Predicting the dose of warfarin for therapeutic anticoagulation.

The validity of a previously described technique for predicting warfarin requirements based on the anticoagulant response to a fixed loading dose was assessed prospectively in 57 patients. There was a close relationship between the predicted and initially observed daily warfarin dose required to maintain the patient within the therapeutic range for anticoagulation. The significant relationship between predicted and observed maintenance dose persisted at 4 and 12 weeks although it decreased with increasing time. The relationship between observed and predicted maintenance requirement of warfarin was not affected by the concomitant use of intermittent intravenous injections of heparin when 9 hr was allowed to elapse between the previous dose of heparin and the thrombotest estimation on which the prediction was based. It is concluded that the method is valuable in predicting an individual's warfarin requirement, although it does not obviate the need for regular monitoring of anticoagulant control.