Abstract
Background and PurposeIn TBâHIV coâinfection, prompt initiation of TB therapy is recommended but antiâretroviral treatment (ART) is often delayed due to potential drugâdrug interactions between rifampicin and efavirenz. In a longitudinal cohort study, we evaluated the effects of efavirenz/rifampicin coâtreatment and time of ART initiation on CYP3A induction.Experimental ApproachTreatmentânaĂŻve TBâHIV coâinfected patients (n = 102) were randomized to efavirenzâbasedâART after 4 (n = 69) or 8 weeks (n = 33) of commencing rifampicinâbased antiâTB therapy. HIV patients without TB (n = 94) receiving efavirenzâbasedâART only were enrolled as control. Plasma 4ÎČâhydroxycholesterol/cholesterol (4ÎČâOHC/Chol) ratio, an endogenous biomarker for CYP3A activity, was determined at baseline, at 4 and 16 weeks of ART.Key ResultsIn patients treated with efavirenz only, median 4ÎČâOHC/Chol ratios increased from baseline by 269% and 275% after 4 and 16 weeks of ART, respectively. In TBâHIV patients, rifampicin only therapy for 4 and 8 weeks increased median 4ÎČâOHC/Chol ratios from baseline by 378% and 576% respectively. After efavirenz/rifampicin coâtreatment, 4ÎČâOHC/Chol ratios increased by 560% of baseline (4 weeks) and 456% of baseline (16 weeks). Neither time of ART initiation, sex, genotype nor efavirenz plasma concentration were significant predictors of 4ÎČâOHC/Chol ratios after 4 weeks of efavirenz/rifampicin coâtreatment.Conclusion and ImplicationsRifampicin induced CYP3A more potently than efavirenz, with maximum induction occurring within the first 4 weeks of rifampicin therapy. We provide pharmacological evidence that early (4 weeks) or deferred (8 weeks) ART initiation during antiâTB therapy has no significant effect on CYP3A induction.LINKED ARTICLESThis article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc
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