Microemulsion-based delivery of triamcinolone acetonide to posterior segment of eye using chitosan and butter oil as permeation enhancer: an in vitro and in vivo investigation

The aim of the study was to formulate a microemulsion (ME) using chitosan (CH) and the butter oil (BO) as a permeation enhancer for targeting drug to the posterior segment of the eye, via topical route. Triamcinolone acetonide (TA) was selected as the model drug since it undergoes extensive first-pass metabolism, leading to poor oral bioavailability of 23%. For optimisation of BO concentration, different ratios of TA:BO were prepared by simple physical mixing in the ratio of 1:9 to 9:1 and diffusion study was performed. MEs containing TA, TA:BO and TA CH ME were formulated by water titration method. Globule sizes of TA ME, TA:BO ME and TA CH ME were found to be 66.06 +/- 0.32nm, 78.52 +/- 1.50nm and 97.30 +/- 2.50nm, respectively. In ex vivo diffusion studies using goats eye, TA:BO ME (31.33 +/- 0.46 and 33.98 +/- 0.23) and TA CH ME (24.10 +/- 0.41 and 27.00 +/- 0.18) showed higher percentage of drug diffusion in comparison to TA ME (13.29 +/- 0.41and 15.56 +/- 0.34) and TA solution (8.20 +/- 1.04 and 10.39 +/- 0.22) in presence and in absence of vitreous humour. Fluorescence intensity of coumarin-6 (as a marker) loaded ME with BO and CH was found to be higher, confirming their role in altering membrane permeability and facilitating coumarin-6 diffusion to the posterior chamber. Overall, it was concluded that BO enhances the bioavailability of TA across the retina, thereby proving its potential as permeation enhancer in facilitating drug delivery to the posterior segment of the eye.