Tablet, 500 mg
Injection, 250 mg (sodium salt)

Sulfadiazine and sulfisoxazole are intermediate-acting sulfonamides with broad spectrum activity against a wide range of Gram-positive and Gram-negative organisms. They are readily absorbed from the gastrointestinal tract and widely distributed in the body. The serum half-life is 10-12 hours. After partial acetylation in the liver they are excreted in the urine.

Uses:
Secondary prevention of rheumatic fever.

Dosage:

Adults: 1 g daily in 2 divided doses.
Children: 150 mg/kg/day in 2 divided doses.

Contraindications: Hypersensitivity to sulfonamides; severe renal or hepatic function impairment; porphyria; first trimester pregnancy.

Precautions: The red blood cell count should be monitored regularly throughout therapy to detect signs of bone-marrow depression. Any patient suspected of being sensitive to sulfonamides should never receive them again. Presumptive signs include skin rashes and evidence of haemolysis such as dark urine and purpura.

Sulfadiazine is less soluble in urine than many other sulfonamides. High urinary output must be maintained and patients should be advised to drink 1.0-1.5 litres of alkaline water daily.

Use in pregnancy: Sulfadiazine is contraindicated during the first trimester. Administration of sulfonamides can induce severe hypersensitivity reactions in the mother. Their action in displacing bilirubin from protein-binding sites has given rise to concern. Based on data derived from premature neonates, sulfonamides may promote kernicterus. Although they readily cross the placental barrier there is no conclusive evidence that the fetus is at risk.

Adverse effects: Nausea, vomiting, diarrhoea and headache sometimes occur.

Sulfonamide-induced hypersensitivity reactions, although uncommon, may be severe. They include rare life-threatening cutaneous reactions such as erythema multiform (Stevens-Johnson syndrome) and toxic epidermal necrolysis. Crystalluria may result in dysuria, renal colic, haematuria and acute renal obstruction.

Other infrequent reactions include granulocytopenia, agranulocytosis, aplastic anaemia, thrombocytopenic purpura and toxic hepatitis. Occasionally, haemolysis may occur in individuals deficient in glucose-6-phosphate dehydrogenase.

Drug Interactions: Concomitant administration of other drugs that interfere with folic acid metabolism (other than pyrimethamine) should be avoided whenever possible.

Overdosage: Continuous forced diuresis may be beneficial and an alkaline urine should be maintained. Treatment is otherwise symptomatic.

Storage: Preparations should be stored protected from light.