Associations between ABCB1, CYP2A6, CYP2B6, CYP2D6, and CYP3A5 alleles in relation to efavirenz and nevirapine pharmacokinetics in HIV-infected individuals.

BACKGROUND: Human immunodeficiency virus (HIV)-infected individuals show large interindividual variation in response to antiretroviral therapy. Efavirenz (EFV) and nevirapine (NVP) are nonnucleoside reverse transcriptase inhibitors, which are prescribed in combination with other antiretroviral therapy in so-called highly active antiretroviral therapy. Recent studies provide evidence for the role of cytochrome P450 (CYP) genes, in particular CYP2B6, in relation to EFV and NVP pharmacokinetics. In this study, the authors investigated whether common ABCB1, CYP2A6, CYP2B6, CYP2D6, and CYP3A5 alleles are associated with plasma concentrations of EFV and NVP in HIV-infected individuals. METHODS: Plasma drug concentrations were quantified by high-performance liquid chromatography in 143 HIV-infected individuals receiving either EFV or NVP. Genotyping for common alleles was performed by restriction fragment length polymorphism and Taqman assays. Individuals were genotyped for 11 single-nucleotide polymorphisms in 5 genes. CYP2B6 haplotypes were reconstructed by PHASE. RESULTS: Plasma EFV concentrations were positively associated with CYP2B6 c.516G>T, c.785A>G, and c.983A>G single-nucleotide polymorphisms in HIV-infected individuals. Increased plasma concentrations of EFV and NVP were present in individuals with the CYP2B6*6/*6 or *6/*18 haplotype compared with CYP2B6*1/*1 [increase of 62% (95% confidence interval, 44.0-80.1) and 24% (95% confidence interval, 7.0-40.0), respectively, P < 0.01]. No significant association with other genes in relation to EFV or NVP concentrations was found. CONCLUSIONS: In this study, a strong association of CYP2B6*6 and CYP2B6*18 alleles in relation to EFV and NVP plasma concentrations was found, which confirmed previous studies.

Influence of sex on propofol metabolism, a pilot study: implications for propofol anesthesia.

PURPOSE: The basis of high intersubject variability of propofol metabolism is unclear. Therefore, we examined the influence of genetic polymorphisms of the key metabolizing enzymes cytochrome P450 2B6 (CYP2B6) and uridine diphosphate (UDP)-glucuronosyltransferase 1A9 (UGT1A9), age, and sex on propofol biotransformation in vitro and in vivo. METHODS: Plasma concentrations of propofol, 4-hydroxypropofol, and their glucuronides were measured over 20 min in 105 patients after a single intravenous bolus of propofol. Propofol 4-hydroxylation activity, genotypes, and content of CYP2B6 protein in 68 human livers were determined. The common single nucleotide polymorphisms (SNPs) for the CYP2B6 and UGT1A9 genes were analyzed by polymerase chain reaction (PCR). RESULTS: Plasma levels of propofol metabolites showed high interindividual variability (range of coefficient of variation 89-128%). This was supported by in vitro data showing similar variability of propofol 4-hydroxylation in liver microsomes and 1.9-fold higher CYP2B6 protein content in the livers from women. No significant relationships were revealed between the SNPs studied and propofol metabolism. However, patients' sex had a pronounced effect on propofol metabolism. Thus, women had higher amounts of propofol glucuronide (1.25-fold; p = 0.03), 4-hydroxypropofol-1-glucuronide (2.1-fold; p = 0.0009), and 4-hydroxypropofol-4-glucuronide (1.7-fold; p = 0.02) as shown by the weight-corrected area under the time-plasma concentration curve of metabolites. Additionally, the sexual dimorphism in 4-hydroxypropofol glucuronidation was prominent in the 35- to 64-year-old subgroup. CONCLUSIONS: No significant effects of CYP2B6 and UGT1A9 SNPs or age on propofol metabolism were revealed in this pilot study, but there was a pronounced effect of sex, a finding that indicates an important factor for the previously described sex difference in systemic clearance of propofol seen.

Mycophenolic acid-related diarrhea is not associated with polymorphisms in SLCO1B nor with ABCB1 in renal transplant recipients.

OBJECTIVE: We investigated the association between genetic polymorphisms in ABCB1 and SLCO1B and mycophenolic acid (MPA) pharmacokinetics, and MPA-related diarrhea and leukopenia in 338 kidney transplant recipients. METHODS: A total of 338 patients participating in an international, randomized-controlled clinical trial were genotyped for ABCB1 and SLCO1B. Patients were all treated with mycophenolate mofetil and either cyclosporine or tacrolimus. MPA-area under the curve (AUCs), MPA-glucuronide AUCs and acylglucuronide-AUCs were measured on days 3 and 10, and months 1, 3, 6, and 12 after kidney transplantation. RESULTS: The risk of developing diarrhea was 1.8-fold higher in patients cotreated with tacrolimus compared with patients cotreated with cyclosporine (95% confidence interval: 1.03-3.13; P=0.038). ABCB1 and SLCO1B SNPs were not associated with dose-adjusted exposure to MPA, MPA-glucuronide, nor acylglucuronide-MPA nor with the incidence of diarrhea or leukopenia. CONCLUSION: Genotyping for ABCB1 or SLCO1B pretransplantation is unlikely to be of clinical value for individualization of MPA therapy.

Age and CYP3A5 genotype affect tacrolimus dosing requirements after transplant in pediatric heart recipients.

BACKGROUND: Tacrolimus is one of the commonly used immunosuppressive drugs for pediatric heart transplants. Large variation exists in pharmacokinetics during the direct post-transplant period, resulting in an increased risk of adverse events. Limited data are available on the interaction of age, CYP3A5 and ABCB1 genotype, and disease severity on the variation in disposition and outcome in pediatric heart transplant recipients. METHOD: We studied the relationship between age and CYP3A5 and ABCB1 genotype and the Pediatric Risk of Mortality (PRISM) score on tacrolimus dose (mg/kg), steady-state trough concentrations, and concentration/dose ratio, as well as rejection and renal function for 14 days after heart transplant in children. RESULTS: Tacrolimus was administered to 39 children (median age, 6.0 years) after transplant. A correlation was found between the age at the time of transplant and the tacrolimus dosing requirements (r(s) = -0.447, p = 0.004) and the concentration/dose ratio (r(s) = 0.351, p = 0.029). CYP3A5 expressors required median (interquartile range) higher doses of tacrolimus (0.14 [0.09] vs 0.06 [0.04] mg/kg/12 hours, p = 0.001), and had lower concentration/dose ratios (45.34 [44.54] vs 177.78 [145.38] ng/ml per mg/kg/12 hours, p < 0.0001). This relationship was not seen with the ABCB1 genotype. Age and CYP3A5 genotype predicted the tacrolimus dosing requirements as well as the concentration/dose ratio (R(2) = 0.351, p = 0.001 and R(2) = 0.521, p < 0.001). No relationship was found between any of the CYP3A5 or ABCB1 genotypes and the estimated glomerular filtration rate. CONCLUSION: Younger age and CYP3A5 expressor genotype were independently associated with higher dosing requirements and lower tacrolimus concentration/dose ratios.

A new functional CYP3A4 intron 6 polymorphism significantly affects tacrolimus pharmacokinetics in kidney transplant recipients.

BACKGROUND: Tacrolimus (Tac) is a potent immunosuppressant with considerable toxicity. Tac pharmacokinetics varies between individuals and thus complicates its use in preventing rejection after kidney transplantation. This variability might be caused by genetic polymorphisms in metabolizing enzymes. METHODS: We used TaqMan analyses to evaluate the impact of a newly discovered CYP3A4 (cytochrome P450, family 3, subfamily A, polypeptide 4) single-nucleotide polymorphism (SNP) (rs35599367C>T; CYP3A4*22) on Tac pharmacokinetics in 185 renal transplant recipients who participated in an international randomized controlled clinical trial (fixed-dose, concentration-controlled study). RESULTS: The overall mean daily-dose requirement to reach the same predose Tac blood concentration was 33% lower for carriers of the T variant allele than for rs35599367CC patients (95% CI, -46% to -20%; P = 0.018). When combined with the *3 genotype of the CYP3A5 (cytochrome P450, family 3, subfamily A, polypeptide 5) gene, the rs35599367C>T SNP was also associated with a risk of supratherapeutic Tac concentrations (>15 µg/L) during the first 3 days after surgery, with an odds ratio of 8.7 for carriers of the CYP3A4 T allele plus CYP3A5*3/*3 (P = 0.027) and 4.2 for the CYP3A4 CC homozygotes plus CYP3A5*3/*3 (P = 0.002), compared with CYP3A4 CC homozygotes having 1 or 2 CYP3A5*1 alleles. The overall increase in the Tac dose-adjusted trough blood concentration was +179% for carriers of the CYP3A4 T allele with CYP3A5*3/*3 (P < 0.001), +101% for CYP3A4 CC homozygotes with CYP3A5*3/*3 (P < 0.001), and +64% for CYP3A4 T allele carriers with CYP3A5*1 (P = 0.020),compared with CYP3A4 CC homozygotes with CYP3A5*1. CONCLUSIONS: The CYP3A4 rs35599367C>T polymorphism is associated with a significantly altered Tac metabolism and therefore increases the risk of supratherapeutic Tac concentrations early after transplantation. Analysis of this CYP3A4*22 SNP may help in identifying patients at risk of Tac overexposure.

The interactions of age, genetics, and disease severity on tacrolimus dosing requirements after pediatric kidney and liver transplantation.

PURPOSE: In children, data on the combined impact of age, genotype, and disease severity on tacrolimus (TAC) disposition are scarce. The aim of this study was to evaluate the effect of these covariates on tacrolimus dose requirements in the immediate post-transplant period in pediatric kidney and liver recipients. METHODS: Data were retrospectively collected describing tacrolimus disposition, age, CYP3A5 and ABCB1 genotype, and pediatric risk of mortality (PRISM) scores for up to 14 days post-transplant in children receiving liver and renal transplants. Initial TAC dosing was equal in all patients and adjusted using therapeutic drug monitoring. We determined the relationship between covariates and tacrolimus disposition. RESULTS: Forty-eight kidney and 42 liver transplant recipients (median ages 11.5 and 1.5 years, ranges 1.5-17.7 and 0.05-14.8 years, respectively) received TAC post-transplant. In both transplant groups, younger children (<5 years) needed higher TAC doses than older children [kidney: 0.15 (0.07-0.35) vs. 0.09 (0.02-0.20) mg/kg/12h, p = 0.046, liver: 0.12 (0.04-0.32) vs. 0.09 (0.01-0.18) mg/kg/12h, p = 0.038]. In kidney but not liver transplants, CYP3A5 expressors needed significantly higher TAC doses than nonexpressors [0.15 (0.07-0.20) vs. 0.09 (0.02-0.35) mg/kg/12h, P = 0.001]. In these patients, age and CYP3A5 genotype were independently associated with TAC dosing requirement. In liver, but not kidney transplant patients, homozygous ABCB1 T-T-T haplotype carriers needed higher TAC doses than noncarriers [0.26 (0.15-0.32) vs. 0.11 (0.01-0.25) mg/kg/12h, p = 0.013]. CONCLUSION: CYP3A5 genotype may explain variation in tacrolimus disposition early after transplant in pediatric kidney recipients, independent of age-related variation. In contrast, in pediatric liver recipients, variation in tacrolimus disposition appears related to age and ABCB1 genotype. These findings illustrate the importance of the interplay among age, genotype, and transplant organ on tacrolimus disposition.

General maternal medication use, folic acid, the MDR1 C3435T polymorphism, and the risk of a child with a congenital heart defect.

OBJECTIVE: We sought to investigate maternal and child functional MDR1 C3435T polymorphism, periconception medication, folic acid use, and the risk of a congenital heart defect (CHD) in the offspring. STUDY DESIGN: MDR1 3435C>T genotyping was performed in 283 case triads (mother, father, child) and 308 control triads. Information on periconception medication and folic acid use was obtained through questionnaires. RESULTS: Mothers with MDR1 3435CT/TT genotype and using medication showed a significant association with the risk of a child with CHD (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.3-4.3) compared to mothers with MDR1 3435CC genotype not using medication. This risk increased without folic acid use (OR, 2.8; 95% CI, 1.2-6.4), and decreased in folic acid users (OR, 1.7; 95% CI, 0.8-3.7). Children carrying the MDR1 3435CT/TT genotype and periconceptionally exposed to medication without folic acid did not show significant risks. CONCLUSION: Mothers carrying the MDR1 3435T allele, using medication without folic acid, are at nearly 3-fold increased risk for CHD in the offspring.

Maternal medication use, carriership of the ABCB1 3435C > T polymorphism and the risk of a child with cleft lip with or without cleft palate.

Gene-environment interactions in the periconceptional period play an increasing role in the pathogenesis of birth defects, including cleft lip and/or cleft palate (CL/P). The P-glycoprotein, encoded by the ABCB1 gene, is suggested to protect the developing embryo from medication and other xenobiotic exposures. Furthermore, maternal medication use during early pregnancy is a significant risk factor for CL/P offspring. Therefore, the aim of this study is to investigate the association between the maternal and child's functional ABCB1 3435C > T polymorphism, periconceptional medication exposure, and the risk of a child with CL/P. A case-control study was performed among 175 mothers and 98 of their children with CL/P and 83 control mothers and their 65 children. Information on medication and folic acid use was collected. Mothers carrying the 3435TT genotype and using medication showed a 6.2-fold (95% CI = 1.6-24.2) increased risk of having a child with CL/P compared to mothers carrying the 3435CC genotype and not using medication. Periconceptional folic acid use reduced this risk by approximately 30% (OR = 3.9, 95% CI = 0.9-18.0). Mothers carrying the 3435TT genotype, using medication and not taking folic acid showed the highest risk estimate (OR = 19.2, 95% CI = 1.0-369.2). These data suggest that mothers who carry the ABCB1 3435C > T polymorphism are at significantly increased risk for having offspring with CL/P, especially mothers using medication in the periconceptional period.

Common ATP-binding cassette B1 variants are associated with increased digoxin serum concentration.

BACKGROUND AND OBJECTIVE: Digoxin is a known substrate of ATP-binding cassette B1 (ABCB1/MDR1). The results of studies on the association between ABCB1 polymorphisms and digoxin kinetics, however, remain contradictory. Almost all studies were small and involved only single dose kinetics. The goal of this study was to establish ABCB1 genotype effect on digoxin blood concentrations in a large cohort of chronic digoxin users in a general Dutch European population. METHODS: Digoxin users were identified in the Rotterdam Study, a prospective population-based cohort study of individuals aged 55 years and above. Digoxin blood levels were gathered from regional hospitals and laboratories. ABCB1 single nucleotide polymorphisms (SNPs) 1236C-->T, 2677G-->T/A, and 3435C-->T were assessed on peripheral blood DNA using Taqman assays. We studied the association between the ABCB1 genotypes and haplotypes, and digoxin blood levels using linear regression models adjusting for potential confounders. RESULTS: Digoxin serum levels and DNA were available for 195 participants (56.4% women, mean age 79.4 years). All three ABCB1 variants were significantly associated with serum digoxin concentration (0.18-0.21 microg/l per additional T allele). The association was even stronger for the 1236-2677-3435 TTT haplotype allele [0.26 mug/l (95% CI 0.14-0.38)], but absent for other haplotypes (CGC allele considered referent), suggesting an interaction of SNPs in a causal haplotype instead of individual SNP effects. CONCLUSION: We found that the common ABCB1 1236C-->T, 2677G-->T, and 3435C-->T variants and the associated TTT haplotype were associated with higher digoxin serum concentrations in a cohort of elderly European digoxin users in the general population.

A new CYP3A5 variant, CYP3A5*11, is shown to be defective in nifedipine metabolism in a recombinant cDNA expression system.

A new CYP3A5 variant, CYP3A5*11, was found in a white European subject by DNA sequencing. The CYP3A5*11 allele contains a single nucleotide polymorphism (SNP) (g.3775A>G) in exon 2, which results in a Tyr53Cys substitution, and a g.6986A>G splice change, the latter SNP previously reported in the defective CYP3A5*3 allele. However, the CYP3A5*3 is not a null allele because this variant is associated with leaky splicing, resulting in small amounts of functional protein still being produced. Therefore, we constructed a cDNA coding for the newly identified CYP3A5.11 protein by site-directed mutagenesis, expressed it in Escherichia coli, and partially purified it. Whereas bacteria transformed with wild-type CYP3A5*1 cDNA expressed predominantly cytochrome P450 (P450), those transfected with CYP3A5*11 expressed a significant amount of denatured cytochrome P420 in addition to P450, suggesting the protein to be unstable. CYP3A5.11 exhibited a 38% decrease in the V(max) for nifedipine metabolism, a 2.7-fold increase in the K(m), and a 4.4-fold decrease in the CL(int) of nifedipine compared with CYP3A5.1. A polymerase chain reaction-restriction fragment length polymorphism genotyping procedure was developed and used to genotype DNA of 500 white individuals for CYP3A5*11. No additional examples of this allele were identified. In summary, individuals carrying the rare CYP3A5*11 allele are predicted to have lower metabolism of CYP3A5 substrates than individuals expressing CYP3A5*3.

ABCB1 gene polymorphisms are not associated with treatment outcome in elderly acute myeloid leukemia patients.

OBJECTIVES: The classical multidrug resistance (MDR) gene MDR1 (ABCB1) encodes for the drug efflux pump P-glycoprotein (P-gp). P-gp expression is an adverse prognostic factor for treatment outcome in acute myeloid leukemia (AML) and is more frequently observed in older patients. Single-nucleotide polymorphisms of the ABCB1 gene, C1236T, G2677T, and C3435T, have been associated with altered drug metabolism and treatment outcome. We prospectively determined these single-nucleotide polymorphisms in AML blasts in a cohort of patients aged 60 years or older with AML and evaluated their relevance with regard to P-gp function and expression, ABCB1 messenger ribonucleic acid (mRNA) expression, and clinical outcome. METHODS: We have analyzed purified bone marrow-derived leukemic blasts, obtained at diagnosis, in 150 patients who were treated within a multicenter, randomized, phase 3 trial of elderly patients with AML. The significance of the allelic ABCB1 variants of C1236T, G2677T, and C3435T was evaluated with respect to P-gp expression and function in leukemic blasts and ABCB1 mRNA expression levels, and these values were correlated with treatment outcome. RESULTS: P-gp function and expression in leukemic blasts and ABCB1 mRNA levels in patients with AML did not vary significantly among any of the allelic variants of ABCB1. None of these allelic variations predicted a difference in complete response rate and survival endpoints. CONCLUSIONS: In AML patients aged 60 years or older, allelic ABCB1 variations of C1236T, G2677T, or C3435T are not associated with altered P-gp function or with MDR1 expression at the transcriptional or translational level in leukemic blasts, and they do not significantly affect clinical prognosis.

MDR1 gene polymorphisms are associated with neuropsychiatric adverse effects of mefloquine.

BACKGROUND: Mefloquine, a drug used for treatment and prophylaxis of malaria, is known for its neuropsychiatric adverse effects. We hypothesized that neuropsychiatric adverse effects of mefloquine are associated with polymorphisms in the MDR1/ABCB1 gene that encodes for the efflux pump P-glycoprotein. METHODS: The association between MDR1 C1236T, G2677T, and C3435T single-nucleotide polymorphisms and the occurrence of neuropsychiatric adverse effects was examined in a prospective cohort study of 89 healthy white travelers taking mefloquine. RESULTS: Of the subjects, 27 (28%) reported neuropsychiatric adverse effects, women significantly more frequently than men. Allele frequencies of the C1236T, G2677T, and C3435T polymorphisms were similar to those found in other white populations, and there was no significant association between any of the individual polymorphisms and neuropsychiatric adverse effects. However, women with the 1236TT, 2677TT, and 3435TT genotypes had a higher risk of neuropsychiatric adverse effects than the reference groups of women with heterozygous and homozygous CC or GG genotypes, with odds ratios of 6.3 (95% confidence interval [CI], 1.1-36.9), 10.5 (95% CI, 1.1-100.6), and 5.4 (95% CI, 1.1-30.0), respectively. The association for women homozygous for the 1236-2677-3435 TTT haplotype was even stronger (P = .004) than the effect of any of the individual polymorphisms. No associations with mefloquine blood levels were observed. CONCLUSION: In this study the MDR1 1236TT, 2677TT, and 3435TT genotypes, along with the 1236-2677-3435 TTT haplotype, were associated with neuropsychiatric adverse effects of mefloquine in women. MDR1 polymorphisms may play an important role in predicting the occurrence of neuropsychiatric adverse effects of mefloquine, particularly in female travelers.

Propofol pharmacokinetics and pharmacodynamics for depth of sedation in nonventilated infants after major craniofacial surgery.

BACKGROUND: To support safe and effective use of propofol in nonventilated children after major surgery, a model for propofol pharmacokinetics and pharmacodynamics is described. METHODS: After craniofacial surgery, 22 of the 44 evaluated infants (aged 3-17 months) in the pediatric intensive care unit received propofol (2-4 mg . kg-1 . h-1) during a median of 12.5 h, based on the COMFORT-Behavior score. COMFORT-Behavior scores and Bispectral Index values were recorded simultaneously. Population pharmacokinetic and pharmacodynamic modeling was performed using NONMEM V (GloboMax LLC, Hanover, MD). RESULTS: In the two-compartment model, body weight (median, 8.9 kg) was a significant covariate. Typical values were Cl = 0.70 . (BW/8.9)0.61 l/min, Vc = 18.8 l, Q = 0.35 l/min, and Vss = 146 l. In infants who received no sedative, depth of sedation was a function of baseline, postanesthesia effect (Emax model), and circadian night rhythm. In agitated infants, depth of sedation was best described by baseline, postanesthesia effect, and propofol effect (Emax model). The propofol concentration at half maximum effect was 1.76 mg/l (coefficient of variation = 47%) for the COMFORT-Behavior scale and 3.71 mg/l (coefficient of variation = 145%) for the Bispectral Index. CONCLUSIONS: Propofol clearance is two times higher in nonventilated healthy children than reported in the literature for ventilated children and adults. Based on the model, the authors advise a propofol dose of 30 mg/h in a 10-kg infant to achieve values of 12-14 on the COMFORT-Behavior scale and 70-75 on the Bispectral Index during the night. Wide pharmacodynamic variability emphasizes the importance of dose titration.

Interpatient variability in the pharmacokinetics of the HIV non-nucleoside reverse transcriptase inhibitor efavirenz: the effect of gender, race, and CYP2B6 polymorphism.

AIMS: To characterize the demographic and pharmacogenetic factors that influence interpatient variability in the plasma concentrations of the HIV non-nucleoside reverse transcriptase inhibitor efavirenz. METHODS: Data from all samples analyzed for efavirenz in our TDM service in 2002 and 2003 were reviewed. Information on gender, age, body weight, height, race, hormonal contraceptive use (in a subset of patients), and time between sampling and last intake was recorded. PCR-restriction fragment length polymorphism analysis was performed to detect the cytochrome P450 2B6 (CYP2B6) C1459T variant (present in CYP2B6*6 and CYP2B6*7) which is associated with low CYP2B6 activity. RESULTS: A total of 255 patients were included in this analysis. The median plasma efavirenz concentration was 2.50 (interquartile range: 1.85-3.55) mg l(-1). Eight patients (3.1%) were considered to have a subtherapeutic plasma concentration (<1.0 mg l(-1)) and 48 (18.9%) a toxic efavirenz concentration (>4.0 mg l(-1)). Gender, time after last intake, and race were the only factors that were significantly related to plasma efavirenz concentration in a multivariate analysis. No influence was observed for body weight, hormonal contraceptive use, and the presence of the CYP2B6 C1459T polymorphism. CONCLUSIONS: Gender and race are important factors in determining interpatient variability in plasma efavirenz concentrations which were unaffected by the presence of the CYP2B6 C1459T polymorphism. Physicians should be particularly alert for signs of efavirenz-induced toxicity in females and non-Caucasian patients.

Population pharmacokinetics of cyclosporine in kidney and heart transplant recipients and the influence of ethnicity and genetic polymorphisms in the MDR-1, CYP3A4, and CYP3A5 genes.

OBJECTIVE: Our objective was to determine the relationship between single nucleotide polymorphisms (SNPs) in the multidrug resistance 1 (MDR-1) gene and the cytochrome P450 (CYP) genes CYP3A4 and CYP3A5 and the pharmacokinetics of cyclosporine (INN, ciclosporin). METHODS: Cyclosporine pharmacokinetics of 151 kidney and heart transplant recipients undergoing maintenance therapy was described by use of nonlinear mixed-effects modeling (NONMEM) according to a 2-compartment pharmacokinetic model with first-order absorption and elimination. All patients were genotyped for the CYP3A4*1B and *3 , CYP3A5*3 and *6 , and MDR-1 3435C-->T SNPs. RESULTS: For a typical 70-kg white patient, the following parameters were estimated: absorption rate constant, 1.27 h -1; absorption time lag, 0.47 hour; oral volume of distribution of the central and peripheral compartment, 56.3 and 185.0 L, respectively; oral clearance (Cl/F), 30.7 L/h; and oral intercompartmental clearance, 31.7 L/h. Estimated interpatient variability of Cl/F was 28%. Cl/F was significantly correlated with weight and ethnicity; Cl/F was 13% higher (95% confidence interval, 8%-18%; P < .005) in white patients than in black and Asian patients. In carriers of a CYP3A4*1B variant allele, Cl/F was 9% (95% confidence interval, 1%-17%; P < .05) higher compared with CYP3A4*1 homozygotes, and this effect was independent of ethnicity or weight. Incorporation of these covariates into the NONMEM model did not markedly reduce interpatient variability of Cl/F. None of the other SNPs studied significantly influenced any of the pharmacokinetic parameters. CONCLUSION: Patients carrying a CYP3A4*1B variant allele have a significantly higher oral cyclosporine clearance compared with patients homozygous for CYP3A4*1 . However, this genetic effect on cyclosporine disposition was small, and genotyping of transplant recipients for CYP3A4 is thus unlikely to assist in planning initial cyclosporine dosing.

Genetic polymorphisms of the CYP3A4, CYP3A5, and MDR-1 genes and pharmacokinetics of the calcineurin inhibitors cyclosporine and tacrolimus.

BACKGROUND: The calcineurin inhibitors cyclosporine (INN, cyclosporin) and tacrolimus have a narrow therapeutic index and show considerable interindividual variability in their pharmacokinetics. The low oral bioavailability of calcineurin inhibitors is thought to result from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A4 and CYP3A5 and the multidrug efflux pump P-glycoprotein, encoded by MDR-1. OBJECTIVE: Our objective was to determine the role of genetic polymorphisms in CYP3A4, CYP3A5, and MDR-1 with respect to interindividual variability in cyclosporine and tacrolimus pharmacokinetics. METHODS: Kidney transplant recipients receiving cyclosporine (n = 110) or tacrolimus (n = 64) were genotyped for CYP3A4*1B and *3, CYP3A5*3 and *6, and MDR-1 C3435T. Dose-adjusted trough levels were determined and correlated with the corresponding genotype. RESULTS: Tacrolimus dose-adjusted trough levels were higher in CYP3A5*3/*3 patients (n = 45) than in *1/*3 plus *1/*1 patients (n = 17), as follows: median and range, 94 (34-398) ng/mL per mg/kg versus 61 (37-163) ng/mL per mg/kg (P <.0001, Mann-Whitney test). CYP3A4*1B allele carriers (n = 10) had lower tacrolimus dose-adjusted trough levels compared with those in patients with the wild-type (*1/*1) genotype (n = 54): median and range, 57 (40-163) ng/mL per mg/kg versus 89 (34-398) ng/mL per mg/kg) (P =.003, Mann-Whitney test). No evidence was found supporting a role for the MDR-1 C3435T polymorphism in tacrolimus dose requirement. None of the polymorphisms studied correlated with cyclosporine dose-adjusted predose concentrations. CONCLUSION: As a group, patients with the CYP3A5*3/*3 genotype require less tacrolimus to reach target predose concentrations compared with CYP3A5*1 allele carriers, whereas CYP3A4*1B carriers require more tacrolimus to reach target trough concentrations compared with CYP3A4*1 homozygotes.

CYP3A5 variant allele frequencies in Dutch Caucasians.

BACKGROUND: Enzymes of the cytochrome P450 3A (CYP3A) family are responsible for the metabolism of >50% of currently prescribed drugs. CYP3A5 is expressed in a limited number of individuals. The absence of CYP3A5 expression in approximately 70% of Caucasians was recently correlated to a genetic polymorphism (CYP3A5*3). Because CYP3A5 may represent up to 50% of total CYP3A protein in individuals polymorphically expressing CYP3A5, it may have a major role in variation of CYP3A-mediated drug metabolism. Using sequencing, have been identified (Hustert et al. Pharmacogenetics 2001;11:773-9; Kuehl et al. Nat Genet 2001;27:383-91) variant alleles *2 through *7 for CYP3A5. Detection of CYP3A5 variant alleles, and knowledge about their allelic frequency in specific ethnic groups, is important to establish the clinical relevance of screening for these polymorphisms to optimize pharmacotherapy. METHODS: In a group of 500 healthy Dutch Caucasian blood donors, we determined the allelic frequency of the CYP3A5*2, *3, *4, *5, *6, and *7 alleles by use of newly developed PCR-restriction fragment length polymorphism assays. RESULTS: The frequency of the defective CYP3A5*3 allele in the Dutch Caucasian population was 91%, followed by the CYP3A5*2 (1%) and CYP3A5*6 (0.1%) alleles. The CYP3A5*4, *5, and *7 alleles were not detected. CONCLUSIONS: On the basis of its allelic frequency, screening for the CYP3A5*3 allele in the Caucasian population is extremely relevant. In addition, screening for the CYP3A5*2 allele may be taken into consideration in individuals heterozygous for the CYP3A5*3 allele. The CYP3A5*4, *5, *6, and *7 alleles have low allelic frequencies that do not support initial screening.