Thiamazole

Thiamazole, also called methimazole, is an antithyroid medication that inhibits thyroid peroxidase and thereby reduces thyroid hormone synthesis.

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Thyroid peroxidase: An enzyme that catalyzes iodination of thyroglobulin and coupling reactions required to synthesize thyroid hormones. Thiamazole inhibits this enzyme, blocking key steps in thyroid hormone synthesis.
Graves' disease: An autoimmune disorder in which antibodies stimulate the thyroid and commonly cause hyperthyroidism. Thiamazole is widely used to control hormone production in this common cause of hyperthyroidism.
Agranulocytosis: A severe reduction in neutrophils that sharply increases susceptibility to infection. This rare, serious adverse effect can occur during thiamazole treatment and requires urgent assessment.
Thionamide: A class of antithyroid drugs that suppress thyroid hormone synthesis, including thiamazole and propylthiouracil. Thiamazole is a thionamide, sharing its central synthesis-blocking action with related drugs.
Thyroglobulin: A protein made by thyroid cells that serves as the scaffold and precursor for thyroid hormone production. Thyroid peroxidase modifies iodine-bearing residues on this protein; existing stores help explain delayed drug effects.
Hyperthyroidism: A condition in which the thyroid gland produces or releases excessive thyroid hormone. Thiamazole is prescribed to reduce excessive hormone synthesis in suitable cases.
Cholestatic liver injury: Liver injury in which impaired bile flow causes findings such as jaundice and elevated cholestatic enzymes. Thiamazole can rarely cause cholestatic liver injury, making new jaundice a significant warning sign.
Levothyroxine: A synthetic form of thyroxine used to replace deficient thyroid hormone. Levothyroxine supplies thyroid hormone, the opposite therapeutic direction from thiamazole.
Thyroid hormone: Hormones produced by the thyroid gland, principally thyroxine and triiodothyronine, that regulate metabolism and development. Thiamazole reduces the synthesis of these hormones rather than directly neutralizing circulating hormone.
Thyroid storm: A life-threatening exacerbation of thyrotoxicosis involving severe systemic manifestations. Thiamazole may be included in urgent treatment, alongside measures that control hormone release and its effects.