title: Anticoagulation-related outcomes in patients receiving warfarin after starting levofloxacin or gatifloxacin.
abstract: OBJECTIVE
  To compare anticoagulation-related outcomes in patients receiving stable dosages of warfarin who started levofloxacin or gatifloxacin therapy.
  
  
  METHODS
  Retrospective medical record review.
  
  
  METHODS
  Veterans Affairs medical center.
  
  
  METHODS
  Of 92 patients receiving the same dosages of warfarin for at least 4 weeks before starting antibiotic therapy, 54 received levofloxacin between January and September 2003, and 38 received gatifloxacin between January and September 2004.
  
  
  RESULTS
  Data were obtained through the hospital's pharmacy, laboratory, and general patient databases and through electronic medical records. The INRs evaluated were prefluoroquinolone use, defined as the last INR measured before the start of antibiotic therapy (up to 4 wks earlier), and postfluoroquinolone use, defined as any INR measured during antibiotic therapy through 1 week after discontinuation of the antibiotic. Analyzed outcomes included the percentage of patients with postfluoroquinolone INRs that were above 4, that exceeded the therapeutic goal, or that exceeded the goal by more than 1 point; INR changes of more than 0.5, 1, or 1.5 points above the INR before fluoroquinolone use; major or minor bleeding events; requirement for vitamin K administration; warfarin dosage reduction or withholding doses; and warfarin-related hospital, emergency, or urgent care admissions or visits. No significant differences were noted in baseline characteristics with regard to age, sex, prefluoroquinolone INR, or anticoagulation indications between the two groups. The percentage of patients with a postfluoroquinolone INR above 4 was 2% (1 of 54 patients) in the levofloxacin group versus 21% (8 of 38 patients) in the gatifloxacin group (p=0.003). The percentage of patients receiving vitamin K in the levofloxacin and gatifloxacin groups was 0% (0 of 54 patients) and 11% (4 of 38, p=0.026), respectively. For the other anticoagulation-related outcomes, no significant differences were noted between the groups.
  
  
  CONCLUSIONS
  Patients receiving warfarin who take gatifloxacin may be at higher risk for an INR above 4 compared with those taking levofloxacin. Close monitoring of warfarin therapy while concomitantly receiving gatifloxacin is warranted.
authors.affiliation: Pharmacy Service, Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Mathews
authors.forename: Jean
authors.initials: J
authors.lastname: Cole
authors.forename: Russell A
authors.initials: RA
authors.lastname: Ryono
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects / Q000627:therapeutic use*; D019992:Databases as Topic; D016903:Drug Monitoring; D004359:Drug Therapy, Combination; D005260:Female; D024841:Fluoroquinolones / Q000009:adverse effects / Q000627:therapeutic use*; D000077734:Gatifloxacin; D006787:Hospitals, Veterans; D006801:Humans; D019934:International Normalized Ratio; D064704:Levofloxacin; D008297:Male; D015242:Ofloxacin / Q000009:adverse effects / Q000627:therapeutic use*; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D016896:Treatment Outcome; D014481:United States; D014859:Warfarin / Q000009:adverse effects / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D024841:Fluoroquinolones; D014859:Warfarin; D064704:Levofloxacin; D015242:Ofloxacin; D000077734:Gatifloxacin