Abstract
The concept of DDS (Drug Delivery System), involving the concept of TTS (Transdermal Therapeutic System), was created in recent years in an attempt to obtain maximal therapeutic effects of drugs whose clinical usefulness was established. Recent progress in DDS and TTS technologies depends in large part on the development and advance of polymer science, especially the improvement of techinologies utilizing polymer membranes. Two classes of membranes play a major role in transdermal absorbability of drugs in TTS, i.e., systhetic polymer membranes containes in the TTS preparations and the human skin acting as a defensive barrier. To reduce the barrier property of the horny layer of the human skin the developmement of efficient absorption enhancers constitutes a crucial point for the development of useful TTS preparations.
The determination of diffusion coefficients is essential to predict drug adsorbability in TTS, and several theoretical formulae (e.g., Fick's laws for solute permeation, absolute reaction theory for drug permeation analysis, and permeation theory of electrically charged solute) have been applied for such purpose. The development of TTS chiefly consists in the development of the system (i.c., reservoir type or matrix type) and the development of methods of enhancing drug transdermal adsorbability (i.e., transdermal absorption enhancers, transdermal absorption enhancing compositions, iontophoresis, and prodrugs).
The development of TTS preparations is intimately associated with the research and development of polymer membranes. Namely, it is true that not only the TTS preparations make use of polymer membranes, but also most of reserch approaches and procedures in TTS depend on polymer (membrane) science.
