Influence of different formulation variables on the performance of transdermal drug delivery system containing tizanidine hydrochloride: in vitro and ex vivo evaluations

The present study was aimed at preparation of transdermal patches of tizanidine HCl, evaluation of the effect of polymers on in vitro release pattern of the drug, and the effect of permeation enhancers on the penetration of the drug through the rabbit skin. Various proportions of hydrophilic (HPMC) and hydrophobic (Eudragit L-100) polymers were used with PEG 400 as film-forming agent, and Span 20 or DMSO as permeation enhancer. The formulations were assessed for physicochemical characteristics and in vitro drug release studies using USP paddle over disc method in phosphate buffered saline (pH 7.4) at 32.0 +/- 1 degrees C. On the basis of in vitro studies and physicochemical evaluations, S03-A and S04-A were selected at Eudragit : HPMC ratios of 8:2 and 7:3, respectively, for further ex vivo analysis. The effects of different concentrations of Span 20 and DMSO were evaluated on excised rabbit skin using Franz diffusion cell. Cumulative drug permeation, flux, permeability coefficient, target flux, and enhancement ratio were calculated and compared with the control formulations. Kinetic models and Tukey's multiple comparison test were applied to evaluate the drug release patterns. Formulation SB 03 PE containing Eudragit L-100:HPMC (7:3) with Span 20 (15% w/w) produced the highest enhancement in drug permeation, and followed zero order kinetic model with super case-II drug release mechanism.