Brief Report: Effect of Acute Administration of Acetysalicylic Acid on the Prothrombin Activity of Bishydroxycoumarin-Treated Rats

The administration of a single oral dose of acetylsalicylic acid (100 mg./Kg.) to bishydroxycoumarin-treated male albino rats significantly decreased the one-stage prothrombin time of blood collected 20 hr. after administration of the analgesic. This antagonistic effect of acetylsalicylic acid resulted in a mean increase of 12 per cent in the prothrombin activity of rats given the anticoagulant intraperitoneally compared to an increase of 6 to 7 per cent in those taking it orally. In the latter animals the intensity of the effect seems to be related to the time that elapses between administration of the two drugs.