cidyl Values after Ingestion of Phenazopyridine Hydrochloride

taken through this procedure for Placidyl (1). Curve A shows the scan of the chromogen formed when a urine sample, collected from a person who about 3 h before had ingested one 200mg Pyridium tablet, was diluted fivefold and taken through the assay. Curve B is a similar scan of the chromogen formed when a solution containing 2 mg/dl of Placidyl was taken through the same procedure. These spectra are indistinguishable. Table 1 shows the apparent Placidyl concentrations found by this colonmetric method in urine and serum of persons who had ingested phenazopyridine hydrochloride. Urine No. 1 and serum No. 1 were collected about 8 h after a subject had ingested one 200-mg Pynidium tablet; urine No. 2 and serum No. 2 were collected about 3 h after a different subject had ingested one 200-mg Pynidium tablet. Urine No. 3 and serum No. 3 were collected from a patient who was taking four Azotrex capsules per day, which each contain 50 mg of phenazopynidine hydrochloride. None of these individuals was taking Placidyl. The method can still be used to determine Placidyl in the presence of Pyridiuni by carrying the sample through the complete procedure, but substituting a blank reagent [50 ml of coned. H2S04 and 100 ml of acetic acid:water (1:1, by vol)] for the Placidyl color reagent. The Placidyl concentration can then be determined from the difference between the absorbance of a sample reacted with the color reagent and that of a sample reacted with the blank reagent. For a specimen with a high concentration of Pyridium, the specimen must be dilutedbeforea sample is taken through the procedure so that the absorbance of the chromogen can be measured. Obviously, samples with low Placidyl concentrations would be diluted below the sensitivityof the method and this procedure would be unsuitable for the determination of such small amounts. However, higher concentrations of Placidyl, such as are seen in overdose situations, could easily be measured in the presence of Pynidium. The characteristic reddish-orange color was an easily observable indication that Pyridium was present in these urine samples, but was not observed inthesesera.