Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BACTRIM PEDIATRIC vs INJECTAPAP
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) 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.
Acetaminophen is a centrally acting analgesic and antipyretic; its exact mechanism is not fully understood but involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system and modulation of descending serotonergic pathways. It does not have significant anti-inflammatory activity.
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)
Management of mild to moderate pain,Reduction of fever
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.
1 g intravenous every 6 hours or 650 mg intravenous every 4 hours; maximum 4 g per day.
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).
2-3 hours in adults; prolonged to 4-6 hours in neonates and patients with hepatic impairment.
Sulfamethoxazole is metabolized via acetylation and glucuronidation; trimethoprim is metabolized via oxidation (demethylation) and conjugation. CYP450 enzymes have minor involvement.
Primarily metabolized in the liver via conjugation (glucuronidation and sulfation) at therapeutic doses; a minor pathway via cytochrome P450 (CYP2E1, CYP1A2, and CYP3A4) produces a toxic metabolite (NAPQI) which is normally detoxified by glutathione.
Renal: sulfamethoxazole 85% (30% unchanged, rest as acetylated and glucuronide conjugates), trimethoprim 60-80% (10-30% unchanged). Fecal/biliary: <4%.
Renal: 2-5% unchanged; hepatic metabolism to glucuronide and sulfate conjugates, then renal excretion of metabolites. Biliary/fecal: minimal (<5%).
Sulfamethoxazole: 70% bound to albumin. Trimethoprim: 42-46% bound to albumin and alpha-1-acid glycoprotein.
10-25% bound to albumin at therapeutic concentrations.
Sulfamethoxazole: 0.15-0.3 L/kg. Trimethoprim: 1.3-2.0 L/kg indicating extensive tissue distribution.
0.8-1.0 L/kg; suggests distribution into total body water.
Oral: sulfamethoxazole 100%; trimethoprim 100% (both well absorbed).
IV: 100%; oral: 60-90% (first-pass metabolism); rectal: 30-50%.
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.
For GFR 30-60 m L/min: no adjustment; for GFR <30 m L/min: extend interval to every 8 hours; maximum 3 g per day.
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.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%, maximum 2 g per day; Child-Pugh C: contraindicated.
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.
For weight ≥50 kg: 1 g every 6 hours; for weight 10-50 kg: 15 mg/kg every 6 hours; for weight <10 kg: 7.5 mg/kg every 6 hours; all intravenous.
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.
No specific dose adjustment required; consider decreased hepatic function and concomitant medications; maximum 3 g per day for patients with risk factors for hepatotoxicity.
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.
Acetaminophen has been associated with cases of acute liver failure, hepatotoxicity is primarily due to overdose. Risk is increased in patients with underlying liver disease, chronic alcohol use, and those taking multiple acetaminophen-containing products.
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.
Risk of hepatotoxicity, especially with doses exceeding 4 g/day or in patients with liver impairment,Severe skin reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, and acute generalized exanthematous pustulosis,Hypersensitivity reactions,Use caution in patients with G6PD deficiency,Avoid use with other acetaminophen-containing products
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.
Hypersensitivity to acetaminophen or any component of the formulation
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.
No significant food interactions. However, concurrent ingestion of alcohol may increase risk of hepatotoxicity; avoid alcohol while on therapy.
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.
FDA Category C. Acetaminophen crosses the placenta. No evidence of teratogenicity in humans with standard doses. First trimester: limited data suggest no increased risk of major malformations. Second and third trimesters: chronic high-dose use may be associated with increased risk of childhood asthma and attention-deficit/hyperactivity disorder (ADHD). Overdose poses risk of maternal and fetal hepatotoxicity.
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.
Acetaminophen is excreted into breast milk in low concentrations (M/P ratio approximately 0.91-1.42). Reported infant dose is less than 2% of maternal weight-adjusted dose. Considered compatible with breastfeeding. Use lowest effective dose for shortest duration.
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.
No dose adjustment required for standard therapeutic use. Increased clearance in pregnancy may require shorter dosing intervals for pain control; consider maximum daily dose of 3 g/day instead of 4 g/day. Avoid prolonged use >48 hours without medical supervision.
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.
Acetaminophen injection is indicated for treatment of acute pain and fever. Use with caution in hepatic impairment. Avoid in patients with severe active liver disease. Monitor liver function tests with prolonged use. Do not exceed maximum daily dose (4 g/day in adults). Use the smallest effective dose for the shortest duration.
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.
Do not take more than the recommended dose. Overdose can cause severe liver damage.,Inform your healthcare provider if you have liver disease or drink alcohol regularly.,Check other medications for acetaminophen to avoid double dosing.,Seek immediate medical attention if you experience signs of liver injury (e.g., yellowing skin/eyes, dark urine, upper stomach pain).,This medication is administered by intravenous infusion; do not attempt self-administration.
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 PEDIATRIC vs INJECTAPAP, answered by our medical review team.
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.. INJECTAPAP is a Non-Opioid Analgesic that works by Acetaminophen is a centrally acting analgesic and antipyretic; its exact mechanism is not fully understood but involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system and modulation of descending serotonergic pathways. It does not have significant anti-inflammatory activity.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between BACTRIM PEDIATRIC and INJECTAPAP 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 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.. The standard adult dose of INJECTAPAP is: 1 g intravenous every 6 hours or 650 mg intravenous every 4 hours; maximum 4 g per day.. 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 PEDIATRIC and INJECTAPAP 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 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. INJECTAPAP is classified as Category C. FDA Category C. Acetaminophen crosses the placenta. No evidence of teratogenicity in humans with standard doses. First trimester: limited data suggest no increased risk of major ma. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.