SNEDDS and SMEDDS as lipid nanocarriers for improving dissolution rate and bioavailability of poorly soluble drugs

An increase in the proportion of poorly aqueous soluble drugs that exhibit problems in oral bioavailability is one of the major problems in formulation development. Formulation of lipid-based nanocarriers, such as self-nanoemulsifying drug delivery systems (SNEDDS) and self-microemulsifying drug delivery systems (SMEDDS) have received a lot of attention in recent years as an approach for overcoming poor solubility and oral bioavailability of drugs. SNEDDS are isotropic mixtures of oil, surfactant (HLB>12) and cosurfactant. These systems are spontaneously emulsified in situ when exposed to gastrointestinal tract (GIT) fluids, forming oil-in-water nanoemulsions with droplet size of 100–250 nm. Self-microemulsifying drug delivery systems (SMEDDS), in comparison, contain a higher content of hydrophilic surfactants and cosurfactants, wherein lipid content is reduced. After the dispersion in aqueous media, SMEDDS form homogeneous, transparent, isotropic, and thermodynamically stable microemulsions, with droplet size of less than 100 nm. However, SMEDDS and SNEDDS are normally prepared as liquids that have some disadvantages, e.g., high production costs, low stability and portability, low drug loading, and different dosage forms. Irreversible drug/excipient precipitation may also be problematic. More importantly, the large quantity of surfactants in the formulations can induce gastrointestinal irritation. In order to avoid these problems, numerous approaches have been established for transforming liquid SMEEDS/SNEEDS into solid dosage forms, such as adsorption onto porous carriers, spray-drying, freeze drying, melting granulation, extrusion, etc. Solid self-emulsifying drug delivery systems combine the advantages of liquid formulation (i.e., enhanced solubility and bioavailability) with those of solid dosage forms (e.g., low production cost, convenience of process control, high stability and reproducibility, and better patient compliance). This chapter provides a review of the current state and recent progress in SMEEDS and SNEEDS formulation development, with particular emphasis on the approaches for overcoming their limitations and enabling wider commercial application of these lipid nanocarriers.


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