Twenty-one healthy, male volunteers completed this double-blind, randomized, two-period, crossover study to determine the possible pharmacodynamic and pharmacokinetic interaction of the concomitant administration of rivastatin and warfarin sodium in healthy volunteers. The study comprised 2 treatment periods of 8 days each, with a medication-free period of 14 days between the 2 treatment periods. According to the randomization, the volunteers received either 300 micrograms of rivastatin or matching placebo once daily during the treatment periods. On day 4 of each treatment period, the volunteers also received a single oral dose of 25 mg of warfarin sodium together with rivastatin or matching placebo. The effect of rivastatin on both the pharmacokinetics and pharmacodynamics (prothrombin time and clotting factor VII activity) of warfarin sodium, and the effect of warfarin sodium on the pharmacokinetics of rivastatin were investigated. Blood sample assays included the analysis of both R- and S-warfarin, because it is known that the enantiomers differ in anticoagulant potency. The study results indicate that the concomitant administration of rivastatin and warfarin does not affect the pharmacokinetics of R- and S-warfarin, or the pharmacodynamics of warfarin. Furthermore, the administration of warfarin sodium does not affect the pharmacokinetics of rivastatin.