In patients taking methimazole, which adverse effect is important to monitor due to its potential seriousness?

• A. Agranulocytosis
• B. Hypertension
• C. Hypokalemia
• D. Hyperglycemia

Answer: (A)

Agranulocytosis is the key adverse effect to monitor with methimazole. This is a severe drop in neutrophils, a type of white blood cell essential for fighting infections. Because neutropenia dramatically raises the risk of serious infections and sepsis, recognizing it early is crucial. Patients should be educated to seek urgent care for fever, sore throat, or other signs of infection, especially during the first months of therapy when the risk is higher. Baseline white blood cell/neutrophil counts should be obtained before starting treatment, with periodic monitoring thereafter and prompt CBC if new infection symptoms arise. If agranulocytosis is suspected, stop methimazole immediately and manage the infection, sometimes with hospitalization or growth factor support.

Hypertension, hypokalemia, and hyperglycemia are not typical, dose-limiting adverse effects of methimazole and do not carry the same immediate danger as agranulocytosis.