Abstract

Euthyroidism could not be achieved in a 41-year-old woman with primary hypothyroidism despite escalating doses of oral levothyroxine as high as 600 µg and 100 µg of triiodothyronine daily. Clinical and biochemical evidence of hypothyroidism persisted even with the administration of intramuscular levothyroxine. There was no history compatible with drug-induced malabsorption of levothyroxine. Evaluation of serum showed no thyroid hormone autoantibodies. After hospitalization, intravenous levothyroxine therapy returned thyroid hormone to normal concentrations. Moreover, thyroid hormone loading tests revealed normal oral absorption of both levothyroxine and triiodothyronine. Noncompliance with medical treatment leading to pseudomalabsorption of levothyroxine should be considered in patients who have persistent hypothyroidism with high-dose replacement therapy.persistent hypothyroidism with high-dose replacement therapy.