Methotrexate and co-trimoxazole — GPhC CRA MCQ

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HardDrug InteractionsMethotrexate and co-trimoxazoleGPhC CRA

A patient using a combined oral contraceptive is starting rifampicin for six months. They want to avoid pregnancy and ask whether taking the pill at a different time will preserve efficacy. What is the best advice?

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Correct answer: E — Use contraception unaffected by induction during and after rifampicin

Use contraception unaffected by induction during and after rifampicin: Rifampicin is a potent enzyme inducer that reduces combined-hormonal-contraceptive exposure; a copper IUD, levonorgestrel IUS or depot medroxyprogesterone is not compromised in the same way. Continue the combined pill twelve hours after each rifampicin dose: Enzyme induction persists throughout the dosing interval and is not prevented by separating tablets. Change to a standard progestogen-only pill without added precautions: Progestogen-only pills are also vulnerable to enzyme induction and are not a reliable simple substitute. Double the combined-pill dose during the first rifampicin week: Six months of potent induction cannot be managed by a brief unreviewed dose increase. Use condoms only until the first rifampicin pack is finished: The interaction persists for the whole rifampicin course and for a period after the inducer is stopped.

Reference: BNF: rifampicin: https://bnf.nice.org.uk/drugs/rifampicin/; CoSRH/FSRH clinical guidance: drug interactions with hormonal contraception: https://www.cosrh.org/Common/Uploaded%20files/documents/drug-interactions-with-hormonal-contraception-5may2022.pdf