Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
SULFAMETHOXAZOLE vs GANTRISIN
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.
Competitive inhibitor of dihydropteroate synthase, blocking para-aminobenzoic acid (PABA) incorporation into dihydropteroic acid, thereby inhibiting bacterial folate synthesis and nucleic acid production.
Urinary tract infections,Otitis media,Acute exacerbations of chronic bronchitis,Traveler's diarrhea,Pneumocystis jirovecii pneumonia treatment and prophylaxis,Toxoplasmosis
Acute, recurrent, or chronic urinary tract infections,Chancroid,Cholera,Inclusion conjunctivitis (trachoma),Malaria (in combination with pyrimethamine),Meningococcal meningitis prophylaxis,Nocardiosis,Otitis media (acute),Pneumocystis jirovecii pneumonia (in combination with trimethoprim),Prostatitis,Shigellosis,Toxoplasmosis (in combination with pyrimethamine),Upper respiratory tract infections,Severe acne,Rheumatic fever prophylaxis,Ulcerative colitis (adjunctive),Actinomycosis,Brucellosis,Coccidioidomycosis,Granuloma inguinale,Lymphogranuloma venereum,Soft tissue infections
800 mg sulfamethoxazole with 160 mg trimethoprim (DS tablet) orally every 12 hours.
2-4 g orally initially, then 4-8 g daily in 3-6 divided doses
9-11 hours in adults with normal renal function. Prolonged in renal impairment: up to 20-30 hours. In neonates, 6-12 hours.
7-12 hours (mean 10 hours); prolonged to 20-50 hours in renal impairment (Cr Cl <30 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 10-50 m L/min: 50% of dose; Cr Cl <10 m L/min: 25% of dose
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% and monitor; Child-Pugh C: avoid use due to risk of toxicity.
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.
FDA Pregnancy Category C. First trimester: risk of kernicterus in neonates, particularly if maternal bilirubin elevated; may cause hemolytic anemia in G6PD-deficient fetuses. Second/third trimester: increased risk of bilirubin displacement and kernicterus; caution in maternal sulfonamide hypersensitivity, rare reports of congenital malformations but not clearly attributable.
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 (sulfisoxazole) is a short-acting sulfonamide antibiotic. It is highly protein-bound and undergoes hepatic acetylation; acetylated metabolites may crystallize in urine. Ensure adequate hydration to prevent crystalluria. Monitor renal function and CBC due to risk of agranulocytosis. Contraindicated in infants <2 months and in pregnancy near term due to kernicterus risk.
"The metabolism of Sulfisoxazole can be decreased when combined with Sulfamethoxazole."
"The metabolism of Fluconazole can be decreased when combined with Sulfamethoxazole."
"The metabolism of Clotrimazole can be decreased when combined with Sulfamethoxazole."
No interactions on record
Common clinical questions about SULFAMETHOXAZOLE vs GANTRISIN, 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 is a Sulfonamide Antibiotic that works by Competitive inhibitor of dihydropteroate synthase, blocking para-aminobenzoic acid (PABA) incorporation into dihydropteroic acid, thereby inhibiting bacterial folate synthesis and nucleic acid production.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between SULFAMETHOXAZOLE and GANTRISIN 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 is: 2-4 g orally initially, then 4-8 g daily in 3-6 divided doses. 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 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 is classified as Category C. FDA Pregnancy Category C. First trimester: risk of kernicterus in neonates, particularly if maternal bilirubin elevated; may cause hemolytic anemia in G6PD-deficient fetuses. Secon. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.
Primarily hepatic via N4-acetylation and glucuronidation; major metabolite is N4-acetylsulfisoxazole.
Primarily renal; ~80-90% excreted unchanged in urine, with 15-30% as acetylated metabolite. Biliary/fecal <5%.
Renal: 70% as unchanged drug; hepatic metabolism: 30% as acetylated metabolites; biliary: <3%
~65-70% bound, primarily to albumin.
98-99% (primarily to albumin; also to alpha-1-acid glycoprotein)
0.15-0.3 L/kg (approx 10-20 L in adults), reflecting distribution primarily into extracellular fluid.
0.36 L/kg (range 0.28-0.44 L/kg); indicates distribution primarily in extracellular fluid
Oral: ~85-100% (well absorbed); no significant first-pass metabolism.
Oral: 85-100% (well absorbed); IM: 70-80% (due to depot effect)
No specific Child-Pugh based adjustments; use with caution in severe hepatic impairment
8 mg/kg sulfamethoxazole (with 1.6 mg/kg trimethoprim) orally every 12 hours; up to 1600 mg sulfamethoxazole per dose.
>2 months: 75 mg/kg initially, then 120-150 mg/kg/day in 4-6 divided doses, max 6 g/day
Adjust based on renal function; monitor for hypoglycemia, hyperkalemia, and folate deficiency; avoid in combination with ACE inhibitors and ARBs.
Consider age-related renal decline; adjust based on Cr Cl
None
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.
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).
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 alcohol as it may cause disulfiram-like reaction. No specific food interactions; maintain adequate fluid intake.
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 (Gantrisin) is excreted into breast milk; M/P ratio approx 0.1–0.4. Risk of kernicterus in preterm or jaundiced infants, or G6PD deficiency. Generally contraindicated during breastfeeding in first month of life; may use with caution in older healthy infants, but alternatives preferred.
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.
No specific dose adjustment for sulfisoxazole in pregnancy; however, due to increased renal clearance and volume of distribution in pregnancy, monitor therapeutic efficacy and adjust if needed; contraindicated at term (increased risk of kernicterus).
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 with a full glass of water and drink plenty of fluids throughout the day to prevent kidney problems.,Complete the full course of medication even if you feel better.,Avoid prolonged sun exposure and use sunscreen; this drug can cause photosensitivity.,Report any skin rash, sore throat, fever, unusual bleeding, or bruising immediately.,Do not take if you have a history of sulfa allergy.