Abstract
Studies were made of the effects of buffer components (phosphate-citrate isotonic buffer) on absorption of sulfonamides and of a reconfirmation was established of the equation presented previously in reference to an intestinal absorption of drugs. Absorption of sulfonamides from phosphate-citrate isotonic buffer of pH 5.8 decreased following preperfusion with pH 3.3 or 7.6 isotonic buffer, while it was not decreased when pretreated with Tyrode's solution. Dilution of phosphate-citrate isotonic buffer with 0.9% NaCl, whose pH was adjusted by a continuous titration of 0.1N HCl or 0.1N NaOH resulted in an enhancement of the increase. It was concluded that when phosphate or citrate ions were used as perfusion medium possible influences on the intestinal mucous membrane should be considered. When phosphate-citrate isotonic buffer was used, pH for maximum absorption did not correspond with pH for the maximum fraction of undissociated drug molecules, but when 0.9% NaCl whose pH was adjusted was used as perfusion medium, pH-profile of absorption corresponded with that of the undissociated fraction of drugs. Regarding such correspondence further study seems necessary in under way.
