Antithyroid Drugs

Propylthiouracil and methimazole are thioamides that are used in the treatment of hyperthyroid conditions.  Thioamides inhibit the peroxidase enzyme which incorporates iodine into a precursor of thyroid hormone. Inhibition of the peroxidase enzyme results in decreased production of thyroid hormone.  Propylthiouracil and methimazole both have potentially severe side effects including agranulocytosis and hepatotoxicity. Both medications can be teratogenic with propylthiouracil being the preferred of the two agents to be used in the first trimester.

Iodide can be used at high concentrations to inhibit thyroid hormone synthesis.  Iodide can firm the thyroid tissue, which assists with thyroid surgery. Radioactive iodine can be used as a pharmacologic ablation of the thyroid gland in settings of hyperthyroidism.  

Class Drugs

• Propylthiouracil

• Methimazole

• Iodide

Class Mechanism of Action

See individual drugs

Class Applications

Hyperthyroidism

Thyroid storm

Class Adverse Effects

See individual drugs

Drug Table

Drug Name	Application	Comments	Image
Propylthiouracil		Mechanism of Action; -Inhibits iodination and condensation of precursor molecules in production of T3/T4 in thyroid cells; -Inhibits conversion of T4 to T3 peripherally; Adverse Effects; -Agranulocytosis; -Hepatotoxicity; -Teratogenic but preferred agent in 1st trimester of pregnancy due to decreased effect when compared to methimazole	"Propane" "Thigh" "Urine"
Methimazole		Mechanism of Action; -Inhibits iodination and condensation of precursor molecules in production of T3/T4 in thyroid cells; -Inhibits conversion of T4 to T3 peripherally; Adverse Effects; -Agranulocytosis; -Hepatotoxicity; -Teratogenic	"Meth" "Maze"
Iodide		Mechanism of Action; -Inhibits iodination of precursors to thyroid hormone in thyroid tissue; -Effect last for 2-3 days; -Inhibits release of thyroid hormone from thyroglobulin; -Decreases vascularity of thyroid; -Useful prior to thyroid surgery and during thyroid storm; -Not a long-term treatment option as thyroid gland adjusts to higher levels of iodide; Adverse Effects; -Oral/throat swelling/sores; -Rash; -Metallic taste in mouth	"Iodinated Salt"