MTX Co-trimoxazole Toxicity — RACP Adult Medicine MCQ
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Correct answer: A — Stop both interacting medicines, assess urgently for sepsis and organ injury, and give folinic-acid rescue when indicated
The best answer is “Stop both interacting medicines, assess urgently for sepsis and organ injury, and give folinic-acid rescue when indicated”. Co-trimoxazole and methotrexate produce additive antifolate toxicity and may impair methotrexate elimination. Mucositis and pancytopenia require immediate cessation, blood counts, renal and liver assessment, infection management and specialist-guided folinic acid; growth factor or transfusion is used according to severity. Routine folic acid alone is not adequate rescue.
Reference: Australian Prescriber: Managing the drug treatment of rheumatoid arthritis: https://australianprescriber.tg.org.au/articles/managing-the-drug-treatment-of-rheumatoid-arthritis.html