Generic Name

Phenazopyridine

Brand Names

P‑PH Y, P‑Ph, A‑Phil, etc.) is a synthetic urinary analgesic and antispasmodic agent used primarily for symptomatic relief of lower urinary tract irritation.

Mechanism

Phenazopyridine exerts its effect locally in the urinary tract.
• Acts as a weak anticholinergic, reducing smooth‑muscle tone and spasms.
• Interferes with pain‑transducing receptors in the bladder urothelium, producing a rapid analgesic effect.
• It does not possess antibacterial activity; therefore, its role is strictly symptomatic.

Pharmacokinetics

• Absorption: Poorly absorbed from the GI tract; ~20–30 % bioavailability.
• Distribution: Widely distributed; high plasma protein binding (~>85 %).
• Metabolism: Minimal hepatic metabolism; largely excreted unchanged.
• Excretion: Predominantly renal (≈70 %) with the remainder excreted in bile.
• Half‑life: 2.5–3 h (short; supports 4–6 h dosing intervals).
• Special Populations: Reduced clearance in renal impairment; dose adjustment may be required.

Indications

• Cystitis (acute, uncomplicated) – pain, burning, and urgency relief.
• Urethritis – symptom control.
• Post‑operative bladder discomfort after genitourinary procedures.
• Used in conjunction with antibiotics when an infection is present; not a substitute for antimicrobial therapy.

Contraindications

• Pregnancy Category C – should be avoided unless clearly needed.
• Breastfeeding – excreted in milk; contraindicated.
• G6PD deficiency – risk of hemolytic anemia and methemoglobinemia.
• Severe hepatic impairment – data limited.
• Concurrent MAO inhibitors – theoretical additive sympathomimetic risk.
• Red/blue‑colored urinary discoloration – may cause diagnostic confusion; counsel patients.

Dosing

• Administration: Oral tablets or liquid; take with water.
• Duration: Not longer than 3 consecutive days without medical review.
• Break‑through pain: Consider short‑acting analgesic (e.g., acetaminophen) if needed.

Adverse Effects

• Common:
• Urinary discoloration (orange/red) – harmless, self‑limited.
• Nausea, vomiting, diarrhea, abdominal cramping.
• Headache, dizziness, vertigo.
• Rash or pruritus (rare).
• Serious:
• Hemolytic anemia and methemoglobinemia in G6PD‑deficient patients.
• Severe allergic reactions (anaphylaxis) – rare.
• Persistent hematuria or renal dysfunction (rare).

Monitoring

• Urine color: Educate patients about expected orange/red discoloration.
• Renal function: Baseline serum creatinine; repeat if symptoms of worsening kidney function appear.
• Hemoglobin/Hct: In G6PD‑deficient or symptomatic patients.
• Signs of hemolysis: Dark urine, pallor, jaundice.
• Methemoglobin level: Rarely needed; consider if cyanosis, hypoxia.
• Symptom resolution: Should occur within 48–72 h; persistent pain may indicate unresolved infection.

Clinical Pearls

• Symptom‑Focused Use Only: Phenazopyridine relieves pain but does not treat infection; always pair with appropriate antibiotics for cystitis/urethritis.
• Orange‑Colored Urine – commonly misinterpreted as hematuria; pre‑inform patients to reduce anxiety.
• Avoid Long‑Term Use: Cumulative toxicity is low, but prolonged daily use >3 days increases risk for renal changes and hemolysis.
• G6PD Screening: Essential in populations with higher prevalence (e.g., African‑American, Mediterranean, Southeast Asian).
• Renal Dose Titration: In patients with CrCl < 30 mL/min, consider reducing dose to 50 mg q4–6 h, but do not exceed 400 mg/day.
• Drug Interactions: Minimal, but caution with other CYP3A4 substrates; no clinically significant interactions reported.
• Patient Counseling: Emphasize adequate hydration, start lowest effective dose, stop immediately if jaundice or severe dizziness occurs.

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• *Prepared for medical students and clinicians: a concise, evidence‑based resource on Phenazopyridine.*