ABSTRACT
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-naïve HIV-infected adults who received FTC [200 mg once a day (q.d.)], ddI (400 mg q.d. if > or =60 kg; 250 mg q.d. if <60 kg) and EFV (600 mg q.d.) 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 (AUC(0-24 h)), maximum (Cmax) and minimum (Cmin) plasma concentrations, time to reach Cmax (Tmax), and the elimination half-life (t(1/2)). EFV plasma concentrations were also measured during follow-up. RESULTS: Median PK parameters for FTC, ddI and EFV, respectively, were as follows. AUC(0-24 h): 7.2, 7.0 and 36.4 h x 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; t(1/2): 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.
