Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
BACTRIM PEDIATRIC vs OFIRMEV
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.
OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.
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,Management of moderate to severe pain with adjunctive opioid analgesics,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.
IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.
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).
Terminal elimination half-life is 2-3 hours in adults (2.5-3 hours in children). Clinically, dosing every 4-6 hours is needed to maintain therapeutic levels.
Sulfamethoxazole is metabolized via acetylation and glucuronidation; trimethoprim is metabolized via oxidation (demethylation) and conjugation. CYP450 enzymes have minor involvement.
Acetaminophen is primarily metabolized in the liver via conjugation with glucuronide (50-60%) and sulfate (20-30%). A minor amount is oxidized by cytochrome P450 (CYP2E1, CYP1A2, CYP3A4) to a toxic reactive metabolite (NAPQI), which is normally detoxified by glutathione. At toxic doses, glutathione is depleted, leading to NAPQI accumulation and hepatotoxicity.
Renal: sulfamethoxazole 85% (30% unchanged, rest as acetylated and glucuronide conjugates), trimethoprim 60-80% (10-30% unchanged). Fecal/biliary: <4%.
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
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. Indicates distribution into total body water.
Oral: sulfamethoxazole 100%; trimethoprim 100% (both well absorbed).
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
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.
No dose adjustment required for GFR ≥30 m L/min. For GFR <30 m L/min, extend dosing interval to every 8 hours; maximum daily dose 3000 mg.
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 Class A: No adjustment. Child-Pugh Class B: Reduce total daily dose by 50% (max 2000 mg/day). Child-Pugh Class C: Contraindicated or use with extreme caution; reduce dose to 50% of standard and extend interval to every 8 hours; maximum 2000 mg/day.
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.
Weight-based: <10 kg: 7.5 mg/kg/dose every 6 hours; 10-50 kg: 15 mg/kg/dose every 6 hours; >50 kg: 1000 mg every 6 hours or 650 mg every 4 hours. Maximum single dose: 15 mg/kg (up to 1000 mg); maximum daily dose: 75 mg/kg (up to 4000 mg).
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; consider reduced renal function. For Cr Cl <30 m L/min, extend interval to every 8 hours. Maximum daily dose: 3000 mg in frail elderly or with comorbidities.
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, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen at doses that exceed 4000 mg per day, and often involve more than one acetaminophen-containing product.
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 serious hepatotoxicity, especially with doses >4000 mg/day or in patients with underlying liver disease,Risk of severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis) – discontinue at first sign of rash,Risk of hypersensitivity reactions including anaphylaxis,Use caution in patients with severe hepatic impairment, active hepatic disease, or alcoholism,Avoid concurrent use of 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.
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
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 known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
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.
Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dose use in third trimester may be associated with preterm birth or low birth weight. Avoid prolonged use above recommended doses.
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 in breast milk in low concentrations (M/P ratio approximately 0.9-1.0). Considered compatible with breastfeeding; peak milk levels occur 1-2 hours after maternal dosing. 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 during pregnancy. Pharmacokinetic changes in pregnancy (increased volume of distribution, clearance) may lead to lower peak concentrations but standard dosing remains effective. Maximum single dose: 1 g; maximum daily dose: 4 g.
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.
OFIRMEV (acetaminophen) injection is an IV formulation of acetaminophen used for pain and fever management. It is a prodrug that requires no hepatic conversion, providing rapid onset of action. Monitor for hepatotoxicity; maximum daily dose is 4 grams in adults but lower in patients with hepatic impairment or malnutrition. Do not exceed 1 gram per dose. Hypotension and anaphylaxis have been reported. Not interchangeable with oral acetaminophen due to dose equivalency. Use with caution in patients with alcohol use disorder.
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.
OFIRMEV is given intravenously for pain or fever.,Do not take additional acetaminophen-containing medications while receiving OFIRMEV.,Report any signs of allergic reaction (rash, itching, swelling, trouble breathing).,Seek immediate medical attention if you experience severe abdominal pain, yellowing of skin or eyes, or dark urine.,Inform your healthcare provider about all medications you are taking, especially blood thinners.
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 OFIRMEV, 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.. OFIRMEV is a Non-opioid Analgesic that works by OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between BACTRIM PEDIATRIC and OFIRMEV 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 OFIRMEV is: IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.. 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 OFIRMEV 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. OFIRMEV is classified as Category C. Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dos. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.