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Quinidine-Induced Hypoprothrombinemic Hemorrhage in Patients on Chronic Warfarin Therapy

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Copyright ©, 1968, by The American College of PhysiciansThe American College of Physicians

Ann Intern Med. 1968;68(3):511-517. doi:10.7326/0003-4819-68-3-511
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In three patients whose prothrombin-complex activity was being chronically maintained in the therapeutic range by warfarin sodium, the institution of quinidine therapy was followed within 6 to 10 days by excessive hypoprothrombinemia and hemorrhages. No other causes for the sudden drop in prothrombin level could be found. In two patients the one-stage prothrombin time remained slightly prolonged when warfarin was stopped and quinidine continued. When the third patient discontinued quinidine, the original dose of warfarin was again required to lower the prothrombin content into the therapeutic range.

Both quinidine and quinine can depress the prothrombin-complex activity of normal individuals. They act synergistically with warfarin and other oral anticoagulants to depress vitamin K-sensitive hepatic clotting factor synthesis. Their use in patients on anticoagulant therapy can precipitate serious hypoprothrombinemic hemorrhages. When quinidine therapy is started in such patients, their prothrombin time must be closely followed, and a reduction in anticoagulant requirements should be anticipated.





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