Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
GANTANOL vs AZO GANTANOL
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 sulfonamide that inhibits bacterial dihydropteroate synthase, preventing folate synthesis. Trimethoprim inhibits bacterial dihydrofolate reductase, blocking tetrahydrofolate production. The combination produces sequential blockade of folate metabolism, leading to bactericidal activity.
Phenazopyridine is an azo dye with local analgesic effect on urinary tract mucosa via unknown mechanism; sulfamethoxazole is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis.
Urinary tract infections,Acute otitis media,Acute exacerbations of chronic bronchitis,Traveler's diarrhea,Pneumocystis jirovecii pneumonia (treatment and prophylaxis),Toxoplasmosis (prophylaxis in immunocompromised patients),Shigellosis,Nocardiosis
Urinary tract infections (UTIs) when sulfonamide therapy is indicated (FDA),Pain relief of urinary tract irritation (phenazopyridine component)
800 mg orally every 12 hours for 5-7 days.
AZO GANTANOL (phenazopyridine + sulfamethoxazole) is not a standard combination product. Assuming separate components: Sulfamethoxazole 800 mg and Trimethoprim 160 mg (as Bactrim DS) orally every 12 hours. For phenazopyridine: 200 mg orally three times daily after meals.
Terminal elimination half-life: 8-12 hours in healthy adults; prolonged in renal impairment (up to 24-36 hours in Cr Cl <30 m L/min).
Sulfamethoxazole terminal half-life: 9-12 hours in adults with normal renal function (Cr Cl >80 m L/min); prolonged to 20-50 hours in CKD (Cr Cl <30 m L/min); phenazopyridine half-life: 9-11 hours
Sulfamethoxazole is metabolized primarily by N-acetylation and glucuronidation. Trimethoprim undergoes O-demethylation and oxidative metabolism. Both are excreted renally.
Sulfamethoxazole is primarily metabolized by N-acetylation in the liver (N-acetyltransferase 2); phenazopyridine is metabolized in the liver via glucuronidation and sulfation.
Renal: 70% as unchanged drug; hepatic metabolism: 20% (glucuronidation); fecal: 10%.
Renal: 70% as sulfamethoxazole (30% acetylated), N5-acetylated metabolite accounts for 15%; fecal: 20% of dose excreted unchanged in bile; biliary: minor contribution (<5%)
85-90% primarily to albumin.
Sulfamethoxazole: 65-70% bound to albumin; phenazopyridine: >99% bound (mainly to albumin)
0.15-0.3 L/kg; indicates limited extravascular distribution, primarily confined to plasma and interstitial fluid.
Sulfamethoxazole: 0.21-0.28 L/kg (for a 70 kg person: ~15-20 L); phenazopyridine: 4.5-5.5 L/kg (extensive tissue binding, e.g., urinary tract)
Oral: 90-95%; Intravenous: 100%.
Oral sulfamethoxazole: 85-95% (well absorbed); phenazopyridine: approximately 90% absorbed
Cr Cl 30-60 m L/min: 800 mg every 24 hours. Cr Cl 15-29 m L/min: 800 mg every 48 hours. Cr Cl <15 m L/min or hemodialysis: 800 mg every 48-72 hours.
Sulfamethoxazole/Trimethoprim: Cr Cl >30 m L/min: no adjustment; Cr Cl 15-30 m L/min: reduce standard dose by 50% or extend interval to 24 hours; Cr Cl <15 m L/min: contraindicated. Phenazopyridine: contraindicated in renal impairment.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 50%. Child-Pugh Class C: use contraindicated.
Sulfamethoxazole/Trimethoprim: Child-Pugh A: no adjustment; Child-Pugh B: use with caution, no specific dose reduction; Child-Pugh C: contraindicated (risk of hepatotoxicity). Phenazopyridine: cautious use in severe hepatic impairment.
15 mg/kg orally every 6 hours for children 2 months to 12 years; maximum 2 g/day.
Sulfamethoxazole/Trimethoprim: 6-12 mg/kg/day of trimethoprim component divided every 12 hours; maximum 320 mg trimethoprim/day. Phenazopyridine: not recommended in children <12 years.
Use with caution; start at 400 mg every 12 hours due to age-related renal decline. Monitor for toxicity.
Sulfamethoxazole/Trimethoprim: monitor renal function; reduce dose if Cr Cl <30 m L/min. Increased risk of hyperkalemia and sulfonamide-induced adverse effects. Phenazopyridine: cautious use due to potential renal impairment and CNS effects.
Fatal hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, and hepatic necrosis have occurred. Also associated with fatal hematologic toxicities (e.g., agranulocytosis, aplastic anemia). Coadministration with methotrexate increases risk of megaloblastic anemia.
Sulfonamides, including sulfamethoxazole, may cause severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and agranulocytosis.
Hypersensitivity and skin reactions (discontinue at first sign of rash). Hemolysis in G6PD-deficient patients. Risk of hepatotoxicity, including cholestatic jaundice and hepatic necrosis. Photosensitivity. Severe renal and hepatic impairment. Use caution in elderly, folate-deficient patients, and those with megaloblastic anemia. Possible hyperkalemia with high-dose treatment in renal impairment.
Risk of hypersensitivity reactions including SJS/TEN; blood dyscrasias (agranulocytosis, aplastic anemia); hepatotoxicity; renal impairment; photosensitivity; interference with urine glucose tests.
Hypersensitivity to sulfonamides, trimethoprim, or any component. History of drug-induced hypersensitivity reactions. Severe hepatic impairment. Severe renal impairment (Cr Cl <15 m L/min) not on dialysis. Megaloblastic anemia due to folate deficiency. Pregnancy (especially first trimester) and lactation (near term). Concurrent use with dofetilide.
Hypersensitivity to sulfonamides or phenazopyridine; porphyria; severe renal impairment (Cr Cl <30 m L/min); G6PD deficiency; infants <2 months; pregnancy at term; lactation.
Avoid alcohol during and for 3 days after therapy. Limit high-potassium foods if using high doses. Take with food to reduce GI upset.
Avoid foods high in vitamin K (e.g., leafy greens) as sulfamethoxazole may potentiate warfarin effects. Maintain adequate fluid intake; dehydration increases crystalluria risk. No specific food avoidance required beyond general hydration.
First trimester: Sulfonamides cross the placenta; risk of kernicterus in neonates if used near term. Animal studies show cleft palate and other anomalies at high doses. Human data insufficient; avoid use in first trimester unless benefit outweighs risk. Second/third trimester: Risk of neonatal jaundice and hemolytic anemia in G6PD deficiency; contraindicated after 38 weeks or near delivery due to kernicterus risk.
Phenazopyridine: No adequate studies; animal studies show no fetal harm but not conclusive. Sulfamethoxazole: First trimester – Possible increased risk of neural tube defects; second and third trimesters – Risk of kernicterus in neonate due to bilirubin displacement; avoid near term. Trimethoprim: First trimester – Folate antagonist, increased risk of neural tube defects and cardiovascular anomalies; second and third trimesters – No specific documented risks but theoretical folate antagonism.
Sulfamethoxazole is excreted into breast milk with a milk-to-plasma ratio of approximately 0.1. Based on limited data, not recommended in nursing mothers at term due to potential for neonatal kernicterus and hemolysis in G6PD-deficient infants; caution if used in preterm or jaundiced infants.
Phenazopyridine: Excreted in breast milk; significance unknown; use caution. Sulfamethoxazole: Excreted in breast milk; M/P ratio ~0.2-0.3; risk of kernicterus in jaundiced or G6PD-deficient infants; avoid in nursing mothers of ill or premature infants. Trimethoprim: Excreted in breast milk; M/P ratio ~0.8-1.0; considered compatible by AAP but monitor infant for folate deficiency.
No specific dose adjustments required for pregnancy alone. Consider increased clearance in pregnancy; monitor for therapeutic efficacy. Use lowest effective dose for shortest duration.
Pregnancy alters pharmacokinetics: Increased renal clearance may reduce sulfamethoxazole and trimethoprim levels; however, no dose adjustment is routinely recommended due to lack of data. Standard doses for urinary tract infection: one tablet (phenazopyridine 200 mg/sulfamethoxazole 400 mg/trimethoprim 80 mg) four times daily. Use lowest effective dose for shortest duration.
Gantanol (sulfamethoxazole) is a sulfonamide antibiotic often used in combination with trimethoprim (co-trimoxazole). Monitor for hypersensitivity reactions, especially in HIV patients. Adjust dose in renal impairment (Cr Cl <30 m L/min avoid). Hydrate to prevent crystalluria.
AZO GANTANOL combines phenazopyridine (a urinary analgesic) with sulfamethoxazole (a sulfonamide antibiotic). Monitor for sulfonamide hypersensitivity reactions (e.g., Stevens-Johnson syndrome). Phenazopyridine discolors urine orange-red; advise patients to avoid confusion with hematuria. Adjust sulfamethoxazole dose in renal impairment (Cr Cl <30 m L/min contraindicated).
Take with a full glass of water to prevent kidney stones.,Complete full course even if feeling better.,Avoid prolonged sun exposure; use sunscreen.,Report rash, fever, or sore throat immediately.,Do not use if allergic to sulfa drugs.
Take with a full glass of water to reduce risk of crystalluria.,Urine may turn orange-red; this is harmless and subsides after stopping the drug.,Complete full course even if symptoms improve; do not skip doses.,Avoid prolonged sun exposure; sulfonamides cause photosensitivity.,Report rash, fever, sore throat, or unusual bruising immediately.
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 GANTANOL vs AZO GANTANOL, answered by our medical review team.
GANTANOL is a Sulfonamide Antibiotic that works by Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydropteroate synthase, preventing folate synthesis. Trimethoprim inhibits bacterial dihydrofolate reductase, blocking tetrahydrofolate production. The combination produces sequential blockade of folate metabolism, leading to bactericidal activity.. AZO GANTANOL is a Sulfonamide Antibiotic that works by Phenazopyridine is an azo dye with local analgesic effect on urinary tract mucosa via unknown mechanism; sulfamethoxazole is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between GANTANOL and AZO GANTANOL 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 GANTANOL is: 800 mg orally every 12 hours for 5-7 days.. The standard adult dose of AZO GANTANOL is: AZO GANTANOL (phenazopyridine + sulfamethoxazole) is not a standard combination product. Assuming separate components: Sulfamethoxazole 800 mg and Trimethoprim 160 mg (as Bactrim DS) orally every 12 hours. For phenazopyridine: 200 mg orally three times daily after meals.. 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 GANTANOL and AZO GANTANOL 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. GANTANOL is classified as Category C. First trimester: Sulfonamides cross the placenta; risk of kernicterus in neonates if used near term. Animal studies show cleft palate and other anomalies at high doses. Human data . AZO GANTANOL is classified as Category C. Phenazopyridine: No adequate studies; animal studies show no fetal harm but not conclusive. Sulfamethoxazole: First trimester – Possible increased risk of neural tube defects; seco. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.