Phenazopyridine

148.1 Ų [M-H]- [CCS Type: DT; Buffer gas: N2; Ionization: ESI-; Dataset: TOXCAST; Source Identifier: DTXSID1021118]

138.87 Ų [M+H-H2O]+ [CCS Type: TW; Method: calibrated with polyalanine and drug standards]

Phenazopyridine acts as a local anesthetic offering relief from irritating conditions of the urinary tract. It relieves urinary urgency frequency, burning, pain, and discomfort. **A note on urine and skin discoloration and interference with test results** Yellowing of the skin or sclerae of the eyes may indicate that the accumulation of phenazopyridine has occurred. This may be a consequence of overdose, decreased renal function, taking the drug for over two days. Elderly patients may be at particular risk due to a decline in renal function, potentiating the risk of phenazopyridine accumulation. The drug should be discontinued if yellowing of the skin or sclerae is observed. Hemolytic anemia is a risk of phenazopyridine, especially in cases of overdose. In addition to the above effects, this drug may impart an orange or red color of urine and feces, causing staining of clothing. Other body fluids may also be stained, and in patients wearing contact lenses, phenazopyridine may cause lens staining. Due to its orange-red color, this drug may interfere with laboratory requiring colorimetric, spectrophotometric or fluorometric methods of analysis. In patients with G6PD enzyme deficiency, this drug poses a greater risk of hemolysis, even at normal doses and is not recommended. **A note on carcinogenesis** Based on the results of in vivo studies in rats, this drug has been listed as a carcinogen in the USA since 1981. Rats given this drug were found to demonstrate increased rates of hepatocellular carcinoma and colorectal tumors. Use this agent with caution and limit the administration of this drug when possible.

The full mechanism of action of phenazopyridine is not fully elucidated, however, it is reported to exert a direct topical analgesic effect on the mucosal lining of the urinary tract via the inhibition of voltage-gated sodium channels and possibly group A nerve fibers, as suggested by the results of a study in rats. The above actions likely lead to the relief of unpleasant urinary symptoms.