ABSTRACT
Toward the latter part of the last century, there were considerable expectations for
transdermal delivery and a number of very successful products have been
developed. However, the number of chemical entities that has been delivered
successfully using the transdermal route is very small. There are two major
reasons for this. Firstly, the skin is a very good barrier and there is a limitation
that only a few milligrams of drug can be delivered daily over a reasonable area.
Secondly, many materials can act adversely in the skin and produce irritant or
allergic responses. Developing a modern medicine is a very costly process and
therefore it is important to determine the feasibility of delivering a candidate using
the transdermal route before embarking on a full developmental program. The
strategies for this include an examination of the physicochemical properties of the
candidate followed by in vitro testing. With this information, a certain amount of
confidence is gained before costly development is started. One of the first
compounds to be delivered transdermally was nitroglycerin (or glyceryl trinitrate,
GTN) and the types of study conducted with it are representative of those that
should be considered in a feasibility study.
