Thyroid hormones, iodine and antithyroid drugs

Abstract

This chapter discusses several thyroid hormones, iodine, and antithyroid drugs, as well as their adverse effects. Thyroid hormones have both direct and indirect effects on bone metabolism, and the association between overt hyperthyroidism and loss of bone mineral density has been well established. Many patients taking thyroxine in standard dosages have serum thyroid-stimulating hormone (TSH) concentrations below the reference range, which is often accompanied by a modest increase in serum-free thyroxine. Interactions between thyroxine and other drugs are unusual, but there are instances where a patient with coronary artery disease, hyperlipidemia, and hypothyroidism has shown that the ingestion of cholestyramine within the six hours of ingestion of thyroxine should be avoided because cholestyramine can bind thyroxine irreversibly and reduce its absorption, thereby leading, in some cases, to undertreatment of hypothyroidism. In view of the association between the dosage of thionamide and the development of agranulocytosis, as well as the lack of good evidence for improved clinical or biochemical responses, if initial doses of carbimazole of greater than 30 mg/day (propylthiouracil 300 rag/day) are used, higher doses should be avoided.