title: Successful anticoagulation and continuation of tramadol therapy in the setting of a tramadol-warfarin interaction.
abstract: 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.
authors.affiliation: Pharmacy Department, Harper University Hospital, Detroit, Michigan 48201, USA. pdumo@dmc.org
authors.forename: Peter A
authors.initials: PA
authors.lastname: Dumo
authors.forename: Luba A
authors.initials: LA
authors.lastname: Kielbasa
mesh_terms: D000368:Aged; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000925:Anticoagulants / Q000627:therapeutic use*; D001416:Back Pain / Q000188:drug therapy; D004347:Drug Interactions; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D011655:Pulmonary Embolism / Q000517:prevention & control; D014147:Tramadol / Q000627:therapeutic use*; D020246:Venous Thrombosis / Q000517:prevention & control; D014859:Warfarin / Q000627:therapeutic use*
chemical_list: D000701:Analgesics, Opioid; D000925:Anticoagulants; D014147:Tramadol; D014859:Warfarin