Biomedical Engineering Reference
In-Depth Information
span could be short or long depending on the needs of the specific
therapy.
Stability : The stability of drug-carrier formulations is required
for long-term shelf life as a pharmaceutical product, and also upon
administration until the system reaches the target. Stability for a
drug-carrier formulation means: chemical stability of the drug and
of all carrier materials; retention of drug activity; retention of a
carrier's structural integrity; retention of the drug encapsulation-
level achieved at the end of production.
The second set of requirements, designated to avoid problems
introduced by the carrier itself, is also self-explanatory. As will
be discussed later in this chapter, constructing carriers from
biomaterials helps toward meeting these requirements.
1.1.3
Major Categories of Drug Carriers
Drug carriers can be divided into two categories (Figure 1.3).
In the first category, the carrier is a macromolecule, from
biological or synthetic origins, carrying several drug molecules
attached covalently, directly or through spacers [6-10]. The drug-
carrier bond should obviously be of a type cleavable at the target.
These carriers have been termed soluble or linear, even though the
macromolecule is not necessarily linear.
In the second category, the carrier is a particle that can also be
made from biological or synthetic components. The drug molecules
are encapsulated within the particle with no need for covalent
binding [1-5].
Figure 1.3 The two major categories of drug delivery systems. See also
Color Insert.
Particulate carriers can be further divided into several sub-
categories (Figure 1.3): particles in which the shell and the interior
are made from diff erent components, the interior usually containing
 
Search WWH ::




Custom Search