The potential interaction between oral anticoagulants and acetaminophen in everyday practice

Pharm World Sci. 2002 Oct;24(5):201-4. doi: 10.1023/a:1020555321857.


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.

Publication types

  • Comparative Study
  • Multicenter Study

MeSH terms

  • Acetaminophen / administration & dosage
  • Acetaminophen / blood*
  • Administration, Oral
  • Aged
  • Aged, 80 and over
  • Anticoagulants / administration & dosage
  • Anticoagulants / blood*
  • Chi-Square Distribution
  • Drug Interactions / physiology
  • Female
  • Humans
  • International Normalized Ratio
  • Linear Models
  • Male
  • Middle Aged


  • Anticoagulants
  • Acetaminophen