Interaction between Cyclosporine and Warfarin

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To the editor: Many drugs are known to affect the pharmacokinetics of warfarin and cyclosporine leading to either an increase or decrease in the biologic activity of these two drugs (1, 2). However, there have been no reports of a possible interaction between these two drugs. We report a negative interaction in a patient receiving both cyclosporine and warfarin.

A 39-year-old man was diagnosed with pure erythrocyte aplasia in June 1984. He was treated unsuccessfully with standard immunosuppressive methods. In January 1986, he was started on oral cyclosporine and prednisone with a resulting reticulocytosis and rise in hemoglobin level beginning