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Focal epilepsy treated with lamotrigine — MSRA MCQ

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Hardall topics relevant for this examFocal epilepsy treated with lamotrigineMSRA

A 29-year-old woman with focal epilepsy requests combined oral contraception. She has been seizure-free for 3 years on lamotrigine 200 mg twice daily monotherapy. She takes no enzyme-inducing medicines and has normal renal and hepatic function. She has no migraine with aura, venous thromboembolism risk factors or other contraindication to combined hormonal contraception. She understands that a copper intrauterine device, levonorgestrel intrauterine system and progestogen-only options would avoid the relevant interaction, but declines these because she specifically wants a combined oral contraceptive. She wishes to minimise both breakthrough seizures and adverse effects from fluctuating lamotrigine concentrations. What is the most appropriate prescribing plan?

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Correct answer: B — Initiate a continuous ethinylestradiol/levonorgestrel regimen and increase lamotrigine by 50–100 mg/day each week, guided by clinical response and, if used, concentrations

Ethinyloestradiol-containing contraception increases lamotrigine clearance substantially, reducing lamotrigine exposure and risking loss of seizure control. This patient is not taking an enzyme inducer, so the SmPC dosing advice for starting combined hormonal contraception applies: her maintenance lamotrigine dose will usually need to increase, using increments of 50–100 mg/day per week according to individual clinical response. A pre-treatment and follow-up lamotrigine concentration may help establish whether her previous exposure is maintained. A continuous combined regimen is preferable to a 21/7 regimen because inactive-pill intervals permit lamotrigine concentrations to rise transiently, potentially producing dose-related adverse effects. This is particularly important in a patient whose seizures have been stable on a fixed dose. A is unsafe because it combines reduced active-pill lamotrigine exposure with substantial concentration fluctuation during the hormone-free interval. B avoids the fluctuation but leaves her vulnerable to reduced lamotrigine exposure and breakthrough seizures. D uses an inappropriate immediate dose escalation and retains the pill-free interval; titration should be gradual. E moves lamotrigine in the wrong direction: stopping oestrogen-containing contraception may require dose reduction, whereas starting it usually requires dose escalation. Non-oestrogen contraception would avoid this interaction, but she has made an informed choice to decline it.

Reference: Epilepsies in children, young people and adults (NG217): Principles of treatment, safety, monitoring and withdrawal (Updated 2025) — https://www.nice.org.uk/guidance/ng217/chapter/principles-of-treatment-safety-monitoring-and-withdrawal Lamotrigine 100 mg tablets: Summary of Product Characteristics (2026) — https://www.medicines.org.uk/emc/product/4739/smpc