Paracetamol: a haemorrhagic risk factor in patients on warfarin

• Published in: British journal of clinical pharmacology 2005-03, Vol.59 (3), p.371-374
• Main Authors: Mahé, I., Bertrand, N., Drouet, L., Simoneau, G., Mazoyer, E., Bal dit Sollier, C., Caulin, C., Bergmann, J. F.
• Format: Article
• Language: English
• Subjects: Acetaminophen; Adult; Aged; Aged, 80 and over; Analgesics, Non-Narcotic; anticoagulant; Anticoagulants - adverse effects; Biological and medical sciences; bleeding; Contraindications; Cross-Over Studies; Double-Blind Method; Drug Synergism; Drug Therapy, Combination; Hemorrhage - chemically induced; Humans; INR; interaction; International Normalized Ratio; Medical sciences; Middle Aged; paracetamol; Pharmacology. Drug treatments; Prospective Studies; Risk Factors; Short Reports; warfarin; Warfarin - adverse effects
• ISSN: 0306-5251; 1365-2125
• DOI: 10.1111/j.1365-2125.2004.02199.x

Aim To quantify the effect of paracetamol on the anticoagulant effect of warfarin under normal clinical conditions. Patients and methods In a prospective double‐blind, cross‐over, placebo‐controlled study, 11 patients on stable warfarin therapy received in random order two 14‐day regimens of paracetamol 4 g day−1 or placebo, with a 14‐day or more wash‐out period in between, time necessary to fulfil the inclusion criteria. Results In patients on paracetamol, the mean maximum increase in the International Normalized Ratio (INR) observed was 1.04 ± 0.55 vs. 0.20 ± 0.32 in those on placebo (P = 0.003). The mean maximum INR observed was significantly higher with paracetamol than with placebo (3.47 vs. 2.61, P = 0.01). In patients receiving paracetamol, the mean observed INR was significantly increased after 4 days (+ 0.6 ± 0.6, P