Pyrison

Indication
Acute malaria, Malaria prophylaxis, Toxoplasmosis
Administration
Should be taken with food.
Adult Dose
Oral Acute malaria Adult: As a single dose, in combination with a sulfonamide: 75 mg pyrimethamine with 1.5 g sulfadoxine. 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. 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 Dose
Oral Acute malaria 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. Prophylaxis of malaria 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. Congenital Toxoplasmosis >2 Months Old Loading dose: 2 mg/kg/day divided q12hr PO for 2 days Maintenance.: First 2-6 months old: 1 mg/kg PO qD for 2-6 months old; THEN remainder of 12 months old; 1 mg/kg PO 3 times/week Toxoplasmosis Loading dose: 2 mg/kg/d divided q12hr PO for 3 days Maintenance: 1 mg/kg PO qD for 4 weeks < 2 months old: Safety and efficacy not established _ Contraindication Hypersensitivity, resistant malaria, megaloblastic anaemia secondary to folate deficiency. Pregnancy and lactation. Mode of Action 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. Precaution 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. Lactation: enters breast milk, do not nurse _ Side Effect Rashes, macrocytic anaemia (high dose), leucopenia, thrombocytopenia, megaloblastic anaemia, pancytopenia, abdominal pain, vomiting, atrophic glossitis. Depression, Fever, Insomnia, Lightheadedness, Malaise, Seizures, Dermatitis, Erythema multiforme Potentially Fatal: Cutaneous reactions e.g. erythema multiforme and Stevens-Johnson syndrome and toxic epidermal necrolysis with sulfadoxine at large doses. _ Interaction 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.