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Emergency contraception following recent carbamazepine use — DFSRH MCQ

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EasyEpilepsyEmergency contraception following recent carbamazepine useDFSRH

A 32-year-old woman presents 36 hours after condom failure and requests emergency contraception. She has a regular 28-day menstrual cycle and is on day 10. After several years of carbamazepine therapy for focal epilepsy, her neurologist changed her treatment to levetiracetam 14 days ago. She has taken both medicines as prescribed and has had no other unprotected sexual intercourse this cycle. Following counselling, she declines a copper intrauterine device and requests oral emergency contraception. Which oral regimen is most appropriate?

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

Reveal the answer and explanation

Correct answer: E — Administer levonorgestrel 3 mg as a single dose now

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

Carbamazepine induces hepatic CYP450 enzymes, increasing the metabolism of both levonorgestrel and ulipristal acetate. This interaction remains clinically relevant for 28 days after the enzyme inducer is stopped; changing to non-enzyme-inducing levetiracetam only 14 days ago therefore does not remove the interaction. The copper IUD is the preferred emergency contraceptive because its efficacy is unaffected by enzyme induction, but she has declined it. FSRH guidance supports a single 3 mg dose of levonorgestrel in this situation, with counselling that its effectiveness has not been established. A is inadequate because the standard 1.5 mg dose may have reduced exposure during residual enzyme induction. B is attractive because ulipristal is generally more effective than levonorgestrel near ovulation, but enzyme induction may reduce its effectiveness. C is incorrect because double-dose ulipristal is not recommended. D is therefore the best available oral regimen. E provides the same total levonorgestrel dose but not according to the recommended regimen: the two 1.5 mg tablets should be taken together as a single 3 mg dose. She should also receive advice about ongoing contraception and pregnancy testing if her next menstrual period is delayed or abnormal.

Reference: FSRH Guideline: Emergency Contraception (Amended July 2023) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-guideline-emergency-contraception03dec2020-amendedjuly2023-11jul.pdf Levonelle 1500 microgram tablet — Summary of Product Characteristics (Checked August 2026) — https://www.medicines.org.uk/emc/product/133/smpc