The potential for drug supersaturation during intestinal processing of lipid-based formulations may be enhanced for basic drugs.

Co-administration of poorly water-soluble drugs (PWSD) with dietary or formulation lipids stimulates the formation of lipid colloidal phases such as vesicular and micellar species, and significantly expands the drug solubilization capacity of the small intestine. The mechanism of drug absorption from the solubilizing phases, however, has not been fully elucidated. Recently, we observed that drug supersaturation may be triggered during endogenous processing of lipid colloidal phases containing medium-chain lipid digestion products and that this may represent a mechanism to reverse the reduction in thermodynamic activity inherent in drug solubilization and thereby enhance absorption. The current studies expand these preliminary findings and explore the supersaturation tendency of five model PWSD during endogenous processing of intestinal colloidal phases containing long-chain lipid digestion products. Bile-lipid concentration ratios progressively increase during colloid transit through the gastrointestinal tract due to biliary dispersion of lipid digestion products and lipid absorption. The supersaturation potential was therefore evaluated under conditions of increasing bile and decreasing lipid concentrations and was found to be greater for the basic drugs cinnarizine (CIN) and halofantrine (HF), than the neutral drugs fenofibrate (FF) and danazol (DAN), and acidic drug meclofenamic acid (MFA). Assessment of intestinal absorptive flux using rat jejunal perfusion experiments subsequently showed that the absorption enhancement afforded by bile dilution of lipid colloidal phases was greater for CIN than DAN. The results confirm that bile plays a significantly greater role in the absorption of CIN (a weak base) from long-chain intestinal colloids when compared to DAN (an uncharged molecule) and that the difference reflects a greater propensity for supersaturation as intestinal colloids are dispersed and diluted by bile. The data suggest that coadministered digestible lipids may be particularly suited to enhance the absorption of poorly water-soluble weak bases.