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Clozapine Tachycardia — MRCPsych Paper B MCQ

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ModerateSchizophrenia & PsychosisClozapine TachycardiaMRCPsych Paper B

A 35-year-old man with schizophrenia started clozapine 3 weeks ago and is undergoing gradual dose titration. His resting pulse, which was 76 beats/min before treatment, is now repeatedly 108–112 beats/min. ECG shows sinus tachycardia. He is calm and has no fever, chest pain, dyspnoea, flu-like symptoms or calf symptoms. Blood pressure and oxygen saturation are normal, as are C-reactive protein, high-sensitivity troponin and thyroid-stimulating hormone. His caffeine consumption is unchanged. What is the most likely explanation for the tachycardia?

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Correct answer: A — Clozapine-induced sinus tachycardia

The most likely explanation is clozapine-induced sinus tachycardia. Tachycardia is a very common adverse effect of clozapine and occurs particularly during the initial weeks of treatment. The temporal relationship to initiation and titration, together with sinus rhythm and otherwise reassuring assessment, supports this answer. Persistent resting tachycardia must nevertheless prompt consideration of clozapine-associated myocarditis, particularly early in treatment; normal CRP and high-sensitivity troponin and the absence of fever, chest pain, dyspnoea or flu-like symptoms make this less likely here. Pulmonary embolism is less likely without respiratory symptoms, hypoxia or suggestive leg symptoms. Normal TSH argues against thyrotoxicosis, while unchanged caffeine intake and the absence of evident anxiety make those alternatives less likely.

Reference: Clozapine Viatris 200 mg Tablets, Summary of Product Characteristics, sections 4.4 and 4.8, revised February 2026. https://www.medicines.org.uk/emc/product/102058/smpc