Low oral bioavailability as a consequence of low water solubility of drugs is a growing challenge to the development of new pharmaceutical products. One of the most popular approaches of oral bioavailability and solubility enhancement is the utilization of lipid-based drug delivery systems. Their use in product development is growing due to the versatility of pharmaceutical lipid excipients and drug formulations, and their compatibility with liquid, semi-solid, and solid dosage forms. Lipid formulations, such as self-emulsifying (SEDDS), self-microemulsifying SMEDDS) and self--nanoemulsifying drug delivery systems (SNEDDS) were explored in many studies as an efficient approach for improving the bioavailability and dissolution rate of poorly water-soluble drugs. One of the greatest advantages of incorporating poorly soluble drugs into such formulations is their spontaneous emulsification and formation of an emulsion, microemulsion or nanoemulsion in aqueous media. This review article focuses on the following topics. First, it presents a classification overview of lipid-based drug delivery systems and mechanisms involved in improving the solubility and bioavailability of poorly water-soluble drugs. Second, the article reviews components of lipid-based drug delivery systems for oral use with their characteristics. Third, it brings a detailed description of SEDDS, SMEDDS and SNEDDS, which are very often misused in literature, with special emphasis on the comparison between microemulsions and nanoemulsions.Keywords: lipid-based drug delivery systems (LBDDS), self-emulsifying drug delivery systems (SEDDS), self--microemulsifying drug delivery systems (SMEDDS), self-nanoemulsifying drug delivery systems (SNEDDS), microemulsions, nanoemulsions

This study indicates that a liquid and solid SMEDDS is a strategy for solubility enhancement in the future development of orally delivered dosage forms.

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The purpose of this study was to compare different solidification techniques (i.e., adsorption technique, spray-drying process, high-shear granulation, fluid-bed granulation) for preparing solid SMEDDS powders by using solid carriers identified as appropriate and to produce a single (tablets) or multiunit (minitablets) solid dosage form based on prepared solid SMEDDS loaded with naproxen in a dissolved (6% w/w) or supersaturated (18% w/w) state. Among the solidification techniques and carriers tested, the powders produced using the spray-drying process and maltodextrin (MD) as a carrier exhibited the best self-microemulsifying properties, comparable with liquid SMEDDS. Furthermore, DoE (Design of Experiments) showed that pressure at the nozzle and pump speed (regulating feed flow rate) applied during spray drying had a major and significant influence on self-microemulsifying properties (mean droplet size and PDI) of the solid SMEDDS prepared. Furthermore, it was shown that compression of solid SMEDDS into (mini) tablets influences its self-microemulsifying properties in a negative direction. This resulted in lowering the dissolution profile of naproxen from tablets and minitablets in comparison with liquid and solid SMEDDS. However, all compressed SMEDDS formulations still had considerable influence on the dissolution profile and solubility enhancement of naproxen.