Improvement of XZP8257 Dissolution Properties Through Amorphous and Mixed-Phase Precipitate Formation in Biorelevant...

Although precipitation of poorly soluble drugs in the gastrointestinal (GI) tract is often considered detrimental to bioavailability, the solid-state nature of the precipitate, either crystalline or amorphous, may critically redefine its impact. Contrasting with reported crystalline precipitates of weakly basic drugs, this study investigates XZP8257 (C₂₇H₂₃Cl₂N₃O₄S), a poorly soluble weakly acidic/zwitterionic compound (BCS II), to explore how GI fluid composition governs precipitate formation and its resulting physicochemical properties. Precipitates were generated in simulated intestinal media with varied bile salt concentrations and pH values. Their solid-state forms were characterized using XRD, SEM, FTIR, and DSC, whereas dissolution performance was evaluated via equilibrium solubility and intrinsic dissolution rate (IDR) measurements. Elevated bile salt concentrations induced a molecular structural transition in XZP8257 and facilitated the formation of crystalline-amorphous mixed precipitates, a phenomenon distinct from the crystalline precipitates typically reported. These novel precipitates exhibited a 5.29- to 22.1-fold increase in equilibrium solubility and a 0.7- to 2.35-fold improvement in IDR compared to the crystalline API. This study reveals that for weakly acidic compounds like XZP8257, precipitate formation in the GI tract can lead to high energy, readily redissolving solid forms, potentially enhancing rather than limiting absorption. This challenges the uniform negative view of precipitation and underscores the necessity of compound-specific precipitate characterization to accurately predict oral absorption, especially in physiologically based biopharmaceutics models.