A Comprehensive Review on Self-Microemulsifying Drug Delivery Systems: From Design and Evaluation to Regulatory Challenges
Abstract
Weak aqueous solubility still remains one of the major problems encountered in the discovery and development of new drugs, particularly for BCS Class II and IV drugs where the low solution and permeability lead to low oral bioavailability. Formulation systems used for these drugs have often only partially incorporated this limitation. Thus, there is huge scope for integrating formulation strategies with a self-micro-emulsification tool to optimize absorption, solubilization and permeability of drugs of low aqueous solubility. Self Microemulsifying drug delivery systems (SMEDDS) have proved to be lipophilic formulations developed to improve solubility and systemic availability of drugs which are poorly water soluble. SMEDDS are makeup of a mixture of oil, surfactant and co-surfactants which form forming transparent micro-emulsions containing the drug, when in contact with the luminal environment of GI tract. Nanometer sized droplets have a very large interfacial area which facilitate the liquid digestion process and enhance the rate of intestinal absorption of drug. The biopharmaceutical performance can be greatly enhanced by improved permeability, lowered interfacial tension and thermodynamic stability. The selection of excipients should be done carefully while designing SMEDDS; excipients should be safe for human use, compatible with drug, enhance safety profile of parenteral design while ensuring ease of manufacturing, stability and parameters acceptable for regulatory approval. These systems are prepared as a liquid formulation or converted into solid form SMEDDS using techniques such as spray drying, melt granulation or adsorption onto solid carriers. Characterization of Liquid Smeeds involve studying of droplet size, cloud point, zeta potential etc. In the process of developing liquid SMEDDS for a drug, both in vitro and in vivo results should be studied. Studies involving evaluation of bioavailability of various drugs confirms the potential of this formulation. With successful commercial products and an expanding interest in clinical applications, SMEDDS are showing the way forward to future oral drug delivery.
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