Self-Emulsifying Drug Delivery Systems

This review article explains how self-emulsifying drug delivery systems can increase the solubility and bioavailability of poorly soluble drug.
Jul 02, 2008


Table 1
Self-emulsifying drug delivery systems (SEDDSs) have gained exposure for their ability to increase solubility and bioavailability of poorly soluble drugs. SEDDSs are isotropic mixtures of oils and surfactants, sometimes containing cosolvents, and can be used for the design of formulations in order to improve the oral absorption of highly lipophilic compounds. SEDDSs emulsify spontaneously to produce fine oil-in-water emulsions when introduced into an aqueous phase under gentle agitation. SEDDS can be orally administered in soft or hard gelatine capsules and form fine, relatively stable oil-in-water emulsions upon aqueous dilution. This article presents an overview of SEDDSs and their applications.

In recent years, the formulation of poorly soluble compounds presented interesting challenges for formulation scientists in the pharmaceutical industry. Up to 40% of new chemical entities discovered by the pharmaceutical industry are poorly soluble or lipophilic compounds, which leads to poor oral bioavailability, high intra- and inter-subject variability, and lack of dose proportionality (1).

In the oral formulation of such compounds, a number of attempts—such as decreasing particle size, use of wetting agents, coprecipitation, and preparation of solid dispersions— have been made to modify the dissolution profile and thereby improve the absorption rate. Recently, much attention has focused on lipid-based formulations to improve the bioavailability of poorly water soluble drugs. Among many such delivery options, like incorporation of drugs in oils (2), surfactant dispersion (3), emulsions (4) and liposomes (5), one of the most popular approaches are the self-emulsifying drug delivery systems (SEDDSs).

SEDDSs are mixtures of oils and surfactants, ideally isotropic and sometimes containing cosolvents, which emulsify spontaneously to produce fine oil-in-water emulsions when introduced into an aqueous phase under gentle agitation. Self-emulsifying formulations spread readily in the gastrointestinal (GI) tract, and the digestive motility of the stomach and the intestine provide the agitation necessary for selfemulsification. These systems advantageously present the drug in dissolved form and the small droplet size provides a large interfacial area for the drug absorption (6). SEDDSs typically produce emulsions with a droplet size between 100–300 nm while self-microemulsifying drug delivery systems (SMEDDSs) form transparent microemulsions with a droplet size of less than 50 nm. When compared with emulsions, which are sensitive and metastable dispersed forms, SEDDSs are physically stable formulations that are easy to manufacture. Thus, for lipophilic drug compounds that exhibit dissolution rate-limited absorption, these systems may offer an improvement in the rate and extent of absorption and result in more reproducible blood-time profiles (7).