Genotype-phenotype associations of cytochrome P450 3A4 and 3A5 polymorphism with midazolam clearance in vivo

The molecular basis for the wide interindividual variability of cytochrome P450 (CYP) 3A metabolic activity was studied in vivo at a genetic level. A single oral dose of midazolam was administered to 26 healthy subjects. The variability in midazolam oral clearance was 11-fold. No differences in midazolam oral clearance related to gender or ethnicity were observed. Selective sequencing of CYP3A4 and CYP3A5 genes revealed 18 single nucleotide polymorphisms (SNPs), including 8 novel CYP3A4 SNPs. Thirteen novel CYP3A4 haplotypes, 2 novel CYP3A5 haplotypes, and 1 major novel multigene haplotype (CYP3A4*VI-CYP3A5*3A) were also identified. No significant genotype-phenotype or haplotype-phenotype associations were found for any of the SNPs or haplotypes studied, including CYP3A4*1B, CYP3A5*3, and CYP3A5*6, even when ethnicity was considered. The only exceptions were the haplotype CYP3A4*VI and the multigene haplotype CYP3A4*VI-CYP3A5*3A. The carriers of the haplotype CYP3A4*VI had a 1.8-fold higher clearance of midazolam in black subjects (ANOVA on ranks, P = .028) compared with other individuals, and the carriers of the multigene haplotype CYP3A4*VI-CYP3A5*3A had a 1.7-fold higher clearance in the entire population (ANOVA on ranks, P = .012). In conclusion, these results indicate that the genetic variants identified so far in the CYP3A4 and CYP3A5 genes have only a limited impact on CYP3A-mediated drug metabolism in vivo.