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)
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.
Find a vet near you →Safety
CBC every 1–2 weeks (neutropenia, thrombocytopenia)Folinic acid supplementation complianceClinical/PCR responseRetinal exam (ocular toxoplasmosis)
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.
Find a vet near you →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.
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.
Find a vet near you →References
References
The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.
Textbooks & handbooks — 5
- Plumb's Veterinary Drug Handbook
- Withrow & MacEwen's Small Animal Clinical Oncology
- Merck Veterinary Manual
- NRC Nutrient Requirements of Dogs and Cats
- Veterinary Pharmacology and Therapeutics (Riviere & Papich)
Clinical guidelines & consensus — 4
- ASPCA Animal Poison Control Center Guidelines
- AAHA Diabetes Management Guidelines
- ASPCA Poison Control Guidelines
- RECOVER CPR Guidelines
Journals & peer-reviewed studies — 2
- EPIC Study (J Vet Intern Med 2016)
- JVIM FAT CAT Study
Regulatory & approvals — 1
- CDSCO Veterinary Drug Approval Registry (1969–2026)
Databases — 1
- Washington State University VCPL MDR1 Database