[Oral anticoagulant therapy: analysis of the efficacy of a dosage guide]

An empirical protocol for dosage adjustment in warfarin therapy was evaluated by means of retrospective analysis of the medical records of 106 outpatients at an anticoagulation clinic followed from January 1981 to August 1984. There were 203 cases in which the prothrombin time was abnormal (below the therapeutic range in 123 cases and above the range in 80). The protocol was successful in about 60% of cases in which the prothrombin time before dosage adjustment was below the therapeutic range and in 80% of cases in which it was above the range. Statistical analysis showed that the success rate could be improved by more precise definition of the percentage of dosage change in certain situations. However, individual variation in response of the prothrombin time to a standard dosage change limits the success that can be expected after the initial adjustment. We propose an improved protocol for adjustment of warfarin dosage.