Self-Emulsifying Drug Delivery Systems: Design, Development, and Evaluation

Self-emulsifying drug delivery systems (SEDDS) represent one of the most promising and dynamically evolving lipid-based formulation strategies for enhancing the oral bioavailability of poorly water-soluble drugs, which account for approximately 40% of all currently marketed pharmaceutical compounds and nearly 70-90% of new chemical entities in the developmental pipeline. SEDDS are isotropic mixtures composed of oils, surfactants, and cosolvents that, upon contact with gastrointestinal (GI) fluids under mild agitation, spontaneously generate fine oil-in-water emulsions with droplet sizes typically between 100 and 300 nm for classical SEDDS and below 100 nm for self-nanoemulsifying systems (SNEDDS). The resulting emulsions present a substantially enlarged interfacial surface area that markedly accelerates drug dissolution, enhances membrane permeation, and promotes lymphatic drug absorption, thereby bypassing hepatic first-pass metabolism for certain lipophilic compounds. This review comprehensively addresses the fundamental principles, classification according to Pouton's lipid formulation classification system, excipient selection criteria, thermodynamic basis of self-emulsification, formulation development and optimization strategies, physicochemical characterization methodologies, in vitro and in vivo evaluation approaches, and diverse therapeutic applications of SEDDS. Additionally, the review critically examines persistent challenges including drug precipitation upon dilution, drug loading limitations, thermodynamic stability, in vitro-in vivo correlation (IVIVC), and regulatory excipient safety. Emerging research directions in supersaturable SEDDS, solid-SEDDS conversion, nanoparticle-integrated systems, targeted delivery platforms, and machine learning-assisted formulation design are also discussed.