Objective: The human immundeficiency virus (HIV) protease inhibitor atazanavir is often used in once-daily observed therapy of methadone substituted former opiate drug users. We performed a matched-pairs analysis on 24 patients (12 men/women) taking atazanavir/ritonavir 300/100 mg daily plus reverse transcriptase inhibitors, with (n = 12) or without (n = 12) methadone co-administration.
Methods: Twenty-four-hour pharmacokinetic profiles of atazanavir/ritonavir were assessed at steady-state and measured by liquid chromatography-tandem mass spectrometry. The geometric mean (GM, t test) minimum and maximum plasma drug concentrations (C(min), C(max)), area under the concentration-time curve (AUC), and total clearance (CL(total)) were compared between the groups of pairs, which were matched for age, sex, weight, and ethnicity.
Results: The GM [90% confidence interval (CI)] of the atazanavir C(min), C(max), and AUC of patients taking the methadone oral solution at doses of 20-175 mg/day simultaneously with antiretroviral therapy were impaired compared to patients not taking methadone oral solution: C(min) = 315 (range 197-448) vs. 519 (279-793) ng/mL [GM ratio (GMR) = 0.61, p = 0.229]; C(max) = 1714 (1238-2262) vs. 3190 (2412-4076) ng/mL (GMR = 0.54, p = 0.018); AUC = 21,987 (15,870-29,327) vs. 35,572 (26,211-46,728) ng h/mL (GMR = 0.62, p = 0.074). Methadone dose, which is proportional to the amount of methadone oral solution (10 mg/mL), was significantly correlated to atazanavir C(max) (r (2) = 0.40, p = 0.001) and AUC (r (2) = 0.32, p = 0.006). Ritonavir pharmacokinetics was similar between the groups with C(min), C(max), and AUC GMR of 1.01, 0.80, and 0.96, respectively.
Conclusion: The partial decrease in atazanavir plasma concentrations in patients concomitantly taking racemic methadone oral solution in this daily observed therapy setting deserves further attention, and therapeutic drug monitoring should be considered.