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Emergency contraception in a person taking an enzyme-inducing antiseizure medicine — MSRA MCQ

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Hardall topics relevant for this examEmergency contraception in a person taking an enzyme-inducing antiseizure medicineMSRA

A 24-year-old woman requests emergency contraception 60 hours after a single episode of condom failure. Her last menstrual period began 15 days ago and was normal. She has no pelvic pain, abnormal bleeding or symptoms suggesting pregnancy. She has focal epilepsy treated with carbamazepine modified-release 400 mg twice daily, which she has taken continuously for 3 years. She uses condoms as her usual contraception. She has no contraindication to intrauterine contraception, but after counselling she declines a copper intrauterine device because she does not want an intrauterine method. What is the most appropriate management now?

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

Reveal the answer and explanation

Correct answer: D — Supply levonorgestrel 3 mg as a single oral dose

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

Carbamazepine is a hepatic enzyme inducer that reduces plasma concentrations of both levonorgestrel and ulipristal acetate. A copper IUD is the preferred emergency contraceptive option for someone using an enzyme inducer, but this patient has made an informed refusal and remains within 72 hours of unprotected intercourse. For a person who has used an enzyme-inducing medicine within the preceding 4 weeks and cannot or will not use a copper IUD, the levonorgestrel SmPC advises a double levonorgestrel dose (3 mg) as soon as possible. This is the best available oral option in this exact situation, although the specific double-dose regimen has not been formally studied with enzyme inducers. She should also be advised to use condoms until her next menstrual period and to undertake pregnancy testing if her period is more than 5 days late or is abnormal. A is normally preferred because a copper IUD is not affected by enzyme induction, but it is not appropriate after informed refusal. B is plausible because ulipristal remains licensed up to 120 hours after intercourse; however, carbamazepine substantially reduces ulipristal exposure and ulipristal is not recommended with current or recent enzyme-inducing treatment. C uses the standard dose but does not account for carbamazepine induction. D misses the remaining effective emergency-contraception window.

Reference: Levonelle One Step 1500 microgram tablet - Summary of Product Characteristics (2025) — https://www.medicines.org.uk/emc/product/5576/smpc Ulipristal 30 mg film-coated tablets - Summary of Product Characteristics (2023) — https://www.medicines.org.uk/emc/product/14200/smpc