A tablet for an overactive thyroid (hyperthyroidism), used for Graves' disease and toxic multinodular goiter or to calm symptoms before thyroid surgery or radioactive iodine. It blocks the thyroid from making new hormone, and its most serious risk is a sudden loss of infection-fighting white blood cells.
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Methimazole and other antithyroid drugs are not on the ISMP acute care high-alert list.
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The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.
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No antidote. Overdose may cause nausea, vomiting, epigastric distress, headache, fever, joint pain, itching, and edema, and aplastic anemia or agranulocytosis can appear within hours to days. Hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathy, and CNS stimulation or depression are less frequent. Give supportive care, consider other drugs taken, and contact a poison control center.
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Doses come from the FDA label. Study tool, not for clinical decisions.
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No hepatic dose adjustment on the label, though it is metabolized in the liver. It can cause hepatotoxicity, including acute liver failure: check bilirubin, alkaline phosphatase, ALT, and AST for anorexia, itching, or right upper quadrant pain, and stop promptly for clinically significant abnormality such as transaminases above 3 times the upper limit of normal.
An antithyroid drug that inhibits thyroid hormone synthesis. It differs from the thiouracils mainly by having a 5-membered rather than a 6-membered ring. It does not inactivate T4 and T3 already stored in the thyroid or circulating, and it does not block exogenous thyroid hormone. It is well absorbed from the GI tract, then metabolized by the liver and excreted in the urine.