METHOD FOR STUDYING DRUG-WARFARIN INTERACTIONS

The potential effects of extended-release felodipine on the pharmacokinetics and pharmacodynamics of warfarin were studied in a double-blind crossover study in 12 healthy men. Warfarin dosage was adjusted to achieve stable subtherapeutic anticoagulation. Subjects were then randomized to receive 2 weeks of treatment with 10 mg extended-release felodipine or placebo once daily, and warfarin dosage was adjusted if necessary to maintain stable international normalized ratio. The pharmacokinetics of R-and S-warfarin and the warfarin dose requirement did not differ importantly between periods of treatment with felodipine and placebo. The design of this study is suitable for general use in the identification of possible effects of other drugs on the pharmacokinetics and pharmacodynamics of warfarin. A different approach is needed if there is any reason to expect that warfarin may alter the pharmacokinetics or pharmacodynamics of the test drug.