1. Clinical Overview
Phenazopyridine hydrochloride is a urinary tract analgesic (azo dye) used for the symptomatic relief of pain, burning, urgency, frequency, and discomfort arising from irritation of the lower urinary tract mucosa. It is a local analgesic that exerts a topical anesthetic effect on the urinary tract epithelium. It is NOT an antibiotic and does not treat the underlying infection. It is typically used as an adjunct for the first 2-3 days of antibiotic therapy for urinary tract infections (UTIs) in India.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 30-60 minutes after oral administration. | Approximately 6-8 hours. | Not well quantified but considered good; extensively absorbed from the gastrointestinal tract. |
2. Mechanism of Action
Phenazopyridine exerts a direct topical analgesic effect on the mucosa of the urinary tract (ureters and bladder). The exact mechanism is not fully elucidated but is believed to involve local anesthetic properties, possibly by blocking sodium channels in sensory nerve endings, thereby reducing pain signals from the irritated urothelium.
3. Indications & Uses
- Symptomatic relief of pain, burning, urgency, and frequency associated with acute cystitis (urinary tract infection).
- Symptomatic relief of discomfort following urological procedures (e.g., cystoscopy, catheterization).
4. Dosage & Administration
Adult Dosage: 100 mg to 200 mg orally three times a day after meals. The typical Indian brand strength is 100mg. Maximum duration: 2 days when used with an antibiotic for UTI.
Administration: Administer after meals with a full glass of water to reduce gastric upset. Inform patient that urine will turn orange-red. Do not chew or crush tablets.
5. Side Effects
Common side effects may include:
- Orange-red discoloration of urine (expected, harmless).
- Headache
- Mild dizziness
- Upset stomach/nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Sulfonamides (e.g., Cotrimoxazole) | Increased risk of methemoglobinemia. | Major |
| Nitrates/Nitrites (e.g., Nitroglycerin, Amyl Nitrite) | Increased risk of methemoglobinemia. | Major |
| Dapsone | Increased risk of methemoglobinemia and hemolytic anemia. | Major |
| Primaquine, Chloroquine | Increased risk of hemolysis in G6PD deficient patients. | Moderate |
| Other oxidizing drugs | Increased risk of oxidative stress leading to hemolysis or methemoglobinemia. | Moderate |
| Antacids containing Magnesium/Aluminum | May decrease absorption of phenazopyridine. Separate administration by at least 2 hours. | Minor |
7. Patient Counselling
- DO take this medicine after meals with a full glass of water.
- DO understand this medicine only relieves pain; you MUST take the full course of antibiotic prescribed for the infection.
- DO NOT take this medicine for more than 2 days unless specifically directed by your doctor.
- DO NOT be alarmed if your urine turns orange-red; this is normal and harmless.
- DO NOT wear soft contact lenses as they may become permanently stained.
- DO protect clothing and linens from potential stains from urine.
8. Toxicology & Storage
Overdose: Symptoms of overdose are primarily due to aniline toxicity and include: methemoglobinemia (cyanosis - bluish skin, chocolate-brown blood, dyspnea, lethargy, headache), hemolytic anemia, hepatic necrosis, renal failure (oliguria, anuria), and possible CNS depression or seizures.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.