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Phenazopyridine is a medication which, when excreted by the kidneys into the urine, has a local analgesic effect on the urinary tract. It is often used to help with the pain, irritation, or Urinary urgency caused by urinary tract infections, surgery, or injury to the urinary tract.
In 2023, it was the 275th most commonly prescribed medication in the United States, with more than 800,000 prescriptions.
Phenazopyridine is prescribed for other cases requiring relief from irritation or discomfort during urination; for example, after the use of an in-dwelling Foley catheter, endoscopic (cystoscopy) procedures, or after , prostate, or urinary bladder surgeries that may result in irritation of the epithelial lining of the urinary tract.
Phenazopyridine can cause , upset stomach (especially when not taken with food), or dizziness. Less frequently it can cause a noticeable yellowish pigment change in the skin or eyes. This is due to a depressed excretion via the kidneys causing a buildup of the medication in the skin, and normally indicates a need to discontinue usage. Other such side effects include fever, confusion, shortness of breath, skin rash, and swelling of the face, fingers, feet, or legs. Long-term use may cause yellowing of nails.
Phenazopyridine should be avoided by people with glucose-6-phosphate dehydrogenase deficiency, because it can cause hemolysis (destruction of red blood cells) due to oxidative stress. It has been reported to cause methemoglobinemia after overdose and even normal doses. In at least one case, the patient had pre-existing low levels of methemoglobin reductase, which likely predisposed her to the condition. It has also been reported to cause sulfhemoglobinemia.
Phenazopyridine is an azo dye. Other azo dyes, which were previously used in , printing, and plastic manufacturing, have been implicated as that can cause bladder cancer. While phenazopyridine has never been shown to cause cancer in humans, evidence from animal models suggests that it is potentially carcinogenic.
Pregnancy
This medication has shown no adverse events in animal models, but no human trials have been conducted. It is not known if phenazopyridine is excreted in breast milk.
Pharmacokinetics
The full pharmacokinetic properties of phenazopyridine have not been determined. It has mostly been studied in , but they may not be very representative of humans. Rat models have shown its half-life to be 7.35 hours, and 40% is metabolized hepatically (by the liver).
Mechanism of action
Phenazopyridine's mechanism of action is not well known, and only basic information on its interaction with the body is available. It is known that the chemical has a direct topical analgesic effect on the mucosa lining of the urinary tract. It is rapidly excreted by the kidneys directly into the urine. Hydroxylation is the major form of metabolism in humans, and the Azo compound bond is usually not cleaved. On the order of 65% of an oral dose will be secreted directly into the urine chemically unchanged.
Brand names
In addition to its generic form, phenazopyridine is distributed under the following brand names:
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