Dangerous Drug Interaction: Warfarin-NSAIDs

Impact: Potential for serious bleed¹ (GI, hemorrhage).

Mechanism of Interaction: NSAIDs increase gastric irritation and erosion of the protective lining of the stomach, assisting in the formation of a GI bleed. Additionally, NSAIDs decrease the cohesive properties of platelets necessary in clot formation.

Alternatives to Patient Management: Avoid concomitant use of an NSAID with warfarin.² Identify reason for NSAID therapy. If anti-pyretic effects are desired, then consider acetaminophen. Acetaminophen in doses less than 2g/day on a short-term basis do not appear to affect the INR.² Long-term use of acetaminophen for anti-pyretic and analgesic effects is controversial. If anti-inflammatory effects are necessary, then consider cyclooxygenase-2 (COX-2) inhibitor therapy. The reduction of prevalence of gastric adverse advents with these agents combined with the lack of anti-platelet action, support the cautious use of COX-2 inhibitors in anticoagulation patients.² There are some case reports discussing the elevation of INRs with COX-2 inhibitors. If analgesic effects are desired, caution should also be exhibited with the use of tramadol; there are a few case reports describing an elevation of the INR with concomitant administration of tramadol with warfarin.

Monitoring/Precautions: INR should be monitored every week with co-administration of warfarin with an NSAID. Signs and symptoms of an active bleed should be monitored with particular attention to the appearance and patterns of bruises. Signs of an active bleed include: coughing up blood in the form of coffee grinds (hemoptysis), gingival bleeding, nose bleeds, cola- or tea-colored urine (hematuria), or black, tarry stools (hemoccult positive?).

References: Follow this link for a complete list of references.

The above information serves only as a guide for use by qualified medical practitioners in understanding, handling and avoiding frequent and potentially dangerous drug interactions that occur in long-term care. This presentation is not intended to instruct a practitioner how to treat any medical condition, nor is it intended to replace a practitioner's best clinical judgment. AMDA expressly disclaims responsibility and liability for any adverse effects, damages or other consequences resulting from the use of any of the information contained in this presentation.