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Lamotrigine for Bipolar Depression Prevention — MRCPsych Paper B MCQ

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HardMood DisordersLamotrigine for Bipolar Depression PreventionMRCPsych Paper B

A 35-year-old woman with bipolar I disorder has recovered from a major depressive episode. Her longitudinal course has been predominantly depressive, with infrequent manic episodes. Maintenance monotherapy is being considered. Which drug has a UK marketing authorisation specifically for preventing depressive episodes in adults with bipolar I disorder who experience predominantly depressive episodes, with maintenance evidence showing delayed depressive episodes but no statistically significant advantage over placebo for preventing manic, hypomanic or mixed episodes?

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Correct answer: C — Lamotrigine

Lamotrigine is correct. Its UK indication specifically covers prevention of depressive episodes in adults with bipolar I disorder whose course is predominantly depressive; it is not indicated for acute depressive or manic episodes. In pivotal maintenance studies, lamotrigine delayed depressive episodes compared with placebo, whereas the difference for manic, hypomanic or mixed episodes was not statistically significant. Lithium remains NICE's first-line and most effective long-term treatment for bipolar disorder overall, so it would be correct if the question asked for general relapse prevention rather than depression-focused licensed efficacy. Quetiapine is a NICE-listed alternative when lithium is unsuitable but does not match this specific evidence profile. Valproate and carbamazepine likewise lack this depression-specific UK indication, and valproate is particularly restricted in women of childbearing potential.

Reference: Lamotrigine Milpharm 25 mg tablets, Summary of Product Characteristics, sections 4.1 and 5.1, revised 2026. https://www.medicines.org.uk/emc/product/4736/smpc