Indications |
Oral Acute malaria Adult: As a single dose, in combination with a sulfonamide: 75 mg pyrimethamine with 1.5 g sulfadoxine. Child: 7-13 yr: 50 mg pyrimethamine with 1 g sulfadoxine; 1-6 yr: 25 mg pyrimethamine with 500 mg sulfadoxine; 5-11 mth: 12.5 mg pyrimethamine and 250 mg sulfadoxine. To be taken as a single dose, in combination with a sulfonamide. Oral Prophylaxis of malaria Adult: Pyrimethamine 25 mg as single dose once wkly. 1st dose should be taken 1-2 days before arrival in the endemic area, continue admin during stay and for 4-6 wk after leaving the area. Child: <4 yr: 6.25 mg once wkly; 4-10 yr: 12.5 mg once wkly; >10 yr: 25 mg once wkly. 1st dose should be taken 1-2 days before arrival in the endemic area, continue admin during stay and for 4-6 wk after leaving the area. Oral Toxoplasmosis Adult: 50-75 mg pyrimethamine daily with 1-4 g sulfadiazine daily. Continue at this dosage for 1-3 wk, depending on the patient's response and tolerance, then half the dosage and continue for another 4-5 wk. Child: 1 mg/kg daily 2-4 days then 0.5 mg/kg daily for another 4 wk with usual paediatric dose of sulfadiazine. |
Contraindications |
Hypersensitivity, resistant malaria, megaloblastic anaemia secondary to folate deficiency. Pregnancy and lactation. |
Warnings / Precautions |
Renal or hepatic impairment; folate deficiency; monitor blood and platelet counts every 2 wk with prolonged treatment and large doses. Discontinue use if skin reactions, sore throats or shortness of breath occurs. |
Adverse Reactions |
Rashes, macrocytic anaemia (high dose), leucopenia, thrombocytopenia, megaloblastic anaemia, pancytopenia, abdominal pain, vomiting, atrophic glossitis. Potentially Fatal: Cutaneous reactions e.g. erythema multiforme and Stevens-Johnson syndrome and toxic epidermal necrolysis with sulfadoxine at large doses. |
Drug Interactions |
Lorazepam may induce hepatotoxicity. Increased risk of bone marrow suppression when used with agents that have myelosuppressive properties e.g. proguanil, sulfonamides, zidovudine and cytostatic agents. Increased risk of serious pancytopenia and megaloblastic anaemia when used with co-trimoxazole or other sulfonamides. See Below for More pyrimethamine Drug Interactions |
Mechanism of Actions |
Pyrimethamine is a folic acid antagonist structurally similar to trimethoprim. It inhibits parasitic dihydrofolate reductase, thus inhibiting vital tetrahydrofolic acid synthesis. It is active against pre-erythrocytic forms and is also a slow-acting schizontocide. Onset: Approx 1 hr. Absorption: Almost completely absorbed. Distribution: 80-90% bound to plasma proteins. Crosses the placenta and passes into the breast milk. Metabolism: Metabolised in the liver. Excretion: Excreted via kidney. Half-life is about 4 days. |
Administration |
Should be taken with food. |
ATC Classification |
P01BD01 - pyrimethamine ; Belongs to the class of diaminopyrimidine antimalarials. |
Available As |
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Pyrimethamine
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Pyrimethamine Containing Brands
Pyrimethamine is used in following diseases
Drug - Drug Interactions of Pyrimethamine
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