Chapter 32: Drugs for the Treatment of Thyroid Disorders

Drugs for the Treatment of Thyroid Disorders establishes the critical role of these hormones in metabolism, growth, and development, and explains how peripheral tissues convert T4 into the more potent T3. The discussion moves to the management of hypothyroidism, primarily caused by autoimmune thyroiditis (Hashimoto disease), identifying Levothyroxine (synthetic T4) as the drug of choice due to its stability, long half-life, and favorable pharmacokinetic profile compared to Liothyronine (synthetic T3) or Liotrix. The chapter outlines monitoring protocols involving TSH levels to avoid adverse effects like cardiac stimulation. Conversely, the text explores the treatment of hyperthyroidism (thyrotoxicosis), often resulting from Graves disease. Therapeutic strategies include thioamide drugs like Methimazole and Propylthiouracil (PTU), which inhibit thyroperoxidase to block hormone synthesis. The summary highlights critical clinical distinctions, such as PTU being preferred during the first trimester of pregnancy despite its higher risk of hepatotoxicity, while Methimazole is otherwise preferred for its lower side-effect profile. Significant adverse reactions such as agranulocytosis and cross-sensitivity are also detailed. Adjunctive therapies are discussed, including the use of beta-adrenoceptor antagonists (beta-blockers) like Propranolol to control sympathetic symptoms such as tachycardia and palpitations, particularly in thyroid storm or while awaiting other treatments to take effect. The text further examines the use of Iodide salts (Potassium Iodide), which rapidly inhibit hormone release and reduce gland vascularity prior to surgery. The chapter concludes with a review of Radioactive Iodine (I-131) for tissue ablation in Graves disease and thyroid cancer, noting its contraindication in pregnancy, and addresses the use of potassium iodide as a protective measure against radioactive fallout in nuclear emergencies to prevent thyroid uptake of toxic isotopes.