Assessment of <i>in Vivo</i> Performance of Lipid-Based Formulations: Correlation between <i>in Vitro</i> Drug Release Profiles and <i>in Vivo</i> Absorption Rate Profiles

The purpose of this study was to assess the in vivo absorption enhancement effects of lipid-based formulations (LBFs) through in vitro release studies. The type IIIA-MC (medium-chain) and type IIIA-LC (long-chain) formulations containing a Biopharmaceutics Classification System (BCS) Class II drug (dipyridamole or ketoconazole) were used as model LBFs. The type IIIA-MC formulation, but not the type IIIA-LC formulation, showed a higher initial absorption rate than the control suspension for both model drugs in rats. An in vitro side-by-side chamber system coupled with a lipid digestion model was used to measure free drugs, available for intestinal absorption, that are released from a model LBF. The profiles of free drug concentration on the donor side were determined by calculating the ratio of permeation rate (LBF/suspension) at every sampling interval. The in vitro free drug concentration was immediately supersaturated when the digestion of type IIIA-MC formulation was initiated for both drugs, which would cause the initially high absorption rate in rats. In contrast, the free concentration of the type IIIA-LC formulation became lower than the equilibrium solubility over time for both drugs. Overall, the profiles of in vitro free concentrations were consistent with those of in vivo absorption rates for both drugs and all LBFs. These findings would help predict the in vivo performance and establish an in vitro-in vivo correlation (IVIVC) of LBFs.