additional layer of pressure sensitive adhesive to cover the entire device and affix it to the skin the above four main types of transdermal devices are schematically illustrated in fig1 a 1d a fifth important type not mentioned by wick is the iontophoretic type in which an electrical potential gradient is used for transferring the drug through the skin u2014 see further e g parminder singh et al u201c iontophoresis in drug delivery basic principles and applications u201d critical reviews in therapeutic drug carrier systems 1994 11 2 amp 3 161 213 the above split up into groups is not very strict as variations and combinations of each may be envisaged so may a multi laminate type device encompass a device with many layers in a sandwich construction such as the drug in one layer excipients such as enhancers in a further layer a membrane in another layer and an adhesive in still another layer or it could be composed of several drug in adhesive layers or combinations of the above layers the liquid or gel used in the above reservoir type device could be hydrophilic or lipophilic such as water alcohols mineral oils silicone fluids various copolymers such as ethylene vinyl acetate vinyl acetate or polyvinyl alcohol polyvinyl pyrrolidine the reservoir may also include dyes inert fillers diluents antioxidants penetration enhancers stabilizers solubilizing agents and other pharmacologically inactive pharmaceutical agents being well known in the art the adhesives used are generally of three types being the rubber type encompassing inter alia polyisobutylenes the.