A candidate drug has entered the development phase but there are problems i
n drug delivery. The oral bioavailability is low or provides the wrong plas
ma profile. It is usual that other routes of administration ave proposed su
ch as nasal, pulmonary, transdermal, buccal or rectal drug delivery. These
routes offer advantages but they also require some development time. The si
tuation regarding patents has to be examined, specific formulations must be
manufactured - which can require a large amount of the active drug - and s
ometimes new excipients are used and these have to be documented, and other
animal species may need to be chosen for appropriate evaluation. The bucca
l mucosa is one of the administration sites that might provide an alternati
ve for peroral administration. This review will provide an insight into thi
s route of drug delivery and the formulations that are, or can be, used, an
d it will also describe the challenges or possibilities of this route of ad
ministration.