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DRUG INTERACTIONS
Carcinogenesis, Mutagenesis, Impairment of Fertility
See WARNINGS section for information on carcinogenesis.
Mutagenesis
Pyrimethamine has been shown to be nonmutagenic in the following in vitro assays: the Ames point mutation assay, the Rec assay, and the E. coli WP2 assay. It was positive in the L5178Y/TK +/- mouse lymphoma assay in the absence of exogenous metabolic activation.6 Human blood lymphocytes cultured in vitro had structural chromosome aberrations induced by pyrimethamine.
In vivo, chromosomes analyzed from the bone marrow of rats dosed with pyrimethamine showed an increased number of structural and numerical aberrations.
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OVERDOSAGE
Following the ingestion of 300 mg or more of pyrimethamine, gastrointestinal and/or central nervous system signs may be present, including convulsions. The initial symptoms are usually gastrointestinal and may include abdominal pain, nausea, severe and repeated vomiting, possibly including hematemesis. Central nervous system toxicity may be manifest by initial excitability, generalized and prolonged convulsions which may be followed by respiratory depression, circulatory collapse, and death within a few hours. Neurological symptoms appear rapidly (30 minutes to 2 hours after drug ingestion), suggesting that in gross overdosage pyrimethamine has a direct toxic effect on the central nervous system.
The fatal dose is variable, with the smallest reported fatal single dose being 375 mg. There are, however, reports of pediatric patients who have recovered after taking 375 to 625 mg.
There is no specific antidote to acute pyrimethamine poisoning. In the event of overdosage, symptomatic and supportive measures should be employed. Gastric lavage is recommended and is effective if carried out very soon after drug ingestion. Parenteral diazepam may be used to control convulsions. Folinic acid should also be administered within 2 hours of drug ingestion to be most effective in counteracting the effects on the hematopoietic system (see WARNINGS). Due to the long half-life of pyrimethamine, daily monitoring of peripheral blood counts is recommended for up to several weeks after the overdose until normal hematologic values are restored.
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CONTRAINDICATIONS
Use of DARAPRIM is contraindicated in patients with known hypersensitivity to pyrimethamine or to any component of the formulation. Use of the drug is also contraindicated in patients with documented megaloblastic anemia due to folate deficiency.
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REFERENCES
- Eyles DE, Coleman N. Synergistic effect of sulfadiazine and Daraprim against experimental toxoplasmosis in the mouse. Antibiot Chemother. 1953;3:483-490.
- Jacobs L, Melton ML, Kaufman HE. Treatment of experimental ocular toxoplasmosis. Arch Ophthalmol. 1964;71:111-118.
- Jim RTS, Elizaga FV. Development of chronic granulocytic leukemia in a patient treated with pyrimethamine. Hawaii Med J. 1977;36:173-176.
- Sadoff L. Antimalarial drugs and Burkitt’s lymphoma. Lancet. 1973;2:1262-1263.
- Bahna L. Pyrimethamine. LARC Monogr Eval Carcinog Risk Chem. 1977;13:233-242.
- Clive D, Johnson KO, Spector JKS, et al. Validation and characterization of the L5178Y/TK +/- mouse lymphoma mutagen assay system. Mut Res. 1979;59:61-108.
Manufactured by
DSM Pharmaceuticals, Inc.
Greenville, NC 27834 for
GlaxoSmithKline
Research Triangle Park, NC 27709
©2003, GlaxoSmithKline. All rights reserved.
RL-1179
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