Effect of aprepitant on the pharmacokinetics and pharmacodynamics of warfarin

Objective To examine the effect of aprepitant on the pharmacokinetics and pharmacodynamics of warfarin. Aprepitant is a neurokinin-1 (NK₁)-receptor antagonist developed as an antiemetic for chemotherapy-induced nausea and vomiting.Methods This was a double-blind, placebo-controlled, randomized, two-period, parallel-group study. During period 1, warfarin was individually titrated to a stable prothrombin time (expressed as international normalized ratio, INR) from 1.3 to 1.8. Subsequently, the daily warfarin dose remained fixed for 10–12 days. During period 2, the warfarin dose was continued for 8 days, and on days 1–3 administered concomitantly with aprepitant (125 mg on day 1, and 80 mg on days 2 and 3) or placebo. At baseline (day –1 of period 2) and on day 3, warfarin pharmacokinetics was investigated. INR was monitored daily. During period 2, warfarin trough concentrations were determined daily.Results The study was completed by 22 healthy volunteers (20 men, 2 women). On day 3, steady-state pharmacokinetics of warfarin enantiomers after aprepitant did not change, as assessed by warfarin AUC_0-24h and C_max. However, compared with placebo, trough S(–) warfarin concentrations decreased on days 5–8 (maximum decrease 34% on day 8, P<0.01). The INR decreased after aprepitant with a mean maximum decrease on day 8 of 11% versus placebo (P=0.011).Conclusion These data are consistent with a significant induction of CYP2C9 metabolism of S(–) warfarin by aprepitant. Subsequently, in patients on chronic warfarin therapy, the clotting status should be monitored closely during the 2-week period, particularly at 7–10 days, following initiation of the 3-day regimen of aprepitant with each chemotherapy cycle.