Phenazopyridine

Phenazopyridine is excreted in the urine where it exerts a topical analgesic effect on the mucosa of the lower urinary tract. This action helps to relieve pain, burning, urgency and frequency. The precise mechanism of action is unknown.

The pharmacokinetic properties of phenazopyridine have not been fully elucidated. Phenazopyridine and its metabolites are rapidly excreted by the kidneys. In a small number of healthy subjects, 90% of a 600 mg/day oral dose of phenazopyridine was eliminated in the urine in 24 hours, 41% as unchanged drug and 49% as metabolites.

The oral administration of phenazopyridine hydrochloride to dogs showed that the drug accumulated selectively in lacrimal and nictitans glands and the glands of Moll, and caused a reduction of tear flow. The drug or its metabolic derivative was detectable by light microscopy as an accumulation in the cytoplasm within 48 hours after drug administration. Electron microscopy showed that the product detected was localized in secretory granules. The results suggest that phenazopyridine hydrochloride affects the synthesis of secretory granules and causes progressive destruction of affected cells.