skip to main content

Emergency contraception during residual enzyme induction from lumacaftor/ivacaftor — DFSRH MCQ

Instant feedback + full explanation. One question, done properly.

HardCystic FibrosisEmergency contraception during residual enzyme induction from lumacaftor/ivacaftorDFSRH

A 27-year-old woman with cystic fibrosis attends for emergency contraception. She has used an etonogestrel implant for 10 months. Until 12 days ago she had taken lumacaftor/ivacaftor (Orkambi) continuously for 18 months; her respiratory team then changed her directly to elexacaftor/tezacaftor/ivacaftor with ivacaftor (Kaftrio). She takes no other interacting medication and has had no vomiting or severe diarrhoea. She had condomless vaginal intercourse 36 hours ago. There was no other condomless intercourse during the preceding 3 weeks. She has no symptoms of pregnancy, and a urine pregnancy test today is negative. After discussion of relative effectiveness, she declines insertion of a copper intrauterine device but wishes to retain her implant. 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: B — Give levonorgestrel 3 mg now, advise condoms or abstinence until 28 days after the final Orkambi dose, and arrange a pregnancy test 21 days after intercourse

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

Lumacaftor is a strong inducer of CYP3A and UGT pathways. Orkambi can therefore reduce exposure to contraceptive progestogens, and an etonogestrel implant should not be relied upon during treatment. Enzyme induction remains clinically relevant for 28 days after the inducer is stopped, so changing to Kaftrio 12 days ago has not yet restored reliable implant protection. Emergency contraception is indicated for intercourse during this residual induction period. A copper IUD is the preferred emergency method because enzyme induction does not affect it, but she has declined it. FSRH advises that levonorgestrel 3 mg may then be offered within 96 hours, explaining that effectiveness in enzyme-inducer users is uncertain. Additional precautions are required until 28 days after the final Orkambi dose, followed by pregnancy testing 21 days after the episode. B incorrectly treats the change to Kaftrio as immediately abolishing the interaction. C is inferior because enzyme induction can reduce ulipristal exposure and the circulating progestogen from the implant could additionally antagonise its ovulation-delaying effect. D uses the standard levonorgestrel dose rather than the advised doubled dose. E does not address pregnancy risk from intercourse already experienced; replacing the implant also cannot overcome ongoing residual enzyme induction.

Reference: Orkambi 100 mg/125 mg film-coated tablets — Summary of Product Characteristics (11 November 2025) — https://www.medicines.org.uk/emc/product/8952/smpc 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 FSRH Guideline: Emergency Contraception (March 2017, amended April 2026) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-guideline-emergency-contraception03dec2020-amendedjuly2023-11jul.pdf