Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
SULFAMETHOXAZOLE vs GANTRISIN PEDIATRIC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: June 2026 · OpiCalc Medical Review Team
Displaces dihydropteroate synthetase from its substrate para-aminobenzoic acid (PABA), inhibiting bacterial folate synthesis. Bacteriostatic against susceptible organisms.
Sulfisoxazole is a competitive inhibitor of bacterial dihydropteroate synthase, preventing the incorporation of para-aminobenzoic acid (PABA) into dihydrofolate, thereby inhibiting bacterial folic acid synthesis.
Urinary tract infections,Otitis media,Acute exacerbations of chronic bronchitis,Traveler's diarrhea,Pneumocystis jirovecii pneumonia treatment and prophylaxis,Toxoplasmosis
FDA-labeled: Treatment of acute, recurrent or chronic urinary tract infections (primarily pyelonephritis, pyelitis, and cystitis) due to susceptible organisms (E. coli, Klebsiella, Enterobacter, Proteus, Morganella, and Pseudomonas); acute otitis media in children; inclusion conjunctivitis; nocardiosis; and toxoplasmosis (as adjunctive therapy with pyrimethamine).,Off-label: Prevention of recurrent otitis media; treatment of bacillary dysentery; and treatment of chancroid.
800 mg sulfamethoxazole with 160 mg trimethoprim (DS tablet) orally every 12 hours.
2-4 g initially, then 4-6 g/day in 3-6 divided doses orally, depending on severity. Alternatively, for sulfisoxazole (the active moiety), typical adult dose is 500 mg to 1 g orally every 6 hours. IM use: 50 mg/kg initially, then 100 mg/kg/day in divided doses every 6-8 hours. IV use: Not recommended in pediatric formulation.
9-11 hours in adults with normal renal function. Prolonged in renal impairment: up to 20-30 hours. In neonates, 6-12 hours.
Terminal elimination half-life is 6-12 hours (prolonged in renal impairment; up to 30 hours in patients with creatinine clearance <10 m L/min).
Primarily metabolized in the liver via N-acetylation by N-acetyltransferase 2 (NAT2) and glucuronidation. Minor metabolism via CYP450.
Cr Cl >30 m L/min: no adjustment; Cr Cl 15-30 m L/min: 50% dose every 24 hours; Cr Cl <15 m L/min: contraindicated.
Cr Cl >50 m L/min: no adjustment; Cr Cl 10-50 m L/min: administer every 12-24 hours; Cr Cl <10 m L/min: administer every 24-48 hours or avoid use due to risk of crystalluria. For hemodialysis: supplemental dose after dialysis.
Fatalities have occurred due to severe reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Use in pregnancy at term or in nursing mothers may cause kernicterus.
First trimester: Associated with increased risk of neural tube defects, cardiovascular anomalies, and cleft palate due to folate antagonism. Second/third trimester: Risk of kernicterus in neonates if used near term due to bilirubin displacement; avoid after 32 weeks gestation.
Sulfisoxazole (Gantrisin) is a sulfonamide antibiotic. First trimester: No evidence of teratogenicity in humans, but animal studies show cleft palate and skeletal anomalies at high doses. Second and third trimesters: Risk of kernicterus in neonates due to bilirubin displacement from albumin; avoid use near term.
Sulfamethoxazole is often combined with trimethoprim (co-trimoxazole) for synergy. Monitor for hypersensitivity reactions, especially in patients with sulfa allergies. Use with caution in patients with folate deficiency, G6PD deficiency, or renal impairment. Adjust dose in Cr Cl 15-30 m L/min; contraindicated if Cr Cl <15 m L/min. Avoid in infants <2 months due to risk of kernicterus. May potentiate warfarin, sulfonylureas, and phenytoin.
GANTRISIN PEDIATRIC (sulfisoxazole) is a sulfonamide antibiotic primarily used for urinary tract infections and otitis media in children. It is contraindicated in infants <2 months due to risk of kernicterus. Monitor for crystalluria, hematuria, and hypersensitivity reactions. Alkalinization of urine increases solubility and reduces crystalluria risk. Do not use with methenamine.
"Sulfamethoxazole may increase the hypoglycemic activities of Levomilnacipran."
"Sulfamethoxazole may increase the hypoglycemic activities of Desvenlafaxine."
"Sulfamethoxazole may increase the hypoglycemic activities of Alogliptin."
No interactions on record
Common clinical questions about SULFAMETHOXAZOLE vs GANTRISIN PEDIATRIC, answered by our medical review team.
SULFAMETHOXAZOLE is a Sulfonamide Antibiotic that works by Displaces dihydropteroate synthetase from its substrate para-aminobenzoic acid (PABA), inhibiting bacterial folate synthesis. Bacteriostatic against susceptible organisms.. GANTRISIN PEDIATRIC is a Sulfonamide Antibiotic that works by Sulfisoxazole is a competitive inhibitor of bacterial dihydropteroate synthase, preventing the incorporation of para-aminobenzoic acid (PABA) into dihydrofolate, thereby inhibiting bacterial folic acid synthesis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between SULFAMETHOXAZOLE and GANTRISIN PEDIATRIC depend on the specific clinical indication. These are both Sulfonamide Antibiotic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of SULFAMETHOXAZOLE is: 800 mg sulfamethoxazole with 160 mg trimethoprim (DS tablet) orally every 12 hours.. The standard adult dose of GANTRISIN PEDIATRIC is: 2-4 g initially, then 4-6 g/day in 3-6 divided doses orally, depending on severity. Alternatively, for sulfisoxazole (the active moiety), typical adult dose is 500 mg to 1 g orally every 6 hours. IM use: 50 mg/kg initially, then 100 mg/kg/day in divided doses every 6-8 hours. IV use: Not recommended in pediatric formulation.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between SULFAMETHOXAZOLE and GANTRISIN PEDIATRIC in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. SULFAMETHOXAZOLE is classified as Category D/X. First trimester: Associated with increased risk of neural tube defects, cardiovascular anomalies, and cleft palate due to folate antagonism. Second/third trimester: Risk of kernict. GANTRISIN PEDIATRIC is classified as Category C. Sulfisoxazole (Gantrisin) is a sulfonamide antibiotic. First trimester: No evidence of teratogenicity in humans, but animal studies show cleft palate and skeletal anomalies at high. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.
Sulfisoxazole is primarily metabolized via acetylation and glucuronidation in the liver; it can also undergo oxidation by cytochrome P450 enzymes. Approximately 70% of the drug is excreted renally as unchanged drug and metabolites.
Primarily renal; ~80-90% excreted unchanged in urine, with 15-30% as acetylated metabolite. Biliary/fecal <5%.
Primarily renal (70-100% as unchanged drug and acetylated metabolites) via glomerular filtration and tubular secretion; <10% fecal.
~65-70% bound, primarily to albumin.
50-60% bound to albumin.
0.15-0.3 L/kg (approx 10-20 L in adults), reflecting distribution primarily into extracellular fluid.
0.2-0.3 L/kg; distributes into extracellular fluid, CSF (30-80% of plasma concentration with inflamed meninges), and tissues.
Oral: ~85-100% (well absorbed); no significant first-pass metabolism.
Oral: ~70-100% (sulfisoxazole acetyl suspension yields equivalent systemic exposure to sulfisoxazole base).
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% and monitor; Child-Pugh C: avoid use due to risk of toxicity.
Child-Pugh A: no adjustment; Child-Pugh B: cautious use, dose reduction may be needed; Child-Pugh C: contraindicated or avoid use due to risk of hepatotoxicity.
8 mg/kg sulfamethoxazole (with 1.6 mg/kg trimethoprim) orally every 12 hours; up to 1600 mg sulfamethoxazole per dose.
Children ≥2 months: initial dose 75 mg/kg, then 150 mg/kg/day orally divided every 4-6 hours, not to exceed 6 g/day. For sulfisoxazole: 70 mg/kg loading dose, then 150 mg/kg/day divided every 4-6 hours. Contraindicated in infants <2 months unless used for congenital toxoplasmosis.
Adjust based on renal function; monitor for hypoglycemia, hyperkalemia, and folate deficiency; avoid in combination with ACE inhibitors and ARBs.
Use with caution due to age-related renal impairment. Start at lower end of dosing range; monitor renal function and adjust based on Cr Cl. Increased risk of crystalluria and hypersensitivity reactions; ensure adequate fluid intake.
Sulfonamides have been associated with severe hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Fatalities have occurred. Discontinue if rash or other serious adverse reactions occur.
Do not administer to patients with hypersensitivity to sulfonamides. Avoid use in patients with severe renal or hepatic impairment. Monitor for skin rashes, fever, pallor, or other signs of serious adverse reactions. Caution in patients with folate deficiency, G6PD deficiency, or porphyria. May cause photosensitivity.
Use with caution in patients with renal or hepatic impairment, G6PD deficiency (risk of hemolytic anemia), porphyria, or severe allergies; maintain adequate fluid intake to prevent crystalluria; monitor complete blood counts and urinalysis; avoid use in infants <2 months of age (except for congenital toxoplasmosis) due to risk of kernicterus.
Hypersensitivity to sulfonamides or any component. Patients with marked hepatic damage or severe renal insufficiency. Use in pregnancy at term and during lactation (risk of kernicterus). Infants less than 2 months of age (except for treatment of congenital toxoplasmosis).
Hypersensitivity to sulfonamides; infants <2 months of age (except for congenital toxoplasmosis); pregnant women at term; nursing mothers; patients with porphyria; concurrent use with methenamine (risk of crystalluria).
Avoid high-potassium foods (e.g., bananas, oranges, potatoes) if patient is on concurrent potassium-sparing diuretics or has renal impairment, as sulfamethoxazole may increase potassium levels. No significant food interactions otherwise, but maintain adequate hydration.
Avoid acidic foods and beverages (e.g., citrus juices, carbonated drinks) as they may decrease urine p H and increase risk of crystalluria. Maintain adequate hydration with water. No specific food-drug interactions reported.
Compatible with caution; low levels in breast milk (M/P ratio ~0.2-0.3). Potential risk of kernicterus in premature or hyperbilirubinemic neonates; monitor infant for jaundice.
Sulfisoxazole is excreted into breast milk. M/P ratio not established. Potential for kernicterus in jaundiced or G6PD-deficient infants; avoid breastfeeding during therapy. The American Academy of Pediatrics considers it compatible with caution in healthy full-term infants.
No dose adjustment required for sulfamethoxazole component alone; however, sulfamethoxazole is used in fixed combination with trimethoprim, and pharmacokinetic changes in pregnancy (increased volume of distribution, increased renal clearance) may necessitate monitoring, but standard dosing is typically unchanged.
Pregnancy may alter pharmacokinetics of sulfonamides; increased renal clearance may reduce serum levels. Therapeutic drug monitoring not standard; adjust dose based on clinical response and infection severity. Avoid use during third trimester.
Take with a full glass of water to prevent crystalluria and maintain adequate fluid intake.,Complete the full course even if symptoms improve to prevent resistance.,Avoid prolonged sun exposure; use sunscreen as photosensitivity may occur.,Report any rash, sore throat, fever, or unusual bleeding immediately.,Notify your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Do not take if you have a known allergy to sulfonamides or thiazide diuretics.
Take this medication with a full glass of water and drink plenty of fluids to prevent kidney stones.,Complete the full course even if symptoms improve.,Avoid prolonged sun exposure; use sunscreen as this drug may cause photosensitivity.,Report any rash, sore throat, fever, or unusual bleeding/bruising immediately.,Inform your doctor if you have kidney disease, G6PD deficiency, or are pregnant/breastfeeding.