Elevated serum concentrations of triiodothyronine in hypothyroid patients. Values for patients receiving USP thyroid

R. Penny and S. D. Frasier

Serum concentrations of thyroxine (T4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were measured for 14 hypothyroid patients while they were receiving USP desiccated thyroid and after six weeks of therapy with comparable doses of levothyroxine sodium (Na-l-thyroxine). Therapy with USP thyroid caused supraphysiologic elevations in the concentration of T3 in 13 patients. Treatment with levothyroxine resulted in serum concentrations of T3 that were within the range of normal. We believe the preferable therapy for hypothyroidism is levothyroxine.