Conventional and Novel Solubility Enhancement Techniques: An Updated Review

Poor aqueous solubility always remains a major challenge in the preparation and development of oral drug delivery systems, as it directly involves and influences the dissolution rate, absorption, and bioavailability. A significant ratio of newly discovered drug molecules reveals low water solubility, particularly those belonging to BCS Class II and IV, requiring the use of new effective solubility enhancement strategies. Conventional approaches like pH adjustment, use of cosolvents, hydrotropy, particle size reduction, micronization, solid dispersions, complexation, eutectic systems, and micellar solubilization are widely used for particle size reduction and solubility enhancement. In addition to this, advanced and emerging techniques including nanosizing, nanosuspensions, supercritical fluid processing, sono-crystallization, ultra-rapid freezing, solvent deposition, and hot-melt extrusion are highlighted for their potential to enhance dissolution behaviour and oral bioavailability. The role of polymeric carriers and surfactants in stabilizing drug particles, avoiding recrystallization, and improving the wettability also emphasized in this selected topic. This review not only provides a comprehensive overview of both conventional and novel techniques employed to improve the solubility of poorly water-soluble drugs but also focuses on the importance of choosing a suitable solubility enhancement method based on the physicochemical properties of the drug and formulation requirements, thereby aiding in the rational design of effective pharmaceutical dosage forms.