Clinical Observations of Possible Barbiturate Interference With Anticoagulation

Sixty-seven bleeding reactions occurred during anticoagulant therapy. In 14 patients, enzyme induction appeared to be a factor, and two of these patients died. The records were reviewed of 52 patients who were admitted for myocardial infarction and treated with anticoagulants. Forty patients received barbiturates and showed more erratic control of anticoagulant effect (and a shorter prothrombin time in spite of a larger dose of warfarin sodium) than the group not receiving barbiturates. Barbiturate interference with anticoagulant activity of coumarin drugs by enzyme induction is well documented in animals. Circumstantial evidence suggests that it also occurs in man. Awareness of this type of drug interaction and close attention to proper anticoagulant dose based on frequent prothrombin determinations can prevent some of the problems that occur during anticoagulant treatment.