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ANTIPARASITIC PRODUCTS, INSECTICIDES AND REPELLENTS › ANTIPROTOZOALS › ANTIMALARIALS › Diaminopyrimidines
pyrimethamine
P01BD01
Adult Dosing
- Toxoplasmosis: 50-75 mg daily with a sulfonamide and leucovorin
- Malaria prophylaxis: 25 mg once weekly
Pediatric Dosing
- Toxoplasmosis (infants/children): 2 mg/kg/day divided every 12-24 hours for 3 days, then 1 mg/kg/day with a sulfonamide and leucovorin
- Malaria prophylaxis: Age-dependent weekly dosing (e.g., 6.25 mg to 25 mg weekly)
Indications
- Treatment of toxoplasmosis in combination with a sulfonamide
- Chemoprophylaxis of malaria
Mechanism of Action
- Inhibits parasitic dihydrofolate reductase (DHFR), interfering with folic acid synthesis and nucleic acid production
Contraindications
- Documented hypersensitivity to pyrimethamine
- Megaloblastic anemia due to folate deficiency
- Certain severe hepatic or renal dysfunctions (relative)
Adverse Reactions
- Bone marrow suppression (megaloblastic anemia, leukopenia, thrombocytopenia)
- Hypersensitivity reactions (rash, erythema multiforme, Stevens-Johnson syndrome)
- Gastrointestinal distress (anorexia, nausea, vomiting)
- Atrophic glossitis, CNS toxicity (seizures, ataxia at high doses)
Drug Interactions
- Folic acid antagonists (methotrexate, trimethoprim): increased risk of bone marrow suppression
- Lorazepam: increased risk of hepatotoxicity
- Zidovudine: additive myelosuppression
Curated Content: Needs Vetting Before Put to Clinical Use