Acute Metabolic Responses in Myxedema to Large Doses of Intravenous L -Thyroxine

Two comparable groups of noncomatose hypothyroid patients were given large doses of intravenous L-thyroxine. Group I was given an initial mean injection of 428 µg L-thyroxine and then 100 µg daily for 9 days; group II was given 750 µg initially and 200 µg each day thereafter for 9 days. A fall in serum thyrotrophin was the first metabolic response observed, occurring within the first 24 hours before changes in the basal metabolic rate, serum cholesterol, and creatine phosphokinase were observed. Peripheral conversion of L-thyroxine to triiodothyronine occurred during the first week. Plasma cortisol and human growth-hormone responses to insulin-induced hypoglycemia were blunted before therapy and remained abnormal after 10 days of intravenous L-thyroxine therapy.