Prenatal efavirenz exposure is independently associated with maternal, but not fetal CYP2B6 genotype.

Objectives: Understanding the influence of fetal and maternal genetics on prenatal drug exposure could potentially improve benefit-risk evaluation. In this study, we investigated the impact of two functional polymorphisms in CYP2B6 on prenatal exposure to efavirenz.

Methods: Dried blood spot (DBS) samples were collected from HIV-positive pregnant women ( n  = 112) and their newborns ( n  = 107) at delivery. They were genotyped for single nucleotide polymorphisms in CYP2B6. Efavirenz was quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results: Significant correlations were observed in efavirenz concentration between maternal and newborn ( r  = 0.46, R2  = 0.21, P  < 0.001), and maternal and cord ( r  = 0.83, R2  = 0.68, P  < 0.001) samples. Median (interquartile range) newborn plasma-to-maternal plasma and cord-to-maternal plasma ratios were 0.85 (0.03-3.49) and 0.78 (0.23-1.96), respectively. Newborn efavirenz concentration in DBS varied significantly based on composite maternal CYP2B6 genotype: fast ( CYP2B6 516GG and 983TT, n  = 26), 747 ng/ml (602-1060); intermediate ( CYP2B6 516GT or 983TC n  = 50), 1177 ng/ml (898-1765); and slow ( CYP2B6 516GT and 983TC or 516TT or 983CC, n  = 14), 3094 ng/ml (2126-3812). Composite newborn CYP2B6 genotype was, however, not significantly associated with prenatal exposure. Efavirenz concentration in newborn stratified as fast ( n  = 25), intermediate ( n  = 36), and slow metabolizers ( n  = 19) from prenatal exposure was 999.7 (774-1285), 1240 (709-1984), and 1792 ng/ml (1201-3188), respectively.

Conclusion: The clinical relevance of the observed influence of maternal genetics on prenatal efavirenz exposure requires further investigation.