Pharmacokinetics of emtricitabine, didanosine and efavirenz administered once-daily for the treatment of HIV-infected adults (pharmacokinetic substudy of the ANRS 091 trial)*

Objective This study was conducted to investigate the pharmacokinetics of emtricitabine (FTC), didanosine (ddI), and efavirenz (EFV) when administered in a once-daily combination. Methods Nine antiretroviral-naive HIV-infected adults who received FTC [200 mg once a day (qd)], ddI (400 mg qd if ≥60 kg; 250 mg qd if <60 kg) and EFV (600 mg qd) were studied. The following pharmacokinetic (PK) parameters were determined over 24 h at steady-state after 4 weeks of treatment: area under the plasma concentration vs. time curve (AUC0–24 h), maximum (Cmax) and minimum (Cmin) plasma concentrations, time to reach Cmax (Tmax), and the elimination half-life (t1/2). EFV plasma concentrations were also measured during follow-up. Results Median PK parameters for FTC, ddI and EFV, respectively, were as follows. AUC0–24 h: 7.2, 7.0 and 36.4 h×mg/L; Cmax: 1.8, 2.6 and 2.5 mg/L; Cmin: 0.04, < 0.01 and 1.0 mg/L; Tmax: 1.8, 1.1 and 2.5 h; t1/2: 7.4, 2.3, and 23.7 h. EFV plasma concentrations measured 10–13 h postdosing were higher during follow-up than during the PK study (2.57 vs. 1.19 mg/L, P<0.01). Conclusion The simultaneous administration of FTC, ddI and EFV did not affect the PK parameters of FTC when compared to historical controls. EFV Cmax and Cmin were lower than expected, but the data may have been slightly underestimated in this study. High ddI AUC and Cmax were measured in these patients, and further studies are warranted to confirm this finding.