Abstract

Proper selection of oils, surfactants and cosurfactants along with their optimum concentration is crucial to obtain stable, mild and clinically acceptable nanoemulsions. The focus of the present study was, therefore, to provide an efficient screening approach for the excipients selection for the optimum nanoemulsion formulation development. The oils studied included Lauroglycol 90, Capryol 90, olive oil, jojoba oil, oleic acid and Labrafil M1944. The drug solubility in the oil was taken as the criterion for oil selection. Labrasol, Cremophor EL, Tween 60 and Tween 80 were the surfactants evaluated for determining the solubilizing capacity for the oil. Among them Cremophor EL was found to be an efficient emulsifier for the oil phase. The effect of different cosurfactants such as ethanol, isopropyl alcohol, butanol, propylene glycol, PEG 400 and Carbitol on the phase behaviour of the pseudoternary system Capryol 90/Cremophor EL/cosurfactant/water was investigated. Nanoemulsion region obtained was used as an assessment criterion to evaluate the cosurfactants. The effect of Cremophor EL/carbitol mass ratio on the nanoemulsion formation was also studied by varying the ratio from 3:1 to 1:3 for the further optimization of the system. The highest nanoemulsion region was obtained at Cremophor EL: Carbitol in the mass ratio of 1:1. Formulations were selected from the phase diagram at this mass ratio at a fixed concentration of surfactant mixture (i.e. 45% wt/wt) with increasing concentration of oil (5, 10, 15, 20% wt/wt) and subjected to thermodynamic stability tests. The optimized formulations were characterized for particle size, viscosity, pH and refractive index measurements. The droplet size of all the selected formulations was found to be less than 100 nm. The formulations were thermodynamically stable and can be effectively used for the drug delivery applications.

Keywords: Nanoemulsions, solubility, oil, surfactant, cosurfactant, pseudoternary phase diagram