Products
Pyrimethamine is commercially available in tablet form (Daraprim). The combination Fansidar (+ sulfadoxine) is off the market (malaria).
Structure and properties
Pyrimethamine (C12H13ClN4, Mr = 248.7 g/mol) is a diaminopyrimidine. It exists as a white crystalline powder or as colorless crystals and is practically insoluble in water.
Effects
Pyrimethamine (ATC P01BD01) has antiparasitic properties. It is an antiprotozoal agent effective against , plasmodia and . It interferes with protozoan folic acid metabolism by inhibiting the activation of folic acid through competitive inhibition of dihydrofolate reductase. Pyrimethamine has a long half-life of approximately 85 hours.
Indications
For treatment of toxoplasmosis in combination with a sulfonamide (e.g., sulfadiazine).
Dosage
According to the SmPC. Calcium folinate must be substituted during treatment to reduce the risk for bone marrow suppression. Sulfonamides should always be taken with adequate fluids.
Contraindications
- Hypersensitivity
For complete precautions, see the drug label.
Interactions
Drug interactions are possible with other folic acid antagonists, lorazepam, antacids, and kaolin.
Adverse effects
The most common possible adverse effects include anemia, blood count abnormalities (leukopenia, thrombocytopenia), vomiting, nausea, diarrhea, rash, and headache.
