Adsorption of phenazopyridine hydrochloride on pharmaceutical adjuvants.

The adsorption of the urinary tract analgesic, phenazopyridine hydrochloride (PN . HCl), on some silicates as pharmaceutical adjuvants was studied. From Langmuir adsorption isotherms the adsorption capacities were determined. The results revealed that the adsorption capacities of veegum and bentonite were comparatively higher than kieselguhr, talc and kaolin. High adsorption capacities of veegum and bentonite were also obtained at pH values ranging between 2 to 4 simulating those of the stomach juice. Bioavailability studies proved that bentonite decreased the rate as well as extent of absorption of PN . HCl from rats.