COUMARIN THERAPY. PROTHROMBIN ACTIVITY AFTER TERMINATION OF TREATMENT.

Twelve patients receiving coumarin type hypoprothrombinemic agents were studied before, during and after termination of therapy, the prothrombin proconvertin method having been used to assay the prothrombin activity complex. In no instance was post treatment "rebound" demonstrated. Prothrombin activity levels returned to pretreatment values only after ten days following termination of coumarin or Dicumarol administration. If a reactivation of thrombotic tendency occurs following discontinuance of anticoagulant therapy, it would not appear to be related to a "rebound" of prothrombin activity above that which is "normal" for the individual patient. Patients tend to return to the same level of prothrombin activity present before initiation of coumarin therapy.