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Incorrect desogestrel progestogen-only pill use after vomiting — DFSRH MCQ

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EasyPregabalinIncorrect desogestrel progestogen-only pill use after vomitingDFSRH

A 34-year-old woman uses desogestrel 75 micrograms daily, taken at 22:00, for contraception. She has taken it correctly for several months. She has recently started pregabalin for neuropathic pain and is concerned that an antiepileptic medicine may reduce contraceptive efficacy. She took both medicines at 22:00 yesterday but vomited at 00:30. She did not take a replacement desogestrel tablet and attends at 12:30 today. She has had no vaginal intercourse for 8 days and is not planning intercourse today. There has been no further vomiting or diarrhoea. Which is the most appropriate management?

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

Reveal the answer and explanation

Correct answer: C — Take a desogestrel tablet now, take the next tablet at 22:00, and use condoms or abstain for 48 hours

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

Vomiting occurred 2.5 hours after the desogestrel POP was taken, within the 3–4-hour interval during which absorption may be incomplete. A replacement tablet should therefore have been taken. Because none was taken within 12 hours of the original 22:00 due time, this is managed as a missed desogestrel POP: take the most recent missed tablet immediately, continue the next tablet at the usual time, and use condoms or abstain until correct pill-taking has resumed for 48 hours. Pregabalin does not induce hepatic enzymes. It undergoes negligible metabolism and is predominantly excreted unchanged in urine, so starting it does not itself require additional contraception or discontinuation of the POP. B incorrectly applies a 7-day precaution interval, which is used after missed active drospirenone POP tablets rather than a desogestrel POP. C overlooks the potentially unabsorbed tablet and the fact that the replacement window is measured from when the original tablet was due, not from the time of vomiting. D incorrectly treats pregabalin as an enzyme inducer; abrupt discontinuation may also cause withdrawal symptoms. E is unnecessary because emergency contraception is considered after incorrect desogestrel POP use only when unprotected intercourse occurs from the time the pill is missed until correct use has resumed for 48 hours; no intercourse occurred during that risk interval.

Reference: FSRH Guideline: Progestogen-only Pills (August 2022, amended April 2026) — https://www.fsrh.org/Common/Uploaded%20files/documents/fsrh-ceu-clinical-guideline-progestogen-only-pills-aug22-amended-11july-2023-.pdf Pregabalin MSN 25 mg hard capsules: Summary of Product Characteristics (Revised 6 February 2026; emc updated 2 March 2026) — https://www.medicines.org.uk/emc/product/13386/smpc