Successful Anticoagulation and Continuation of Tramadol Therapy in the Setting of a Tramadol‐Warfarin Interaction

Tramadol is a commonly used synthetic opioid with the advantage of lowering the potential for dependence. Two reports of a tramadol-warfarin drug interaction have been published, and the current product insert states that increased international normalized ratios (INRs) with concomitant tramadol-warfarin use have been reported. We report a tramadol-warfarin drug interaction that caused a supratherapeutic INR in a 65-year-old man in previously stable condition who was being treated at our anticoagulation clinic. Within 6 days of starting tramadol 50 mg twice/day, the patient's INR rose from 2.5 to 6.14. He elected to continue therapy with the tramadol. A 30% dosage reduction from warfarin 60 to 42 mg/week was eventually needed. To our knowledge, this is the first case report of the successful continuation of tramadol after a tramadol-warfarin drug interaction. Based on our experience, we suggest an empiric dosage reduction of 25-30% in warfarin followed by repeat measurement of the INR within 1 week in patients who are starting tramadol therapy. As an alternative, maintaining the current dose of warfarin, followed by a repeat INR determination in 3 days, may be appropriate.