Bioavailability, bioequivalence, and in vitro-in vivo correlation of oxybutynin transdermal patch in rabbits

The first objective of the proposed research work includes comparative bioavailability and bioequivalence evaluation of oxybutynin transdermal patch with respect to different permeation enhancers. The second objective was to evaluate different in vitro methods along with synthetic membranes toward development of an in vitro-in vivo correlation. Oleic acid (fatty acid), Soluphor P (2-pyrrolidone, cosolvent), menthol (volatile oil), and dipropylene glycol (plasticizer) were selected as representatives from different classes of permeation enhancers. A random, crossover, single-dose pharmacokinetic study was carried out on male New Zealand white rabbits to determine bioavailability and bioequivalence. The obtained pharmacokinetic data were correlated with in vitro drug release using convolution-deconvolution approach. All developed formulations were found to be bioequivalent with respect to the marketed patch (Oxytrol (R)) on the basis of level of C-max, AUC(0-96), and AUC(total) (0.8-1.25). A biphasic linear correlation was obtained pertaining to differential diffusion behavior of the drug in vivo during the experimental timeframe. Because of close resemblance to skin, Cuprophan (R) membrane was found to be more suitable for developing an IVIVC than Millipore (R) membrane.