Structure
Methimazole is an antithyroid drug with a thiourea structure, featuring a methyl group attached to the nitrogen of the thiourea moiety.
Chemical Formula: C₄H₈N₂S
Mode of Action
Thyroid Hormone Synthesis Inhibition: Similar to propylthiouracil, methimazole inhibits thyroid peroxidase, blocking iodination of tyrosine residues and coupling of iodotyrosines to form T3 and T4.
Iodine Organification Inhibition: Prevents the incorporation of iodine into thyroid hormones.
Peripheral Conversion Inhibition: Minimally inhibits the peripheral conversion of T4 to T3.
Uses:
Hyperthyroidism: Treats Graves' disease, toxic multinodular goiter, and toxic adenoma by reducing thyroid hormone synthesis.
Thyroid Storm: Less commonly used than propylthiouracil but still effective in managing acute hyperthyroid crises.
Thyroid Cancer Preparation: Lowers thyroid hormone levels prior to radioactive iodine therapy or surgical intervention.
Thyroiditis: Manages hyperthyroidism associated with thyroiditisd state, where thyroid hormone levels are normal
Side Effects of Methimazole
Agranulocytosis: Risk of severe white blood cell count reduction.
Hepatotoxicity: Potential liver damage.
Rash and Allergic Reactions: Includes skin rashes, itching, and other hypersensitivity responses.
Gastrointestinal Disturbances: Nausea, vomiting, and abdominal pain.
Joint Pain: May cause arthralgia and myalgia.