Studies on complexes. XX. Effect of complex formation on drug absorption from alimentary tract.

Abstract

Absorption rates of carbazochrome and nicotinamide in the presence of each complexing agent (caffeine and hydroxyethyltheophylline, respectively) were determined in order to make sure that the increase or decrease of absorption rate in the presence of the complexing agent was due to the intra-luminal complex formation. The rate was determined by pretreatment, tied loop, and everted methods. In addition, the effect of buffer composition and the addition of the third additive to the complexing system were studied. These results suggest that the effect of complexing agent on the absorption rate of drug is apparently due to complex formation. To demonstrate the specificity of the small intestine by comparing with the rat stomach, carbazochrome-caffeine complexing system was examined on the absorption rate from the stomach. It was found that the small intestine did not behave specifically to the absorption of carbazochrome in the presence of caffeine. A theoretical equation was derived to obtain the stability constant at the surface of the absorption rate-limiting barrier. The constant did not differ appreciably from that determined in the bulk solution. A good fit of the absorption rate to the theoretical model suggested that the stability constant at the surface of the absorption rate-limiting barrier was similar to that in the bulk solution.