title: Lack of effect of omeprazole in oral acenocoumarol anticoagulant therapy.
abstract: 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 controls (56.5%). A higher dose was necessary in 30 of 118 omeprazole patients (25.4%), compared with 84 of 299 controls (28.0%). In 14 of 118 omeprazole patients (11.9%) a lowering of the anticoagulant dose was required, compared with 46 of 299 controls (15.4%).
  
  
  CONCLUSIONS
  We found no evidence of any interaction between omeprazole and acenocoumarol. It seems likely that omeprazole can be administered safely to patients treated with acenocoumarol.
authors.affiliation: Dept. of Gastroenterology and Hepatology, Slotervaart Hospital, Amsterdam, The Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: Vreeburg
authors.forename: G M
authors.initials: GM
authors.lastname: De Vlaam-Schluter
authors.forename: P H
authors.initials: PH
authors.lastname: Trienekens
authors.forename: P
authors.initials: P
authors.lastname: Snel
authors.forename: G N
authors.initials: GN
authors.lastname: Tytgat
mesh_terms: D000074:Acenocoumarol / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D000284:Administration, Oral; D000368:Aged; D000897:Anti-Ulcer Agents / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D000925:Anticoagulants / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D016022:Case-Control Studies; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008099:Liver / Q000378:metabolism; D008297:Male; D009853:Omeprazole / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000627:therapeutic use; D010437:Peptic Ulcer / Q000188:drug therapy; D012189:Retrospective Studies
chemical_list: D000897:Anti-Ulcer Agents; D000925:Anticoagulants; D000074:Acenocoumarol; D009853:Omeprazole