Pyrimethamine
Pyrimethamine is an antiparasitic medication primarily used to treat and prevent toxoplasmosis, often in combination with sulfadiazine, and for malaria prophylaxis in certain regions. It works by inhibiting dihydrofolate reductase, an enzyme essential for folic acid synthesis in parasites, thereby disrupting their DNA production and replication. This medication requires careful dosing and is typically reserved for specific parasitic infections rather than common conditions.
Pyrimethamine is an antiparasitic drug used to treat toxoplasmosis and prevent malaria by inhibiting folic acid synthesis in parasites.
Key facts at a glance
- ATC
- P01BD01
- RxNorm
- 9010
- Generic
- Pyrimethamine
- Class
- atc-p01
- Brands
- Rebalance, Daraprim
- Availability
- rx
- Lactation
- unknown
- Routes
- oral
- Forms
- tablet, suspension
- Regions
- US, EU, CN, JP
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Treatment of toxoplasmosis (often combined with sulfadiazine), malaria prophylaxis (particularly in chloroquine-resistant areas), and adjunctive therapy for isosporiasis. May be used in immunocompromised patients, pregnant women for congenital toxoplasmosis prevention, and individuals with HIV/AIDS who have or are at risk for toxoplasmosis.
Pyrimethamine inhibits dihydrofolate reductase, a key enzyme in folic acid metabolism. By blocking this enzyme, it prevents the conversion of dihydrofolate to tetrahydrofolate, which is essential for DNA and RNA synthesis in susceptible parasites. This antiproliferative effect is more pronounced in parasites than in human cells at therapeutic doses.
Often prescribed with sulfadiazine and leucovorin (folinic acid) to enhance efficacy and reduce bone marrow toxicity. Can cause hematologic adverse effects including megaloblastic anemia, leukopenia, and thrombocytopenia. Requires regular blood monitoring during prolonged therapy. Contraindicated in patients with known hypersensitivity and should be used with caution in pregnancy (folic acid supplementation recommended) and renal impairment.
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy