What is Pyrimethamine used for?

Pyrimethamine is indicated for: Toxoplasmosis, Toxoplasmosis/Neosporosis.

Which species have cited Pyrimethamine dosing data?

Pyrimethamine dosing in the ExoticRx formulary covers 2 species: Cat (Domestic), Dog (Domestic).

Is Pyrimethamine a controlled substance?

Pyrimethamine is not federally scheduled in the US. Controlled-drug status differs by country — verify your local rules.

What are the side effects of Pyrimethamine?

Reported side effects, adverse reactions, and contraindications for Pyrimethamine: Bone marrow suppression possible — monitor CBC. Supplement with folinic acid (leucovorin). Teratogenic. Do not use in pregnant animals.

Pyrimethamine

US brand names:Daraprim

Calculate dosage

Sourced from published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.

Pyrimethamine is dosed at 0.25–1 mg/kg PO q24h; 0.25-0.5 mg/kg may be given q12h in dogs, per Plumb's Veterinary Drug Handbook, 10th ed., printed p.1100 (corpus PDF p.1127), Dosages > DOGS; corroborated by BSAVA Small Animal Formulary 10th ed., Pyrimethamine, printed p.354 (corpus PDF p.370) - 'Dogs, Cats: Toxoplasmosis/neosporosis: 1 mg/kg p.o. q24h or divided q12h for 4 weeks, alongside sulphonamides'. Verify against current literature before clinical use.

Drug Class

Antiparasitic

Routes

Indications

ToxoplasmosisToxoplasmosis/Neosporosis

Mechanism of Action

Inhibits dihydrofolate reductase in protozoa, blocking folic acid synthesis required for DNA replication. Synergistic with sulfonamides.

Side effects & warnings

Bone marrow suppression possible — monitor CBC. Supplement with folinic acid (leucovorin). Teratogenic. Do not use in pregnant animals.

Species with Pyrimethamine dosing data (2 dose rules)

Cat (Domestic)Dog (Domestic)

Species references:All Cat (Domestic) drugs All Dog (Domestic) drugs

Evidence levels across 2 dose rules

Moderate×2

Each ExoticRx dose rule is graded by the strength of its primary evidence — see the editorial process.

Backed by 2 published sources

· Foster SF, Martin P. Lower respiratory tract infections in cats: Reaching beyond empirical therapy. J Feline Med Surg. 2011;13:313-332. doi:10.1016/j.jfms.2011.06.001 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1127 (2026-08-01).
· Plumb's Veterinary Drug Handbook, 10th ed., printed p.1100 (corpus PDF p.1127), Dosages > DOGS; corroborated by BSAVA Small Animal Formulary 10th ed., Pyrimethamine, printed p.354 (corpus PDF p.370) - 'Dogs, Cats: Toxoplasmosis/neosporosis: 1 mg/kg p.o. q24h or divided q12h for 4 weeks, alongside sulphonamides'

Sample dosing (2 of 2 cited rules)

A dog/cat sample is shown here. Cited dosing for all 2 species — reptiles, birds, pocket pets, livestock, and equine — is free on the per-species pages above. Pro adds the weight-based calculator for every species.

Species	Route	Dose	Frequency	Evidence	Source
Dog (Domestic)	PO	0.25–1 mg/kg	q24h; 0.25-0.5 mg/kg may be given q12h	Moderate	Plumb's Veterinary Drug Handbook, 10th ed., printed p.1100 (corpus PDF p.1127), Dosages > DOGS; corroborated by BSAVA Small Animal Formulary 10th ed., Pyrimethamine, printed p.354 (corpus PDF p.370) - 'Dogs, Cats: Toxoplasmosis/neosporosis: 1 mg/kg p.o. q24h or divided q12h for 4 weeks, alongside sulphonamides'
Cat (Domestic)	PO	0.25–0.5 mg/kg	q12h	Moderate	Foster SF, Martin P. Lower respiratory tract infections in cats: Reaching beyond empirical therapy. J Feline Med Surg. 2011;13:313-332. doi:10.1016/j.jfms.2011.06.001 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1127 (2026-08-01).

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