Topical administration is an appealing method for drug delivery due to its non-invasiveness, selfcontrolled
application, avoidance of first-pass metabolism in the liver and reduction of systemic side effects compared
to other conventional routes such as oral and parenteral. However, topical administration must overcome the
permeable barriers that skin and mucosa represent for the drug to achieve its desired therapeutic effect.
Penetration of drugs through human skin is mainly impaired by the stratum corneum— the uppermost keratinized
skin layer. In contrast, the stratified squamous epithelium (a nonkeratinized tissue) represents the major physical
barrier for transbuccal drug administration in humans.
Different technologies have been studied to enhance the bioavailability or local effects of drugs administered through skin and buccal
mucosa. Those technologies involve the use of physical or chemical enhancers and new dosage forms such as vesicles, cyclodextrins,
nanoparticles and other complex systems. Combinations of these technologies may further increase drug delivery in some cases.
As analgesia is one of the main therapeutic effects sought through topical administration, this paper focuses on the review of drug delivery
systems to improve the topical and transdermal/transbuccal drug delivery of substances with known analgesic action. A discussion of
their possibilities and limitations is also included.