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St John’s wort interaction with an etonogestrel implant — DFSRH MCQ

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HardDepressionSt John’s wort interaction with an etonogestrel implantDFSRH

A 30-year-old woman has used an etonogestrel implant for 18 months. Seventeen days ago, she started an over-the-counter St John’s wort preparation for recurrent depressive symptoms without seeking medical advice. She has not used additional contraception and had condomless intercourse 60 hours ago; there has been no other intercourse since starting St John’s wort. She has no symptoms of pregnancy, and a urine pregnancy test is negative. After counselling, she declines a copper intrauterine device, wishes to retain her implant and agrees to stop St John’s wort today and arrange review of her depression. Which contraceptive management plan is most appropriate?

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

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Correct answer: A — Give levonorgestrel 3 mg now, retain the implant, advise condoms for 28 days after the last St John’s wort dose, and repeat the pregnancy test 21 days after intercourse

St John’s wort induces hepatic CYP450 enzymes and can reduce etonogestrel exposure, so an in-date implant cannot be assumed to have provided effective contraception. Emergency contraception is therefore indicated after intercourse occurring during St John’s wort use. A copper IUD is preferred because enzyme induction does not affect it, but she has declined this option. FSRH recommends considering double-dose levonorgestrel emergency contraception (3 mg); its effectiveness in this setting is uncertain, but it is the appropriate oral option. Ulipristal acetate is not recommended because enzyme induction may reduce its exposure and the circulating progestogen from the implant may antagonise its ovulation-delaying effect. The implant need not be removed because St John’s wort use has been short term and she will discontinue it. However, enzyme induction may persist, so condoms or abstinence are required until 28 days after the last dose. A pregnancy test 21 days after the relevant intercourse is needed because today’s negative test cannot exclude conception 60 hours ago. A uses an inadequate levonorgestrel dose. B overlooks both pharmacokinetic and pharmacodynamic concerns with ulipristal. C stops additional precautions too early. E incorrectly assumes that an in-date implant remains reliable during enzyme induction. NICE also advises against St John’s wort for depression because preparations vary and clinically serious drug interactions include hormonal contraceptives.

Reference: FSRH Guideline: Emergency Contraception (December 2017, amended July 2023) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-guideline-emergency-contraception03dec2020-amendedjuly2023-11jul.pdf Clinical Guidance: Drug Interactions with Hormonal Contraception (May 2022) — https://www.fsrh.org/Common/Uploaded%20files/documents/drug-interactions-with-hormonal-contraception-5may2022.pdf Depression in adults: treatment and management — Recommendations (2022) — https://www.nice.org.uk/guidance/ng222/chapter/Recommendations