Method of Action
Azo is the brand name for phenazopyridine hydrochloride. It is also available under other names including Uristat and Pyridium. Azo acts as an analgesic within the urinary tract, so it is commonly recommended for individuals with urinary discomfort from a urinary tract infection (UTI) or recent catheter use. The active ingredient is processed quickly by the kidneys and is then expelled into the urine. In the urinary tract it provides pain relief by soothing the mucous lining, although the exact mechanism is not yet known. Azo does not fight infection, but rather eases the symptoms of infection or other types of urinary irritation. Thus it is useful for urinary discomfort due to an infection, but will not actually cure the infection. A 2004 study published in the journal Annals of Family Medicine found that only 57 percent of individuals purchasing over-the-counter (OTC) phenazopyridine knew how the substance worked, and a 2003 study in the Journal of General Internal Medicine reported that such individuals have more than double the risk of taking it in lieu of seeking medical advice.
Typical Use of Azo
Azo Standard is available as 95 mg pills, and instructions indicate that the proper does is two pills up to three times a day. A maximum-strength version is also available with 97.5 mg pills. Prescription phenazopyridine comes in 200 mg pills, and users take one pill at a time. Doctors often recommend that a patient take Azo for the first two days of antibiotic treatment to ease the pain and burning while the antibiotic takes effect. The package instructions and most doctors caution against taking Azo for more than two days, as it can mask the presence of a more serious problem.
In addition to relieving urinary tract pain, Azo has one other obvious effect: it causes a change in the color of urine. The active component is a dye, and at the concentrations that result from taking OTC or prescription levels it colors the urine orange or red. The dye can also leak somewhat between eliminations, so many users wear panty liners or dark-colored underpants. Because of this color change, doctors are usually unable to do an in-office urinalysis. The typical urine test for a UTI involves assessing the color of urine, which cannot be done when Azo changes its color. For this reason, some experts recommend holding off on taking Azo when a person first experiences urinary discomfort, until a doctor can conduct a diagnosis. If Azo does make an in-office test impossible, a doctor can send the urine sample off for a culture to determine if E. coli or another bacterial culprit is present. The doctor may or may not be willing to prescribe an antibiotic before the test results are in.
- MedlinePlus: Phenazopyridine
- Journal of General Internal Medicine; Usage Patterns of Over-the-Counter Phenazopyridine (Pyridium); Shi CW, Asch SM, Fielder E, Gelberg L, Brook RH, Leake B, Shapiro MF, Dowling P, Nichol M; 2003
- Annals of Family Medicine; Consumer Knowledge of Over-the-Counter Phenazopyridine; Shi CW, Asch SM, Fielder E, Gelberg L, Nichol MB; 2004