SULFADIAZINE SODIUM
Clinical safety rating: avoid
May potentiate the effects of warfarin and sulfonylureas Can cause crystalluria and Stevens-Johnson syndrome.
Sulfadiazine is a competitive inhibitor of dihydropteroate synthase, blocking the conversion of p-aminobenzoic acid (PABA) to dihydropteroate, thereby inhibiting bacterial folic acid synthesis.
| Metabolism | Primarily hepatic metabolism via acetylation (N-acetyltransferase) and glucuronidation; also undergoes renal tubular reabsorption and elimination. |
| Excretion | Renal: 60-85% (via glomerular filtration and tubular secretion, with acetylation in liver reducing solubility and increasing crystalluria risk). Biliary/fecal: less than 15%. Unchanged drug and acetylated metabolites both excreted. |
| Half-life | Terminal elimination half-life: 10-20 hours (prolonged in renal impairment; context: requires dose adjustment in CrCl <50 mL/min). |
| Protein binding | 50-60% (primarily to albumin; decreased binding in uremia or hypoalbuminemia). |
| Volume of Distribution | 0.5-0.8 L/kg (extensive distribution into tissues, including CSF and placenta; Vd larger in neonates and children). |
| Bioavailability | Oral: 85-95% (well absorbed; food delays absorption but does not reduce extent). |
| Onset of Action | Intravenous: within 30 minutes (achievement of therapeutic CSF concentrations within 2-4 hours). Oral: 1-2 hours (peak concentration at 3-6 hours). |
| Duration of Action | Intravenous: 6-12 hours (dosing every 4-6 hours for systemic infections; with probenecid, duration may be extended). Oral: 6-8 hours (short half-life requires frequent dosing for sustained effect). |
| Molecular Weight | 250.28 |
2-4 g IV initially, then 1-2 g IV every 6-8 hours; oral dose: 2-4 g loading, then 1-2 g every 6 hours
| Dosage form | INJECTABLE |
| Renal impairment | CrCl >50 mL/min: no adjustment; CrCl 10-50 mL/min: administer every 8-12 hours; CrCl <10 mL/min: administer every 12-24 hours; hemodialysis: administer after dialysis |
| Liver impairment | No specific guidelines; use caution in severe hepatic impairment due to potential for reduced metabolism |
| Pediatric use | Neonates: 100 mg/kg IV once, then 50 mg/kg every 12 hours; Infants and children: 50-100 mg/kg IV loading dose, then 50-100 mg/kg/day divided every 6 hours; maximum 6 g/day |
| Geriatric use | Use with caution; monitor renal function and adjust dose based on creatinine clearance; avoid in patients with severe renal impairment |
| 1st trimester | Contraindicated due to risk of kernicterus and teratogenic effects (folate antagonism). Avoid use in the first trimester. |
| 2nd trimester | Use only if clearly needed; may cause hemolytic anemia in G6PD-deficient fetuses. Monitor bilirubin levels. |
| 3rd trimester | Contraindicated near term (after 36 weeks) due to risk of kernicterus in neonates. Avoid use in third trimester. |
Clinical note
May potentiate the effects of warfarin and sulfonylureas Can cause crystalluria and Stevens-Johnson syndrome.
| FDA category | Positive |
| Placental transfer | Sulfadiazine crosses the placenta readily, achieving fetal plasma levels comparable to maternal levels. Competes with bilirubin for albumin binding, increasing risk of kernicterus. |
| Breastfeeding |
â– FDA Black Box Warning
Fatalities have occurred due to severe reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias.
| Common Effects | other infections |
| Serious Effects |
Hypersensitivity to sulfonamides or any componentPorphyriaSevere hepatic or renal impairmentPregnancy at term (after 36 weeks)Infants <2 months of age (except for congenital toxoplasmosis)Breastfeeding in infants with G6PD deficiency or hyperbilirubinemia
| Precautions | Monitor for hypersensitivity reactions, severe cutaneous adverse reactions (SCARs), hematologic toxicity, renal impairment (crystalluria), and photosensitivity. Use with caution in G6PD deficiency, hepatic impairment, and during pregnancy (risk of kernicterus in neonates). |
| Food/Dietary |
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| Sulfadiazine is excreted into breast milk. Use caution in nursing mothers, especially if infant is premature, ill, or has G6PD deficiency. Avoid in infants with hyperbilirubinemia or jaundice. |
| Lactation Rating | L3 (Moderately Safe) - Use with caution; potential for adverse effects in infant, especially if G6PD deficiency or jaundice present. |
| Teratogenic Risk | Sulfadiazine sodium crosses the placenta. First trimester: Risk of teratogenicity not established; limited human data, animal studies show cleft palate at high doses. Second and third trimesters: Risk of kernicterus in neonates, especially near term, due to bilirubin displacement from albumin binding. Avoid use after 38 weeks gestation. |
| Fetal Monitoring | Monitor maternal CBC, renal function, and liver function tests. Assess for hypersensitivity reactions (Stevens-Johnson syndrome, hepatotoxicity). Fetal monitoring: Ultrasound for growth restriction if used long-term; avoid near term due to kernicterus risk. |
| Fertility Effects | No specific data on sulfadiazine sodium affecting fertility in humans. Animal studies have not shown impaired fertility at therapeutic doses. |
| Avoid high-acid foods (e.g., citrus juices, tomatoes) as they may increase crystalluria risk. Maintain high fluid intake; avoid alcohol and caffeine which can exacerbate dehydration. No specific food-drug interactions reported. |
| Clinical Pearls | Administer IV slowly over 30-60 minutes to minimize thrombophlebitis. Monitor renal function and urinalysis given poor solubility; alkalinize urine (pH >7.15) with sodium bicarbonate to prevent crystalluria. Maintain adequate hydration (≥2 L/day in adults). Therapeutic levels: 100-150 mg/L total sulfonamide. Contraindicated in infants <2 months (except congenital toxoplasmosis) and at term pregnancy (kernicterus risk). Causes hypoglycemia with sulfonylureas; enhances warfarin effect. |
| Patient Advice | Take with a full glass of water and drink plenty of fluids throughout the day to prevent kidney problems. · Avoid prolonged sun exposure and use sunscreen; this medicine increases sensitivity to sunlight. · Report immediately any skin rash, sore throat, fever, unusual bleeding, or yellowing of eyes/skin. · Do not use if you are pregnant, planning pregnancy, or breastfeeding without consulting your doctor. · Complete the full course of therapy as prescribed; do not skip doses or stop early. |