Microemulsions are isotropic and thermodynamically stable dispersed micro-heterogeneous systems composed of water, oil and amphiphile.1) Their stability and unique solubilization properties have drawn attention for their use as vehicles for drug delivery. Microemulsions have the ability to protect labile drugs, control their release, increase their solubility and bioavailability and reduce patient variability. It has been proven possible to formulate preparations suitable for different routes of administration viz., oral, topical, ocular, pulmonary and intravenous. Microemulsion contains nanometer-sized droplets of oil or water. If the droplets are non interacting the resulting microemulsion will be low in viscosity. On other hand high viscosity and optically clear (microemulsion gel) microemulsions results due to the interaction of cylindrical or wormlike micelles in microemulsion formulations. Microemulsion systems containing lecithin and low water content leads to the formation of microemulsion gel and the utility of the resulting gels have been reported to deliver the drugs through skin.
2,3)Although various types of microemulsions have been reported as being nontoxic, but microemulsion systems composed of regulatory approved excipients for pharmaceutical uses are limited. The choice of oil is limited to medium chain glycerides or fatty acid esters such as isopropyl myristate (IPM), isopropyl palmitate and ethyl or methyl esters of lauric, myristic and oleic acid.2) Uses of pure plant oils have also been reported in recent literature.4-7) Microemulsification of most widely used oil IPM for topical application has been achieved by using lecithin, polyoxyethylene sorbitan n-acyl esters (polysorbate 85, 80, 60, 40), sodium bis-2-ethyl hexyl sulphosuccinate (AOT), sucrose esters, polyoxyethylene (4) lauryl ether, C(12) Eo(8) as surfactants and short chain alcohols (ethanol, propanol, butanol), amines, alkanoic acid, poly ethylene glycol alkyl ethers, sorbitol, sucrose, sucrose ester, propylene glycol, lysolecithin, 2-acyl lysolecithin, mono alkyl phosphate as co-surfactants. 2,[8][9][10][11][12][13][14] In respect of convenience of formation and use, the oil IPM is better choice in comparison with other physiologically tolerable oils.
13)According to reports, medium chain fatty acids, mono-, di-, and tri-glycerides, particularly caprylic/capric mono-/diglycerides have been used independently in mixed micelle, emulsion and microemulsion formulations and as absorption enhancers for a number of drugs, since they have been found to be physiologically well tolerated.15) Further, mono-/diglycerides or polyol fatty acid esters have also been used as a permeation enhancer. 16,17) In view of the above-mentioned prospects, more investigations on micelle and microemulsion formulation using glycerides of the above categories is warranted.In the present study, IPM has been used as oil phase with poloysorbate 80 (polyoxyethylene sorbiton mono oleate) and caprylic/capric mono-/di-glycerides (MDG) as surfactant and co-surfactan...
