The aim of the current study was to develop self-nanoemulsifying systems (SNES) of enalapril (EN) in an attempt to improve the solubility of the sparingly soluble drug, enalapril and enhance its in-vitro release. The solubility of EN in oily phases, surfactants and cosurfactants was determined to identify the components of SNES. The SNES of EN were prepared using the oils; oleic acid, capryol 90 and labrafil M1944CS, the sufactants; tween 80 and labrasol and the co-surfactant; Transcutol HP. Pseudo-ternary phase diagrams were constructed to identify the self-emulsifying regions and to optimize emulsifier to co-emulsifier ratio and the concentration of oil. The nanoemulsion regions in the diagrams are plotted and the wider region indicated the better self-emulsification efficiency. Systems which include tween 80 and labrasol showed highest self-emulsification region when used with transcutol HP in concentration ratio (2:1). However increasing the surfactant to co-surfactant ratio to be (3:1) mostly didn’t increase the self-emulsification region. So Sys.1, Sys.2, Sys.3, Sys.4, Sys.5 and Sys.6 which contain surfactant and co-surfactant in ratio 2:1 were chosen for completing this study. The prepared SNES (Sys.1, Sys. 2, Sys.3, Sys.4, Sys.5 and Sys.6) were evaluated for their drug content, in-vitro drug release, emulsification time, dispersibility, droplet size, zeta potential and morphological study of the SNES globules. The physicochemical compatibility studies of EN and its physical mixture with different materials used in SNES preparation were carried out using DSC and FTIR analysis. It can be concluded that the optimal SNES formulae (Sys.1, Sys.3 and Sys.5) had nanometer charged particle size (10.32 to 70.65), clear appearance in dispersibility test and they released drug more than (99%) within one minute.
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