self-emulsifying drug delivery system

A self-emulsifying drug delivery system is an oily mixture that does nothing visible in the bottle, but the moment it meets the watery contents of the gut and gentle stirring, it spontaneously breaks up into countless tiny droplets, like a drop of dish soap suddenly clouding a sink of water. The drug is carried dissolved in those droplets.

It is supplied as a clear preconcentrate, an isotropic blend of oil, surfactant, and often a co-solvent, frequently filled into a capsule. When swallowed it disperses on contact with gut fluids, aided by the stomach and intestinal movements, to form a fine oil-in-water emulsion or microemulsion. Because the poorly water-soluble drug is already dissolved and presented as an enormous surface area of fine droplets, it stays in solution and is absorbed far more readily than from a conventional tablet.

These systems are especially valuable for lipophilic, poorly soluble drugs whose absorption is otherwise erratic and dependent on food, the classic success being early cyclosporine formulations. The challenges are that high surfactant levels can irritate the gut, the drug may precipitate out if it falls out of solution after dispersion, capsule compatibility and stability must be managed, and only a limited drug dose fits in the small oily volume of a capsule.