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Lamotrigine — DFSRH MCQ

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HardLamotrigineDFSRH

A 34-year-old woman with focal epilepsy takes lamotrigine 400 mg daily as monotherapy. Six months ago, when she started a combined oral contraceptive containing ethinylestradiol 30 micrograms and levonorgestrel, her neurologist increased lamotrigine from 200 mg daily because of falling serum concentrations. She has remained seizure-free. She is on day 18 of a correctly used 21-day pill packet. Neurological review has now confirmed two stereotyped attacks of migraine with visual aura: a scintillating scotoma developed gradually over 15 minutes, resolved within 40 minutes and was followed by unilateral headache. There are no features suggesting transient ischaemia or another secondary cause. She wishes to stop combined hormonal contraception and accepts copper intrauterine device insertion today. Pregnancy is reasonably excluded, and there is no contraindication to insertion. She takes no valproate, carbamazepine or other inducer or inhibitor of lamotrigine glucuronidation. Which is the most appropriate management plan?

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

Reveal the answer and explanation

Correct answer: A — Insert the copper intrauterine device, stop the combined pill now, obtain an active-pill lamotrigine level and arrange specialist-guided gradual dose reduction with clinical monitoring

Explanation lettering: D = shown as C · E = shown as D · C = shown as E

Confirmed migraine with aura makes combined hormonal contraception UKMEC 4, so the pill should not be continued merely to facilitate antiepileptic dose adjustment. The copper intrauterine device provides highly effective contraception without interacting with lamotrigine. Ethinylestradiol induces lamotrigine glucuronidation and can approximately double its clearance. Her 400 mg dose was specifically established during oestrogen exposure; stopping the pill may therefore halve clearance and substantially increase lamotrigine concentrations, causing dizziness, diplopia, ataxia or other toxicity. Specialist coordination is required: the licensed product information advises that the maintenance dose may need reduction by up to 50%, generally by 50–100 mg weekly over about three weeks and no faster than 25% of the total daily dose per week. Day 18 is an appropriate point to obtain an active-treatment reference concentration; a post-discontinuation sample should not be taken during the first week alone. B delays anticipatory adjustment and uses an inappropriately timed level. C prolongs contraindicated oestrogen exposure and permits a marked concentration rise during the hormone-free interval. D overlooks the effect of contraception on lamotrigine and substitutes a method whose effectiveness during lamotrigine use is uncertain. E is incorrect because combined contraception is not tapered, and intermittent tablets would create unpredictable hormone and lamotrigine exposure.

Reference: FSRH Guideline: Combined Hormonal Contraception (January 2019, amended October 2023) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-guideline-combined-hormonal-contraception-october-2023.pdf FSRH Clinical Guidance: Drug Interactions with Hormonal Contraception (May 2022) — https://www.fsrh.org/Common/Uploaded%20files/documents/drug-interactions-with-hormonal-contraception-5may2022.pdf Lamictal Tablets Summary of Product Characteristics (5 November 2025) — https://www.medicines.org.uk/emc/product/8052/smpc