Contribution of calcium ion sequestration by polyoxyethylated nonionic surfactants to the enhanced colonic absorption of p-aminobenzoic acid.

Enhanced absorption of p-aminobenzoic acid (PABA) from the colon by polyoxyethylated nonionic surfactants was investigated using an in situ perfusion technique. The order of their absorption-enhancing effect was as follows: polyoxyethylene lauryl ether greater than polyoxyethylene sorbitan fatty acid esters approximately equal to polyoxyethylene fatty acid esters. The coexistence of calcium chloride in the perfusing solution caused a partial reverse in this enhancement. The calcium ion sequestration capacity of the surfactants was correlated with their ability to enhance colonic absorption of PABA. The findings suggest that calcium ion sequestration by the surfactants contributes to their enhancement of the colonic absorption of PABA.