IN THE COURSE of long-term ambulatory management of cardiac patients with an anticoagulant, sodium warfarin, five individuals also received phenylbutazone for various arthritic manifestations. In all patients a significant dramatic increase in the prothrombin time was observed, at times accompanied by hemorrhagic episodes. In each case, the unexpected effects occurred rapidly at the end of the usual course of treatment with 200 to 300 mg of phenylbutazone daily for five to seven days.
A relationship of phenylbutazone to some factors of the coagulation mechanism has been suggested by several investigators, though the available reports do not support consistently positive ideas. For example, Humble1 stated that the clotting of blood was diminished by phenylbutazone alone, but that the prothrombin time was also lengthened in 30% of the patients receiving this drug. In two individuals it was prolonged as much as two minutes. These findings have not been duplicated by other
Eisen MJ. Combined Effect of Sodium Warfarin and Phenylbutazone. JAMA. 1964;189(1):64-65. doi:10.1001/jama.1964.03070010070021