NO EFFECT OF SHORT-TERM OMEPRAZOLE INTAKE ON ACENOCOUMAROL PHARMACOKINETICS AND PHARMACODYNAMICS

Aims To investigate the effect of omeprazole on the pharmacokinetics o f R- and S-acenocoumarol and on their combined anticoagulant activity. Methods Eight healthy male subjects completed a double-blind, randomi zed, placebo-controlled, two-way cross-over study. Subjects were given either omeprazole 40 mg or placebo once daily for 3 days. On day 2 of each study period, a single 10 mg oral dose of racemic acenocoumarol was administered and venous blood samples were collected for pharmacok inetic and pharmacodynamic assessments. A wash-out period of 2 weeks s eparated the two study periods. Results The pharmacokinetics of R-and S-acenocoumarol (AUG 3016 +/- 221 and 233 +/- 14 ng ml(-1) h, respecti vely) did not change after omeprazole (AUG 2929 +/- 256 and 220 +/- 18 ng ml(-1) h, respectively). Anticoagulant activity (INRmax 1.7 +/- 0. 1) was unaffected by co-administration of omeprazole (INRmax 1.7 +/- 0 .1). Conclusions The shea-term intake of omeprazole does not affect ac enocoumarol pharmacokinetics or pharmacodynamics. These data differ fr om the results of previous studies on the effect of omeprazole on warf arin, suggesting a different in vivo interaction profile of omeprazole on acenocoumarol than on warfarin. Drug interaction studies with oral anticoagulants should not be restricted to the use of warfarin.