A synergistic, long-acting, fixed-dose combination antibacterial agent belonging to the sulfonamide and diaminopyrimidine classes. It provides sequential dual blockade of the bacterial folate synthesis pathway, leading to bactericidal activity against a wide range of susceptible organisms. Its long half-life allows for less frequent dosing, improving patient compliance.
Adult: One tablet (Sulfamethopyrazine 400mg + Trimethoprim 80mg) once daily. For severe infections, initial dose may be two tablets on the first day, followed by one tablet daily.
Note: Administer orally with a full glass of water. Can be taken with or without food, but taking with food may reduce GI upset. Maintain adequate fluid intake (at least 2-3 liters daily) to prevent crystalluria. Complete the full prescribed course.
The combination acts synergistically via sequential inhibition of two consecutive enzymes in the bacterial folate biosynthesis pathway. Sulfamethopyrazine, a sulfonamide, is a structural analog of para-aminobenzoic acid (PABA). It competitively inhibits dihydropteroate synthase, preventing the incorporation of PABA into dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, the next enzyme in the pathway, preventing the conversion of dihydrofolic acid to tetrahydrofolic acid. This dual blockade depletes tetrahydrofolate, a crucial cofactor for bacterial DNA, RNA, and protein synthesis, leading to bactericidal effects.
Pregnancy: Category D (Indian/old FDA). Trimethoprim is a folate antagonist. Avoid in first trimester (teratogenic risk) and near term (risk of kernicterus). Use only if potential benefit justifies the potential fetal risk.
Driving: May cause dizziness or headache. Patients should not drive or operate machinery until they know how the medicine affects them.
| Warfarin | Increased anticoagulant effect, risk of bleeding | Major |
| Methotrexate | Increased methotrexate toxicity (bone marrow suppression, hepatotoxicity) | Major |
| Phenytoin | Increased phenytoin levels, risk of toxicity | Major |
| Sulfonylureas (e.g., Glipizide) | Enhanced hypoglycemic effect | Moderate |
| Cyclosporine | Increased risk of nephrotoxicity and reduced cyclosporine efficacy | Moderate |
| ACE Inhibitors (e.g., Ramipril) | Increased risk of hyperkalemia | Moderate |
| Thiazide Diuretics | Increased risk of thrombocytopenia | Moderate |
| Rifampicin | Increased metabolism of trimethoprim, reducing efficacy | Moderate |
Same composition (Sulfamethopyrazine (400mg) + Trimethoprim (80mg)), different brands: