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Warfarin-acetaminophen drug interaction revisited.
K L Shek1, L N Chan, E Nutescu
1Department of Pharmacy Practice, University of Illinois at Chicago, College of Pharmacy, 60612, USA.
Pharmacotherapy
|October 8, 1999
Summary
Acetaminophen may increase warfarin
Area of Science:
- Pharmacology
- Internal Medicine
- Clinical Pharmacy
Background:
- Physicians and pharmacists commonly recommend acetaminophen for pain and fever in patients taking warfarin.
- Recent evidence suggests a potential safety concern with this common practice.
Purpose of the Study:
- To investigate the interaction between acetaminophen and warfarin.
- To evaluate the safety of using acetaminophen in patients undergoing warfarin therapy.
Main Methods:
- A comprehensive literature search was conducted.
- Included human studies and case reports from 1966-1999.
- Databases searched included MEDLINE and IPA.
Main Results:
- Evidence indicates acetaminophen may potentiate the anticoagulant effect of warfarin.
- The exact mechanism of this interaction remains unclear.
- Excessive doses (> 1.3 g/day) or prolonged use (> 2 weeks) of acetaminophen may increase risks.
Conclusions:
- Acetaminophen remains a suitable analgesic and antipyretic for warfarin patients when used cautiously.
- Avoid excessive amounts and prolonged administration of acetaminophen.
- Frequent monitoring of international normalized ratios (INRs) is crucial for safe anticoagulation.