Lack of effect of omeprazole in oral acenocoumarol anticoagulant therapy.

Background: Omeprazole is eliminated almost completely by hepatic metabolism within the cytochrome P-450 system and might inhibit the oxidative metabolism of other drugs. This is particularly relevant for compounds with a narrow therapeutic range, such as acenocoumarol. In this study we evaluated the effect of omeprazole use in patients receiving continuous acenocoumarol therapy. Methods: One thousand and fifty-seven patients receiving long-term oral acenocoumarol combined with omeprazole were selected retrospectively. In 118 of these patients omeprazole was considered the only factor of possible influence on anticoagulant therapy. The control group consisted of 299 age- and sex-matched patients taking acenocoumarol without interfering medication. Dose adjustment of acenocoumarol on starting omeprazole therapy was indicated by clinically relevant changes in coagulation time. Results: No adaptation of the anticoagulant dose was necessary in 74 of 118 omeprazole patients (62.7%), compared with 169 of 299 co...