Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CETAMIDE vs BACTRIM
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
CETAMIDE is an antimicrobial combination of sulfadiazine (a sulfonamide) and trimethoprim. Sulfonamides inhibit dihydropteroate synthase, blocking folate synthesis; trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of folic acid metabolism.
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.
Urinary tract infections,Acute otitis media,Shigellosis,Pneumocystis jirovecii pneumonia,Traveler's diarrhea (off-label)
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)
500 mg orally every 6 hours; maximum 4 g per day.
1 DS tablet (160 mg TMP/800 mg SMX) orally every 12 hours for 10-14 days.
6-8 hours; prolonged (up to 30 hours) in severe renal impairment (Cr Cl <30 m L/min).
Sulfamethoxazole: 9-12 hours (prolonged in renal impairment); Trimethoprim: 8-10 hours (prolonged in renal impairment).
Sulfadiazine is metabolized via acetylation (N-acetyltransferase) and glucuronidation; trimethoprim is metabolized by oxidative pathways (N-oxidation, N-demethylation) and conjugated with glucuronic acid.
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.
Primarily renal (85-90%) as unchanged drug; biliary/fecal (5-10%).
Renal: sulfamethoxazole 20-30% unchanged, trimethoprim 40-70% unchanged; biliary/fecal: minimal (<10%) for both components.
20-25% bound to albumin.
Sulfamethoxazole: 70% bound to albumin; Trimethoprim: 30-40% bound to albumin.
0.5-0.8 L/kg; indicates distribution into total body water.
Sulfamethoxazole: 0.21 L/kg; Trimethoprim: 1.8 L/kg (high tissue penetration including lung, kidney, and CSF).
Oral: 90-100% (well absorbed).
Oral: 100% for both components (well absorbed).
Cr Cl 10-50 m L/min: 250 mg every 6 hours. Cr Cl <10 m L/min: 250 mg every 12 hours.
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.
Child-Pugh Class C: avoid use; Class A or B: no adjustment needed.
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.
10-15 mg/kg orally every 6 hours; maximum 100 mg/kg/day.
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.
Consider dose reduction based on renal function; initial dose not to exceed 2 g per 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).
Sulfonamides have been associated with fatal reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias.
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.
Increased risk of hypersensitivity reactions (SJS, TEN); hematologic toxicity (agranulocytosis, thrombocytopenia); hepatotoxicity; renal toxicity due to crystalluria; hemolytic anemia in G6PD-deficient patients; photosensitivity.
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 to sulfonamides or trimethoprim; severe hepatic or renal impairment; megaloblastic anemia due to folate deficiency; pregnancy (especially first trimester and near term); lactation; pediatric patients <2 months of age.
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)
No significant food interactions known. No dietary restrictions required.
Avoid high-potassium foods (bananas, oranges, potatoes) if hyperkalemia is a concern. No specific food interactions; however, maintain adequate fluid intake to prevent crystalluria.
Pregnancy category C. First trimester: Potential risk of neural tube defects based on animal studies. Second and third trimesters: Increased risk of premature closure of ductus arteriosus and oligohydramnios due to prostaglandin synthesis inhibition. Limited human data; avoid unless benefit outweighs risk.
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.
Excreted in breast milk in low quantities. M/P ratio not established. Potential risk of adverse effects in nursing infants (e.g., renal dysfunction, bleeding). Use with caution if alternative therapies are not available.
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.
No standard dosing adjustment during pregnancy. Increased renal clearance and volume of distribution in pregnancy may reduce efficacy; consider dose titration based on clinical response. Avoid in third trimester if possible.
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.
Cetamide (sulfacetamide sodium) is a topical ophthalmic sulfonamide used for bacterial conjunctivitis. Monitor for hypersensitivity, as cross-allergy with other sulfonamides may occur. Use with caution in patients with dry eye syndrome or corneal abrasions. Avoid prolonged use to prevent superinfection. Administer with clean hands and do not touch dropper tip to any surface.
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.
Wash hands before and after applying the eye drops.,Do not touch the dropper tip to your eye or any other surface.,Wait 5 minutes between different eye drops if using more than one type.,Complete the full course of treatment even if symptoms improve.,Do not wear contact lenses during treatment unless directed by your doctor.,Stop use and contact your doctor if you experience rash, itching, or swelling.,Keep the bottle tightly closed when not in use and store at room temperature.
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.
"Sulfacetamide may reduce the efficacy of picosulfuric acid, a stimulant laxative, through antibiotic-mediated disruption of the gut microbiota. The conversion of picosulfate to its active metabolite, BHPM, relies on bacterial azoreductase enzymes in the colon. Sulfacetamide's antibacterial activity against colonic flora can decrease this bioactivation, leading to diminished laxative effect and potential treatment failure for constipation or bowel preparation."
"The risk or severity of adverse effects can be increased when Methenamine is combined with Sulfacetamide."
"The risk or severity of adverse effects can be increased when Sulfacetamide is combined with Mecamylamine."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CETAMIDE vs BACTRIM, answered by our medical review team.
CETAMIDE is a Sulfonamide antibiotic that works by CETAMIDE is an antimicrobial combination of sulfadiazine (a sulfonamide) and trimethoprim. Sulfonamides inhibit dihydropteroate synthase, blocking folate synthesis; trimethoprim inhibits dihydrofolate reductase, producing sequential blockade of folic acid metabolism.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CETAMIDE and BACTRIM 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 CETAMIDE is: 500 mg orally every 6 hours; maximum 4 g per day.. The standard adult dose of BACTRIM is: 1 DS tablet (160 mg TMP/800 mg SMX) orally every 12 hours for 10-14 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 CETAMIDE and BACTRIM 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. CETAMIDE is classified as Category C. Pregnancy category C. First trimester: Potential risk of neural tube defects based on animal studies. Second and third trimesters: Increased risk of premature closure of ductus art. 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 . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.