Pirimetamiinisulfadiatsiinia

Pirimetamiinisulfadiatsiinia is a fixed‑dose combination medication containing pyrimethamine and sulfadiazine. It is used mainly to treat toxoplasmosis and certain other protozoal infections, usually as part of a regimen that also includes folinic acid (leucovorin) to reduce bone marrow toxicity.

Mechanism of action: Pyrimethamine inhibits dihydrofolate reductase in parasites, blocking thymidylate synthesis and DNA replication. Sulfadiazine inhibits dihydropteroate synthase, further impairing folate synthesis. Together they have a synergistic effect against Toxoplasma gondii and other susceptible organisms.

Indications: Acute toxoplasmic encephalitis and other manifestations of toxoplasmosis, particularly in patients with AIDS or other immunocompromised states; often used when first‑line therapy is indicated; sometimes employed as adjunctive therapy in severe cases.

Administration and monitoring: usually administered orally; duration depends on the infection. Leucovorin rescue is standard to mitigate folate antagonism. Patients should be monitored with regular blood counts and liver and kidney function tests, and observed for signs of hypersensitivity or rash.

Adverse effects and precautions: bone marrow suppression (anemia, thrombocytopenia), leukopenia, and/megaloblastic anemia due to folate antagonism; rash, fever, hypersensitivity reactions; hepatotoxicity; photosensitivity. Pregnancy is contraindicated in the first trimester. Sulfadiazine can cause hemolysis in G6PD deficiency. Caution is advised when used with other antifolate drugs.

Contraindications: hypersensitivity to sulfa drugs; severe folate deficiency; pregnancy in the first trimester; significant liver or kidney disease without appropriate dose adjustment.

Pharmacokinetics: both components are active after oral administration; sulfadiazine is largely protein-bound; hepatic metabolism with renal excretion. Interactions can occur with methotrexate, warfarin, and other folate‑antagonist therapies.