Population Pharmacokinetics of Efavirenz in an Unselected Cohort of HIV-1-Infected Individuals

Excerpt

We read with interest the recent article Population Pharmacokinetics of Efavirenz in an Unselected Cohort of HIV-1-Infected Individuals by Kappelhoff et al.[1] and support the conclusion that an individual dose administration strategy based on patient characteristics and population pharmacokinetics may lead to optimisation of efavirenz-based therapy. However, we think it is important to point out that the statement in the Discussion section that efavirenz is primarily metabolised by the isoenzyme cytochrome P450 (CYP) 3A4 is not supported by the available data. Efavirenz is predominantly metabolised by CYP2B6,[2] which is subject to considerable genetic variation. It is well documented that the G516T allele of the CYP2B6 gene is associated with higher plasma concentrations of efavirenz, with the potential to increase frequency of toxicity.[3‐6] Indeed, Kappelhoff et al.[7] have discussed the impact of CYP2B6 polymorphism in another recent publication on the 2NN study. Other genetic variants of CYP2B6 have recently been tested on the metabolism of efavirenz in vitro.[8] It is also known that the frequency of the G516T single nucleotide polymorphism (SNP) is higher among Black Africans than Caucasians,[6] although this is of limited relevance to the study by Kappelhoff et al.[1] as the population they describe is predominantly Caucasian. …