Formulation Strategies to Enhance the Solubility of Poorly Water-Soluble Drugs and Phytochemicals: Current Advances and Challenges

The low water solubility of numerous drug candidates and phytochemicals continues to pose a significant challenge in pharmaceutical development, greatly limiting their bioavailability and therapeutic performance. This review presents a detailed overview of formulation strategies aimed at improving the solubility and dissolution of poorly aqueous-soluble compounds. The biopharmaceutics classification system and the relevance of in vitro-in vivo correlation, as well as key challenges in formulation development, are briefed. Solid-state and particle engineering approaches, including micronization, supercritical fluid technology, electrospinning, and cryogenic techniques, are discussed. Extensive critical examination of amorphous solid dispersions and their preparation methods, as well as crystallization inhibition strategies, is covered. Cocrystallization is highlighted as a promising approach, with emphasis on design principles and preparation methods. Various solubilization techniques, such as pH modification, cosolvency, hydrotropy, micellar solubilization, and cyclodextrin-based complexation, including advanced hybrid systems, are also explored. Emerging solvent platforms, such as deep eutectic systems and lipid-based and nanotechnology-driven approaches, are reviewed for their role in improving solubility and drug delivery. Additionally, enabling technologies such as liquisolid systems and hydrophilic polymers are addressed. Despite notable progress, limitations such as scalability, reproducibility, regulatory constraints, and long-term safety persist. Overall, this review provides integrated insights into formulation design approaches to enhance the solubility and therapeutic efficacy of poorly soluble drugs.