perspectively, consideration of clinical and additional patient-related factors may improve the model's performance. In summary, the current study has shown that PBPK modeling may offer valuable contributions for pharmacokinetic research in clinical drug therapy.

Population Pharmacokinetic Modeling of Cyclosporine Among Malaysian Renal Transplant Patients: An Evaluation of Methods to Handle Missing Doses in Conventional Drug-Monitoring Data

Cyclosporine is a primary drug in transplant immunosuppression regimens. It has a narrow therapeutic index and variable pharmacokinetic behavior. This study aimed to develop a population pharmacokinetic model of cyclosporine in Malaysian renal transplant recipients as well as to evaluate the performances of different methodsfor handling missing doses. A total of 2804 concentrationts predose and 2 hours after doses were collected retrospectively from 113 renal transplant patients on cyclosporine in Penang General Hospital. Model structure and pharmacokinetic parameters were estimated using nonlinear mixed-effects modeling software. Missing doses were handled using different methods to evaluate their performance. Covariate analysis was performed using stepwise forward addition (P < .05) followed by backward elimination (P < .001). Prediction-corrected visual predictive check and sampling-importance resampling methods were used to validate the final model. A 1-compartment model with first-order absorption and elimination best fitted the data. All methods to handle missing doses performed well with the missing dose method being superior to other methods and thus was applied in the final model. Cyclosporine clearance (CL/F) was estimated as 15.1 L/h, and volume of distribution (V/F) was 108 L. Postoperative time, sex, and calcium channel blockers were identified as significant covariates on CL/F, whereas sex and cholesterol level were identified as significant covariates on V/F. This is the first population pharmacokinetic model developed in Malaysian renal transplant patients using a large sample with an evaluation of different methods to handle missing doses in less informative conventional therapeutic drug-monitoring data.

Towards precision medicine: interrogating the human genome to identify drug pathways associated with potentially functional, population-differentiated polymorphisms

Drug response variations amongst different individuals/populations are influenced by several factors including allele frequency differences of single nucleotide polymorphisms (SNPs) that functionally affect drug-response genes. Here, we aim to identify drugs that potentially exhibit population differences in response using SNP data mining and analytics. Ninety-one pairwise-comparisons of >22,000,000 SNPs from the 1000 Genomes Project, across 14 different populations, were performed to identify ‘population-differentiated’ SNPs (pdSNPs). Potentially-functional pdSNPs (pf-pdSNPs) were then selected, mapped into genes, and integrated with drug–gene databases to identify ‘population-differentiated’ drugs enriched with genes carrying pf-pdSNPs. 1191 clinically-approved drugs were found to be significantly enriched (Z > 2.58) with genes carrying SNPs that were differentiated in one or more population-pair comparisons. Thirteen drugs were found to be enriched with such differentiated genes across all 91 population-pairs. Notably, 82% of drugs, which were previously reported in the literature to exhibit population differences in response were also found by this method to contain a significant enrichment of population specific differentiated SNPs. Furthermore, drugs with genetic testing labels, or those suspected to cause adverse reactions, contained a significantly larger number (P < 0.01) of population-pairs with enriched pf-pdSNPs compared with those without these labels. This pioneering effort at harnessing big-data pharmacogenomics to identify ‘population differentiated’ drugs could help to facilitate data-driven decision-making for a more personalized medicine.

Science-based Ethnic Bridging in Drug Development; Review of Recent Precedence and Suggested Steps Forward

BACKGROUND

Exposure, safety and/or efficacy of drugs are subject to potential differences between human races or ethnicities, as acknowledged by regulatory guidance and by label texts of various, but not all approved drugs.

OBJECTIVE

The objective of the present review was to assess recent regulatory precedence on drug use and race or ethnicity, with the goal of identifying opportunities for increasing the informative value of clinical ethnic or racial bridging in drug development.

METHODS

Recently, (January 2014-July 2018) FDA approved drug product label texts and approval packages were reviewed for claims, comments and underlying data on use of the product in specific ethnic or racial groups.

RESULTS

Among the 266 FDA-approved products, no product with unambiguous race- or ethnicity specific dosing instructions was retrieved. A small majority (55%) was approved with a claim or comment on race or ethnicity, and of these, a large majority (87%) was based on population pharmacokinetic data analysis. Statements were often related to incidence of a genotype for drug metabolizing enzyme or for other risk factors, or were related to body weight. Absence of clinically relevant exposure differences were often justified in terms of exposure ratios that notably exceeded the typical 0.80-1.25 no-effect boundary.

CONCLUSIONS

Recent precedence reflected a pragmatic, descriptive approach of racial or ethnic bridging, apparently meeting current regulatory expectations, whilst not resulting in strict guidance to prescribers. We recommend further work on defining the objectives of bridging studies, as well as criteria for their design and data analysis. Regarding the latter, we recommend investigating the value of prospectively defined tests for similarity with appropriate follow-up analysis in the case where the test has failed.

External evaluation of population pharmacokinetic models for ciclosporin in adult renal transplant recipients

AIMS

Several population pharmacokinetic (popPK) models for ciclosporin (CsA) in adult renal transplant recipients have been constructed to optimize the therapeutic regimen of CsA. However, little is known about their predictabilities when extrapolated to different clinical centres. Therefore, this study aimed to externally evaluate the predictive ability of CsA popPK models and determine the potential influencing factors.

METHODS

A literature search was conducted and the predictive performance was determined for each selected model using an independent data set of 62 patients (471 predose and 500 2-h postdose concentrations) from our hospital. Prediction-based diagnostics and simulation-based normalized prediction distribution error were used to evaluate model predictability. The influence of prior information was assessed using Bayesian forecasting. Additionally, potential factors influencing model predictability were investigated.

RESULTS

Seventeen models extracted from 17 published popPK studies were assessed. Prediction-based diagnostics showed that ethnicity potentially influenced model transferability. Simulation-based normalized prediction distribution error analyses indicated misspecification in most of the models, especially regarding variance. Bayesian forecasting demonstrated that the predictive performance of the models substantially improved with 2-3 prior observations. The predictability of nonlinear Michaelis-Menten models was superior to that of linear compartmental models when evaluating the impact of structural models, indicating the underlying nonlinear kinetics of CsA. Structural model, ethnicity, covariates and prior observations potentially affected model predictability.

CONCLUSIONS

Structural model is the predominant factor influencing model predictability. Incorporation of nonlinear kinetics in CsA popPK modelling should be considered. Moreover, Bayesian forecasting substantially improved model predictability.

Association of Extrarenal Adverse Effects of Posttransplant Immunosuppression With Sex and ABCB1 Haplotypes

Extrarenal adverse effects (AEs) associated with calcineurin inhibitor (CNI) and mycophenolic acid (MPA) occur frequently but are unpredictable posttransplant complications. AEs may result from intracellular CNI accumulation and low activity of P-glycoprotein, encoded by the ABCB1 gene. Since ABCB1 single nucleotide polymorphisms (SNPs) and sex influence P-glycoprotein, we investigated haplotypes and extrarenal AEs. A prospective, cross-sectional study evaluated 149 patients receiving tacrolimus and enteric coated mycophenolate sodium or cyclosporine and mycophenolate mofetil. Immunosuppressive AE assessment determined individual and composite gastrointestinal, neurologic, aesthetic, and cumulative AEs. Lipids were quantitated after 12-hour fast. ABCB1 SNPs: c.1236C>T (rs1128503), c.2677G>T/A (rs2032582), and c.3435C>T (rs1045642) were determined with haplotype associations computed using the THESIAS program, and evaluated by immunosuppression, sex and race using multivariate general linear models. Tacrolimus patients exhibited more frequent and higher gastrointestinal AE scores compared with cyclosporine with association to CTT (P = 0.018) and sex (P = 0.01). Aesthetic AE score was 3 times greater for cyclosporine with TTC haplotype (P = 0.005). Females had higher gastrointestinal (P = 0.022), aesthetic (P < 0.001), neurologic (P = 0.022), and cumulative AE ratios (P < 0.001). Total cholesterol (TCHOL), low-density lipoproteins (LDL), and triglycerides were higher with cyclosporine. The TTC haplotype had higher TCHOL (P < 0.001) and LDL (P = 0.005). Higher triglyceride (P = 0.034) and lower high-density lipoproteins (P = 0.057) were associated with TTT with sex-adjusted analysis. ABCB1 haplotypes and sex were associated with extrarenal AEs. Using haplotypes, certain female patients manifested more AEs regardless of CNI. Haplotype testing may identify patients with greater susceptibility to AEs and facilitate CNI individualization.

The transferability from rat subacute 4-week oral toxicity study to translational research exemplified by two pharmaceutical immunosuppressants and two environmental pollutants with immunomodulating properties

Exposure to chemicals may have an influence on the immune system. Often, this is an unwanted effect but in some pharmaceuticals, it is the intended mechanism of action. Immune function tests and in depth histopathological investigations of immune organs were integrated in rodent toxicity studies performed according to an extended OECD test guideline 407 protocol. Exemplified by two immunosuppressive drugs, azathioprine and cyclosporine A, and two environmental chemicals, hexachlorobenzene and benzo[a]pyrene, results of subacute rat studies were compared to knowledge in other species particular in humans. Although immune function has a high concordance in mammalian species, regarding the transferability from rodents to humans various factors have to be taken into account. In rats, sensitivity seems to depend on factors such as strain, sex, stress levels as well as metabolism. The two immunosuppressive drugs showed a high similarity of effects in animals and humans as the immune system was the most sensitive target in both. Hexachlorobenzene gave an inconsistent pattern of effects when considering the immune system of different species. In some species pronounced inflammation was observed, whereas in primates liver toxicity seemed more obvious. Generally, the immune system was not the most sensitive target in hexachlorobenzene-treatment. Immune function tests in rats gave evidence of a reaction to systemic inflammation rather than a direct impact on immune cells. Data from humans are likewise equivocal. In the case of benzo[a]pyrene, the immune system was the most sensitive target in rats. In the in vitro plaque forming cell assay (Mishell-Dutton culture) a direct comparison of cells from different species including rat and human was possible and showed similar reactions. The doses in the rat study had, however, no realistic relation to human exposure, which occurs exclusively in mixtures and in a much lower range. In summary, a case by case approach is necessary when testing immunotoxicity. Improvements for the translation from animals to humans related to immune cells can be expected from in vitro tests which offer direct comparison with reactions of human immune cells. This may lead to a better understanding of results and variations seen in animal studies.

The Effect of ABCB1 C3435T Polymorphism on Cyclosporine Dose Requirements in Kidney Transplant Recipients: A Meta-Analysis

Cyclosporine A (CsA) is a substrate of the multi-drug efflux pump P-glycoprotein (P-gp) encoded by ABCB1. Among the various single nucleotide polymorphisms (SNPs) of ABCB1, C3435T has been extensively investigated to determine the relationship with the pharmacokinetics of CsA. However, the results are controversial. This meta-analysis was designed to evaluate the influence of C3435T SNP on the dose-adjusted trough (C0 /D) and peak (Cmax /D) concentrations of CsA. Based on a literature search of four authoritative databases, 13 studies since 2001 concerning 1293 kidney transplant recipients were included. The results indicated a significant difference of C0 /D and Cmax /D between 3435CC and 3435TT genotype carriers (weighted mean difference (WMD) of C0 /D: 4.18 (ng ml(-1))/(mg kg(-1)), 95% CIs: 1.00-7.37, p = 0.01; WMD of Cmax /D: 20.85 (ng ml(-1))/(mg kg(-1)), 95% CIs: 2.25-39.46, p = 0.03). Subgroup analysis by ethnicity demonstrated that C0 /D was lower in Asian CC versus TT genotype carriers (WMD = 10.32 (ng ml(-1))/(mg kg(-1)), 95% CIs: 4.78-15.85, p = 0.0003) but did not vary by genotype for Caucasian recipients. Moreover, significant variation of C0 /D was found at 1 week and 1-3 months after transplantation between CC and TT genotype carriers. Therefore, this meta-analysis showed a correlation between ABCB1 C3435T polymorphism and the dose-adjusted concentration of CsA. Patients with 3435CC genotype will require a higher dose of CsA to achieve target therapeutic concentrations when compared with 3435TT carriers after kidney transplantation, especially in the Asian population and especially during the early and middle time periods after transplantation.

A mechanistic framework for in vitro-in vivo extrapolation of liver membrane transporters: prediction of drug-drug interaction between rosuvastatin and cyclosporine

Background and Objectives

The interplay between liver metabolising enzymes and transporters is a complex process involving system-related parameters such as liver blood perfusion as well as drug attributes including protein and lipid binding, ionisation, relative magnitude of passive and active permeation. Metabolism- and/or transporter-mediated drug–drug interactions (mDDIs and tDDIs) add to the complexity of this interplay. Thus, gaining meaningful insight into the impact of each element on the disposition of a drug and accurately predicting drug–drug interactions becomes very challenging. To address this, an in vitro–in vivo extrapolation (IVIVE)-linked mechanistic physiologically based pharmacokinetic (PBPK) framework for modelling liver transporters and their interplay with liver metabolising enzymes has been developed and implemented within the Simcyp Simulator^®.

Methods

In this article an IVIVE technique for liver transporters is described and a full-body PBPK model is developed. Passive and active (saturable) transport at both liver sinusoidal and canalicular membranes are accounted for and the impact of binding and ionisation processes is considered. The model also accommodates tDDIs involving inhibition of multiple transporters. Integrating prior in vitro information on the metabolism and transporter kinetics of rosuvastatin (organic-anion transporting polypeptides OATP1B1, OAT1B3 and OATP2B1, sodium-dependent taurocholate co-transporting polypeptide [NTCP] and breast cancer resistance protein [BCRP]) with one clinical dataset, the PBPK model was used to simulate the drug disposition of rosuvastatin for 11 reported studies that had not been used for development of the rosuvastatin model.

Results

The simulated area under the plasma concentration–time curve (AUC), maximum concentration (C_max) and the time to reach C_max (t_max) values of rosuvastatin over the dose range of 10–80 mg, were within 2-fold of the observed data. Subsequently, the validated model was used to investigate the impact of coadministration of cyclosporine (ciclosporin), an inhibitor of OATPs, BCRP and NTCP, on the exposure of rosuvastatin in healthy volunteers.

Conclusion

The results show the utility of the model to integrate a wide range of in vitro and in vivo data and simulate the outcome of clinical studies, with implications for their design.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-013-0097-y) contains supplementary material, which is available to authorized users.

African American renal transplant recipients (RTR) require higher tacrolimus doses to achieve target levels compared to white RTR: does clotrimazole help?

The number of African Americans (AAs) on the kidney waiting list is increasing in the United States. Several studies showed that AAs are at higher risk for rejection and graft loss. Because of genetic polymorphisms, AAs may metabolize calcineurin inhibitors faster than Caucasian (C) individuals. The goal of this study is to evaluate the tacrolimus (TAC) dose required to reach therapeutic levels and to assess the impact of clotrimazole on TAC metabolism in AAs compared to C patients. One hundred forty-two AA renal transplant recipients (RTRs) were compared to 309 C RTRs. Demographics were similar in both groups. Induction therapy and maintenance immunosuppression were similar in both groups and included TAC, mycophenolate acid (MPA), and steroids. The goal in all RTRs was to maintain a 12-hour trough level of 10 to 15 ng/mL in the first 3 months, 8 to 10 ng/mL for the first year, and 5 to 8 ng/mL thereafter. To achieve these levels, AA RTRs require a significantly higher dosage of TAC compared to C patients (5.9 ± 2.9 vs 3.6 ± 2 mg/d, respectively, P < .0001). By multivariate analysis, TAC dose requirements were not affected by age, gender, MPA or prednisone dose, diabetes, and renal function. Adding clotrimazole (CTM) to the RTR regimen significantly reduced the TAC dose requirements in all RTRs. When CTM was used, the TAC dose requirement was not statistically significantly different between AA and C patients (2.6 ± 1.2 mg/d vs 1.8 ± 1.5 mg/d, P = .07). We conclude that AAs required a higher TAC dose to reach the desired trough level in RTRs compared to C RTRs. The use of CTM eliminates the need for higher doses of TAC in AA RTRs. Thus, CTM may aid AA RTRs in achieving therapeutic TAC levels while reducing drug costs.

Immunomodulating options for liver transplant patients

Much has changed since the early years of liver transplantation. Improvements in post-transplant survival are largely due to more selective and less toxic immunosuppression regimens and advances in operative and perioperative care. This has allowed liver transplantation to become an extremely successful treatment option for patients with endstage liver disease. Beginning with cyclosporine, a cyclic endecapeptide of fungal origin and the first of the calcineurin inhibitors to find widespread use, immunosuppressive regimens have evolved to include additional calcineurin inhibitors, steroids, mTOR inhibitors, antimetabolites and antibodies, mostly targeting T-cell activation. This review will present currently available immunosuppressive agents used in the perioperative period of liver transplantation, as well as maintenance treatments, tailoring therapeutic strategies for specific populations, and advances in immune monitoring and tolerance.

Bioequivalence and tolerability assessment of a novel intravenous ciclosporin lipid emulsion compared to branded ciclosporin in Cremophor ® EL

BACKGROUND

Ciclosporin is used as an immunosuppressant in current clinical practice but recent research implies novel indications for the drug, such as neuro- and cardioprotection. The intravenous formulation currently on the market, Sandimmune(®) Injection (Sandimmune(®)), uses Cremophor(®) EL as emulsifying excipient. Cremophor(®) EL is known to cause hypersensitivity reactions in some patients, ranging from skin reactions to potentially fatal anaphylactic shock.

OBJECTIVES

The primary objective was to assess if CicloMulsion(®), a Cremophor(®) EL-free lipid emulsion of ciclosporin for intravenous administration, is bioequivalent to Sandimmune(®), and the secondary objective was to compare the tolerability profiles of the two preparations.

METHODS

This was a single-centre, open-label, subject-blind, laboratory-blind, single-dose, randomized, two-treatment, two-period, two-sequence crossover study of the pharmacokinetics of two formulations of intravenous ciclosporin. Fifty-two healthy volunteer subjects were administered 5 mg/kg of each of the two formulations of ciclosporin as a 4-h intravenous infusion. The last blood sample was acquired 48 h after the end of the infusion. Bioequivalence assessments according to current guidelines were performed.

RESULTS

The geometric mean ratios for CicloMulsion(®)/Sandimmune(®) (90 % confidence interval [CI]) were 0.90 (0.88, 0.92) for AUC(0-last) (area under the blood concentration-time curve from time zero to time of last measurable concentration) and 0.95 (0.92, 0.97) for C(max) (maximum blood concentration). For all additional variables analysed, the 90 % CIs were also within the accepted bioequivalence range of 0.80-1.25. One anaphylactoid and one anaphylactic reaction, both classified as serious adverse events, were reported after treatment with Sandimmune(®). No serious adverse events were recorded after treatment with CicloMulsion(®).

CONCLUSION

We have assessed the pharmacokinetics and tolerability of a new Cremophor(®) EL-free lipid emulsion of ciclosporin, CicloMulsion(®), compared to Sandimmune(®). The proportion of adverse events was significantly higher for the Cremophor(®) EL-based product Sandimmune(®). We conclude that CicloMulsion(®) is bioequivalent to Sandimmune(®) and exhibits fewer adverse reactions.

Cyclosporine inhibition of hepatic and intestinal CYP3A4, uptake and efflux transporters: application of PBPK modeling in the assessment of drug-drug interaction potential

PURPOSE

To apply physiologically-based pharmacokinetic (PBPK) modeling to investigate the consequences of reduction in activity of hepatic and intestinal uptake and efflux transporters by cyclosporine and its metabolite AM1.

METHODS

Inhibitory potencies of cyclosporine and AM1 against OATP1B1, OATP1B3 and OATP2B1 were investigated in HEK293 cells +/- pre-incubation. Cyclosporine PBPK model implemented in Matlab was used to assess interaction potential (+/- metabolite) against different processes (uptake, efflux and metabolism) in liver and intestine and to predict quantitatively drug-drug interaction with repaglinide.

RESULTS

Cyclosporine and AM1 were potent inhibitors of OATP1B1 and OATP1B3, IC(50) ranging from 0.019-0.093 μM following pre-incubation. Cyclosporine PBPK model predicted the highest interaction potential against liver uptake transporters, with a maximal reduction of >70% in OATP1B1 activity; the effect on hepatic efflux and metabolism was minimal. In contrast, 80-97% of intestinal P-gp and CYP3A4 activity was reduced due to the 50-fold higher cyclosporine enterocytic concentrations relative to unbound hepatic inlet. The inclusion of AM1 resulted in a minor increase in the predicted maximal reduction of OATP1B1/1B3 activity. Good predictability of cyclosporine-repaglinide DDI and the impact of dose staggering are illustrated.

CONCLUSIONS

This study highlights the application of PBPK modeling for quantitative prediction of transporter-mediated DDIs with concomitant consideration of P450 inhibition.

Effects of the CYP3A5*3 variant on cyclosporine exposure and acute rejection rate in renal transplant patients: a meta-analysis

BACKGROUND

Whether the loss-of-function allele CYP3A5*3 variant is associated with significantly impaired metabolism of cyclosporine A (CsA) in transplant patients is still controversial because of the lack of prospective, large-scale clinical studies performed among diversely ethnic populations.

OBJECTIVES

This meta-analysis was designed to determine whether the CYP3A5*3 variant could affect CsA blood concentrations and the rate of acute rejection in renal transplant recipients.

METHODS AND RESULTS

All relevant publications were retrieved online from 1966 to March 2010, in which 14 studies were chosen, and 1821 renal transplant patients were enrolled. The results showed that there were significant differences in the CsA dose-adjusted trough concentration (C0) between the CYP3A5*3/*3 and CYP3A5*1/*1 carriers [weighted mean difference (WMD): 10.06 mug/l per mg/kg, 95% confidence interval (CI): 3.12-17.00, P=0.004] and between the non-CYP3A5*1 allele carriers and the CYP3A5*1 allele carriers (WMD: 8.32 mug/l per mg/kg, 95% CI: 3.16-13.49, P=0.002). In addition, a subgroup analysis stratified by ethnicity indicated that a significant difference in CsA dose-adjusted C0 was observed between the non-CYP3A5*1 allele carriers and the CYP3A5*1 allele carriers in Asian patients, but not in Caucasian patients. Moreover, a significant difference in the mean daily dose was observed between the non-CYP3A5*1 allele carriers and the CYP3A5*1 allele carriers (WMD: -0.19 mg/kg, 95% CI: -0.31 to -0.07, P=0.002). However, the meta-analysis suggested that there was little or no association of the CYP3A5*3 variant with the acute rejection rate in renal transplant patients treated with CsA [odds ratio=0.94, 95% CI: 0.57-1.54, P=0.80].

CONCLUSION

We concluded that the CYP3A5*3 variant could be associated, to a certain extent, with increased CsA dose-adjusted C0 in blood and reduced mean daily doses, but that this genetic variant allele seemed to have little effect on the acute rejection rate in renal transplant patients taking CsA.

Recipient-based approach to tailoring immunosuppression in liver transplantation

Improvements in the field of transplant immunosuppression (IS) have led to significant advances in long-term survival of liver transplant recipients. Despite this progress, survival rates vary depending on recipient, donor and/or perioperative factors. Tailoring IS based on recipient factors is of growing interest among health care providers involved in the care of organ transplant recipients. To date there is no consensus document addressing individualized IS therapy for liver transplant recipients. This review will discuss the information available on the effect of the various IS drugs on recipient-based factors such as age, ethnicity, and liver disease etiology.

Prediction of metabolic drug clearance in humans: in vitro-in vivo extrapolation vs allometric scaling

Previously in vitro-in vivo extrapolation (IVIVE) with the Simcyp Clearance and Interaction Simulator has been used to predict the clearance of 15 clinically used drugs in humans. The criteria for the selection of the drugs were that they are used as probes for the activity of specific cytochromes P450 (CYPs) or have a single CYP isoform as the major or sole contributor to their metabolism and that they do not exhibit non-linear kinetics in vivo. Where data were available for the clearance of the drugs in at least three animal species, the predictions from IVIVE have now been compared with those based on allometric scaling (AS). Adequate data were available for estimating oral clearance (CLp.o.) in 9 cases (alprazolam, sildenafil, caffeine, clozapine, cyclosporine, dextromethorphan, midazolam, omeprazole and tolbutamide) and intravenous clearance in 6 cases (CLi.v.) (cyclosporine, diclofenac, midazolam, omeprazole, theophylline and tolterodine). AS predictions were based on five different methods: (1) simple allometry (clearance versus body weight); (2) correction for maximum life-span potential (CL x MLP); (3) correction for brain weight (CL x BrW); (4) the use of body surface area; and (5) the rule of exponents. A prediction accuracy was indicated by mean-fold error and the Pearson product moment correlation coefficient. Predictions were considered successful if the mean-fold error was <or=2. IVIVE predictions were accurate in 14 of 15 cases (mean-fold error range: 1.02-4.00). All five AS methods were accurate in 13, 11, 10, 10 and 14 cases, respectively. However, in some cases the error of AS exceeded fivefold. On the basis of the current results, IVIVE is more reliable than AS in predicting human clearance values for drugs mainly metabolized by CYP450 enzymes. This suggests that the place of AS methods in pre-clinical drug development warrants further scrutiny.

A Comparison of the Pharmacokinetics and Pharmacodynamics of Docetaxel between African-American and Caucasian Cancer Patients: CALGB 9871

PURPOSE

Increased clearance of drugs, such as oral cyclosporine, that are CYP3A and/or ABCB1 (P-gp/MDR1) substrates was reported in African-American compared with Caucasian patients. We hypothesized that the pharmacokinetics and pharmacodynamics of docetaxel, an i.v. administered cytotoxic and substrate for CYP3A4, CYP3A5, and ABCB1, would differ between African-American and Caucasian patients.

EXPERIMENTAL DESIGN

We investigated population pharmacokinetics and pharmacodynamics and the pharmacogenetics of CYP3A4, CYP3A5, and ABCB1 in African-American and Caucasian cancer patients who received docetaxel 75 or 100 mg/m(2) as a 1-h i.v. infusion. Plasma docetaxel concentrations were measured by high-performance liquid chromatography. Clinical toxicity and absolute neutrophil count (ANC) were monitored on days 8, 15, and 22 postadministration of docetaxel. Using a limited sampling strategy and nonlinear mixed-effects modeling, each patient's docetaxel clearance was estimated. Genotyping for known polymorphisms in CYP3A4, CYP3A5, and ABCB1 was done.

RESULTS

We enrolled 109 patients: 40 African-Americans (26 males; 14 females), with a median age of 61 years (range, 29-73), and 69 Caucasians (43 males; 26 females), with a median age of 63 years (range, 38-81). There was no difference in the geometric mean docetaxel clearance between African-American patients [40.3 L/h; 95% confidence interval (95% CI), 19.3-84.1] and Caucasian patients (41.8 L/h; 95% CI, 22.0-79.7; P = 0.6). We observed no difference between African-American and Caucasian patients in the percentage decrease in ANC nor were docetaxel pharmacokinetic parameters related to the genotypes studied.

CONCLUSIONS

Docetaxel clearance and its associated myelosuppression were similar in African-American and Caucasian cancer patients.

Bosentan is a substrate of human OATP1B1 and OATP1B3: inhibition of hepatic uptake as the common mechanism of its interactions with cyclosporin A, rifampicin, and sildenafil

The elimination process of the endothelin receptor antagonist bosentan (Tracleer) in humans is entirely dependent on metabolism mediated by two cytochrome P450 (P450) enzymes, i.e., CYP3A4 and CYP2C9. Most interactions with concomitantly administered drugs can be rationalized in terms of inhibition of these P450 enzymes. The increased bosentan concentrations observed in the presence of cyclosporin A, rifampicin, or sildenafil, however, are incompatible with this paradigm and prompted the search for alternative mechanisms governing these interactions. In the present article, we identify bosentan and its active plasma metabolite, Ro 48-5033 (4-(2-hydroxy-1,1-dimethyl-ethyl)-N-[6-(2-hydroxy-ethoxy)-5-(2-methoxy-phenoxy)-[2,2']bipyrimidinyl-4-yl]-benzenesulfonamide), as substrates of the human organic anion transporting polypeptides (OATP) OATP1B1 and OATP1B3. Bosentan uptake into Chinese hamster ovary cells expressing these OATP transporters was efficiently inhibited by cyclosporin A and rifampicin with IC(50) values significantly below their effective plasma concentrations in humans. The phosphodiesterase-5 inhibitor sildenafil was also shown to interfere with OATP-mediated transport, however, at concentrations above those achieved in therapeutic use. Therefore, inhibition of bosentan hepatic uptake may represent an alternative/complementary mechanism to rationalize some of the pharmacokinetic interactions seen in therapeutic use. A similar picture has been drawn for drugs like pitavastatin and fexofenadine, drugs that are mainly excreted in unchanged form. Bosentan elimination, in contrast, is entirely dependent on metabolism. Therefore, the described interactions with rifampicin, cyclosporin A, and, to a lesser extent, sildenafil represent evidence that inhibition of hepatic uptake may become the rate-limiting step in the overall elimination process even for drugs whose elimination is entirely dependent on metabolism.

Effect of widely used combinations of antiretroviral therapy on liver CYP3A4 activity in HIV-infected patients

AIMS

To evaluate the effects of combined antiretroviral drugs (HAART) on liver CYP3A4 activity using the [(14)C-N-methyl]-erythromycin breath test (ERMBT).

METHODS

HIV-infected patients (31 women, 30 men) with mean (+/- SD) age of 38 +/- 9 years were enrolled and underwent complete clinical and laboratory evaluation. Patients were divided into five groups and were treated with two nucleoside analogues (NAs) and one of the following: nelfinavir alone (n = 13), any ritonavir-boosted protease inhibitor with (n = 8) or without (n = 13) nevirapine, nevirapine alone (n = 15), or a third NA (n = 12). Three or four ERMBTs were performed 7 days prior to (D-7) and at the beginning of treatment (D0), D14 (only for patients taking nevirapine) and on D28.

RESULTS

Mean baseline liver CYP3A4 activity displayed high interindividual variability (47%) but low intraindividual variability (15%). Women had 30% higher ERMBT values than men [2.7 +/- 1.3 vs. 1.9 +/- 0.7; 95% confidence interval (CI) 20.5, 49.5; P = 0.003]. The ERMBT data correlated with body weight, alpha- and beta-globulins and alanin aminotransferases (0.10 < r(s) < 0.20; P < 0.01). Whereas nevirapine had no effect on liver CYP3A4 activity, nelfinavir-based and ritonavir-boosted drug regimens inhibited it by 69% (95% CI 64.7, 72.9; P = 0.005) and by 95% (95% CI 93.3, 96.7; P = 0.001), respectively.

CONCLUSION

Evaluation of the effect of HAART on liver CYP3A4 activity may aid in preventing inappropriate treatment regimens in HIV-infected patients.

Evaluation of performance factors affecting two formulations of cyclosporine in pediatric renal transplant patients

Success of renal transplantation in children is largely due to improvements in immunosuppressant therapy since the introduction of calcineurin inhibitors. The aim of this study was to identify possible factors that result in formulation differences in the exposure of pediatric patients to cyclosporine (CsA). We examined the handling of the two major formulations of CsA in a group of pediatric renal transplant recipients. The pharmacokinetic profiles of both formulations were assessed, and the data stratified to assess the effects of age, gender, time posttransplant, and other concomitant drug therapy on the two CsA formulations. The microemulsified formulation (MEC) enhanced bioavailability compared to the older oil-based formulation (CYA), especially at C2, with more predictable and consistent absorption in children. This higher bioavailability allowed a 15% reduction of dosing to achieve equal drug exposure. The concentration achieved by MEC at C2 demonstrated a much higher correlation with area under the concentration curve (AUC) than the concentration at C0. In the case of CYA a strong correlation was obtained between AUC and the concentrations obtained at both C0 and C2. Calcium channel blockers increased AUC(0-8) for both CsA formulations. Norfloxacin and pravastatin cotreatment had no effect on either of the CsA formulations. In contrast, the bioavailability of CsA was increased in boys using MEC formulation but this gender-based difference was absent during the use of CYA. This suggests that caution is required for introduction of new formulations of drugs to pediatric patients to evaluate differential effects of age, gender, and concomitant drug therapy.

Effects of genetic polymorphisms of CYP3A4, CYP3A5 and MDR1 on cyclosporine pharmacokinetics after renal transplantation

1. The calcineurin inhibitor cyclosporine is widely used to prevent allograft rejection after solid organ transplantation. It has a narrow therapeutic index and shows considerable interindividual differences in its pharmacokinetics. Interindividual differences in the activity and expression of the metabolising enzymes cytochrome P450 (CYP) 3A4 and 3A5 and the multidrug efflux pump P-glycoprotein (P-gp) contribute considerably to cyclosporine pharmacokinetics. Variability in the activity of CYP3A4, CYP3A5 and P-gp could be considered to result from genetic polymorphisms encoding their genes. 2. The aim of the present study was to evaluate retrospectively the effects of genetic polymorphisms of CYP3A4, CYP3A5 and MDR1 on cyclosporine dose adjusted trough blood concentration during the early period after renal transplantation in Chinese patients. 3. One hundred and six renal transplant recipients in China were genotyped by polymerase chain reaction-restriction fragment length polymorphism for CYP3A4*18A, CYP3A5*3 and MDR1 C3435T. Cyclosporine whole blood levels were measured by fluorescence polarization immunoassay. Dose-adjusted trough blood concentrations (C(0)) were determined and compared among the different genotype groups. 4. The frequency of the CYP3A4*18A, CYP3A5*3 and MDR1 C3435T variant alleles were 0.005 (95% confidence interval (CI) 0.048, 0.0049), 0.783 (95% CI 0.781, 0.785) and 0.528 (95% CI 0.526, 0.531), respectively, and these alleles exhibited incomplete linkage disequilibrium. The median cyclosporine dose-adjusted C(0) in CYP3A5*1/*1 genotype subjects (n = 6) was 14.8 ng/mL per mg per kg (range 11.1-26.8 ng/mL per mg per kg), in CYP3A5*1/*3 patients (n = 34) it was 23.7 ng/mL per mg per kg (range 9.0-61.0 ng/mL per mg per kg) and for CYP3A5*3/*3 patients (n = 66) it was 26.4 ng/mL per mg per kg (range 9.8-85.8 ng/mL per mg per kg; P = 0.012, Kruskal-Wallis test). Accordingly, cyclosporine dose-adjusted C0 was larger in CYP3A5 non-expressors than expressors in the first week after renal transplantation. In addition, wild-type homozygotes (n = 21) for MDR1 C3435T had a slight but significantly lower dose-adjusted C0 compared with heterozygotes (n = 58): 17.7 (10.3-60.8) versus 26.4 (9.0-67.3) ng/mL per mg per kg, respectively (P = 0.014, Mann-Whitney U-test). 5. In conclusion, the present study shows that genetic polymorphisms in CYP3A5 may be responsible, in part, for the large interindividual variability of cyclosporine pharmacokinetics during the early phase after renal transplantation in Chinese patients. Patients with the CYP3A5*3 variant genotype require a low dose of cyclosporine to reach target levels compared with those with the CYP3A5*1 allele.

Pharmacogenetic differences and drug-drug interactions in immunosuppressive therapy

With the advent of new immunosuppressants and formulations, the elucidation of molecular targets and the evolution of therapeutic drug monitoring, the field of organ transplantation has witnessed significant reductions in acute rejection rates, prolonged graft survival and improved patient outcome. Nonetheless, challenges persist in the use of immunosuppressive medications. Marked interindividual variability remains in drug concentrations and drug response. As medications with narrow therapeutic indices, variations in immunosuppressant concentrations can result in acute toxicity or transplant rejection. Recent studies have begun to identify factors that contribute to this variability with the promise of tailoring immunosuppressive regimens to the individual patient. These advances have uncovered differences in genetic composition in drug-metabolising enzymes, drug transporters and drug targets. This review focuses on commonly used maintenance immunosuppressants (including cyclosporin, mycophenolate mofetil, tacrolimus, sirolimus, everolimus, azathioprine and corticosteroids), examines current studies on pharmacogenetic differences in drug-metabolising enzymes, drug transporters and drug targets and addresses common drug-drug interactions with immunosuppressant therapies. The potential role of drug-metabolising enzymes in contributing to these drug-drug interactions is briefly considered.

Prediction of in vivo drug clearance from in vitro data. I: impact of inter-individual variability

The Simcyp Population-Based ADME Simulator was used to predict median drug clearances and their associated variance from in vitro data. Fifteen drugs satisfied the entry criteria for the study and the relevant information (in vitro metabolism data and in vivo human clearance values) were collated from the literature. Predicted values of median clearances fell within 2-fold of observed values for 73% of the drugs (oral route) and 78% of the drugs (intravenous route) when microsomal binding was disregarded, and for 93% (oral) and 100% (intravenous) when it was considered. Irrespective of whether microsomal binding was considered, the predicted fold variability fell within 2-fold of the observed variability for 80% (oral) and 67% (intravenous) of the drugs.

The influence of CYP3A gene polymorphisms on cyclosporine dose requirement in renal allograft recipients

Cyclosporine is a substrate of cytochrome P-450 3A (CYP3A) subfamily of enzymes and characterized by a narrow therapeutic range with wide interindividual variation in pharmacokinetics. A few single-nucleotide polymorphisms detected in CYP3A genes have been shown to correlate significantly with the CYP3A protein expression and activity. We therefore postulated that these polymorphisms could be responsible for some of the interindividual variation in cyclosporine pharmacokinetics. The objective of our study is to determine correlation if any between single-nucleotide polymorphisms of CYP3A5 and CYP3AP1 on cyclosporine dose requirement and concentration-to-dose ratio in renal allograft recipients. Cyclosporine-dependent renal allograft recipients were genotyped for CYP3A5 A6986G and CYP3AP1 G-44A. The cyclosporine dosages prescribed and the corresponding cyclosporine trough levels for each patient were recorded so that cyclosporine dose per weight (mg/kg/day) and concentration-to-dose ratio (C(0)/D, whereby C(0) is trough level and D is daily dose per weight) could be calculated. A total of 67 patients were recruited for our study. The dose requirement for 1, 3, and 6 months post-transplantation ranged 2.3-11.4, 1.0-9.0, and 1.4-7.2 mg/kg/day, respectively. Patients with *1*1*1*1 (n=5) CYP3A5- and CYP3AP1-linked genotypes needed higher dose of cyclosporine compared to patients with *1*3*1*3 (n = 27) and *3*3*3*3 (n = 33) linked genotypes in months 3 and 6 post-transplantation (P < 0.016). The identification of patients with *1*1*1*1 by CYP3A5 and CYP3AP1 genotyping may have a clinically significant and positive impact on patient outcome with reduced rejection rate by providing pretransplant pharmacogenetic information for optimization of cyclosporine A dosing.

HIV/AIDS: a minority health issue

HIV infection among racial and ethnic minorities is an ongoing health crisis. The disproportionate impact of HIV infection on racial and ethnic minorities has affected communities already struggling with many social and economic challenges, such as poverty, substance abuse, homelessness,unequal access to health care, and unequal treatment once in the health care system. Superimposed on these challenges is HIV infection, the transmission of which is facilitated by many of these factors. Although the epidemic is disproportionately affecting all racial and ethnic minorities, within these minority populations women are particularly affected. The care and management of racial and ethnic minorities who have HIV infection has been complicated by the unequal access to health care and the unequal treatment once enrolled in health care. Health insurance status, lack of concordance between the race of the patient and the provider, and satisfaction with the quality of their care all impact on treatment outcomes in this population. In addition, the provider must be aware of the many comorbid conditions that may affect the delivery of care to minority patients living with HIV infection: depression, substance and alcohol abuse, and posttraumatic stress disorders. The impact of these comorbid conditions on the therapeutic relationship, including treatment and adherence, warrants screening for these disorders and treating them when identified. Because the patient provider relationship has been repeatedly identified as a predictor of higher adherence, developing and maintaining a strong therapeutic alliance is critical. Participation of racial and ethnic minorities in HIV clinical trials, as in other disease states, has been very poor. Racial and ethnic minorities have been chronically underrepresented in HIV clinical trials, despite their overrepresentation in the HIV epidemiology. This underrepresentation seems to be the result of a combination of factors including (1) provider bias in referring to clinical trials, (2) mistrust of clinical research, (3) past poor experience with the health care system, and (4) the conspiracy theories of HIV disease. The paucity of minority health care professionals and minority investigators in HIV research further affects minority participation in clinical research. To improve racial and ethnic minority participation in clinical trials a sustained effort is necessary at multiple levels. Increased recruitment and retention is an ongoing need, and one that will not be satisfactorily addressed until there are better community-academic and research partner-ships, and the research questions posed also address issues of concern and significance to the affected community. Reduction in barriers to participation in clinical trials, especially given the many competing needs of racial and ethnic minority patients, is also needed. Multidisciplinary HIV care teams and research staff with training in cultural competency and cultural sensitivity may also be helpful. Prevention of HIV infection remains essential, especially among those seeking care for HIV infection. Despite several published recommendations for the inclusion of HIV prevention in the clinical care setting, studies have documented how few providers actually achieve this goal, especially those who care for disadvantaged patients. Although there are many barriers to discussing HIV risk behaviors and prevention strategies in an office visit,including time constraints and potential provider discomfort in discussing these matters, clinical visits represent an important opportunity to reinforce HIV prevention and possibly decrease further HIV transmission.

CYP3A5 polymorphism and the ethnic differences in cyclosporine pharmacokinetics in healthy subjects

To determine the relationship between CYP3A5 polymorphism and cyclosporine pharmacokinetic parameters among healthy volunteers, an oral cyclosporine (CsA) pharmacokinetic study was performed in 16 healthy subjects. Blood CsA concentrations were measured by high-performance liquid chromatography. Concentration-versus-time data were analyzed by a noncompartmental method using WinNonLin, and the blood samples were genotyped for the CYP3A5 using the polymerase chain reaction and pyrosequencing. CsA pharmacokinetic parameters were dichotomized and compared using the 1-way ANOVA test according to the CYP3A5*3C genotype. There were 6 homozygous A/A (wild type), 6 homozygous G/G (variant), and 4 heterozygous A/G genotypes for CYP3A5*3 C in these 16 healthy volunteers. All whites were G/G group, and all African Americans except 1 were either A/A or A/G group. The mean AUC (ng x h/mL) of CsA for the 3 genotype groups were 4962 +/- 1074 (A/A), 6677 +/- 1153 (G/G), and 5416 +/- 1817 (A/G), (A/A versus G/G, P = 0.03), and the mean CL/F (mL/min/kg) were 15.6 +/- 3.1 (A/A), 12.0 +/- 2.3 (G/G), and 14.7 +/- 5.9 (A/G), (A/A versus G/G, P = 0.04). None of the other parameters were significantly different among the 3 genotypes. In conclusion, the CYP3A5*3C polymorphism appears to affect AUC and CL/F of oral CsA significantly in healthy subjects, which may partly explain some of the differences of pharmacokinetics in CsA between African Americans and whites.

Differences in drug pharmacokinetics between East Asians and Caucasians and the role of genetic polymorphisms

Interethnic variability in pharmacokinetics can cause unexpected outcomes such as therapeutic failure, adverse effects, and toxicity in subjects of different ethnic origin undergoing medical treatment. It is important to realize that both genetic and environmental factors can lead to these differences among ethnic groups. The International Conference on Harmonization (ICH) published a guidance to facilitate the registration of drugs among ICH regions (European Union, Japan, the United States) by recommending a framework for evaluating the impact of ethnic factors on a drug's effect, as well as its efficacy and safety at a particular dosage and dosage regimen. This review focuses on the pharmacokinetic differences between East Asians and Caucasians. Differences in metabolism between East Asians and Caucasians are common, especially in the activity of several phase I enzymes such as CYP2D6 and the CYP2C subfamily. Before drug therapy, identification of either the genotype and/or the phenotype for these enzymes may be of therapeutic value, particularly for drugs with a narrow therapeutic index. Furthermore, these differences are relevant for international drug approval when regulatory agencies must decide if they accept results from clinical trials performed in other parts of the world.

Genetic polymorphisms of the human MDR1 drug transporter

P-glycoprotein is an ATP-dependent efflux pump that contributes to the protection of the body from environmental toxins. It transports a huge variety of structurally diverse compounds. P-glycoprotein is involved in limiting absorption of xenobiotics from the gut lumen, in protection of sensitive tissues (brain, fetus, testis), and in biliary and urinary excretion of its substrates. P-glycoprotein can be inhibited or induced by xenobiotics, thereby contributing to variable drug disposition and drug interactions. Recently, several SNPs have been identified in the MDR1 gene, some of which can affect P-glycoprotein expression and function. Potential implications of MDR1 polymorphisms for drug disposition, drug effects, and disease risk are discussed.

A review and assessment of potential sources of ethnic differences in drug responsiveness

The International Conference on Harmonization (ICH) E5 guidelines were developed to provide a general framework for evaluating the potential impact of ethnic factors on the acceptability of foreign clinical data, with the underlying objective to facilitate global drug development and registration. It is well recognized that all drugs exhibit significant inter-subject variability in pharmacokinetics and pharmacologic response and that such differences vary considerably among individual drugs and depend on a variety of factors. One such potential factor involves ethnicity. The objective of the present work was to perform an extensive review of the world literature on ethnic differences in drug disposition and responsiveness to determine their general significance in relation to drug development and registration. A few examples of suspected ethnic differences in pharmacokinetics or pharmacodynamics were identified. The available literature, however, was found to be heterologous, including a variety of study designs and research methodologies, and most of the publications were on drugs that were approved a long time ago.

Association of the CYP3A4*1B 5'-flanking region polymorphism with cyclosporine pharmacokinetics in healthy subjects

To determine the relationship between CYP3A4*1B polymorphism and cyclosporine pharmacokinetic parameters among healthy volunteers, the oral cyclosporine pharmacokinetic study was performed in 14 healthy subjects. Blood cyclosporine concentrations were measured by a high performance liquid chromatography. Concentration-time data were analyzed by a non-compartmental method using WinNonLin, and the blood samples were genotyped for the CYP3A4*1B 5'-promotor region using the polymerase chain reaction and a restriction digest. Each cyclosporine pharmacokinetic parameter was compared using the one-way ANOVA test according to his or her CYP3A4*1B genotype. There were four (4) homozygous A/A (wild-type), four (4) homozygous G/G (variant) and six (6) heterozygous A/G genotypes for CYP3A4*1B in these 14 healthy volunteers. The mean AUC/D (ng.hr/mL/mg) of CsA were 21.5 +/- 6.0 (A/A), 11.7 +/- 3.2 (G/G) and 19.2 +/- 2.3 (A/G), P = 0.0103 and the mean CL/F (L/hr) were 49.4 +/- 13.9 (A/A), 83.5 +/- 16.0 (G/G), and 52.5 +/- 5.6 (A/G), P = 0.0024. All other parameters were not significantly different among the three genotypes.

Pharmacokinetics of an everolimus-cyclosporine immunosuppressive regimen over the first 6 months after kidney transplantation

The pharmacokinetics of everolimus were characterized over the first 6 months post transplant in 731 patients receiving either 0.75 or 1.5 mg bid everolimus in addition to cyclosporine and corticosteroids. Pharmacokinetic data consisted of 4014 everolimus trough concentrations (Cmin) obtained in all patients and 659 area under the concentration-time curve (AUC) -profiles obtained at months 2, 3, and 6 in a subset of 261 patients. Cmins averaged 4.3 +/- 2.4 and 7.2 +/- 4.2 ng/mL at 0.75 and 1.5 mg bid, indicating a 20% under-proportionality at the upper dose level. Cmins were 19-34% lower in the first month compared with months 2 through 6-values. AUC was dose-proportional and stable over time, averaging 77 +/- 32 and 136 +/- 57 ng.h.mL-1 at the two dose levels. Within- and between-patient variability in AUC were 27% and 31%, respectively. There was no influence of sex, age (16-66 years), or weight (42-132 kg) on AUC. Everolimus exposure was significantly lower by an average 20% in blacks. Everolimus exposure was relatively stable over the first 6 months post transplant, with no major departure from dose-proportionality over the therapeutic dose range. Weight-adjusted dosing (mg/kg) does not appear warranted. Black patients may have lower bioavailability and/or higher clearance of everolimus compared with white patients.

Gender, ethnicity and genetics in cardiovascular disease: part 1: Basic principles

Prior to 1993, most drug efficacy and safety trials were conducted in white males, although gender and racial differences in pharmacodynamics and pharmacokinetics have been documented since the early 1900s. Over the last 2 decades, supported by the FDA and legislation, attempts to include more women and minorities in clinical drug trials have been made, with limited success. Yet, there are important differences in pathophysiology and pharmacogenetics, as well as pharmacotherapeutic effectiveness. This is the first of 2 articles that review the basic scientific principles of such differences. In particular, genetic polymorphisms of cardiovascular candidate genes and drug metabolism are described. The pharmacodynamic and pharmacokinetic variations among genders and ethnicities are summarized.

Frequency distribution of C3435T mutation in exon 26 of the MDR1 gene in a Spanish population

P-glycoprotein (PGP) is a transmembrane efflux transporter with an important role in drug therapy. The level of PGP expression leads to relevant consequences in terms of efficacy and toxicity by modulating drug disposition. A single nucleotide polymorphism (SNP) in exon 26 of the gene C3435T was recently associated to PGP levels and substrate uptake. Persons who were homozygous for the T-allele had significantly decreased PGP expression compared with C/C persons. Due to this fact and bearing in mind the important differences among populations regarding the frequencies of persons carrying mutations affecting drug disposition, the authors wanted to study the prevalence of this genetic trait in their population. DNA samples from 408 persons were assayed by a PCR-RFLP method. The results showed that the distributions of the C/C, T/T, and C/T genotypes in the Spanish population were 26%, 22%, and 52%, respectively. With regard the C-allele frequency, which has been studied in several populations, the result in their population was 52%, significantly lower (P < 0.0001) than that found in African populations and similar to several Asian and Caucasian (UK) populations (P > 0.05). By contrast, the C-allele frequency in southwest Asian, German, and Portuguese populations was significantly lower than in the Spanish population (P < 0.001, P < 0.01, and P < 0.05, respectively). The great differences found between their population and others, such as the African and southwest Asian populations, could have important therapeutic implications when drugs that are a substrate of PGP are used.

Improvement of cyclosporin A determination in whole blood by reversed-phase high-performance liquid chromatography

A chromatographic method was developed for the determination of cyclosporin A in human whole blood using reversed-phase HPLC at room temperature. Most previous reports carried out this liquid chromatographic separation at temperatures above 70 degrees C. The present procedure greatly improves the detection limit by controlling peak broadening effects, as well as the lifetime of the column at room temperature. Under optimal conditions and using ketoconazole as an internal standard, the calibration graph was linear in the range of 16-1000 microg/L with a relative standard deviation of 3.72% at 150 microg/L and 2.45% at 300 microg/L (n = 11) of cyclosporin A. The detection limit was of 5.0 microg/L cyclosporin A. By this procedure, cyclosporin A pharmacokinetic parameters in healthy Chinese subjects were studied. The developed method could be applied to the quantification of cyclosporin A in human blood samples and allows the study of its pharmacokinetics in routine laboratories.

Pharmacokinetic Interactions between Cyclosporine and Protease Inhibitors in HIV + Subjects

With advances in antiretroviral therapy, many HIV+ individuals are living longer lives and some are developing end-stage renal and/or hepatic disease requiring transplantation. These patients require concomitant use of immunosuppressants (e.g., cyclosporine [CsA]) and antiretrovirals (e.g., protease inhibitors [PIs]), which exhibit narrow therapeutic windows and are substrates and inhibitors of cytochrome P450 3A enzymes and the cellular transporter P-glycoprotein. In this pilot study, HIV+ subjects on either oral nelfinavir (NFV) or indinavir (IND) with nondetectable viral loads and normal renal and hepatic function had 12 hour pharmacokinetic (PK) studies on 3 separate days: PIs alone, PIs+intravenous CsA, and PIs+oral CsA to determine the extent of PK interactions between these medications. PIs and CsA concentrations were measured by LC/MS in plasma and whole blood, respectively. Nine subjects (n=7 on NFV, n=2 on IND) completed the study. Only the results of those subjects taking NFV are reported. Oral co-administration of CsA increased NFV T(max) from 2.6+/-0.9 to 3.2+/-0.8 h (p<0.05), and AUC(0-infinity) from 27.9+/-15.2 to 43.2+/-27.1 mg(*)h/mL (p=0.06). Intravenous CsA did not appreciably alter oral pharmacokinetics of NFV. Both CsA and NFV PK parameters exhibited a high degree of intersubject variability, underscoring the need for routine therapeutic drug monitoring of both CsA and PIs in HIV+ subjects undergoing transplantation.

The influence of MDR1 polymorphisms on P-glycoprotein expression and function in humans

The MDR1 (ABCB1) gene product P-glycoprotein is a membrane protein, which functions as an ATP-dependent exporter of xenobiotics from cells. Its importance was first recognized because of its role in the development of multidrug resistance (MDR) of cultured tumor cells against various anticancer agents. It is now, however, well established that this transporter is not only expressed in tumor cells, but also in normal tissues with excretory function (intestine, liver, kidney). Since P-glycoprotein has a very broad substrate specificity, it determines disposition of a broad variety of drugs. Moreover, induction and inhibition of P-glycoprotein are new mechanisms for drug interactions in humans. Very recently, systematic screens of the MDR1 gene have identified multiple single nucleotide polymorphisms. Some of those appear to be associated with altered transporter function and expression. This review discusses the currently available data on the influence of MDR1 polymorphisms on P-glycoprotein tissue expression, drug disposition, treatment outcome and disease risk.

C3435T polymorphism in the MDR1 gene affects the enterocyte expression level of CYP3A4 rather than Pgp in recipients of living-donor liver transplantation

The bioavailability of structurally unrelated drugs is limited by active secretion via the multidrug resistance gene (MDR1) product P-glycoprotein (Pgp) from enterocyte into lumen as well as intestinal metabolism by cytochrome P450 IIIA4 (CYP3A4). In the present study, we analyzed whether genetic polymorphism of the MDR1 had some influence on the intestinal expression levels of Pgp and CYP3A4 and the tacrolimus concentration/dose ratio over the first postoperative days in recipients of living-donor liver transplantation (LDLT). Genotyping assays were performed for the major 10 polymorphisms in the MDR1 gene by the polymerase chain reaction-restriction enzyme length polymorphism method. The allele frequencies of variations at five positions were almost comparable with those in the former studies in Caucasians and Japanese, but there was no variation at the other five positions. Although no polymorphism correlated with the intestinal expression of MDR1 mRNA or the tacrolimus concentration/dose ratio in the LDLT recipients, the C3435T polymorphism significantly affected the intestinal expression level of CYP3A4 mRNA as follows; 3435C/C>3435C/T (P < 0.05 vs. 3435C/C)>3435T/T (P < 0.01 vs. 3435C/C). Therefore, the identified polymorphisms including C3435T in the MDR1 gene were indicated to have no influence on the intestinal expression level of Pgp or the tacrolimus concentration/dose ratio in the recipients of LDLT. On the other hand, the C3435T polymorphism of MDR1 was suggested to correlate with the enterocyte expression of CYP3A4 rather than Pgp linking unknown genetic variation in CYP3A4 gene.

C3435T mutation in exon 26 of the human MDR1 gene and cyclosporine pharmacokinetics in healthy subjects

To determine the relationship between C3435T mutation in exon 26 of the human multidrug resistant 1 (MDR1) gene and cyclosporine pharmacokinetic parameters among healthy volunteers, the oral cyclosporine pharmacokinetic study was performed for 14 healthy subjects. Blood cyclosporine concentrations were measured by HPLC. Concentration-time data were analyzed by a noncompartmental method using WinNonLin, and the blood samples were genotyped for the C3435T polymorphism of MDR1 gene using the PCR and a restriction digest. Each cyclosporine pharmacokinetic parameter was compared using the Mann-Whitney U test according to his or her P-gp genotype. There were seven (7) homozygous C/C, six (6) C/T, and one (1) homozygous T/T genotypes in these 14 healthy volunteers. According to their genotypes, mean t(max) 1.6 +/- 0.3 hours, mean C(max) 1337 +/- 329 ng/mL, mean Cl/F 66.5 +/- 18.3 L/h, and mean AUC 5642 +/- 1577 ng.h/mL in C/C group and mean t(max) 2.0 +/- 0.6 hours, mean C(max) 1540 +/- 721 ng/mL, mean Cl/F 55.2 +/- 18.9 L/h, and mean AUC 6902 +/- 1405 ng.h/mL in C/T+T/T group. Although Cmax and AUC in C/T and T/T group were 15% and 22% larger than those in C/C group, none of these parameter comparisons was statistically significant. There were no statistical differences in cyclosporine pharmacokinetics among different MDR1 genotypes in these 14 healthy subjects.