Clozapine is considered treatment-resistant schizophrenia's gold-standard drug. Which potentially fatal haematological adverse effect requires mandatory ANC (absolute neutrophil count) monitoring, and what ANC level necessitates immediate clozapine cessation?
- A Agranulocytosis; ANC <500/mm³ ✓
- B Thrombocytopenia; platelet count <50,000/mm³
- C Aplastic anaemia; haemoglobin <7 g/dL
- D Eosinophilia; eosinophil count >1000/mm³
Correct answer: A. Agranulocytosis; ANC <500/mm³
Explanation
Clozapine-induced agranulocytosis (ANC <500/mm³) is a potentially fatal adverse effect occurring in about 0.8–1% of patients, typically in the first 6 months of treatment. Mandatory ANC monitoring is weekly for the first 6 months, fortnightly for months 6–12, and monthly thereafter. Clozapine must be immediately discontinued if ANC falls below 500/mm³; mild-moderate neutropenia (ANC 500–1500) warrants increased monitoring. Re-challenge is contraindicated after agranulocytosis. Eosinophilia (>3000/mm³) can also require suspension due to risk of myocarditis.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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