Diffusion model for the study of a drug from the hydrophilic matrix of a transdermal therapeutic system through a model polymeric membrane

Conclusions The kinetics of drug supply described above from gel-like hydrophilic matrices of a TTS through human skin, or a polymeric membrane imitating itin vitro, are analogous to the kinetics of the release of a drug from a reservoir TTS through an attached polymeric membrane controlling the rate. Studying the kinetics of drug supply from diffusion matrices of TTS through a polymeric membrane imitating skin enables modeling of the kinetics of transdermal drug supplyin vitro andin vivo. The adequacy of such modeling is determined by the correlation between the diffusion coefficients of the drug in the membrane and skin epidermis and the distribution coefficients of the drug between skin and matrix or between membrane and matrix, which are subject to experimental determination.The transdermal supply of drug with kinetics of zero order (i.e. at a rate constant with time) may be effected from a TTS of the membrane-reservoir type containing a membrane specially controlling the rate or from a matrix TTS. In the latter case the function of the membrane controlling the rate of drug supply is fulfilled by the human skin at the point of application of the TTS, while the TTS diffusion matrix acts as a reservoir containing drug on the skin surface and limits the maximally achievable rate of drug release from the TTS to the skin according to equation 12. The competence of such an approach is occasionally questioned because of fears that the permeability of skin for a drug depends markedly on the point of application of the TTS and on the special features of the patient's skin. The effect of skin permeability at the point of application on the rate of transdermal drug supply has been studied well in [21] and a standard place for the application of a TTS may be the correct choice. The vast scope for the clinical application of the various TTS available at the present time indicates that individual variability of skin permeability is not so great and may be displayed mainly by a reduced permeability of the skin for a drug. Unlike membrane-reservoir TTS the majority of matrix TTS may be divided into portions of various size without disturbing their efficiency. This raises the possibility of continuously regulating the dose (by the area of application for TTS of this type).Translated from Khimiko-farmatsevticheskii Zhurnal, Vol. 28, No. 10, pp. 38–45, October, 1994.