Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALFENTA vs AZO GANTANOL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.
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.
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Urinary tract infections (UTIs) when sulfonamide therapy is indicated (FDA),Pain relief of urinary tract irritation (phenazopyridine component)
Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.
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.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
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
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Sulfamethoxazole is primarily metabolized by N-acetylation in the liver (N-acetyltransferase 2); phenazopyridine is metabolized in the liver via glucuronidation and sulfation.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Renal: 70% as sulfamethoxazole (30% acetylated), N5-acetylated metabolite accounts for 15%; fecal: 20% of dose excreted unchanged in bile; biliary: minor contribution (<5%)
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Sulfamethoxazole: 65-70% bound to albumin; phenazopyridine: >99% bound (mainly to albumin)
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
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)
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
Oral sulfamethoxazole: 85-95% (well absorbed); phenazopyridine: approximately 90% absorbed
No specific dose adjustment is recommended for renal impairment; however, alfentanil is primarily metabolized in the liver and its pharmacokinetics are not significantly altered in renal failure.
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.
In hepatic impairment (Child-Pugh class A, B, C): Reduce dose by 50% and titrate carefully due to prolonged elimination half-life. Consider lower initial doses and extended dosing intervals.
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.
Children (1-12 years): Induction of anesthesia: 10-20 mcg/kg IV; maintenance: 5-10 mcg/kg IV or infusion 0.5-1 mcg/kg/min. For neonates and infants: Dose individualization required; titrate to effect.
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.
Elderly patients (>65 years): Reduce initial dose by 30-50% and administer slowly. Due to decreased clearance and increased sensitivity, lower infusion rates (e.g., 0.3-0.5 mcg/kg/min) may be needed.
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.
Risk of respiratory depression, particularly in elderly or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death.
Sulfonamides, including sulfamethoxazole, may cause severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and agranulocytosis.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Risk of hypersensitivity reactions including SJS/TEN; blood dyscrasias (agranulocytosis, aplastic anemia); hepatotoxicity; renal impairment; photosensitivity; interference with urine glucose tests.
Hypersensitivity to alfentanil or any component; significant respiratory insufficiency; severe asthma; paralytic ileus; concurrent use of MAOIs (or within 14 days); acute or postoperative pain management in children (except for procedural sedation).
Hypersensitivity to sulfonamides or phenazopyridine; porphyria; severe renal impairment (Cr Cl <30 m L/min); G6PD deficiency; infants <2 months; pregnancy at term; lactation.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
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.
Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effects were observed at clinically relevant doses; however, high doses caused embryotoxicity and increased fetal mortality. Trimester-specific risks: First trimester - potential for minor malformations based on limited human data; second trimester - possible risk if used chronically; third trimester - prolonged use may lead to neonatal respiratory depression, withdrawal syndrome, or opioid dependence. Use only if benefits outweigh risks.
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.
Alfentanil is excreted into human breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. Estimated infant dose is <1% of maternal weight-adjusted dose, which is considered clinically insignificant. However, due to potential for neonatal opioid effects, caution is advised; monitor infant for drowsiness, respiratory depression, and feeding difficulties. Consider alternative analgesics with established safety profiles, such as acetaminophen or ibuprofen, for lactation.
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.
Pregnancy can alter pharmacokinetics of alfentanil. Increased plasma volume and distribution may require higher doses to achieve same effect, while decreased plasma protein binding may increase free fraction, potentiating effects. Alpha-1-acid glycoprotein levels change in pregnancy, affecting binding. In third trimester, clearance may be increased by up to 50% due to enhanced hepatic metabolism. Therefore, dose adjustments may be needed: consider starting at low dose and titrating to effect, with close monitoring. For intravenous administration, typical adult doses (5-20 μg/kg) may need adjustments; no standard pregnancy-specific dosing exists. Use the lowest effective dose for the shortest duration. In labor, avoid high doses prior to delivery due to risk of neonatal respiratory depression.
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.
Alfentanil is a potent, rapid-onset, short-acting opioid analgesic used primarily for induction and maintenance of anesthesia. Due to its high protein binding (90%) and rapid redistribution, it has a shorter duration of action than fentanyl, making it suitable for brief, painful procedures. It undergoes hepatic metabolism via CYP3A4, so concomitant use with CYP3A4 inhibitors like ketoconazole or erythromycin can prolong its effects. Use caution in elderly or hypovolemic patients due to increased risk of hypotension. Naloxone reverses respiratory depression. Alfentanil is 5-10 times less potent than fentanyl.
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).
This medication is given only by a healthcare professional in a hospital or surgical setting.,You may feel drowsy, dizzy, or nauseated after receiving this drug.,Report any difficulty breathing or slow heart rate to your healthcare provider immediately.,Avoid alcohol and sedatives for 24 hours after administration, as they can increase side effects.,Do not drive or operate machinery until the effects have fully worn off.
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.
"Propantheline, an anticholinergic agent, can competitively antagonize muscarinic acetylcholine receptors, potentially reducing gastrointestinal motility and secretion. Alfentanil, a mu-opioid receptor agonist, also decreases gastrointestinal motility through central and peripheral opioid receptors. Concomitant use may synergistically inhibit peristalsis, leading to severe constipation, paralytic ileus, or delayed gastric emptying, which can increase the risk of aspiration and complicate anesthesia recovery."
"Alfentanil, a potent opioid analgesic, can cause significant hypotension and respiratory depression. When combined with furosemide, a loop diuretic that reduces blood volume and vascular resistance, there is a synergistic decrease in blood pressure, which may precipitate cardiovascular collapse, especially in patients with compromised circulatory reserves. Additionally, furosemide may enhance the sedative and respiratory depressant effects of alfentanil, leading to increased risk of respiratory acidosis and altered mental status."
"Alfentanil, a potent mu-opioid receptor agonist, can enhance the bradycardic effects of nebivolol, a beta-1 selective blocker with additional nitric oxide-mediated vasodilation. The combination may lead to excessive slowing of heart rate, reduced cardiac output, and potential hemodynamic instability, particularly in patients with underlying cardiac conduction abnormalities or hypovolemia."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALFENTA vs AZO GANTANOL, answered by our medical review team.
ALFENTA is a Opioid Analgesic that works by μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALFENTA and AZO GANTANOL 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 ALFENTA is: Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.. 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.. 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 ALFENTA and AZO GANTANOL 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. ALFENTA is classified as Category C. Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effect. 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.