Absence of Pharmacokinetic and Pharmacodynamic Interactions between Almorexant and Warfarin in Healthy Subjects

BACKGROUND AND OBJECTIVE: Almorexant is the first representative of the new class of orexin receptor antagonists, which could become a new treatment option for insomnia. The present study investigated the potential interaction between almorexant and warfarin. METHODS: In this open-label, two-way crossover, drug–drug interaction study, healthy male subjects received, in a randomized fashion, almorexant 200 mg once daily for 10 days and a single dose of 25 mg warfarin co-administered on day 5 (treatment A) and a single dose of 25 mg warfarin on day 1 (treatment B). Serial blood samples for warfarin pharmacokinetics and pharmacodynamics were drawn during both treatments. RESULTS: Of the 14 enrolled subjects, one withdrew due to an adverse event and 13 completed the study. Almorexant had no effect on the pharmacokinetics of warfarin. The geometric mean ratios (90 % confidence interval) for the area under the plasma concentration–time curve to infinity (AUC(0–∞)) of S- and R-warfarin were 0.99 (0.89, 1.09) and 1.05 (0.95, 1.16), respectively, and for the maximum plasma concentration (C(max)) were 0.99 (0.86, 1.14) and 1.00 (0.88, 1.13), respectively. The main pharmacodynamic variable was the AUC for the international normalized ratio (AUC(INR)). Almorexant had no effect on this variable as demonstrated by a geometric mean ratio of 0.99 (0.82, 1.19). Secondary pharmacodynamic variables including maximum effect (E(max)), the time to the maximum INR, and factor VII plasma concentrations were also not affected by almorexant. CONCLUSION: No dose adjustment of warfarin is necessary when concomitantly administered with almorexant.