Inhibits dihydrofolate reductase (DHFR) in protozoa with much higher affinity than mammalian DHFR (selective toxicity). Blocks folate metabolism needed for DNA synthesis. Synergistic with sulfonamides (sequential folate pathway blockade).
At a glance
Class
Diaminopyrimidine Antiprotozoal
Storage
Store at room temperature, protect from light
Dosing
Used for Toxoplasma, Neospora, and Hepatozoon infections
Used for feline toxoplasmosis (ocular, CNS, systemic)
Safety
CBC every 1–2 weeks (neutropenia, thrombocytopenia)Folinic acid supplementation complianceClinical/PCR responseRetinal exam (ocular toxoplasmosis)
Interactions
No documented interactions.
FAQs
Frequently asked questions
›What is Pyrimethamine?
Pyrimethamine is a diaminopyrimidine antiprotozoal used in pets. Inhibits dihydrofolate reductase (DHFR) in protozoa with much higher affinity than mammalian DHFR (selective toxicity). Blocks folate metabolism needed for DNA synthesis. Synergistic with sulfonamides (sequential folate pathway blockade).
›What is Pyrimethamine used for in pets?
Pyrimethamine is used in veterinary medicine for: Used for Toxoplasma, Neospora, and Hepatozoon infections; Used for feline toxoplasmosis (ocular, CNS, systemic).
›What is the Pyrimethamine dose for dogs?
For dogs, Pyrimethamine is typically dosed as follows — Used for Toxoplasma, Neospora, and Hepatozoon infections: 1 mg/kg PO q24h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Pyrimethamine dose for cats?
For cats, Pyrimethamine is typically dosed as follows — Used for feline toxoplasmosis (ocular, CNS, systemic): 0.25–0.5 mg/kg PO q12h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Pyrimethamine need a prescription?
Yes. Pyrimethamine is a prescription medication and should only be administered under veterinary supervision.
References
References
Textbooks & handbooks
- Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
- Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
- Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
- National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
- The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/
Clinical guidelines & consensus
- Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
- American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.
Journals & peer-reviewed studies
- Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
- Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
- ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control
Regulatory & approvals
- Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/
Databases
- Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet.
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