Hypothyroidism: effect on warfarin anticoagulation.

Although our observation is not the first case of reduced PT response to oral anticoagulants associated with hypothyroidism, it is the only such interaction reported since 1963, and the first case involving warfarin therapy in a human being. We submit this case as a reminder of a potentially forgotten interaction, and to stress the importance of close monitoring in patients receiving warfarin therapy who have concomitant changes in thyroid function.