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April 1968

Drug Interactions With Warfarin

Author Affiliations

Kansas City, Kan

From the departments of medicine and pharmacology, University of Kansas Medical Center, Kansas City, Kan. Dr. Hunninghake was a Public Health Service fellow in clinical pharmacology. He is now at the Department of Pharmacology, University of Minnesota School of Medicine, Minneapolis. Dr. Azarnoff is a Burroughs Wellcome scholar in clinical pharmacology.

Arch Intern Med. 1968;121(4):349-352. doi:10.1001/archinte.1968.03640040043009

Glutethimide, amobarbital, secobarbital, and meprobamate—drugs commonly used in humans—markedly reduce the warfarin plasma half-life (T½) in dogs. Addition of such drugs increases the warfarin required for maintenance of adequate anticoagulation. Withdrawal of these drugs from persons previously receiving anticoagulants could lead to severe bleeding. Clofibrate prolongs the warfarin plasma T½ in dogs. Administration of clofibrate to adequately anticoagulated animals precipitates hemorrhage. Effects of the addition or withdrawal of any drug to the therapeutic regimen of patients receiving oral anticoagulants must be carefully monitored with frequent prothrombin time determinations.