title: Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults.
abstract: BACKGROUND
  Antibiotic medications are associated with an increased risk of bleeding among patients receiving warfarin. The recent availability of data from the Medicare Part D prescription drug program provides an opportunity to assess the association of antibiotic medications and the risk of bleeding in a national population of older adults receiving warfarin.
  
  
  METHODS
  We conducted a case-control study nested within a cohort of 38,762 patients aged 65 years and older who were continuous warfarin users, using enrollment and claims data for a 5% national sample of Medicare beneficiaries with Part D benefits. Cases were defined as patients hospitalized for a primary diagnosis of bleeding and were matched with 3 control subjects on age, race, sex, and indication for warfarin. Logistic regression analysis was used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for the risk of bleeding associated with prior exposure to antibiotic medications.
  
  
  RESULTS
  Exposure to any antibiotic agent within the 15 days of the event/index date was associated with an increased risk of bleeding (aOR 2.01; 95% CI, 1.62-2.50). All 6 specific antibiotic drug classes examined (azole antifungals [aOR, 4.57; 95% CI, 1.90-11.03], macrolides [aOR, 1.86; 95% CI, 1.08-3.21], quinolones [aOR, 1.69; 95% CI, 1.09-2.62], cotrimoxazole [aOR, 2.70; 95% CI, 1.46-5.05], penicillins [aOR, 1.92; 95% CI, 1.21-2.07], and cephalosporins [aOR, 2.45; 95% CI, 1.52-3.95]) were associated with an increased risk of bleeding.
  
  
  CONCLUSIONS
  Among older continuous warfarin users, exposure to antibiotic agents-particularly azole antifungals-was associated with an increased risk of bleeding.
authors.affiliation: Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, 77555, USA. jbaillar@utmb.edu
authors.forename: Jacques
authors.initials: J
authors.lastname: Baillargeon
authors.forename: Holly M
authors.initials: HM
authors.lastname: Holmes
authors.forename: Yu-Li
authors.initials: YL
authors.lastname: Lin
authors.forename: Mukaila A
authors.initials: MA
authors.lastname: Raji
authors.forename: Gulshan
authors.initials: G
authors.lastname: Sharma
authors.forename: Yong-Fang
authors.initials: YF
authors.lastname: Kuo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000009:adverse effects* / Q000627:therapeutic use; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use; D016022:Case-Control Studies; D015897:Comorbidity; D004347:Drug Interactions; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced*; D006801:Humans; D007345:Insurance Claim Review / Q000706:statistics & numerical data; D016015:Logistic Models; D008297:Male; D054524:Medicare Part D / Q000706:statistics & numerical data; D014481:United States; D014859:Warfarin / Q000009:adverse effects* / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D000925:Anticoagulants; D014859:Warfarin