What is methimazole used for and a common adverse effect to monitor?

• A. It inhibits thyroid hormone synthesis; monitor for agranulocytosis and hepatic toxicity (rare)
• B. It decreases thyroid hormone production; monitor for hypoglycemia
• C. It treats hypertension; monitor for renal toxicity
• D. It reduces cholesterol synthesis; monitor for myopathy

Answer: (A)

Methimazole is used to treat hyperthyroidism by decreasing thyroid hormone production. It does this by inhibiting thyroid peroxidase, which blocks the iodination of tyrosine residues and the coupling steps needed to form T3 and T4, so less hormone is produced and circulating levels fall.

A key adverse effect to monitor is agranulocytosis, a dangerous drop in neutrophils that can lead to severe infections. Patients should report fever, sore throat, or other signs of infection promptly, and a CBC may be checked if symptoms occur. Hepatic toxicity is another potential issue, though rare, so watch for signs of liver injury such as jaundice, dark urine, RUQ pain, or elevated liver enzymes.

In short, methimazole inhibits thyroid hormone synthesis and monitoring for agranulocytosis and hepatic toxicity is essential.