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ANTIPARASITIC PRODUCTS, INSECTICIDES AND REPELLENTS › ANTIPROTOZOALS › ANTIMALARIALS › Diaminopyrimidines
pyrimethamine, combinations
P01BD51
Forms & Strengths
- Pyrimethamine 25 mg / Sulfadiazine 500 mg tablets
- Pyrimethamine 25 mg / Leucovorin 5 mg tablets (custom combination packs)
Adult Dosing
- Toxoplasmosis: Pyrimethamine 50-75 mg daily loading dose, followed by 25-50 mg daily, combined with a sulfonamide and leucovorin.
Pediatric Dosing
- Congenital Toxoplasmosis (infants >2 months): Pyrimethamine 2 mg/kg/day for 2 days, then 1 mg/kg/day twice weekly, combined with sulfonamide and leucovorin.
Indications
- Treatment of toxoplasmosis
- Treatment of acute malaria (historically or resistant strains)
Mechanism of Action
- Pyrimethamine inhibits parasitic dihydrofolate reductase (DHFR), blocking synthesis of tetrahydrofolic acid.
- Sulfonamides inhibit folic acid synthesis via dihydropteroate synthase, creating a synergistic dual blockade of the folate pathway.
Contraindications
- Hypersensitivity to pyrimethamine, sulfonamides, or any component
- Documented megaloblastic anemia due to folate deficiency
- Severe hepatic or renal impairment
Adverse Reactions
- Bone marrow suppression (megaloblastic anemia, leukopenia, thrombocytopenia)
- Hypersensitivity reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis related to sulfonamide component)
- Gastrointestinal distress (nausea, vomiting, anorexia)
- Atrophic glossitis
Drug Interactions
- Folic acid antagonists (methotrexate, trimethoprim): increased risk of bone marrow suppression
- Lorazepam: concurrent use with pyrimethamine may cause severe hepatotoxicity
- Zidovudine: increased risk of hematologic toxicity and myelosuppression
Curated Content: Needs Vetting Before Put to Clinical Use