Drug interactions
Pyrimethamine + Sulfisoxazole
Severity: Moderate
Pyrimethamine and Sulfisoxazole: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Sulfisoxazole and pyrimethamine act synergistically against some protozoa but also add to antifolate toxicity in the host, including megaloblastic anaemia, leucopenia and thrombocytopenia.
What this interaction means in plain words
Pyrimethamine and Sulfisoxazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Sequential inhibition of folate synthesis and dihydrofolate reductase gives additive bone marrow suppression.
What to do
Give folinic acid and monitor complete blood counts during combined therapy. Reduce the dose or stop if cytopenias develop.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Pyrimethamine
- Deferiprone + Pyrimethamine Major
- Eliglustat + Pyrimethamine Major
- Acalabrutinib + Pyrimethamine Moderate
- Brexpiprazole + Pyrimethamine Moderate
- Dapsone + Pyrimethamine Moderate
- Folic acid + Pyrimethamine Moderate
Frequently asked questions
Can I take Pyrimethamine with Sulfisoxazole?
MediHelp rates the interaction as moderate. Pyrimethamine and Sulfisoxazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Sulfisoxazole and pyrimethamine act synergistically against some protozoa but also add to antifolate toxicity in the host, including megaloblastic anaemia, leucopenia and thrombocytopenia.
How serious is the interaction between Pyrimethamine and Sulfisoxazole?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Give folinic acid and monitor complete blood counts during combined therapy. Reduce the dose or stop if cytopenias develop.
What other medicines interact with Pyrimethamine?
MediHelp also lists interactions of Pyrimethamine with, for example, Deferiprone, Eliglustat, Acalabrutinib. The full list is on the Pyrimethamine page.
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