Perspective on improving passive human intestinal absorption.

Methods such as pH adjustment, cosolvency, complexation, and micellization are routinely used to increase the concentration of dissolved drug in the gastrointestinal (GI) lumen over that of a saturated solution. However, these solubilizing agents also reduce the membrane-water distribution coefficient so that the membrane transport rate is not changed. Also, dilution of a formulation upon administration results in: (1) a pH change toward that of the GI fluid, (2) an exponential decrease in cosolvency, and (3) disassociation of complexes and the disintegration of micelles. As a result, these solubilizing agents cannot be expected to produce any increase in membrane transport-limited drug absorption over that of a suspension of unformulated drug.