Evaluation of a microemulsion-based gel formulation for topical drug delivery of diclofenac sodium

Abstract

The aim of the current research was to investigate the release of diclofenac sodium, a poorly water-soluble drug from different formulations in vitro. A microemulsion (ME) was prepared using caprylocaproyl polyoxyl-8 glycerides, diethylene glycol monoethyl ether, and propylene glycol monolaurate. For enhancing the viscosity, carbopol was used to form an ME-based gel. The prepared formulations were characterized for physical appearance, droplet size, zeta potential, refractive index, percentage transmittance, heating–cooling cycles, phase separation, pH, conductivity, viscosity, drug content, staining solubility test, transmission electron microscopy and in vitro drug release using Franz diffusion cells. The mean droplets size for ME and ME-based gel-systems were 114.4 ± 0.472, and 178 ± 2.46 nm respectively, whereas the zeta potential values were −33.3 ± 0.64 mV for the former and −33.0 ± 0.40 mV for the latter. No significant variations in the pH nor physical appearance alterations were observed while stability tests were performed. Further, TEM images for drug-loaded ME and the gel exhibited nano-droplets that were spherical in shape. The release rate of diclofenac sodium formulated as ME or as ME gel had the highest release values (76.67 ± 8.63%) and (69.28 ± 7.14%) after 6 h respectively. This was statistically significant (p < 0.0001) compared to the control and different marketed formulations or compounded preparations. The ME-based gel had a higher viscosity suitable for topical administration without dripping. The in vitro result suggested that ME systems are powerful topical vehicles for enhanced penetration of diclofenac sodium.