Which medications increase the risk for warfarin and superwarfarin toxicity by prolonging prothrombin time (PT)?

Updated: Jan 19, 2018
  • Author: Kent R Olson, MD, FACEP; Chief Editor: David Vearrier, MD, MPH  more...
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Answer

Note that the S-isomer is more potent than the R-isomer; thus, drugs that inhibit S-isomer metabolism have a greater effect on PT.

Drugs that inhibit warfarin metabolism include the following:

  • Allopurinol
  • Amiodarone
  • Azole antifungals
  • Capecitabine
  • Cephalosporin antibiotics
  • Chloramphenicol
  • Chlorpropamide
  • Cimetidine
  • Cotrimoxazole
  • Disulfiram
  • Ethanol (acute ingestion)
  • Flutamide
  • Isoniazid (INH)
  • Macrolide antibiotics
  • Metronidazole
  • Omeprazole
  • Penicillin antibiotics
  • Phenytoin
  • Propafenone
  • Propoxyphene
  • Quinidine
  • Quinolone antibiotics
  • Statins (particularly lovastatin and pravastatin)
  • Sulfinpyrazone
  • Sulfonamides
  • Tamoxifen
  • Tolbutamide
  • Zafirlukast
  • Zileuton

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