Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AZO GANTRISIN vs BACTRIM PEDIATRIC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Sulfamethoxazole is a competitive inhibitor of dihydropteroate synthase, blocking bacterial folic acid synthesis. Phenazopyridine is an azo dye with local analgesic effects on urinary tract mucosa.
Bactrim (sulfamethoxazole/trimethoprim) is a combination of two antifolate agents. Sulfamethoxazole inhibits dihydropteroate synthase, blocking the conversion of PABA to dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, preventing the reduction of dihydrofolic acid to tetrahydrofolic acid. Sequential blockade of folate synthesis leads to bacteriostasis.
Urinary tract infections,Pain relief associated with lower urinary tract irritation,Pyelonephritis
Urinary tract infections due to susceptible strains of E. coli, Klebsiella, Enterobacter, Morganella, Proteus, and Providencia,Acute otitis media in children,Acute exacerbations of chronic bronchitis in adults,Shigellosis,Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment,Traveler's diarrhea (FDA-approved),Toxoplasmosis (off-label),Nocardiosis (off-label),Chancroid (off-label),Brucellosis (off-label)
AZO GANTRISIN (phenazopyridine 100 mg / sulfisoxazole 500 mg): 2 tablets orally 4 times daily for 2 days, then 1 tablet 4 times daily for up to 5 days.
Oral: 160 mg trimethoprim / 800 mg sulfamethoxazole (one DS tablet) every 12 hours for 14 days. For Pneumocystis jirovecii pneumonia: 15-20 mg/kg/day of trimethoprim component divided every 6-8 hours.
Sulfamethoxazole: 9-12 hours (adults with normal renal function), prolonged to 20-50 hours in renal impairment; trimethoprim component: 8-11 hours. Clinical context: dosing interval adjusted based on Cr Cl.
Sulfamethoxazole: 9-12 hours (prolonged in renal impairment; up to 30 hours with Cr Cl <30 m L/min). Trimethoprim: 8-10 hours (prolonged to 20-30 hours in severe renal impairment).
Sulfamethoxazole is metabolized primarily via N-acetylation in the liver; phenazopyridine undergoes hepatic metabolism.
Sulfamethoxazole is metabolized via acetylation and glucuronidation; trimethoprim is metabolized via oxidation (demethylation) and conjugation. CYP450 enzymes have minor involvement.
Renal: 70-100% (sulfamethoxazole and metabolites; 15-30% as unchanged drug; remainder as acetylated and glucuronide conjugates). Biliary/fecal: <3%.
Renal: sulfamethoxazole 85% (30% unchanged, rest as acetylated and glucuronide conjugates), trimethoprim 60-80% (10-30% unchanged). Fecal/biliary: <4%.
Sulfamethoxazole: 65-70% bound to albumin; trimethoprim: 40-45% bound to albumin.
Sulfamethoxazole: 70% bound to albumin. Trimethoprim: 42-46% bound to albumin and alpha-1-acid glycoprotein.
Sulfamethoxazole: 0.2-0.3 L/kg (reflects distribution into extracellular fluid, not extensively tissue-bound); trimethoprim: 1-2 L/kg (higher due to lipophilicity, penetrates tissues including prostate and CSF). Clinical meaning: higher Vd of trimethoprim contributes to effective tissue concentrations.
Sulfamethoxazole: 0.15-0.3 L/kg. Trimethoprim: 1.3-2.0 L/kg indicating extensive tissue distribution.
Oral: 85-95% for both components (tablets); suspension: ~90%.
Oral: sulfamethoxazole 100%; trimethoprim 100% (both well absorbed).
Cr Cl 50-80 m L/min: 1 tablet 3-4 times daily; Cr Cl 10-49 m L/min: 1 tablet 2-3 times daily; Cr Cl <10 m L/min: contraindicated.
Cr Cl >30 m L/min: No adjustment. Cr Cl 15-30 m L/min: Reduce dose by 50% (e.g., one DS tablet every 24 hours). Cr Cl <15 m L/min: Contraindicated (unless with hemodialysis). For PJP: Cr Cl 15-29 m L/min: 15-20 mg/kg/day (trimethoprim) divided every 8 hours; Cr Cl <15 m L/min: Not recommended.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% or extend interval; Child-Pugh C: contraindicated.
Child-Pugh Class A: No adjustment. Child-Pugh Class B: Caution; consider reducing dose or monitoring liver function. Child-Pugh Class C: Avoid use due to potential hepatotoxicity and altered metabolism.
Children 6-12 years: 0.5-1.5 teaspoons (2.5-7.5 m L) of suspension (equivalent to 75-225 mg sulfisoxazole and 15-45 mg phenazopyridine) orally 4 times daily; children >12 years: adult dose.
Trimethoprim component dosing: 8 mg/kg/day divided every 12 hours for urinary tract infection or otitis media. For Pneumocystis jirovecii pneumonia (PJP) prophylaxis: 150 mg/m2/day of trimethoprim divided every 12 hours, given 3 times per week. For PJP treatment: 15-20 mg/kg/day of trimethoprim divided every 6-8 hours. Maximum daily dose: 960 mg trimethoprim.
Initiate at lower doses (e.g., 1 tablet 3 times daily) and monitor for renal function and CNS side effects; contraindicated if Cr Cl <50 m L/min.
Monitor renal function and adjust dose based on Cr Cl. Increased risk of hyperkalemia, hematologic toxicity, and adverse reactions. Consider starting at lower end of dosing range. Avoid in patients with Cr Cl <15 m L/min.
Sulfonamides have been associated with severe reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Fatalities have occurred.
Fatalities associated with sulfonamide hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias have been reported. Use in pregnant women at term and in nursing mothers may cause kernicterus.
Risk of severe hypersensitivity reactions, blood dyscrasias, hepatotoxicity, and renal impairment. Use caution in patients with G6PD deficiency, hepatic impairment, or renal insufficiency. Phenazopyridine may cause orange-red discoloration of urine.
Monitor for hypersensitivity reactions, blood dyscrasias, and hepatic injury. Caution in elderly, folate deficiency, impaired renal/hepatic function, G6PD deficiency, and severe allergies or bronchial asthma. Avoid in infants <2 months of age. Use with caution in patients with porphyria or thyroid dysfunction.
Hypersensitivity to sulfonamides or phenazopyridine; severe hepatic or renal impairment; porphyria; G6PD deficiency; pregnancy at term; lactation; children < 12 years (due to phenazopyridine component).
Hypersensitivity to any component (sulfonamides, trimethoprim), severe liver damage, marked renal impairment (Cr Cl <15 ml/min), megaloblastic anemia due to folate deficiency, pregnancy at term, nursing mothers, infants <2 months of age.
Avoid acidic foods and beverages (e.g., citrus fruits, tomatoes, cola) as they may decrease the efficacy of sulfisoxazole by increasing urine acidity, which can reduce solubility and increase risk of crystalluria. Maintain adequate fluid intake; avoid alcohol. No other significant food interactions.
Avoid high-potassium foods if at risk for hyperkalemia (e.g., bananas, oranges, salt substitutes). May reduce folic acid levels; encourage folate-rich foods (leafy greens, legumes). Take with food if GI upset occurs. Avoid alcohol due to disulfiram-like reaction.
Pregnancy Category D. First trimester: Associated with neural tube defects, cardiovascular anomalies, and oral clefts due to antifolate effect of trimethoprim. Second and third trimesters: Risk of kernicterus in newborn due to sulfonamide displacement of bilirubin from albumin, especially near term. Avoid use during pregnancy unless benefit outweighs risk.
First trimester: associated with increased risk of neural tube defects, cardiovascular malformations, and urinary tract anomalies due to folate antagonism (trimethoprim). Second and third trimesters: risk of kernicterus in the newborn due to sulfamethoxazole displacing bilirubin from albumin. Avoid during pregnancy, especially in the first and third trimesters.
Sulfamethoxazole and trimethoprim are excreted into breast milk; M/P ratio not established. Avoid in nursing mothers with infants under 2 months of age due to risk of kernicterus. In older infants, caution if infant has G6PD deficiency or hyperbilirubinemia.
Both components are excreted in breast milk. M/P ratio for sulfamethoxazole is approximately 0.3; for trimethoprim, approximately 1.1. Caution in infants with G6PD deficiency, hyperbilirubinemia, or jaundice. Consider alternatives, especially in preterm or sick infants.
No standard dose adjustment recommended for pregnancy; however, caution due to increased volume of distribution and renal clearance. Monitor for therapeutic efficacy and toxicity. Consider folate supplementation (5 mg folic acid daily) to mitigate antifolate effects.
Dose adjustments are not specifically recommended for pregnancy, but use with caution. Monitor serum drug levels if prolonged therapy. Avoid sulfamethoxazole near term due to risk of kernicterus. Ensure adequate folic acid supplementation (5 mg daily) to mitigate folate antagonism.
AZO GANTRISIN combines phenazopyridine (urinary analgesic) and sulfisoxazole (sulfonamide antibiotic). Phenazopyridine imparts a red-orange color to urine and may stain contact lenses. Sulfisoxazole is contraindicated in infants <2 months due to risk of kernicterus. Use with caution in patients with G6PD deficiency, sulfonamide allergy, or renal impairment. Monitor for crystalluria; ensure adequate hydration. Avoid concurrent use with methenamine due to increased risk of crystalluria.
Bactrim Pediatric (sulfamethoxazole/trimethoprim) is contraindicated in infants <2 months due to risk of kernicterus. Monitor for hyperkalemia, especially in elderly or renal impairment. Use with caution in folate deficiency; supplement folinic acid if prolonged therapy. Avoid in G6PD deficiency due to hemolytic anemia risk.
Take this medication with a full glass of water and drink plenty of fluids throughout the day to prevent kidney stones.,Your urine may turn red-orange; this is harmless but may stain clothing or contact lenses.,Do not use for longer than 2 days unless directed by your doctor, as it only treats symptoms of UTI, not the infection.,Complete the full course of the sulfisoxazole component even if you feel better.,Avoid prolonged sun exposure; sulfonamides may cause photosensitivity. Use sunscreen.,Seek immediate medical attention if you develop skin rash, sore throat, fever, unusual bleeding, or bruising.
Take with a full glass of water to prevent crystalluria.,Complete full course even if symptoms improve.,Avoid prolonged sun exposure; use sunscreen.,Report rash, fever, sore throat, or bruising immediately.,Do not use if allergic to sulfa drugs or thiazide diuretics.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about AZO GANTRISIN vs BACTRIM PEDIATRIC, answered by our medical review team.
AZO GANTRISIN is a Sulfonamide Antibiotic that works by Sulfamethoxazole is a competitive inhibitor of dihydropteroate synthase, blocking bacterial folic acid synthesis. Phenazopyridine is an azo dye with local analgesic effects on urinary tract mucosa.. BACTRIM PEDIATRIC is a Sulfonamide Antibiotic Combination that works by Bactrim (sulfamethoxazole/trimethoprim) is a combination of two antifolate agents. Sulfamethoxazole inhibits dihydropteroate synthase, blocking the conversion of PABA to dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, preventing the reduction of dihydrofolic acid to tetrahydrofolic acid. Sequential blockade of folate synthesis leads to bacteriostasis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between AZO GANTRISIN and BACTRIM PEDIATRIC depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of AZO GANTRISIN is: AZO GANTRISIN (phenazopyridine 100 mg / sulfisoxazole 500 mg): 2 tablets orally 4 times daily for 2 days, then 1 tablet 4 times daily for up to 5 days.. The standard adult dose of BACTRIM PEDIATRIC is: Oral: 160 mg trimethoprim / 800 mg sulfamethoxazole (one DS tablet) every 12 hours for 14 days. For Pneumocystis jirovecii pneumonia: 15-20 mg/kg/day of trimethoprim component divided every 6-8 hours.. 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 AZO GANTRISIN and BACTRIM 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. AZO GANTRISIN is classified as Category C. Pregnancy Category D. First trimester: Associated with neural tube defects, cardiovascular anomalies, and oral clefts due to antifolate effect of trimethoprim. Second and third tri. BACTRIM PEDIATRIC is classified as Category C. First trimester: associated with increased risk of neural tube defects, cardiovascular malformations, and urinary tract anomalies due to folate antagonism (trimethoprim). Second an. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.