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Carbamazepine — DFSRH MCQ

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HardCarbamazepineDFSRH

A 28-year-old woman uses a monophasic combined oral contraceptive containing ethinylestradiol 30 micrograms and levonorgestrel. She has taken every tablet correctly and took today's tablet this morning. Carbamazepine was started 12 days ago for focal epilepsy and is expected to continue long term. She had condomless intercourse 44 hours ago, on day 12 of her current pill packet, and has had no other condomless intercourse in the preceding 3 weeks. A high-sensitivity urine pregnancy test is negative. Her BMI is 24 kg/m². She has no contraindication to depot medroxyprogesterone acetate (DMPA) or intrauterine contraception, but declines both copper and levonorgestrel intrauterine devices. After counselling, she requests DMPA for ongoing contraception. Which is the most appropriate management plan?

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Correct answer: C — Give levonorgestrel 3 mg today, administer DMPA today, advise condoms for 7 days and perform a pregnancy test 21 days after intercourse

Carbamazepine induces hepatic enzymes and can reduce combined hormonal contraceptive effectiveness despite perfect tablet-taking; the intercourse therefore represents a potential contraceptive failure. A copper IUD is the preferred emergency method because enzyme induction does not affect it, but she declines intrauterine contraception. FSRH advises that levonorgestrel 3 mg may then be used, with counselling that its effectiveness in enzyme-inducer users is uncertain. DMPA can be administered immediately after levonorgestrel emergency contraception and its efficacy is not expected to be reduced by enzyme induction. She requires condoms or abstinence for 7 days while DMPA becomes effective and a pregnancy test 21 days after the last condomless intercourse. A fails to address the pregnancy risk from intercourse during enzyme induction. B correctly delays DMPA after ulipristal, but ulipristal exposure may be reduced by carbamazepine and its effectiveness may also be antagonised by recently taken contraceptive progestogen. D uses the standard levonorgestrel dose rather than the advised double dose. E uses an etonogestrel implant, whose contraceptive effectiveness can be reduced during carbamazepine use and for 28 days after it is stopped.

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 Drug Interactions with Hormonal Contraception (May 2022) — https://www.fsrh.org/Common/Uploaded%20files/documents/drug-interactions-with-hormonal-contraception-5may2022.pdf Tegretol 100 mg Tablets — Summary of Product Characteristics (2026) — https://www.medicines.org.uk/emc/product/1040/smpc