Adult: In combination with a sulfonamide or another appropriate antibacterial: Initially, 100 mg for 1-2 days then 25-50 mg daily. Alternatively, 50-75 mg daily in combination with a sulfonamide and leucovorin calcium, for 1-3 weeks depending on patient response and tolerability. Dose may be reduced by 50% and continued for 4-5 weeks. Child: In combination with a sulfonamide or another appropriate antibacterial: 5-6 years Initially, 2mg/kg (Max: 50 mg), then 1mg/kg (Max: 25 mg) daily; >6 years Same as adult dose.
What are the brands available for Pyrimethamine in India?
Monitor CBC and platelets twice weekly in high dose therapy; hepatic and renal function.
Overdosage
Symptoms: Severe and repeated vomiting, nausea, abdominal pain, convulsions, ataxia, tremor, and respiratory depression. Management: Symptomatic and supportive treatment. Maintain the airways and perform gastric lavage. May administer diazepam to control convulsions; calcium folinate for possible folinate deficiency.
Drug Interactions
May cause convulsion with methotrexate in patient with CNS leukaemia, and seizures with antimalarial drugs. Further depression of folate metabolism with co-trimoxazole, proguanil, zidovudine, or cytostatic agents (e.g. methotrexate). Decreased absorption with antacids and kaolin. Increased risk of hepatotoxicity with lorazepam. Potentially Fatal: May cause bone marrow aplasia with daunorubicin, cytosine arabinoside in patient with acute myeloid leukaemia.
Action
Description: Mechanism of Action: Pyrimethamine is an antiparasitic agent. It impairs the protein synthesis and nuclear division of susceptible parasites through the inhibition of the dihydrofolate reductase enzyme. Pharmacokinetics: Absorption: Almost completely absorbed from the gastrointestinal tract. Time to peak plasma concentration: 2-6 hours. Distribution: Mainly distributed in the kidneys, lungs, liver, and spleen. Crosses placenta and enters breast milk. Volume of distribution: 2.9 L/kg. Plasma protein binding: Approx 80-90%. Metabolism: Metabolised in the liver. Excretion: Via urine (16-32%). Elimination half-life: Approx 96 hours.
Chemical Structure
Pyrimethamine Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4993, Pyrimethamine. https://pubchem.ncbi.nlm.nih.gov/compound/Pyrimethamine. Accessed Oct. 27, 2020.
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