Studies on Complexes. XII. Effect of Complex Formation on Drug Absorption from Alimentary Tract. (3)

Abstract

Effect of 1 : 1 complex formation with a nonabsorbable drug (A) and an absorbable one (B) on the absorption of B from rat small intestine according to the recirculating perfusion method in situ was described. The combination of drugs used as the model compounds was riboflavin phosphate (A)-sulpyrin (B), riboflavin phosphate (A)-caffeine (B), riboflavin phsophate (A)-4-aminoantipyrine (B), aminopropylon (A)-sulfamethizole (B), and aminopropylon (A)-sulfisomidine (B). The absorption rate constant of B was influenced by the incorporation of A and the rate was shown to be slowed and dependent on the concentration of A. The effect was rationalized and effectively quantitated by hypothesizing that the complex AB was absorbed little or not absorbed, and that only the noncomplexed form of the absorbable drug was observably absorbed. Complexation of B with A decreased the apparent partition coefficient of B. It is thought that this suggests one possible mechanism for the absorption of complex.