SULFADIAZINE

Clinical safety rating: avoid

Positive evidence of fetus risks but benefits may outweigh risks in some cases

How it works

Competitive inhibitor of dihydropteroate synthase, blocking the synthesis of folic acid in bacteria.

What the body does with it

Metabolism	Hepatic acetylation (N-acetyltransferase) and glucuronidation.
Excretion	Renal excretion of unchanged drug (50-70%) and acetylated metabolites; minor biliary/fecal (<5%)
Half-life	Terminal elimination half-life 10-20 hours (prolonged in renal impairment; may require dose adjustment)
Protein binding	50-70% bound to albumin
Volume of Distribution	0.6-1.0 L/kg (distributes widely, including CSF with inflamed meninges)
Bioavailability	Oral: 70-100% (well absorbed; food may reduce rate)
Onset of Action	Oral: 2-4 hours (time to therapeutic serum concentrations); IV: immediate
Duration of Action	12-24 hours (serum levels above MIC for susceptible organisms); prolonged with renal impairment

Classification & Brands

Dosing & administration

Oral: 2-4 g initially, then 1 g every 4-6 hours for mild to moderate infections; for severe infections, 4 g initially followed by 1.5 g every 4 hours. IV: Not available in IV form in the US; if using oral suspension, adjust accordingly.

Dosage form	TABLET
Renal impairment	CrCl >50 mL/min: standard dosing; CrCl 15-50 mL/min: administer 50% of normal dose at normal intervals or normal dose at extended intervals (every 12-24 hours); CrCl <15 mL/min: avoid use or administer 50% of normal dose every 24-48 hours; hemodialysis: administer after dialysis.
Liver impairment	Child-Pugh Class A: no adjustment necessary; Child-Pugh Class B and C: use with caution, consider dose reduction due to impaired metabolism, no specific guidelines; monitor liver function and adjust based on toxicity.
Pediatric use	Neonates (≥2 months): 75 mg/kg initially, then 150 mg/kg/day divided every 6 hours; maximum 6 g/day. Infants and Children (2 months to 12 years): 50-75 mg/kg initially (max 4 g), then 150 mg/kg/day divided every 4-6 hours (max 6 g/day).
Geriatric use	Elderly patients may have reduced renal function; start with lower doses (e.g., 500 mg every 6 hours) and titrate based on renal function and response; monitor for hypersensitivity and renal toxicity.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

May potentiate the effects of warfarin and sulfonylureas Can cause crystalluria and Stevens-Johnson syndrome.

Breastfeeding

Sulfadiazine is excreted into breast milk (M/P ratio approximately 0.5-0.8). Risk of kernicterus in neonates, especially with G6PD deficiency or prematurity. Avoid use in breastfeeding mothers unless benefit clearly outweighs risk; monitor infant for jaundice, hemolysis, and diarrhea.

Teratogenic Risk

First trimester: Sulfadiazine crosses placenta. Risk of neural tube defects, cleft palate, and cardiovascular anomalies in animal studies; human data limited but potential risk due to folate antagonism. Second trimester: Avoid near term due to risk of kernicterus from bilirubin displacement. Third trimester: Contraindicated in pregnancy near term (after 38 weeks) and during labor due to risk of kernicterus in neonate.

Warnings & precautions

■ FDA Black Box Warning

None.

Side Effect Profile

Common Effects	other infections
Serious Effects

Absolute Contraindications

Hypersensitivity to sulfonamides, pregnancy at term and lactation, infants less than 2 months of age, severe renal or hepatic impairment, porphyria.

Clinical Precautions

Precautions

Severe hypersensitivity reactions (including Stevens-Johnson syndrome), hematologic toxicity (agranulocytosis, aplastic anemia), renal toxicity due to crystalluria, kernicterus in neonates, hemolytic anemia in G6PD deficiency, and photosensitivity.

Clinical Tips & Counseling

Drug interactions

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