Carbimazole — Agranulocytosis
A 26-year-old woman on carbimazole 30 mg/day for Graves' disease returns at 6 weeks with sore throat and fever. What is the most urgent step in her management?
Correct Answer — B
Fever and sore throat in a patient on carbimazole or PTU is agranulocytosis until proven otherwise. This is the most dangerous side effect of antithyroid drugs — a neutrophil count below 0.5×10⁹/L. The drug must be stopped immediately and an urgent FBC performed. Agranulocytosis typically occurs in the first 3 months of therapy. Mortality without treatment is significant. Never continue, increase, or substitute with PTU (which carries the same risk) until agranulocytosis is excluded.
Key concept
Carbimazole safety rule: fever + sore throat → STOP drug immediately + urgent FBC. Agranulocytosis is potentially life-threatening.