<p>Establishing Experimental Parameters for Biphasic Transfer in Vitro Lipolysis Model</p>

Lipid-based‑formulations (LBFs) are widely used to improve oral bioavailability of poorly water‑soluble drugs. Despite their widespread use in predicting formulation performance, standard in vitro lipolysis assays often lack an absorptive sink and fail to capture the transition from gastric to intestinal environments, thereby reducing their predictive relevance for in vivo outcomes. The aim of this study was to develop a biphasic in vitro lipolysis model incorporating an absorptive sink. In this model, the absorptive sink was provided by a decanol layer, and to simulate gastrointestinal transit, two dynamic pH‑transition approaches were employed: a biphasic GI‑transfer model and a biphasic pH‑shift model. Using nilotinib‑loaded LBFs, the study established conditions for this biphasic system and examined how media composition and lipase source influence drug concentrations during formulation dispersion, digestion, and partitioning into the organic sink. The results showed that digestion experiments conducted with either porcine pancreatin or Palatase® 20000 L increased the concentration of nilotinib in the aqueous digestion medium, which correspondingly reduced partitioning of the drug into the decanol layer. For the readily dispersible Type III LBF in the biphasic GI‑transfer setup, nilotinib permeation into the decanol layer decreased compared with a lipid‑free control, likely due to improved drug solubilization in the aqueous digestion phase. In contrast, the poorly dispersible Type I LBF was better suited to the biphasic pH‑shift setup, but it showed higher drug levels in the decanol layer, reflecting rapid partitioning of lipids—and associated crystalline drug—into the organic phase.  Overall, this study establishes suitable conditions for evaluating the lipolysis of LBFs during a dynamic pH transition in the presence of an absorptive sink. This advanced approach provides additional insight to explore digestion‑mediated and/or pH‑mediated supersaturation during digestion of LBFs.