SSRI-MAOI Washout — MRCPsych Paper B MCQ

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ModerateMood DisordersSSRI-MAOI WashoutMRCPsych Paper B

A 50-year-old woman with treatment-resistant depression is being switched from sertraline to phenelzine, an irreversible monoamine oxidase inhibitor. Sertraline has been tapered and stopped, and she is taking no other serotonergic medication. According to the current UK sertraline Summary of Product Characteristics, what is the minimum interval required after her final dose of sertraline before phenelzine can be started?

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Correct answer: A — 1 week

The correct answer is A: 1 week. The UK sertraline SmPC requires sertraline to be discontinued for at least 7 days before an irreversible MAOI such as phenelzine is started, because combining serotonergic reuptake inhibition with MAO inhibition can cause severe serotonin syndrome. In clinical practice, specialist guidance recommends individualising the washout within a 7–14-day range, but the question asks specifically for the SmPC minimum. Two weeks is tempting because the reverse switch—stopping an irreversible MAOI before starting sertraline—requires at least 14 days. Five weeks is associated with switching from fluoxetine because fluoxetine and norfluoxetine have long half-lives. Twenty-four hours and no washout would permit inadequate clearance of sertraline.

Reference: Electronic Medicines Compendium, Sertraline 50mg tablets, Summary of Product Characteristics, sections 4.3 and 4.5, updated 5 June 2026. https://www.medicines.org.uk/emc/product/5760/smpc