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Antidepressant Switching Problems — MRCPsych Paper B MCQ

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HardMood DisordersAntidepressant Switching ProblemsMRCPsych Paper B

A 35-year-old man has taken sertraline 200 mg daily for 8 months for a depressive episode. Because of an insufficient response, sertraline is stopped without dose reduction and venlafaxine modified-release 75 mg daily is started the following morning. Two days later, he develops episodic vertigo, nausea, anxiety, vivid dreams and electric shock-like sensations on moving his head. His temperature is 36.8°C, pulse 88 beats/min and blood pressure 132/78 mmHg. There is no diaphoresis, diarrhoea, tremor, rigidity, hyperreflexia or clonus. What is the most likely explanation?

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Correct answer: A — Sertraline withdrawal after abrupt cessation during the antidepressant switch

The best answer is A. Abrupt cessation of high-dose sertraline can produce withdrawal within the first few days. Dizziness or vertigo, electric shock-like sensory disturbances, nausea, anxiety or agitation, and vivid dreams are characteristic. Early venlafaxine adverse effects could contribute to nausea or anxiety but do not adequately explain the electric shock sensations. Serotonin toxicity is less likely because there is no hyperthermia, autonomic instability, hyperreflexia, rigidity or clonus. Therapeutic-dose venlafaxine toxicity or overdose would more typically cause prominent cardiovascular, neurological or consciousness changes. Hypersensitivity requires features such as rash, urticaria, angioedema or respiratory compromise, while hypertensive urgency is excluded by the normal blood pressure. Antidepressant tapering and switching should be individualised rather than governed by a universal 1–2-week cross-taper.

Reference: Electronic Medicines Compendium. Sertraline 100 mg film-coated tablets: Summary of Product Characteristics, sections 4.4 and 4.8, updated 2025. https://www.medicines.org.uk/emc/product/3516/smpc