Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BACTRIM 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
BACTRIM (sulfamethoxazole/trimethoprim) inhibits bacterial folate synthesis. Sulfamethoxazole, a sulfonamide, inhibits dihydropteroate synthase, blocking PABA incorporation into dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, blocking conversion of dihydrofolic acid to tetrahydrofolic acid. Sequential blockade leads to bactericidal effect.
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,Shigellosis,Pneumocystis jirovecii pneumonia (treatment and prophylaxis),Toxoplasmosis (prophylaxis in immunocompromised),Nocardia infections,Methicillin-resistant Staphylococcus aureus (MRSA) infections (off-label)
Urinary tract infections (UTIs) when sulfonamide therapy is indicated (FDA),Pain relief of urinary tract irritation (phenazopyridine component)
1 DS tablet (160 mg TMP/800 mg SMX) orally every 12 hours for 10-14 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.
Sulfamethoxazole: 9-12 hours (prolonged in renal impairment); Trimethoprim: 8-10 hours (prolonged in renal impairment).
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 via N-acetylation in the liver (N-acetyltransferase-2, NAT2). Trimethoprim is metabolized via O-demethylation and alpha-hydroxylation by cytochrome P450 (CYP) enzymes, mainly CYP3A4, with minor contribution from CYP1A2 and CYP2C9.
Sulfamethoxazole is primarily metabolized by N-acetylation in the liver (N-acetyltransferase 2); phenazopyridine is metabolized in the liver via glucuronidation and sulfation.
Renal: sulfamethoxazole 20-30% unchanged, trimethoprim 40-70% unchanged; biliary/fecal: minimal (<10%) for both components.
Renal: 70% as sulfamethoxazole (30% acetylated), N5-acetylated metabolite accounts for 15%; fecal: 20% of dose excreted unchanged in bile; biliary: minor contribution (<5%)
Sulfamethoxazole: 70% bound to albumin; Trimethoprim: 30-40% bound to albumin.
Sulfamethoxazole: 65-70% bound to albumin; phenazopyridine: >99% bound (mainly to albumin)
Sulfamethoxazole: 0.21 L/kg; Trimethoprim: 1.8 L/kg (high tissue penetration including lung, kidney, and CSF).
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: 100% for both components (well absorbed).
Oral sulfamethoxazole: 85-95% (well absorbed); phenazopyridine: approximately 90% absorbed
Cr Cl >30 m L/min: No adjustment. Cr Cl 15-30 m L/min: 50% of standard dose. Cr Cl <15 m L/min: Contraindicated.
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: Use with caution, monitor for toxicity; consider dose reduction. Child-Pugh Class C: Avoid use.
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.
8 mg/kg/day TMP / 40 mg/kg/day SMX in two divided doses every 12 hours (max 320 mg TMP/1600 mg SMX per day). For PCP treatment: 15-20 mg/kg/day TMP / 75-100 mg/kg/day SMX in 3-4 divided doses.
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.
Initiate at lower doses; monitor renal function closely; contraindicated if Cr Cl <15 m L/min; adjust based on Cr Cl (see renal adjustment).
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.
BACTRIM may cause life-threatening severe adverse reactions including: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Discontinue at first sign of skin rash or any sign of adverse reaction. Hypersensitivity reactions can occur even with re-challenge of the same or other sulfonamides.
Sulfonamides, including sulfamethoxazole, may cause severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and agranulocytosis.
Fatal hypersensitivity reactions including SJS/TEN,Hepatotoxicity and hepatic failure,Blood dyscrasias (leukopenia, thrombocytopenia, agranulocytosis),Clostridioides difficile-associated diarrhea,Renal impairment: risk of crystalluria; maintain adequate fluid intake,Hyperkalemia in patients with renal disease or on potassium-sparing drugs,Megaloblastic anemia in folate-deficient patients,Elderly patients at increased risk of severe adverse reactions,Pregnancy: avoid near term due to risk of kernicterus (sulfonamide displaces bilirubin),Lactation: caution; sulfonamides excreted in breast milk,Photosensitivity
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 immune thrombocytopenia with sulfonamides or trimethoprim,Megaloblastic anemia due to folate deficiency,Severe hepatic or renal impairment (Cr Cl <15 m L/min),Pregnancy at term and during breastfeeding,Infants less than 2 months of age,Combination with dofetilide (increased risk of torsades de pointes)
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 high-potassium foods (bananas, oranges, potatoes) if hyperkalemia is a concern. No specific food interactions; however, maintain adequate fluid intake to prevent crystalluria.
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.
Pregnancy Category D. First trimester: Folate antagonist; associated with neural tube defects, cardiovascular malformations, and cleft palate. Second and third trimesters: Risk of kernicterus in neonates due to displacement of bilirubin from albumin; may cause hemolytic anemia in G6PD-deficient fetuses. Avoid use, especially near term.
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.
Both trimethoprim and sulfamethoxazole are excreted into breast milk. M/P ratio not well defined. Potential for kernicterus in jaundiced or G6PD-deficient infants; may interfere with folate metabolism. Caution advised; consider alternative therapy.
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.
Trimethoprim-sulfamethoxazole dose generally unchanged but avoid in first trimester and near term. If unavoidable, consider increased folate supplementation. No specific pharmacokinetic-driven dose adjustment established; monitor clinical response and adjust based on renal function.
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.
Bactrim is contraindicated in G6PD deficiency due to risk of hemolytic anemia. Monitor renal function and potassium levels, especially in elderly patients, as sulfamethoxazole can cause hyperkalemia. Use with caution in patients with folic acid deficiency or megaloblastic anemia. Avoid in pregnancy at term and in lactating women due to risk of kernicterus. For PCP treatment, high doses may require leucovorin rescue to prevent bone marrow suppression.
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 and stay well-hydrated to prevent crystalluria.,Complete the full course even if symptoms improve.,Report any signs of allergic reaction (rash, fever, sore throat) or severe skin reactions (blistering, peeling).,Avoid prolonged sun exposure; use sunscreen as photosensitivity may occur.,Do not take if you have a history of sulfa allergy or are pregnant/nursing without consulting doctor.
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 BACTRIM vs AZO GANTANOL, answered by our medical review team.
BACTRIM is a Sulfonamide Antibiotic Combination that works by BACTRIM (sulfamethoxazole/trimethoprim) inhibits bacterial folate synthesis. Sulfamethoxazole, a sulfonamide, inhibits dihydropteroate synthase, blocking PABA incorporation into dihydrofolic acid. Trimethoprim inhibits dihydrofolate reductase, blocking conversion of dihydrofolic acid to tetrahydrofolic acid. Sequential blockade leads to bactericidal effect.. 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 BACTRIM and AZO GANTANOL 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 BACTRIM is: 1 DS tablet (160 mg TMP/800 mg SMX) orally every 12 hours for 10-14 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 BACTRIM 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. BACTRIM is classified as Category C. Pregnancy Category D. First trimester: Folate antagonist; associated with neural tube defects, cardiovascular malformations, and cleft palate. Second and third trimesters: Risk of . 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.