Intracellular and plasma efavirenz concentrations in HIV-infected patients switching from successful protease inhibitor-based highly active antiretroviral therapy (HAART) to efavirenz-based HAART (SUSTIPHAR Study).

OBJECTIVES To assess intracellular and plasma efavirenz concentrations in HIV-infected patients who switched to efavirenz-based highly active antiretroviral therapy (HAART) from successful protease inhibitor-based HAART. PATIENTS AND METHODS A total of 49 patients were included in this observational cohort study. At inclusion, all patients had plasma HIV-RNA levels<50 copies/mL and switched to efavirenz combined with two nucleoside reverse transcriptase inhibitors. Intracellular and plasma concentrations were measured 12 h post-dose, 1 month (M1) and 6 months (M6) after starting efavirenz. Virological success (VS) was defined as plasma HIV-RNA level<50 copies/mL within the first 12 months and remaining undetectable at the end of the follow-up. RESULTS VS was documented in 48 patients for at least 12 months (range 12-78 months). High inter-patient variabilities of intracellular and plasma efavirenz concentrations were observed (coefficients of variation>40%). At M1 and M6, respectively, median [Q1; Q3] intracellular efavirenz concentrations were 5300 [2830; 11 530] and 6790 [3870; 8790] ng/mL, median plasma efavirenz concentrations were 2050 [1600; 3100] and 2100 [1410; 2500] ng/mL. No correlation was found between intracellular and plasma concentrations. Plasma efavirenz levels exceeded the proposed threshold of 1000 ng/mL in 96% of patients from M1. CONCLUSIONS For moderately pre-treated HIV-infected patients with few mutations who switched to efavirenz from previous successful HAART, the proposed plasma efficacy-threshold was reached without any dosage adaptation. VS was maintained beyond 12 months, despite high inter-patient and intra-patient variabilities of intracellular and plasma efavirenz concentrations.