Author(s): Kwara A, Lartey M, Sagoe KW, Kenu E, Court MH
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Abstract OBJECTIVE: UDP-glucuronosyltransferase (UGT) 2B7 was recently identified as the main enzyme mediating efavirenz N-glucuronidation. In this study, we determined whether selected UGT2B7 polymorphisms could be used to enhance the prediction of efavirenz plasma concentrations from CYP2B6 and CYP2A6 genotypes. METHODS: Mid-dose efavirenz plasma concentrations were determined in 94 HIV-infected Ghanaian patients at 2-8 weeks of antiretroviral therapy. CYP2B6 and CYP2A6 genotypes had been previously reported. UGT2B7 exon 2 single-nucleotide polymorphisms (SNPs) c.735A>G (UGT2B7*1c; rs28365062) and c.802C>T (H268Y; UGT2B7*2; rs7439366) were determined by direct sequencing with UGT2B7*1a defined as the reference allele. Relationships between efavirenz plasma concentrations, demographic variables and genotypes were evaluated by univariate and multivariate statistical approaches. RESULTS: The mean (+/-SD) mid-dose efavirenz plasma concentration was 3218 (+/-3905) ng/ml with coefficient of variation of 121\%. Independent predictors of efavirenz concentration included CYP2B6 c.516TT genotype (4030 ng/ml increase; 95\% confidence interval 2882-5505 ng/ml, P < 0.001), UGT2B7*1a carrier status (475 ng/ml increase; 95\% confidence interval 138-899 ng/ml, P = 0.004) and CYP2A6*9 and/or *17 carrier status (372 ng/ml increase; 95\% confidence interval 74-742 ng/ml, P = 0.013). Overall, CYP2B6 c.516TT genotype, UGT2B7*1a carrier status and CYP2A6*9 or *17 carrier status accounted for 45.2, 10.1 and 8.6\% of the total variance, respectively. CONCLUSION: Our findings demonstrate independent effects of CYP2A6 and UGT2B7 genetic variation on efavirenz disposition beyond that of the CYP2B6 polymorphisms. The development and testing of a pharmacogenetic algorithm for estimating the appropriate dose of efavirenz should incorporate genotypic data from both the oxidative and glucuronidation pathways.
This article was published in AIDS
and referenced in Journal of Pharmacogenomics & Pharmacoproteomics