Use of solid phase extraction (SPE) to evaluate in vitro skin permeation of aescin

The aim of this work was to evaluate the feasibility of assessing aescin in vitro permeation throughhuman skin by determining the amount of aescin permeated using conventional HPLC proceduresafter extraction of skin permeation samples by means of solid phase extraction (SPE). Aescin in vitroskin permeation was assessed from aqueous solutions and gels using both Franz-type diffusion cellsand flow-through diffusion cells. The SPE method used was highly accurate (mean accuracy 99.66%),highly reproducible (intra-day and inter-day variations lower than 2.3% and 2.2%, respectively) andaescin recovery from normal saline was greater than 99%. The use of Franz-type diffusion cells didnot allow us to determine aescin flux values through excised human skin, therefore aescin skin permeationparameters could be calculated only using flow-through diffusion cells. Plotting the cumulativeamount of aescin permeated as a function of time, linear relationships were obtained from both aqueoussolution and gel using flow-through diffusion cells. Aescin flux values through excised humanskin from aqueous gel were significantly lower than those observed from aqueous solution (p < 0.05).Calculating aescin percutaneous absorption parameters we evidenced that aescin partition coefficientwas lower from the aqueous gel with respect to the aqueous solution. Therefore, the SPE methodused in this study was suitable to determine aescin in vitro skin permeation parameters from aqueoussolutions and gels using a conventional HPLC method for the analysis of the skin permeation samples.