Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CETAMIDE vs AZO GANTRISIN
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.
Sulfamethoxazole is a competitive inhibitor of dihydropteroate synthase, blocking bacterial folic acid synthesis. Phenazopyridine is an azo dye with local analgesic effects on urinary tract mucosa.
Urinary tract infections,Acute otitis media,Shigellosis,Pneumocystis jirovecii pneumonia,Traveler's diarrhea (off-label)
Urinary tract infections,Pain relief associated with lower urinary tract irritation,Pyelonephritis
500 mg orally every 6 hours; maximum 4 g per day.
AZO GANTRISIN (phenazopyridine 100 mg / sulfisoxazole 500 mg): 2 tablets orally 4 times daily for 2 days, then 1 tablet 4 times daily for up to 5 days.
6-8 hours; prolonged (up to 30 hours) in severe renal impairment (Cr Cl <30 m L/min).
Sulfamethoxazole: 9-12 hours (adults with normal renal function), prolonged to 20-50 hours in renal impairment; trimethoprim component: 8-11 hours. Clinical context: dosing interval adjusted based on Cr Cl.
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; phenazopyridine undergoes hepatic metabolism.
Primarily renal (85-90%) as unchanged drug; biliary/fecal (5-10%).
Renal: 70-100% (sulfamethoxazole and metabolites; 15-30% as unchanged drug; remainder as acetylated and glucuronide conjugates). Biliary/fecal: <3%.
20-25% bound to albumin.
Sulfamethoxazole: 65-70% bound to albumin; trimethoprim: 40-45% bound to albumin.
0.5-0.8 L/kg; indicates distribution into total body water.
Sulfamethoxazole: 0.2-0.3 L/kg (reflects distribution into extracellular fluid, not extensively tissue-bound); trimethoprim: 1-2 L/kg (higher due to lipophilicity, penetrates tissues including prostate and CSF). Clinical meaning: higher Vd of trimethoprim contributes to effective tissue concentrations.
Oral: 90-100% (well absorbed).
Oral: 85-95% for both components (tablets); suspension: ~90%.
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 50-80 m L/min: 1 tablet 3-4 times daily; Cr Cl 10-49 m L/min: 1 tablet 2-3 times daily; Cr Cl <10 m L/min: contraindicated.
Child-Pugh Class C: avoid use; Class A or B: no adjustment needed.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50% or extend interval; Child-Pugh C: contraindicated.
10-15 mg/kg orally every 6 hours; maximum 100 mg/kg/day.
Children 6-12 years: 0.5-1.5 teaspoons (2.5-7.5 m L) of suspension (equivalent to 75-225 mg sulfisoxazole and 15-45 mg phenazopyridine) orally 4 times daily; children >12 years: adult dose.
Consider dose reduction based on renal function; initial dose not to exceed 2 g per day.
Initiate at lower doses (e.g., 1 tablet 3 times daily) and monitor for renal function and CNS side effects; contraindicated if Cr Cl <50 m L/min.
Sulfonamides have been associated with fatal reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias.
Sulfonamides have been associated with severe reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Fatalities have occurred.
Increased risk of hypersensitivity reactions (SJS, TEN); hematologic toxicity (agranulocytosis, thrombocytopenia); hepatotoxicity; renal toxicity due to crystalluria; hemolytic anemia in G6PD-deficient patients; photosensitivity.
Risk of severe hypersensitivity reactions, blood dyscrasias, hepatotoxicity, and renal impairment. Use caution in patients with G6PD deficiency, hepatic impairment, or renal insufficiency. Phenazopyridine may cause orange-red discoloration of urine.
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 or phenazopyridine; severe hepatic or renal impairment; porphyria; G6PD deficiency; pregnancy at term; lactation; children < 12 years (due to phenazopyridine component).
No significant food interactions known. No dietary restrictions required.
Avoid acidic foods and beverages (e.g., citrus fruits, tomatoes, cola) as they may decrease the efficacy of sulfisoxazole by increasing urine acidity, which can reduce solubility and increase risk of crystalluria. Maintain adequate fluid intake; avoid alcohol. No other significant food interactions.
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: Associated with neural tube defects, cardiovascular anomalies, and oral clefts due to antifolate effect of trimethoprim. Second and third trimesters: Risk of kernicterus in newborn due to sulfonamide displacement of bilirubin from albumin, especially near term. Avoid use during pregnancy unless benefit outweighs risk.
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.
Sulfamethoxazole and trimethoprim are excreted into breast milk; M/P ratio not established. Avoid in nursing mothers with infants under 2 months of age due to risk of kernicterus. In older infants, caution if infant has G6PD deficiency or hyperbilirubinemia.
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.
No standard dose adjustment recommended for pregnancy; however, caution due to increased volume of distribution and renal clearance. Monitor for therapeutic efficacy and toxicity. Consider folate supplementation (5 mg folic acid daily) to mitigate antifolate effects.
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.
AZO GANTRISIN combines phenazopyridine (urinary analgesic) and sulfisoxazole (sulfonamide antibiotic). Phenazopyridine imparts a red-orange color to urine and may stain contact lenses. Sulfisoxazole is contraindicated in infants <2 months due to risk of kernicterus. Use with caution in patients with G6PD deficiency, sulfonamide allergy, or renal impairment. Monitor for crystalluria; ensure adequate hydration. Avoid concurrent use with methenamine due to increased risk of crystalluria.
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 this medication with a full glass of water and drink plenty of fluids throughout the day to prevent kidney stones.,Your urine may turn red-orange; this is harmless but may stain clothing or contact lenses.,Do not use for longer than 2 days unless directed by your doctor, as it only treats symptoms of UTI, not the infection.,Complete the full course of the sulfisoxazole component even if you feel better.,Avoid prolonged sun exposure; sulfonamides may cause photosensitivity. Use sunscreen.,Seek immediate medical attention if you develop skin rash, sore throat, fever, unusual bleeding, or bruising.
"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 AZO GANTRISIN, 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.. AZO GANTRISIN is a Sulfonamide Antibiotic that works by Sulfamethoxazole is a competitive inhibitor of dihydropteroate synthase, blocking bacterial folic acid synthesis. Phenazopyridine is an azo dye with local analgesic effects on urinary tract mucosa.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CETAMIDE and AZO GANTRISIN 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 AZO GANTRISIN is: AZO GANTRISIN (phenazopyridine 100 mg / sulfisoxazole 500 mg): 2 tablets orally 4 times daily for 2 days, then 1 tablet 4 times daily for up to 5 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 AZO GANTRISIN 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. AZO GANTRISIN is classified as Category C. Pregnancy Category D. First trimester: Associated with neural tube defects, cardiovascular anomalies, and oral clefts due to antifolate effect of trimethoprim. Second and third tri. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.