skip to main content

Fluvoxamine Clozapine — MRCPsych Paper B MCQ

Instant feedback + full explanation. One question, done properly.

HardSchizophrenia & PsychosisFluvoxamine ClozapineMRCPsych Paper B

A patient with treatment-resistant schizophrenia is clinically stable on clozapine. Fluvoxamine is being considered for persistent obsessive-compulsive symptoms. There has been no recent change in smoking or caffeine consumption and there is no evidence of infection. Which statement best describes the expected pharmacokinetic interaction?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Potent CYP1A2 inhibition, with a potentially substantial increase in the clozapine concentration and toxicity risk

Fluvoxamine is a potent inhibitor of CYP1A2, an important pathway in clozapine metabolism. Co-administration can therefore produce a clinically significant and sometimes substantial rise in clozapine concentration, increasing the risk of sedation, seizures and other concentration-related adverse effects. If the combination is considered necessary, it requires specialist oversight, consideration of clozapine dose reduction, clinical observation and clozapine blood-level monitoring. CYP1A2 induction would lower rather than raise clozapine concentrations, while renal tubular competition and protein-binding displacement are not the clinically important mechanisms. Although sertraline is less likely than fluvoxamine to cause a major pharmacokinetic interaction, it is not an automatically suitable substitute: antidepressant selection must account for indication, previous response, other interactions and adverse-effect risks.

Reference: Clozapine Viatris 200 mg Tablets, Summary of Product Characteristics, section 4.5 Interactions, revised February 2026. https://www.medicines.org.uk/emc/product/102058/smpc