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Interaction of Sodium Warfarin and Rifampin: Studies in Man

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Grant support: grant HL 8058-11, National Institutes of Health.

▸Requests for reprints should be addressed to Robert A. O'Reilly, M.D., Department of Medicine, Santa Clara Valley Medical Center, 751 South Bascom Ave., San Jose, CA 95128.

Ann Intern Med. 1974;81(3):337-340. doi:10.7326/0003-4819-81-3-337
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To evaluate the mechanism of the decrease in the hypoprothrombinemia of warfarin therapy induced by rifampin, single doses of warfarin were administered orally as well as intravenously to 10 normal subjects. Rifampin therapy in the usual dosage, 600 mg a day orally, was started 3 days before the warfarin dose and continued for the duration of the hypoprothrombinemia. We found a highly significant decrease in both the mean area of the one-stage prothrombin time (P < 0.001) and the mean area of warfarin in plasma (P < 0.001), in comparison with the effects of warfarin alone administered by the same route. These data rule out any significant effect of rifampin on the gastrointestinal absorption of the anticoagulant and suggest that the antibiotic enhances the elimination of warfarin from the body.


warfarin ; rifampin ; sodium





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