Chapter 31: Thyroid and Antithyroid Drugs

The thyroid gland maintains metabolic homeostasis by secreting thyroxine and triiodothyronine, hormones whose production is regulated by thyroid-stimulating hormone from the anterior pituitary. Understanding the distinctions between primary, secondary, and tertiary hypothyroidism is essential for appropriate treatment selection, as is recognizing the varied presentations of hyperthyroidism including autoimmune conditions, multinodular disease, and acute life-threatening thyroid storm. Diagnostic assessment relies on measurement of thyroid-stimulating hormone levels, free thyroid hormone concentrations, and thyroid-related antibodies to establish disease type and severity. Thyroid replacement therapy utilizes synthetic hormone preparations, with levothyroxine being the preferred agent due to its consistent bioavailability, extended half-life, and peripheral conversion to active triiodothyronine; alternative preparations such as synthetic triiodothyronine and fixed-ratio combinations address individual patient needs when standard therapy proves inadequate. Management of hyperthyroidism employs multiple therapeutic strategies including thioamide antithyroid medications that suppress hormone synthesis, radioactive iodine that irreversibly ablates thyroid tissue, and iodine solutions that decrease gland blood flow before surgical intervention. Adverse effects warrant careful monitoring, particularly agranulocytosis and hepatotoxicity from antithyroid drugs and the development of iatrogenic hypothyroidism from ablative procedures. Nursing practice encompasses thorough baseline evaluation of metabolic and cardiovascular parameters, systematic assessment of therapeutic efficacy and toxic manifestations, and comprehensive patient education addressing medication timing, dietary considerations, and the necessity of lifelong management. Special populations including pregnant patients and older adults require individualized dosing strategies and enhanced surveillance for drug interactions with anticoagulants, cardiac glycosides, and insulin agents.