Doses - PYRIMETHAMINE

Dogs:

For toxoplasmosis:
a) 0.5 - 1 mg/kg PO once daily for 2 days, then 0.25 mg/kg PO once daily for 2 weeks.
Given with sulfadiazine at 30 - 50 mg/kg PO divided bid-qid for 1-2 weeks. (Murtaugh1988)
b) 1 mg/kg PO once daily for 3 days, then 0.5 mg/kg PO once daily. (Kirk 1989)
c) Pyrimethamine: 1 mg/kg PO per day with sulfadiazine at 30 mg/kg PO q12h for 7-10days. Do not use continually for longer than 2 weeks. (Swango, Bankemper, and Kong1989)

Cats:

For toxoplasmosis:
a) 0.5 - 1 mg/kg PO once daily for 2 days, then 0.25 mg/kg PO once daily for 2 weeks.
Given with sulfadiazine at 30 - 50 mg/kg PO divided bid-qid for 1-2 weeks. (Murtaugh1988)
b) For enteroepithelial cycle: 2 mg/kg PO once daily. For extraintestinal cycle: 0.5 - 1mg/kg PO divided bid-tid combined with sulfonamides (e.g., triple sulfa, sulfadiazine) at60 mg/kg PO or IM divided bid-tid. (Lappin 1989)
c) For protozoal myocarditis: Pyrimethamine 1 mg/kg PO once daily for 3 days, thendecrease dose to 0.5 mg/kg PO once a day, with sulfadimethoxine 25 mg/kg PO, IV, or IM once a day. (Ogburn 1988)
d) Pyrimethamine: 0.5 mg/kg PO per day with sulfadiazine at 30 mg/kg PO q12h for 7-10days. Do not use continuously for longer than 2 weeks. Supplementation with folic acid5 mg/day or folinic acid 1 mg/kg/day may alleviate toxicity. (Swango, Bankemper, and Kong 1989)

Horses:

For equine protozoal myeloencephalitis:
a) Pyrimethamine 0.1 - 0.2 mg/kg PO once daily, with trimethoprim/sulfadiazine 15 mg/kg
PO bid. Dosage may be continued for up to 2 months. Reinstitute therapy if animal isstressed; long-term intermittent therapy may be rational. Guarded prognosis; relapsesare not uncommon. (Brewer 1987)
Monitoring Parameters -

1) See adverse effects; CBC with platelet count

2) Clinical efficacy
Client Information - Clients should he instructed to monitor for symptoms of abnormal bleeding, lassitude, etc. that may signal development of hematologic disorders. Accurate dosing of the tabletsin cats may be very difficult as only 25 mg tablets are commercially available. Preferably, customprepared capsules containing the accurate dosage should be prepared.
Dosage Forms/Preparations/FDA Approval Status - Veterinary-Approved Products: None