A Population Pharmacokinetic Approach to Understand the Effect of Efavirenz on CYP3A Activity in Healthy Volunteers Using Midazolam as a Probe
Abstract
Efavirenz induces and inhibits multiple drug-metabolizing enzymes, contributing to significant drug-drug interactions. This study quantified the impact of multiple doses of efavirenz on CYP3A activity via midazolam metabolism using a population pharmacokinetic approach. Healthy volunteers received 1 mg midazolam orally in two sessions: first with a single 600 mg efavirenz dose and then after chronic efavirenz dosing (600 mg/day for 17 days). Midazolam and 1'-hydroxymidazolam were quantified via LC-MS/MS, and CYP2B6, CYP3A4, and CYP3A5 genotypes were assessed using TaqMan assays. Seventy-two volunteers (n = 72) completed sampling after the initial dose, and 58 completed both occasions. Non-linear mixed effects modeling was performed using the stochastic approximation expectation maximization estimation method in NONMEM. The base pharmacokinetic model employed was a two-compartment model with first-order absorption and first-order elimination, incorporating proportional error terms for midazolam and 1'-hydroxymidazolam. Covariate analysis utilized a full model approach to assess the impact of CYP3A4 and CYP3A5 genotypes, self-reported sex, and multiple doses of efavirenz as covariates affecting the formation clearance of 1-OH midazolam. CYP3A5 expressors exhibited a 1.27-fold increase in midazolam clearance compared to non-expressors, while CYP3A4 intermediate metabolizers showed a 0.94-fold decrease relative to normal metabolizers. Clearance was also 1.30-fold higher in…
How strong is the evidence?
Evidence Hub reads this as a clinical trial, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence. Reported size: 72 participants or records.
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