Altered plasma protein binding of drugs in thyroid disease.

The plasma protein binding of propranolol and warfarin was studied in vitro by ultrafiltration in hyper- and hypothyroid patients both before and after treatment. The degree of binding of propranolol was significantly decreased in hyperthyroid patients and increased in hypothyroid patients, and was negatively correlated with serum thyroxine and the free thyroxine index. The plasma protein binding of warfarin was also decreased in hyperthyroid patients, but was unchanged in hypothyroid patients. These results suggest that the binding of both acidic and basic drugs may be altered by thyroid disease.