Anemia: a cause of intolerance to thyroxine sodium

Usual causes of intolerance to thyroxine sodium include coronary artery disease, advanced age, untreated adrenal insufficiency, and severe hypothyroidism. We describe 4 patients with iron deficiency anemia and primary hypothyroidism. After treatment with thyroxine sodium, these patients developed palpitations and feelings of restlessness, which necessitated discontinuation of the thyroid hormone. After the anemia was treated with ferrous sulfate for 4 to 7 weeks, they were able to tolerate thyroxine sodium therapy. Iron deficiency anemia coexisting with primary hypothyroidism results in a hyperadrenergic state. In such patients, we postulate that thyroid hormone administration causes palpitations, nervousness, and feelings of restlessness. Correction of any existing pronounced anemia in hypothyroid patients who are intolerant to thyroxine sodium therapy may result in tolerance to this agent.