Preparation, statistical optimization and in vitro characterization of solid lipid nanoparticles as a potential vehicle for transdermal delivery of tramadol hydrochloride as a hydrophilic Compound

As encapsulation of hydrophilic drugs in the solid lipid nanoparticles (SLNs) is still a challenging issue, the aim of this study was to prepare SLNs containing tramadol hydrochloride as a hydrophilic compound. The SLNs were prepared using glycerol monostearate (GMS), soy lecithin and tween 80 by double emulsification-solvent evaporation technique. The nanoparticles were optimized through a centralcomposite response surface (RSM) method. The independent variables were GMS/lecithin ratio and the amount of drug while dependent responses were size, poly dispersity index (PdI) and zeta potential. The optimized nanoparticles were then freeze dried and their morphology was examined using transmission electron microscopy (TEM). Finally, the in vitro drug release profile from nanoparticles was evaluated and the kinetic of the release was determined. The particle size, PdI, zeta potential, entrapment efficiency and loading efficiency of the optimized SLNs were 131±17.25 nm, 0.21±0.013, -11.2 ±1.04 mV, 89.4±2.38% and 9.49±0.14%, respectively. TEM images revealed de-agglomerated spherical nanoparticles. In vitro release studies showed sustained release of tramadol over 72 h. The release kinetic was best fitted to the first order and Korsmeyer-Peppas kinetic model. The obtained results indicated that tramadol as a hydrophilic compound can entrap appropriately in the solid lipid nanoparticles exhibiting favorable physicochemical properties.