Abstract

There are several strategies for the improvement of the bio-availability of poorly absorbed drugs, such as proteins, peptides, some antibiotics, very hydrophilic drugs in general, and many others. The use of absorption enhancers (absorption promoters) is a very important possibility for that objective and among others has the essential advantage of increasing the absorption of the unmodified drug substance, rather than using a chemical derivative as another alternative to improve bioavailability. As a consequence absorption enhancers have been heavily investigated to advance the therapeutic options for difficult drugs. This chapter reviews the most important results in this field, mainly concentrating on the last three decades. While all relevant routes of drug administration are considered, the main focus is on drug application to the skin, as being the largest human organ. In addition sections have been included on important topical nonsystemic application routes for the local treatment of special organic diseases, for example, ungual and ocular administration. Thereby the aim is to improve the drug penetration into the target areas. Therefore, penetration enhancers is the more adequate denomination for substances used for these purposes. Figure 1 illustrates the drug delivery routes addressed in this chapter.