Bioequivalence of marketed transdermal delivery systems for tulobuterol

Tulobuterol permeation through skin from various transdermal delivery systems has been compared for the bioequivalence among devices marketed. Both the permeation profiles across the hairless mouse skin and the release profiles from the devices were measured under well-controlled in vitro conditions. The release rate of the drug from the devices was appreciably higher than the penetration rate across the intact skin, indicating the skin-controlled delivery systems. However the deviation between the release rate and the permeation rate differs depending upon the system design. The brand patch showed the least difference between the release and permeation profiles among the brand and three generic devices examined. From the in vitro permeation profiles for both intact and stripped skins, the diffusion coefficient and the partition coefficient were evaluated on the basis of bi-layer skin model. The effect of the stratum corneum thickness was then simulated by SKIN-CAD. The simulated profile has suggested that the clinical performance for transdermal tulobuterol delivery is influenced not only by the thickness of the stratum corneum but by the device design as well. This is particularly the case for the stratum corneum, thinner than about 10 microm or damaged skin with the decreased barrier capacity. For the stratum corneum thicker than 20 microm, on the other hand, the clinical performance may not be significantly influenced by the device designs investigated in this study.