1. Clinical Overview
Sulfadiazine is a short-acting sulfonamide antibiotic that acts as a competitive antagonist of para-aminobenzoic acid (PABA), inhibiting bacterial synthesis of dihydrofolic acid. It is primarily used in combination with pyrimethamine for the treatment of toxoplasmosis and as a component of silver sulfadiazine for burn wound prophylaxis. In India, its systemic use is limited due to the availability of newer antibiotics and the risk of severe adverse effects like Stevens-Johnson syndrome.
| Onset | Duration | Bioavailability |
|---|---|---|
| 2-4 hours | 6-12 hours | 70-100% |
2. Mechanism of Action
Sulfadiazine is a structural analogue of para-aminobenzoic acid (PABA). It competitively inhibits the bacterial enzyme dihydropteroate synthase. This prevents the incorporation of PABA into dihydrofolic acid, a precursor of tetrahydrofolic acid, which is essential for the synthesis of purines, thymidine, and ultimately bacterial DNA and RNA.
3. Indications & Uses
- Toxoplasmosis (in combination with pyrimethamine)
- Nocardiosis (as part of combination therapy)
- Rheumatic fever prophylaxis (in penicillin-allergic patients)
4. Dosage & Administration
Adult Dosage: For toxoplasmosis: 2-4 g initially, followed by 2-4 g daily in 4-6 divided doses (with pyrimethamine and folinic acid). For other infections: 2-4 g/day in 3-6 divided doses.
Administration: Take with or after food with a full glass of water. Maintain adequate fluid intake (at least 2-3 L/day) to prevent crystalluria. Do not crush or chew the tablet. Complete the full prescribed course.
5. Side Effects
Common side effects may include:
- Nausea, vomiting, anorexia
- Headache, dizziness
- Photosensitivity reaction
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin | Increased anticoagulant effect; risk of bleeding | Major |
| Methotrexate | Increased methotrexate toxicity (displacement from protein binding) | Major |
| Phenytoin | Increased phenytoin levels and toxicity | Major |
| Sulfonylureas (e.g., Glimepiride) | Enhanced hypoglycemic effect | Moderate |
| Cyclosporine | Decreased cyclosporine levels; risk of transplant rejection | Moderate |
| Pyrimethamine | Synergistic effect against Toxoplasma; increased risk of bone marrow suppression | Moderate (requires folinic acid) |
7. Patient Counselling
- DO take with plenty of water (8-10 glasses a day).
- DO complete the full course of therapy.
- DO use sunscreen and protective clothing to avoid photosensitivity.
- DO inform all your doctors you are taking this medicine.
- DONT take antacids containing magnesium/aluminum within 2 hours of dose.
- DONT take if you have a known sulfa allergy.
- DONT stop medication without consulting your doctor.
8. Toxicology & Storage
Overdose: Nausea, vomiting, dizziness, headache, drowsiness, unconsciousness. Crystalluria, hematuria, oliguria, anuria. Bone marrow depression (pancytopenia). Severe skin reactions.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep out of reach of children.