Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
SULFAPYRIDINE 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
Sulfapyridine is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis and thereby nucleic acid production. It also has anti-inflammatory and immunomodulatory effects in dermatologic conditions through unknown mechanisms.
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.
FDA-approved for dermatitis herpetiformis,Off-label: rheumatoid arthritis, inflammatory bowel disease, and other inflammatory dermatoses
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)
500 mg orally four times daily for initial treatment of dermatitis herpetiformis; maintenance dose 500 mg daily to 1.5 g daily in divided doses.
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.
Terminal elimination half-life: 6–10 hours (prolonged in renal impairment or slow acetylators); clinical context: requires dosing adjustment in renal insufficiency.
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).
Primarily hepatic via N-acetylation (N-acetyltransferase 2, NAT2) and glucuronidation; also undergoes hydroxylation. Excreted renally.
Sulfamethoxazole is metabolized via acetylation and glucuronidation; trimethoprim is metabolized via oxidation (demethylation) and conjugation. CYP450 enzymes have minor involvement.
Renal: approximately 70–80% (30% as unchanged drug, remainder as metabolites, primarily N4-acetylsulfapyridine); biliary/fecal: minor (<5%).
Renal: sulfamethoxazole 85% (30% unchanged, rest as acetylated and glucuronide conjugates), trimethoprim 60-80% (10-30% unchanged). Fecal/biliary: <4%.
Approximately 50–70% bound to albumin.
Sulfamethoxazole: 70% bound to albumin. Trimethoprim: 42-46% bound to albumin and alpha-1-acid glycoprotein.
Vd: 0.25–0.35 L/kg; clinical meaning: indicates distribution primarily into extracellular fluid, with limited tissue penetration.
Sulfamethoxazole: 0.15-0.3 L/kg. Trimethoprim: 1.3-2.0 L/kg indicating extensive tissue distribution.
Oral: 85–100% (well absorbed from gastrointestinal tract).
Oral: sulfamethoxazole 100%; trimethoprim 100% (both well absorbed).
Cr Cl 10-50 m L/min: administer every 8-12 hours. Cr Cl <10 m L/min: administer every 12-24 hours. Avoid use in severe renal impairment.
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 Class A: no adjustment. Child-Pugh Class B or C: avoid use due to potential accumulation and hepatotoxicity.
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.
Not recommended for children due to risk of kernicterus and adverse effects; safety not established.
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.
Start at lower end of dosing range; monitor renal function and for adverse effects; increased risk of sulfonamide-induced reactions.
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.
None.
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.
Severe hypersensitivity reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis), hematologic toxicity (agranulocytosis, hemolytic anemia in G6PD deficiency), hepatotoxicity, renal toxicity. Discontinue if rash or signs of hypersensitivity.
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, porphyria, severe hepatic or renal impairment, pregnancy (especially near term) and lactation, infants <2 months (except for congenital toxoplasmosis).
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.
No specific food interactions. Avoid alcohol as it may increase risk of adverse effects like disulfiram-like reaction. Ensure adequate hydration with water; acidic foods do not significantly affect absorption.
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.
First trimester: Sulfapyridine, a sulfonamide, crosses the placenta. There is a potential risk of neural tube defects and other malformations based on animal studies, but human data are limited. Second and third trimesters: Sulfonamides compete with bilirubin for albumin binding, increasing the risk of kernicterus in the neonate if administered near term. Use is generally avoided after 32 weeks gestation.
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.
Sulfapyridine is excreted into breast milk. The milk-to-plasma (M/P) ratio is approximately 0.45. Low levels are unlikely to cause adverse effects in healthy term infants, but caution is advised in premature, ill, or G6PD-deficient infants due to potential for hemolysis or kernicterus.
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 specific dose adjustments are recommended, but pharmacokinetic changes in pregnancy (increased volume of distribution and renal clearance) may reduce drug levels. Monitor therapeutic response and consider adjusting dose based on clinical indication and serum levels if available.
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.
Sulfapyridine is primarily used for dermatitis herpetiformis (DH). Dose adjustments needed in renal impairment. Monitor for hypersensitivity reactions, hemolytic anemia in G6PD deficiency, and crystalluria. Increase fluid intake to 2-3 L/day to prevent renal toxicity. Not first-line for other infections due to resistance.
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 with a full glass of water and maintain high fluid intake to prevent kidney stones.,Avoid prolonged sun exposure and use sunscreen, as sulfonamides can cause photosensitivity.,Report any skin rash, fever, sore throat, or unusual bleeding immediately.,Complete full course as prescribed, but do not use for viral infections.,Inform doctor if pregnant, breastfeeding, or have glucose-6-phosphate dehydrogenase deficiency.
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
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about SULFAPYRIDINE vs BACTRIM PEDIATRIC, answered by our medical review team.
SULFAPYRIDINE is a Sulfonamide Antibiotic that works by Sulfapyridine is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis and thereby nucleic acid production. It also has anti-inflammatory and immunomodulatory effects in dermatologic conditions through unknown mechanisms.. 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 SULFAPYRIDINE 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 SULFAPYRIDINE is: 500 mg orally four times daily for initial treatment of dermatitis herpetiformis; maintenance dose 500 mg daily to 1.5 g daily in divided doses.. 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 SULFAPYRIDINE 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. SULFAPYRIDINE is classified as Category C. First trimester: Sulfapyridine, a sulfonamide, crosses the placenta. There is a potential risk of neural tube defects and other malformations based on animal studies, but human dat. 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.