Physiologic combinations of synthetic thyroid hormones in myxedema

Abstract

Physiologic combinations of synthetic L‐thyroxine and L‐triiodothyronine, the two naturally occurring thyroid hormones, have been formulated to produce full thyroid hormone replacement in athyreotic patients and at the same time give levels of protein‐bound iodine (PBI) and other thyroid parameters consistent with the patient's metabolic status. The optimal combination contains approximately 175 meg. sodium L‐thyroxine and 50 mcg. L‐triiodothyronine and is calorigenically equivalent to about 180 mg. of a potent porcine preparation of desiccated thyroid, USP. This mixture has the clinical advantage of not requiring standardization, therefore obviating fluctuations in hormonal potency. In addition, it mimics all the metabolic effects of normal thyroid hormone secretions and produces PBI levels commensurate with the patient's metabolic state. It is recommended as a reliable, physiologic, synthetic hormonal combination for use wherever thyroid replacement is indicated.