EVALUATION OF THE BARRIER POTENTIAL OF SOME SYNTHETIC MEMBRANES IN TESTING THE IN VITRO TENOXICAM RELEASE FROM HYDROGELS, USING THE EXPERIMENTAL MODEL WITH FRANZ DIFFUSION CELLS

The present study aimed to investigate the suitability of some porous synthetic membranes as limiting barrier for testing the in vitro tenoxicam release from topical hydrogels. Two cellulose esters-based membranes and three polymeric membranes (polyamide, polyethersulfone and polysulfone) possessing the same pores diameter (0.45 mu m) but different thickness and porosity were tested. The permeability assessment of these synthetic membranes was performed using a system of six Franz diffusion cells accompanied by UV spectrophotometric analysis. Two HPMC-based hydrogel formulations containing tenoxicam either dissolved or suspended in the respective systems were used to evaluate the impact of drug dispersed form on the synthetic membranes resistance on its in vitro diffusion. The results of the in vitro tenoxicam release studies suggested that the tested synthetic membranes behaved either as high-flux or low-flux membranes, whose permeability to tenoxicam depended both on their physical characteristics (especially porosity and tortuosity) and on the dispersed form of TNX in the hydrogels. The overall results suggest that the microfiltration membranes (polyethersulfone and polysulfone), possessing a porosity of over 60% and a maximal thickness of 150 mu m should be the first choice of membrane to be used with Franz diffusion cells for the in vitro performance assessment of topical hydrogels containing tenoxicam.