Biomedical Engineering Reference
In-Depth Information
some examples of research into new classes of biodegradable polymers that
address specifi c weaknesses in the current systems. The chapter does not attempt
to cover the entire range of biodegradable polymers under development as drug
delivery systems or to provide a complete history of the development of the poly(
-
hydroxyl acids) and polyanhydrides, but the reader is referred to more comprehen-
sive review articles throughout.
α
15.2
The Clinical Need for Drug Delivery Systems
Drug delivery systems modify the kinetics or the location of the escape of the drug
from the medicine. Tables 15.1 and 15.2 provide generic reasons for using drug
delivery systems.
For drug delivery systems containing biodegradable polymers, the major motiva-
tions for clinical use have been to deliver drugs that are required for long periods,
are rapidly removed by metabolism or excretion, and are required at sites of
administration that are diffi cult or impossible to reach with oral or conventional
injection routes [1] .
Cancer chemotherapy [2] and long-term replacement of human growth hormone
[3] have been the major clinical foci for research on biodegradable polymer applica-
tions. Zoladex is the most successful (in terms of duration of clinical use and
Table 15.1
Use of a drug delivery system for kinetic control.
Dissolution of drug is too slow
Drug and/or formulation is physically removed from the site of action too rapidly
Metabolism or excretion of the drug is too fast
Drug is required intermittently
Administration is complex, invasive, and/or costly and therefore, dosing frequency needs to
be reduced
Patient compliance (e.g., motivation to remember to take dosage) is poor and consequences
of missing dosages are serious
Table 15.2
Examples of motivations to use a drug delivery system for location control.
Avoid side effects by minimizing exposure of other tissues
Concentrate drug at the site of action
Avoid rapid metabolism or excretion from the body
Accelerate drug transport across cell membranes
The route of administration is technically diffi cult (e.g., injection)
