Background: More than 60% of the new drug molecules are lipophilic in nature. Low aqueous solubility and thus poor bioavailability is the main issue for these drugs for successful formulations into oral dosage form. Self-microemulsifying drug delivery systems (SMEDDS) have gained much attention. These are isotropic mixtures of different components (oil, surfactant and cosurfactant) that quickly disperse in gastrointestinal fluid yielding micro/nano-emulsions. These systems contain solubilized drug that is absorbed by lymphatic pathway along with other pathways like diffusion, collisional transfer, intracellular junctions, biliary acid pathway (BA), biliary acid mixed micelles pathway (BAMM) etc. and thus hepatic first pass metabolism is reduced. Stability of conventional SEDDS is considered very high with reference to other drug delivery systems as liposome, nanoparticles, nanoemulsion and micro emulsion. In fact SEDDS does not contain water in their composition which enhances their chemical and physical stability. Very few works have studied the stability of conventional SEDDS as it was confirmed. The major drawback for conventional SEDDS could be- i) high manufacturing cost (as they have to be filled in soft gelatin capsules); ii) interaction of capsule shell components with SEDDS. Therefore, attention has been given to transform liquid into solid SMEDDS by several techniques such as spray drying, spray cooling, super critical fluid technology and using adsorption carriers. Adsorption using solid carriers (Neusilin, Fujicalin, and dextran) is the successful inexpensive technique at initial research level whereas other requires expensive instrumentation.
Conclusion: Current review focuses on biopharmaceutical aspects, characterization of SMEDDS and excipients used in the formulation, techniques used for conversion of liquid SMEDDS to solid SMEDDS (including examples of various research reports where these techniques are used). Various adsorbent carriers (alongwith their different features) which have been reported in research papers have been detailed. It thoroughly covers patent literature on SMEDDS and research carried on solid SMEDDS as well which is the most imperative part of the review.