Pyrimethamine / Sulfadoxine

What it is and how it works

Sulfadoxine inhibits dihydropteroate synthase and pyrimethamine inhibits dihydrofolate reductase, sequentially blocking folate synthesis in Plasmodium parasites. Both components have long half-lives, allowing single-dose treatment.

Indications

Intermittent preventive treatment of malaria in pregnancy and seasonal malaria chemoprevention (with amodiaquine) in endemic areas; treatment of uncomplicated falciparum malaria in combination with artesunate where effective.

Dosage and administration (summary)

Taken orally as a single dose; for adults, 3 tablets (each 25 mg pyrimethamine/500 mg sulfadoxine), according to national malaria programme guidance.

Contraindications

Hypersensitivity to sulfonamides or pyrimethamine, severe hepatic or renal impairment, megaloblastic anaemia due to folate deficiency, and infants under 2 months; concurrent co-trimoxazole prophylaxis.

Warnings and precautions

Severe cutaneous reactions, including Stevens–Johnson syndrome and toxic epidermal necrolysis, may occur and are a reason for its restricted use; stop at the first sign of rash. Blood dyscrasias and haemolysis in G6PD deficiency may occur, and high-dose folic acid may reduce efficacy.

Pregnancy

Used for intermittent preventive treatment in the second and third trimesters under WHO guidance; avoid in the first trimester and near term.

Storage and supply

Store below 25 °C, protected from light.

Source: reference summary prepared from the EU SmPC/EPAR, BNF and WHO Model Formulary. The approved product information in Iran governs.