Dicumarol and Plasma Antithrombin Activity.∗

Summary With the administration of dicumarol to dogs there are no significant changes in the activity of antithrombin-II, and -III. Antithrombin-IV activity remained but no accurate quantitative measurements were made. In human subjects antithrombin-IV activity also remains and is probably not decreased. The thrombin-titer method of analysis shows that there are very marked changes in the activation rate of prothrombin soon after dicumarol is administered to human subjects. The addition of purfied prothrombin does not restore the activation rate to normal. In contrast to human subjects the activation rate of prothrombin is not reduced in dog plasma when dicumarol is administered.