The potential interaction between oral anticoagulants and acetaminophen in everyday practice

OBJECTIVE: The drug-drug interaction between oral anticoagulants (especially warfarin) and acetaminophen has been described, but evidence is conflicting and evidence for a similar interaction between acenocoumarol or phenprocoumon and acetaminophen is limited. Therefore, a study was performed to determine the influence of acetaminophen on oral anticoagulation with acenocoumarol or phenprocoumon in everyday practice.

METHOD: Included were patients from two Dutch anticoagulant clinics who had used oral anticoagulants for at least three months and who started with acetaminophen (case group) or benzodiazepines (control group).

RESULTS: Fifty-four patients were included who had a first prescription of acetaminophen in their pharmacy record (during oral anticoagulant use) and twenty patients with a first prescription of a benzodiazepine (during oral anticoagulant use). The INR (International Normalized Ratio) difference before and after acetaminophen use was not statistically significant between the two groups and showed no dose dependency.

CONCLUSION: These data do not demonstrate that acetaminophen, in the dosages used in everyday practice, has a clinically relevant influence on the INR in patients using acenocoumarol or phenprocoumon.