An asymptotic analysis of drug delivery from transdermal patches

Many transdermal drug delivery patches are designed to provide a constant steady-state delivery rate, regulated by a rate controlling membrane, for a certain period of time. An adhesive layer is needed to attach the patch intimately to the skin; this layer is generally designed to have little effect on the steady-state release rate. During storage all layers within these patches become saturated with drug, and as a result the delivery profile involves a sizable “burst” of drug prior to reaching a constant delivery rate. In this paper, a mathematical procedure developed by Frisch was used to derive an asymptotic solution to the accumulative amount of drug delivered versus time from which one can deduce the amount of drug released in the burst but not the kinetic details of this start up. It was shown that the adhesive layer can contribute significantly to the amount of burst even when its contribution to the steady-state release rate is negligible.