Drug interactions
Pyrimethamine + Sulfamethoxazole
Severity: Moderate
Pyrimethamine and Sulfamethoxazole: 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
Sulfamethoxazole and pyrimethamine both interfere with folate metabolism and together increase the risk of megaloblastic anaemia and other cytopenias. The pairing is used deliberately in some regimens for its synergy, but toxicity needs attention.
What this interaction means in plain words
Pyrimethamine and Sulfamethoxazole 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 blockade of folate synthesis and reduction produces additive antifolate effects on the bone marrow.
What to do
Provide folinic acid supplementation and monitor complete blood counts regularly. Stop or reduce doses if significant cytopenias occur.
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 Sulfamethoxazole?
MediHelp rates the interaction as moderate. Pyrimethamine and Sulfamethoxazole 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. Sulfamethoxazole and pyrimethamine both interfere with folate metabolism and together increase the risk of megaloblastic anaemia and other cytopenias. The pairing is used deliberately in some regimens for its synergy, but toxicity needs attention.
How serious is the interaction between Pyrimethamine and Sulfamethoxazole?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Provide folinic acid supplementation and monitor complete blood counts regularly. Stop or reduce doses if significant cytopenias occur.
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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