Material and Methods: To evaluate the influence of nevirapine on atazanavir trough concentrations (Ctrough) in a group of HIV-infected patients, we performed an open-label pilot study enrolling patients receiving 300/100 mg atazanavir/ritonavir once daily for 2 weeks or longer. Nevirapine was added at a dose of 200 mg once daily from Days 0 to 14 and 200 mg twice daily from Days 14 to 28. Atazanavir and nevirapine plasma Ctroughs were determined at Days 0 and 28. Atazanavir Ctroughs were compared between Days 0 and 28. Atazanavir and nevirapine Ctroughs at Day 28 were compared with historical controls receiving either 400 mg atazanavir once daily or 200 mg nevirapine twice daily.
Results: Fourteen patients were enrolled and 11 completed the study. The geometric mean (range) atazanavir Ctrough decreased from 0.631 mg/L (range, 0.235-1.87 mg/L) at Day 0 to 0.316 mg/L (range, 0.142-1.109 mg/L) at Day 28 to give a geometric mean ratio of 0.59 (95% confidence interval, 0.38-0.80; P = 0.026); nonetheless, the atazanavir Ctrough remained higher than the minimum effective concentration in 80% of the participants and higher than the median concentration in the control subjects receiving 400 mg atazanavir once daily without ritonavir (geometric mean ratio, 3.20; 95% confidence interval, 1.65-6.22; P = 0.001). The nevirapine Ctrough at Day 28 was slightly higher than in the historical controls on 200 mg nevirapine twice daily without atazanavir (geometric mean ratio, 1.46; 95% confidence interval, 1.04-2.06; P = 0.030).
Conclusion: We conclude that coadministration of 300/100 mg atazanavir/ritonavir once daily plus 200 mg nevirapine twice daily was safe and well tolerated but resulted in a decrease of atazanavir Ctrough by nearly half. Therefore, monitoring atazanavir Ctrough is recommended in patients treated with this drug combination, and increasing the atazanavir dose might be necessary.