Self Microemulsifying Drug Delivery System: a Method for Enhancement of Bioavailability

Oral route is the easiest and most convenient route of drug administration, being non invasive and cost effective, thereby leading worldwide drug delivery market. But major problem encountered in oral formulations (as estimated more than 50 % of oral formulations are found to be poorly aqueous soluble), is low bioavailability, giving rise to further problems like, high inter and intra subject variability, lack of dose uniformity and finally leading to therapeutic failure. The challenging task is to increase the bioavailability of drugs. Number of technological strategies are investigated and reported in literature for improving bioavailability like solid dispersions, cyclodextrins, micronization etc. But Self-microemulsifying Drug Delivery System (SMEDDS) have gained exposure for their ability to increase solubility and bioavailability of poorly aqueous soluble drugs with reduction in dose and also drugs are protected from hostile environment in gut. SMEDDS are isotropic mixture of oil, surfactant, drug and sometimes containing cosurfactant and administered orally which on mild agitation with GI fluids forms o/w microemulsion. This review gives complete overview of SMEDDS but special attention has been paid to formulation design, evaluation and little emphasis on application of SMEDDS. INTRODUCTION: Poor aqueous solubility of lipophilic drugs creates problems in formulation as well as in oral administration. Various approaches have been developed to resolve poor aqueous solubility of lipophilic drugs. As oral route for drug administration is most commonly used among all the routes of administration due to its convenience, noninvasiveness and cost effectiveness it become necessary that drug should have some aqueous as well as some lipid solubility for their absorption. Whenever a drug is administered by oral route it undergoes many steps like solubilisation followed by permeation to produce the desired effect. After oral administration drug solubilises first due to aqueous solubility then undergoes permeation through membrane due to lipid solubility. This solubilization is difficult for drugs which have poor aqueous solubility thus act as the rate limiting step for absorption from gastrointestinal tract. Due to poor aqueous solubility of drug their efficacy also hindered leading to low absorption after oral administration. A part of administered dose of such drug absorbed and reaches to therapeutic site and the remaining part produce toxicity or side effects due to imbalance in biodistribution. For the therapeutic delivery of poorly aqueous soluble active moieties, lipid based formulations are introduced. Various formulation approaches such as micronization, solid dispersions and complexation with cyclodextrin have been used but these approaches have some disadvantages 1, . Advanced approaches include incorporation of active moiety into inert lipid vehicles 3 like oils , surfactant dispersions 5, 6 and selfmicroemulsifying delivery system 7, 8 emulsions 9, 10 and Correspondence to Author: