title: Interaction between acetaminophen and warfarin in adults receiving long-term oral anticoagulants: a randomized controlled trial.
abstract: OBJECTIVE
  We investigated whether acetaminophen, given at 2 g/day and 3 g/day might potentiate the anticoagulant effect of warfarin.
  
  
  METHODS
  Forty-five patients on stable warfarin therapy, enrolled in this prospective, randomized, parallel (three arms), placebo-controlled study, received a 10-day regimen of acetaminophen (2 g/day or 3 g/day) or placebo.
  
  
  RESULTS
  The mean maximal INR increase was 0.70 ± 0.49 and 0.67 ± 0.62 in patients receiving acetaminophen at 2 g/day and 3 g/day, respectively (P=0.01 for the respective comparisons versus placebo). The INR increase became significant on day 3 and was independently and significantly predicted by a maximal decrease in factor II (R(2)=0.36, P<0.0001), factor VII (R (2)=0.46, P<0.0001) and a maximal increase in acetaminophen plasma concentrations (R(2)=0.563, P<0.0001).
  
  
  CONCLUSIONS
  Acetaminophen, at 2 g/day or 3 g/day, enhanced the anticoagulant effect of warfarin in stable patients, thus requiring close INR monitoring in the clinical setting.
authors.affiliation: Unité de Recherches Thérapeutiques-Service de Médecine Interne A, Hôpital Lariboisière, 2 rue Ambroise Paré, 75010, Paris, France.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.forename: Claire
authors.initials: C
authors.lastname: Bal-dit-Sollier
authors.forename: Ludovic
authors.initials: L
authors.lastname: Drouet
authors.forename: Guy
authors.initials: G
authors.lastname: Simoneau
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Alvarez
authors.forename: Sandrine
authors.initials: S
authors.lastname: Pruvot
authors.forename: Romain
authors.initials: R
authors.lastname: Aubourg
authors.forename: Natacha
authors.initials: N
authors.lastname: Berge
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Bergmann
authors.forename: Stéphane
authors.initials: S
authors.lastname: Mouly
authors.forename: Isabelle
authors.initials: I
authors.lastname: Mahé
mesh_terms: D000082:Acetaminophen / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D000925:Anticoagulants / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004347:Drug Interactions; D016903:Drug Monitoring / Q000379:methods; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D014859:Warfarin / Q000494:pharmacology*; D055815:Young Adult
chemical_list: D018712:Analgesics, Non-Narcotic; D000925:Anticoagulants; D000082:Acetaminophen; D014859:Warfarin