Nanoemulsion-Based Strategies for Improving Solubility, Bioavailability, And Therapeutic Applications of Poorly Soluble Drugs: A Review

Poor aqueous solubility is a persistent challenge in pharmaceutical research, with a large
proportion of newly developed drug molecules classified as Biopharmaceutics Classification System
(BCS) class II and IV compounds. Poor solubility often results in low and variable bioavailability,
delayed onset of action, and suboptimal therapeutic outcomes, leading to formulation failure and
increased development costs. Nano-emulsion-based drug delivery systems have gained considerable
attention as an effective approach to overcome these limitations. Nanoemulsions are kinetically stable,
isotropic dispersions of oil and water stabilised by suitable surfactants and co-surfactants, with droplet
sizes typically in the range of 20–200 nm. The nanoscale droplet size provides a markedly increased
interfacial surface area, which enhances drug solubilization, dissolution rate, and permeability across
biological membranes. Additionally, nanoemulsions can protect drugs from chemical and enzymatic
degradation, promote lymphatic uptake, and partially bypass hepatic first-pass metabolism, thereby
improving systemic bioavailability. This review summarises nanoemulsion composition, formulation
strategies, and preparation methods, marketed products, and case studies relevant to pharmaceutical
applications. Furthermore, the mechanisms responsible for solubility and bioavailability enhancement
are outlined, along with recent therapeutic applications via oral, parenteral, topical, ocular, and nasal
routes. Overall, nanoemulsion-based delivery systems represent a platform for improving the therapeutic
performance of poorly water-soluble drugs.