Pyrimethamine (Daraprim) was first reported therapeutically effective against malaria parasites in 1949.1 In 1952 the efficacy of pyrimethamine in destroying organisms of the genus Toxoplasma was demonstrated, but the toxoplasmacidal dose was found to be larger than the antimalarial dose.2 Although the drug is used with clinical benefit,3,4 little has been reported concerning the toxicity of pyrimethamine in the treatment of toxoplasmosis in man.
Pyrimethamine appears to act primarily as a metabolic antagonist in the folic acid pathway of nucleotide synthesis. Schmidt, in 1953, observed that when massive doses of pyrimethamine were administered to monkeys, an acute toxicity developed with convulsive seizures and death.5 Lower doses produced a chronic toxicity, characterized by granulocytopenia and lymphopenia, and depletion of the myeloid elements of the bone marrow. In rats treated with pyrimethamine both myelopoiesis and erythropoiesis were suppressed, and in dogs a moderate leucopenia developed.6 In an
KAUFMAN HE, GEISLER PH. The Hematologic Toxicity of Pyrimethamine (Daraprim) in Man. AMA Arch Ophthalmol. 1960;64(1):140-146. doi:10.1001/archopht.1960.01840010142016