Development and Evaluation of Nanolipid Carriers for Solubility Enhancement of Poorly Water-Soluble Drugs: A Comprehensive Review

Poor aqueous solubility continues to be one of the most formidable barriers in the development of new drug molecules, leading to poor dissolution, low bioavailability, and inconsistent therapeutic response. Approximately 40–60% of newly synthesized drug candidates fall under the category of poorly water-soluble compounds, belonging primarily to Biopharmaceutics Classification System (BCS) Class II and IV. Nanotechnology-based delivery systems, particularly Nanolipid Carriers (NLCs), have emerged as a highly effective approach for improving the solubility and oral absorption of such drugs. NLCs are the second generation of lipid nanoparticles, developed to overcome the limitations of Solid Lipid Nanoparticles (SLNs), offering higher drug loading, enhanced stability, and controlled release. This review provides a comprehensive overview of the development, formulation strategies, evaluation parameters, and applications of NLCs for solubility enhancement. Emphasis is placed on formulation design, optimization approaches, characterization techniques, and in vitro–in vivo correlations. The article also discusses toxicity, safety, and regulatory aspects of NLCs, highlighting their potential for clinical translation.