THYROID HORMONE LEVELS AND PROTEIN BINDING IN PATIENTS ON LONG-TERM DIPHENYLHYDANTOIN TREATMENT

Abstract

The effect of long-term diphenylhydantoin (DPH) treatment on thyroid hormone concentrations and protein binding was determined in a randomized controlled trial. As has been demonstrated previously, total thyroxine (T4) concentrations were significantly depressed in patients on DPH. There was no significant effect on indirect indices of protein binding of thyroid hormones, and the free thyroxine index (FTI) was also significantly depressed. Triiodothyronine (T3) and thyrotropin (TSH) concentrations were either unaffected, or only very slightly affected by DPH. Significant effects on the FTI were still apparent 4 wk after discontinuing treatment. The depression of total T4 levels observed in vivo is probably not due solely to diminished protein binding, but may instead be largely explained by reports suggesting enhanced degradation of T4 following DPH therapy.