Microsponge Gel Approach to Increase the Stability and Efficacy of Avobenzone as a Sun-Protective Agent

Purpose Avobenzone is a broad-spectrum sun-protective agent widely used in the form of creams and lotions. However, it is highly photo-unstable and causes irritation and systemic absorption which needs to be addressed. Microsponges are porous, polymeric carriers that are designed to deliver a pharmaceutical/cosmetic ingredient efficiently at the minimum dose and also to modify the drug release (sustained release) while reducing the skin toxicity problems pertaining to the drug. An attempt was made to formulate avobenzone-loaded microsponge gel. Method The microsponges for the delivery of avobenzone were successfully prepared by quasi-emulsion solvent diffusion method. The formulated microsponges were characterized for production yield, particle size, SEM, % entrapment efficiency, % drug release, FTIR and DSC. The optimized microsponges were further incorporated in hydrogel (HPMC K4M) in different ratios and evaluated for pH, viscosity, homogeneity, spreadability, stability testing, skin irritation study and sun protection factor (SPF) testing. Results The results showed that microsponge were spherical in shape with pore size in the range 0.10-0.30 mu m. The production yield was between the range of 47 and 91.81%. The particle size was obtained within the range of 200 to 399 mu m, indicating that increase in solvent (DCM) concentration reduces the particle size. Entrapment efficiency of formulation was ranging between 60 and 77.40%. In vitro drug release showed prolonged release of the drug for a duration of 8 h, and the % CDR was in the range of 27.79 to 65.66%. The microsponge gel showed good homogeneity and viscosity in the range of 1556 to 2622 cps, and spreadability was between 4.1 and 5.9 g.cm/s. The gel was found to be stable at 40 degrees C temperature and 75% RH, for a duration of 60 days. Microsponge gel was non-irritant on the rat skin and showed controlled release. Conclusion The controlled release and barrier effect of gel from microsponge result in prolonged retention of avobenzone along with decreased permeation activity. Hence, in conclusion, the study revealed enhanced efficacy and reduced toxicity with prolonged release of drug. It also showed better sun protection factor of 25 compared to the marketed preparation which was sun protection factor 20.