Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AZO GANTANOL vs OFIRMEV
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Phenazopyridine is an azo dye with local analgesic effect on urinary tract mucosa via unknown mechanism; sulfamethoxazole is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis.
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 (UTIs) when sulfonamide therapy is indicated (FDA),Pain relief of urinary tract irritation (phenazopyridine component)
Management of mild to moderate pain,Management of moderate to severe pain with adjunctive opioid analgesics,Reduction of fever
AZO GANTANOL (phenazopyridine + sulfamethoxazole) is not a standard combination product. Assuming separate components: Sulfamethoxazole 800 mg and Trimethoprim 160 mg (as Bactrim DS) orally every 12 hours. For phenazopyridine: 200 mg orally three times daily after meals.
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 terminal half-life: 9-12 hours in adults with normal renal function (Cr Cl >80 m L/min); prolonged to 20-50 hours in CKD (Cr Cl <30 m L/min); phenazopyridine half-life: 9-11 hours
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 primarily metabolized by N-acetylation in the liver (N-acetyltransferase 2); phenazopyridine is metabolized in the liver via glucuronidation and sulfation.
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: 70% as sulfamethoxazole (30% acetylated), N5-acetylated metabolite accounts for 15%; fecal: 20% of dose excreted unchanged in bile; biliary: minor contribution (<5%)
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
Sulfamethoxazole: 65-70% bound to albumin; phenazopyridine: >99% bound (mainly to albumin)
10-25% bound to albumin at therapeutic concentrations.
Sulfamethoxazole: 0.21-0.28 L/kg (for a 70 kg person: ~15-20 L); phenazopyridine: 4.5-5.5 L/kg (extensive tissue binding, e.g., urinary tract)
0.8-1.0 L/kg. Indicates distribution into total body water.
Oral sulfamethoxazole: 85-95% (well absorbed); phenazopyridine: approximately 90% absorbed
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
Sulfamethoxazole/Trimethoprim: Cr Cl >30 m L/min: no adjustment; Cr Cl 15-30 m L/min: reduce standard dose by 50% or extend interval to 24 hours; Cr Cl <15 m L/min: contraindicated. Phenazopyridine: contraindicated in renal impairment.
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.
Sulfamethoxazole/Trimethoprim: Child-Pugh A: no adjustment; Child-Pugh B: use with caution, no specific dose reduction; Child-Pugh C: contraindicated (risk of hepatotoxicity). Phenazopyridine: cautious use in severe hepatic impairment.
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.
Sulfamethoxazole/Trimethoprim: 6-12 mg/kg/day of trimethoprim component divided every 12 hours; maximum 320 mg trimethoprim/day. Phenazopyridine: not recommended in children <12 years.
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).
Sulfamethoxazole/Trimethoprim: monitor renal function; reduce dose if Cr Cl <30 m L/min. Increased risk of hyperkalemia and sulfonamide-induced adverse effects. Phenazopyridine: cautious use due to potential renal impairment and CNS effects.
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.
Sulfonamides, including sulfamethoxazole, may cause severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and agranulocytosis.
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.
Risk of hypersensitivity reactions including SJS/TEN; blood dyscrasias (agranulocytosis, aplastic anemia); hepatotoxicity; renal impairment; photosensitivity; interference with urine glucose tests.
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 sulfonamides or phenazopyridine; porphyria; severe renal impairment (Cr Cl <30 m L/min); G6PD deficiency; infants <2 months; pregnancy at term; lactation.
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
Avoid foods high in vitamin K (e.g., leafy greens) as sulfamethoxazole may potentiate warfarin effects. Maintain adequate fluid intake; dehydration increases crystalluria risk. No specific food avoidance required beyond general hydration.
No known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
Phenazopyridine: No adequate studies; animal studies show no fetal harm but not conclusive. Sulfamethoxazole: First trimester – Possible increased risk of neural tube defects; second and third trimesters – Risk of kernicterus in neonate due to bilirubin displacement; avoid near term. Trimethoprim: First trimester – Folate antagonist, increased risk of neural tube defects and cardiovascular anomalies; second and third trimesters – No specific documented risks but theoretical folate antagonism.
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.
Phenazopyridine: Excreted in breast milk; significance unknown; use caution. Sulfamethoxazole: Excreted in breast milk; M/P ratio ~0.2-0.3; risk of kernicterus in jaundiced or G6PD-deficient infants; avoid in nursing mothers of ill or premature infants. Trimethoprim: Excreted in breast milk; M/P ratio ~0.8-1.0; considered compatible by AAP but monitor infant for folate deficiency.
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.
Pregnancy alters pharmacokinetics: Increased renal clearance may reduce sulfamethoxazole and trimethoprim levels; however, no dose adjustment is routinely recommended due to lack of data. Standard doses for urinary tract infection: one tablet (phenazopyridine 200 mg/sulfamethoxazole 400 mg/trimethoprim 80 mg) four times daily. Use lowest effective dose for shortest duration.
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.
AZO GANTANOL combines phenazopyridine (a urinary analgesic) with sulfamethoxazole (a sulfonamide antibiotic). Monitor for sulfonamide hypersensitivity reactions (e.g., Stevens-Johnson syndrome). Phenazopyridine discolors urine orange-red; advise patients to avoid confusion with hematuria. Adjust sulfamethoxazole dose in renal impairment (Cr Cl <30 m L/min contraindicated).
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 reduce risk of crystalluria.,Urine may turn orange-red; this is harmless and subsides after stopping the drug.,Complete full course even if symptoms improve; do not skip doses.,Avoid prolonged sun exposure; sulfonamides cause photosensitivity.,Report rash, fever, sore throat, or unusual bruising immediately.
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 AZO GANTANOL vs OFIRMEV, answered by our medical review team.
AZO GANTANOL is a Sulfonamide Antibiotic that works by Phenazopyridine is an azo dye with local analgesic effect on urinary tract mucosa via unknown mechanism; sulfamethoxazole is a sulfonamide antibiotic that inhibits bacterial dihydropteroate synthase, blocking folate synthesis.. 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 AZO GANTANOL 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 AZO GANTANOL is: AZO GANTANOL (phenazopyridine + sulfamethoxazole) is not a standard combination product. Assuming separate components: Sulfamethoxazole 800 mg and Trimethoprim 160 mg (as Bactrim DS) orally every 12 hours. For phenazopyridine: 200 mg orally three times daily after meals.. 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 AZO GANTANOL 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. AZO GANTANOL is classified as Category C. Phenazopyridine: No adequate studies; animal studies show no fetal harm but not conclusive. Sulfamethoxazole: First trimester – Possible increased risk of neural tube defects; seco. 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.