Summary

The effect of concomitantly administered clopidogrel on anticoagulationstatus was investigated in patients receiving longtermwarfarin therapy. Forty-three patients with non-valvularatrial fibrillation who were receiving long-term warfarin andhad a stable international normalized ratio (INR) between 2and 3 were randomly assigned to clopidogrel 75 mg daily orplacebo for 8 days (Days 1-8). INR (primary endpoint) andplasma levels of warfarin enantiomers (secondary endpoint)were evaluated at Days 3, 6, 9, 13 and 22. Mean INR remained extremely stable in the clopidogrel group, the maximum percentagechange from baseline being 0.6% at Day 6. Plasmalevels of R- and S-warfarin also remained very stable in thosereceiving clopidogrel. No serious adverse events, prematurediscontinuations of study drug or bleeding occurred with clopidogrel.In conclusion, the stable anticoagulation status ofpatients receiving long-term warfarin therapy is unaffected byconcomitant administration of clopidogrel 75 mg daily.