Oral emergency contraception after recent hepatic enzyme-inducer use — DFSRH MCQ

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EasyPrescribingOral emergency contraception after recent hepatic enzyme-inducer useDFSRH

A 32-year-old woman requests emergency contraception after unprotected sexual intercourse 60 hours ago. She was changed from carbamazepine to levetiracetam by her neurologist 14 days ago because of adverse effects. She uses no regular hormonal contraception and takes no other medication. A copper intrauterine device is clinically suitable, but she declines insertion after counselling and requests oral emergency contraception. Which prescription is most appropriate?

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Correct answer: C — Prescribe levonorgestrel 3 mg as a single dose now

Explanation lettering: E = shown as A · A = 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. Crucially, clinically relevant enzyme induction persists for 28 days after the inducing drug is stopped; changing to non-inducing levetiracetam only 14 days ago therefore does not remove the interaction. The copper IUD is the preferred emergency contraceptive because its effectiveness is unaffected by enzyme induction, but it has been declined. FSRH consequently recommends that a single 3 mg dose of levonorgestrel may be offered within the relevant time window, with counselling that effectiveness in this setting is uncertain. Thus, B is the best available oral prescription. A and E provide only the standard total levonorgestrel dose of 1.5 mg, which is inadequate for the recommended enzyme-inducer regimen; dividing that dose does not compensate for accelerated metabolism. C is inappropriate because ulipristal acetate is not recommended during, or within 28 days after, enzyme-inducer exposure. D applies an unsupported dose-doubling strategy: FSRH explicitly advises against double-dose ulipristal acetate. She should also be counselled that oral emergency contraception may be less effective in this setting, advised regarding ongoing contraception and further unprotected intercourse, and offered follow-up pregnancy testing.

Reference: FSRH Guideline: Emergency Contraception (March 2017; amended April 2026) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-guideline-emergency-contraception03dec2020-amendedjuly2023-11jul.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 Ulipristal 30 mg film-coated tablets: Summary of Product Characteristics (Checked 20 August 2026) — https://www.medicines.org.uk/emc/product/14200/smpc