Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BACTRIM vs 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.
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.
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,Acute otitis media,Acute exacerbations of chronic bronchitis,Traveler's diarrhea,Pneumocystis jirovecii pneumonia (treatment and prophylaxis),Toxoplasmosis (prophylaxis in immunocompromised patients),Shigellosis,Nocardiosis
1 DS tablet (160 mg TMP/800 mg SMX) orally every 12 hours for 10-14 days.
800 mg orally every 12 hours for 5-7 days.
Sulfamethoxazole: 9-12 hours (prolonged in renal impairment); Trimethoprim: 8-10 hours (prolonged in renal impairment).
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 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 metabolized primarily by N-acetylation and glucuronidation. Trimethoprim undergoes O-demethylation and oxidative metabolism. Both are excreted renally.
Renal: sulfamethoxazole 20-30% unchanged, trimethoprim 40-70% unchanged; biliary/fecal: minimal (<10%) for both components.
Renal: 70% as unchanged drug; hepatic metabolism: 20% (glucuronidation); fecal: 10%.
Sulfamethoxazole: 70% bound to albumin; Trimethoprim: 30-40% bound to albumin.
85-90% primarily to albumin.
Sulfamethoxazole: 0.21 L/kg; Trimethoprim: 1.8 L/kg (high tissue penetration including lung, kidney, and CSF).
0.15-0.3 L/kg; indicates limited extravascular distribution, primarily confined to plasma and interstitial fluid.
Oral: 100% for both components (well absorbed).
Oral: 90-95%; Intravenous: 100%.
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.
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.
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.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 50%. Child-Pugh Class C: use contraindicated.
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.
15 mg/kg orally every 6 hours for children 2 months to 12 years; maximum 2 g/day.
Initiate at lower doses; monitor renal function closely; contraindicated if Cr Cl <15 m L/min; adjust based on Cr Cl (see renal adjustment).
Use with caution; start at 400 mg every 12 hours due to age-related renal decline. Monitor for toxicity.
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.
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.
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
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.
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, 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.
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 alcohol during and for 3 days after therapy. Limit high-potassium foods if using high doses. Take with food to reduce GI upset.
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.
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.
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.
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.
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.
No specific dose adjustments required for pregnancy alone. Consider increased clearance in pregnancy; monitor for therapeutic efficacy. 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.
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.
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 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.
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 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.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between BACTRIM and 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 GANTANOL is: 800 mg orally every 12 hours for 5-7 days.. 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 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 . 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 . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.