title: Warfarin and acetaminophen interaction: a summary of the evidence and biologic plausibility.
abstract: Ms TS is a 66-year-old woman who receives warfarin for prevention of systemic embolization in the setting of hypertension, diabetes, and atrial fibrillation. She had a transient ischemic attack about 4 years ago when she was receiving aspirin. Her INR control was excellent; however, over the past few months it has become erratic, and her average dose required to maintain an INR of 2.0 to 3.0 appears to have decreased. She has had back pain over this same period and has been taking acetaminophen at doses at large as 650 mg four times daily, with her dose varying based on her symptoms. You recall a potential interaction and wonder if (1) her acetaminophen use is contributing to her loss of INR control, and (2) does this interaction place her at increased risk of warfarin-related complications?
authors.affiliation: Duke Clinical Research Institute, Duke University Medical Center, Durham, NC, USA. renato.lopes@duke.edu
authors.forename: Renato D
authors.initials: RD
authors.lastname: Lopes
authors.forename: John D
authors.initials: JD
authors.lastname: Horowitz
authors.forename: David A
authors.initials: DA
authors.lastname: Garcia
authors.forename: Mark A
authors.initials: MA
authors.lastname: Crowther
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Hylek
mesh_terms: D000082:Acetaminophen / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use; D000368:Aged; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use; D000925:Anticoagulants / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000150:complications / Q000503:physiopathology; D001416:Back Pain / Q000097:blood / Q000150:complications / Q000188:drug therapy; D001711:Biotransformation / Q000187:drug effects; D048909:Diabetes Complications / Q000503:physiopathology; D004347:Drug Interactions; D016903:Drug Monitoring; D004617:Embolism / Q000209:etiology / Q000517:prevention & control; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications / Q000503:physiopathology; D019934:International Normalized Ratio; D014812:Vitamin K / Q000037:antagonists & inhibitors; D014859:Warfarin / Q000009:adverse effects* / Q000493:pharmacokinetics / Q000627:therapeutic use
chemical_list: D018712:Analgesics, Non-Narcotic; D000925:Anticoagulants; D014812:Vitamin K; D000082:Acetaminophen; D014859:Warfarin