Calcium ion sequestration by N-acylamino acids within the rectal membrane and the enhancement of the rectal absorption of sodium ampicillin in rats.

The present study reports the contribution of the calcium ion sequestration capacity of N-acylamino acids, used as absorption promoters, to their absorption-promoting action. Different extents of enhanced rectal absorption of sodium ampicillin by N-acylamino acids were well explained by the predicted amount of calcium ion sequestrated by N-acylamino acids existing in the rectal membranes. The amount of N-acylamino acids that penetrated into the rectal membrane was predicted by the product of the Rm value and the dose of N-acylamino acids. Thus, in the present study, it was demonstrated that the extent of the promoting effect of adjuvants at various doses on the membrane permeability may be predicted by multiplying the calcium ion sequestration capacity obtained in vitro by the lipophilicity and the dose applied to the rectal lumen of adjuvants.