Warfarin: many food and drugs interact.

Clinical bottom line (level 3a)

  1. Many drugs and foods interact with warfarin.
  2. Antibiotics can potentiate or inhibit warfarin's effects.
Wells et al: Annals of Internal Medicine 1994; 121: 676-683
Expires December 2003

The study

Systematic review of any original report of
  • Patients: taking warfarin
  • Intervention: foods and drugs
  • Outcome: interaction with warfarin


    • Articles found in English using MEDLINE, TOXLINE, 1966 to 1993 (search terms: MeSH headings warfarin and drug interactions ) and scanning bibliographies of retrieved articles

    Selection criteria: as above
    Appraisal criteria: detailed in text
    Articles excluded if: drugs not available in USA or Canada

    120 studies were included.

    The evidence

    • anticoagulant effect of warfarin was potentiated by:
      • antibiotics (cotrimoxazole, erythromycin, fluconazole, isoniazid, metronidazole, miconazole)
      • cardiac drugs (amiodarone, clofibrate, propafenone, propranolol, sulfinpyrazone)
      • phenylbutazone
      • piroxicam
      • alcohol (only with concomitant liver disease)
      • cimetidine and omeprazole
    • anticoagulant effect of warfarin was inhibited by:
      • antibiotics (griseofulvin, rifampin, nafcillin)
      • drugs active on central nervous system (barbiturates, carbamazepine, chlordiazepoxide)
      • cholestyramine
      • sucralfate
      • foods and enteral feeds high in vitamin K, and large amounts of avocado

    Citation

    1. Wells PS, Holbrook AM, Crowther NR, et al: Many drugs and foods interact with warfarin. Annals of Internal Medicine 1994; 121: 676-683
    Contributor: Clare Wotton and Bob Phillips, December 2000
    Reviewer:

    Clinical Question.
    Patient on warfarin
    Intervention or Exposure drugs and foods
    Outcome interaction