Drug interactions
Pyrimethamine + Sulfadiazine
Severity: Moderate
Pyrimethamine and Sulfadiazine: 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
This combination is standard therapy for toxoplasmosis because the two drugs act synergistically against the parasite. Both can also suppress bone marrow, causing anaemia, leucopenia or thrombocytopenia.
What this interaction means in plain words
Pyrimethamine and Sulfadiazine 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 (dihydropteroate synthase and dihydrofolate reductase) affects host haematopoietic cells as well as the parasite.
What to do
Give folinic acid (leucovorin) with therapy and monitor complete blood counts regularly. Reduce the dose or interrupt treatment if marked 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 Sulfadiazine?
MediHelp rates the interaction as moderate. Pyrimethamine and Sulfadiazine 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. This combination is standard therapy for toxoplasmosis because the two drugs act synergistically against the parasite. Both can also suppress bone marrow, causing anaemia, leucopenia or thrombocytopenia.
How serious is the interaction between Pyrimethamine and Sulfadiazine?
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 (leucovorin) with therapy and monitor complete blood counts regularly. Reduce the dose or interrupt treatment if marked 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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