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Clozapine GI Hypomotility — MRCPsych Paper B MCQ

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HardSchizophrenia & PsychosisClozapine GI HypomotilityMRCPsych Paper B

A 48-year-old woman with treatment-resistant schizophrenia takes clozapine 600 mg daily. Her trough plasma clozapine concentration is 0.55 mg/L. She has not opened her bowels for 7 days and now has marked abdominal distension, although she denies abdominal pain or vomiting. An abdominal X-ray shows gross faecal loading. What is the immediate priority?

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Correct answer: C — Arrange immediate acute medical assessment for obstruction or ileus before escalating laxative treatment

The correct answer is C. Seven days without defecation, marked abdominal distension and gross faecal loading indicate severe clozapine-induced gastrointestinal hypomotility with possible faecal impaction, obstruction or ileus. Distension is a red flag requiring immediate acute medical assessment even without pain or vomiting; clozapine can reduce awareness of gastrointestinal symptoms. Obstruction must be excluded before laxatives are escalated. Bulk-forming laxatives are inappropriate because hypomotility is the underlying problem. High-dose macrogol may be used for faecal impaction, but only after obstruction has been excluded. Clozapine dose reduction alone and delayed review do not address the immediate potentially fatal complication. The apparently therapeutic plasma level does not reduce the urgency.

Reference: NHS Specialist Pharmacy Service, Managing constipation in people taking clozapine, sections 'When to refer' and 'Treating constipation', 2022, https://sps.nhs.uk/articles/managing-constipation-in-people-taking-clozapine/