Evaluating patients' warfarin requirements.

Seventy consecutive patients receiving warfarin as an anticoagulant were evaluated for the relationship between the response to the loading dose of warfarin and the response to the maintenance dose. No patients were excluded because of complicating diseases or the concurrent use of other drugs. There was a moderate correlation (r = 0.54, p less than 0.01) between response to the loading dose and response to the maintenance dose. Thus, a relatively weak response to a loading dose of warfarin can be used to predict a need for a relatively large maintenance dose in unselected patients requiring anticoagulant therapy. Age seems to be a relatively weak determinant of warfarin sensitivity. Other factors such as the genetic control mechanism, concurrent drug therapy, and complicating diseases apparently are more important determinants.