Physicochemical characterization and stability of flurbiprofen submicron emulsions with various co-emulsifiers for parenteral injection

Submicron emulsions of flurbiprofen were prepared using coconut oil as the oil phase and egg lecithin as the main emulsifier. Various co-emulsifiers were incorporated into the emulsions, including Pluronic F68, oleic acid, and chitosan. The accelerated stability after autoclaving and thermal treatment at 50 °C for 5 days was investigated. The submicron emulsions were assessed by evaluating such parameters as particle size, zeta potential, relaxation time (T₁), pH value, surface tension, and the drug release rate. The addition of chitosan greatly enlarged the particle size by a 6-8-fold increase, thus reducing flurbiprofen release. The emulsion incorporated with Pluronic F68 showed the smallest mean droplet size of 254.30 nm. The T₁ determined by NMR varied from 0.342 to 0.928 which showed that flurbiprofen was located at different sites within the various emulsions. Incorporation of a co-emulsifier did not always provide improved stability. Thermal treatments decreased the pH values and flurbiprofen release from the emulsions. No direct correlation was found among the various physicochemical characteristics in the accelerated stability tests. Oleic acid alone or the combination of oleic acid and Pluronic F-127 F68 generally increased the stability of the submicron emulsions.