Pyrimethamine + Sulfadiazine
Pyrimethamine and Sulfadiazine are administered together as a synergistic combination therapy. Pyrimethamine acts as a folic acid antagonist by inhibiting dihydrofolate reductase, while Sulfadiazine is a sulfonamide antibiotic that inhibits dihydropteroate synthase. Together, they block consecutive steps in the synthesis of folic acid in protozoa, effectively halting the replication of Toxoplasma gondii. Because both agents interfere with human folate pathways to some degree, co-administration of Leucovorin (folinic acid) is mandatory to prevent bone marrow toxicity.
Dosage by Body Weight
Dosages must be strictly calculated and monitored by a healthcare professional, usually a specialist in infectious diseases. For adults, the typical regimen begins with a loading dose of Pyrimethamine (50 to 100 mg), followed by 25 to 50 mg daily, combined with Sulfadiazine (1 g to 1.5 g every 6 hours), plus Leucovorin (10 to 25 mg daily). Pediatric dosing is weight-based, generally requiring Pyrimethamine (1 to 2 mg/kg/day) and Sulfadiazine (100 to 120 mg/kg/day divided into 2 to 4 daily doses). Maintenance of high fluid intake is crucial to prevent sulfadiazine-induced crystalluria.
- Body Weight
- Below 5 kg
- Dose
- Pyrimethamine: 1.25 to 2.5 mg once daily; Sulfadiazine: 100 to 150 mg every 12 hours
- Frequency
- Once daily (Pyrimethamine) / Twice daily (Sulfadiazine)
- Tracking Notes
- Must be prescribed with Leucovorin (folinic acid). Strictly monitor CBC and renal function.
- Body Weight
- 5-7 kg
- Dose
- Pyrimethamine: 2.5 to 5 mg once daily; Sulfadiazine: 250 mg every 12 hours
- Frequency
- Once daily (Pyrimethamine) / Twice daily (Sulfadiazine)
- Tracking Notes
- Ensure high fluid intake to prevent crystalluria. Monitor closely for skin rashes or hypersensitivity.
- Body Weight
- 8-10 kg
- Dose
- Pyrimethamine: 5 to 10 mg once daily; Sulfadiazine: 375 mg every 12 hours
- Frequency
- Once daily (Pyrimethamine) / Twice daily (Sulfadiazine)
- Tracking Notes
- Check complete blood count weekly to monitor for potential bone marrow suppression.
- Body Weight
- 11-15 kg
- Dose
- Pyrimethamine: 12.5 mg once daily; Sulfadiazine: 500 mg every 12 hours
- Frequency
- Once daily (Pyrimethamine) / Twice daily (Sulfadiazine)
- Tracking Notes
- Co-administration of Leucovorin (5-10 mg three times weekly) is required to prevent hematologic adverse effects.
- Body Weight
- 16-20 kg
- Dose
- Pyrimethamine: 12.5 to 25 mg once daily; Sulfadiazine: 750 mg every 12 hours
- Frequency
- Once daily (Pyrimethamine) / Twice daily (Sulfadiazine)
- Tracking Notes
- Ensure the child maintains excellent oral hydration throughout the therapy course.
| Body Weight | Dose | Frequency | Tracking Notes |
|---|---|---|---|
| Below 5 kg | Pyrimethamine: 1.25 to 2.5 mg once daily; Sulfadiazine: 100 to 150 mg every 12 hours | Once daily (Pyrimethamine) / Twice daily (Sulfadiazine) | Must be prescribed with Leucovorin (folinic acid). Strictly monitor CBC and renal function. |
| 5-7 kg | Pyrimethamine: 2.5 to 5 mg once daily; Sulfadiazine: 250 mg every 12 hours | Once daily (Pyrimethamine) / Twice daily (Sulfadiazine) | Ensure high fluid intake to prevent crystalluria. Monitor closely for skin rashes or hypersensitivity. |
| 8-10 kg | Pyrimethamine: 5 to 10 mg once daily; Sulfadiazine: 375 mg every 12 hours | Once daily (Pyrimethamine) / Twice daily (Sulfadiazine) | Check complete blood count weekly to monitor for potential bone marrow suppression. |
| 11-15 kg | Pyrimethamine: 12.5 mg once daily; Sulfadiazine: 500 mg every 12 hours | Once daily (Pyrimethamine) / Twice daily (Sulfadiazine) | Co-administration of Leucovorin (5-10 mg three times weekly) is required to prevent hematologic adverse effects. |
| 16-20 kg | Pyrimethamine: 12.5 to 25 mg once daily; Sulfadiazine: 750 mg every 12 hours | Once daily (Pyrimethamine) / Twice daily (Sulfadiazine) | Ensure the child maintains excellent oral hydration throughout the therapy course. |
Formulation
Purpose
First-line treatment for acute toxoplasmosis, including congenital toxoplasmosis, ocular toxoplasmosis, and toxoplasmic encephalitis in immunocompromised individuals.
Generic Name
Pyrimethamine + SulfadiazineBranded Drug Names
Pyrimethamine + Sulfadiazine is listed as a generic drug name. Common branded medicines that may contain the same active ingredient include:
Scheduled Drug
Yes. This medicine should be supplied or used only according to applicable prescription and regulatory requirements.