| Popis: |
The first part of this chapter focuses on the benefits and limitations of transdermal drug delivery systems (TDDSs). Advantages include convenience, avoidance of presystemic metabolism (first-pass effect) and painlessness. Other benefits include noninvasiveness (or minimal invasiveness in the case of microneedles), the absence of gastric irritation, a more uniform absorption, as well as a faster onset of action. One of the limitations of the transdermal route is that externally introduced chemicals (including medications) have to overcome the stratum corneum before entering into systemic circulation. All drugs currently marketed in the form of TDDSs are very potent and typically, their molecular weights are lower than 500 Daltons. Proteins, peptides, and genes are hydrophilic, electrically charged macromolecules and therefore cannot cross the human skin in therapeutic quantities. The second part of this chapter examines the classification of transdermal patches. Passive transdermal systems belong to three major categories: the reservoir (membrane-controlled), matrix without a rate-controlling membrane, and matrix systems with a rate-controlling membrane. In reservoir transdermal systems, drug flux depends on the diffusion rate across a polymer membrane. In a matrix transdermal system, the medication is incorporated into an adhesive polymer, from which the medication diffuses through the skin into the bloodstream. |
