AZO GANTANOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for AZO GANTANOL (AZO GANTANOL).
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.
| Metabolism | Sulfamethoxazole is primarily metabolized by N-acetylation in the liver (N-acetyltransferase 2); phenazopyridine is metabolized in the liver via glucuronidation and sulfation. |
| Excretion | Renal: 70% as sulfamethoxazole (30% acetylated), N5-acetylated metabolite accounts for 15%; fecal: 20% of dose excreted unchanged in bile; biliary: minor contribution (<5%) |
| Half-life | Sulfamethoxazole terminal half-life: 9-12 hours in adults with normal renal function (CrCl >80 mL/min); prolonged to 20-50 hours in CKD (CrCl <30 mL/min); phenazopyridine half-life: 9-11 hours |
| Protein binding | Sulfamethoxazole: 65-70% bound to albumin; phenazopyridine: >99% bound (mainly to albumin) |
| Volume of Distribution | 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) |
| Bioavailability | Oral sulfamethoxazole: 85-95% (well absorbed); phenazopyridine: approximately 90% absorbed |
| Onset of Action | Oral: analgesic effect (phenazopyridine) within 30-60 minutes; antimicrobial effect (sulfamethoxazole) within 24-48 hours (time to therapeutic concentrations) |
| Duration of Action | Oral: antimicrobial effect persists 12-24 hours post dose (sulfamethoxazole); analgesic effect from phenazopyridine lasts 4-6 hours (urinary analgesic effect) |
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.
| Dosage form | TABLET |
| Renal impairment | Sulfamethoxazole/Trimethoprim: CrCl >30 mL/min: no adjustment; CrCl 15-30 mL/min: reduce standard dose by 50% or extend interval to 24 hours; CrCl <15 mL/min: contraindicated. Phenazopyridine: contraindicated in renal impairment. |
| Liver impairment | 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. |
| Pediatric use | 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. |
| Geriatric use | Sulfamethoxazole/Trimethoprim: monitor renal function; reduce dose if CrCl <30 mL/min. Increased risk of hyperkalemia and sulfonamide-induced adverse effects. Phenazopyridine: cautious use due to potential renal impairment and CNS effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for AZO GANTANOL (AZO GANTANOL).
| Breastfeeding | 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. |
| Teratogenic Risk | 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. |
■ FDA Black Box Warning
Sulfonamides, including sulfamethoxazole, may cause severe hypersensitivity reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, and agranulocytosis.
| Serious Effects |
Hypersensitivity to sulfonamides or phenazopyridine; porphyria; severe renal impairment (CrCl <30 mL/min); G6PD deficiency; infants <2 months; pregnancy at term; lactation.
| Precautions | Risk of hypersensitivity reactions including SJS/TEN; blood dyscrasias (agranulocytosis, aplastic anemia); hepatotoxicity; renal impairment; photosensitivity; interference with urine glucose tests. |
| Food/Dietary | 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. |
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| Fetal Monitoring | Maternal: CBC, renal function, and liver function tests periodically due to sulfamethoxazole/trimethoprim. Fetal: Ultrasound for anomalies if first-trimester exposure; monitor for jaundice and kernicterus in neonate if used near term. |
| Fertility Effects | No known adverse effects on fertility from phenazopyridine. Sulfamethoxazole/trimethoprim may impair folic acid metabolism, potentially affecting spermatogenesis in males; no significant data on female fertility. |
| Clinical Pearls | 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 (CrCl <30 mL/min contraindicated). |
| Patient Advice | 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. |