144 G. Voskerician
cantly above the therapeutic level could induce toxicity leading to serous clinical
complications. In other circumstances, such as the case of administered antibiotics,
a minimum concentration must be maintained for an extended period. If the
antibiotic concentration falls below the acceptable therapeutic level, the intended
therapeutic effect is not reached.
Many of the novel drugs made available to the patient population, if delivered
orally or through an injection regiment must be formulated by taking into account
the limitations of such treatment routes.
3
The traditional oral administration leads
to poor site availability of the active drug component due to:
(a) exposure to the harsh intestinal environment and potential for proteolytic
enzyme degradation,
(b) loss of drug into the intestinal lumen reducing the drug availability at the level
of the intestinal epithelium,
(c) further reduction in active drug availability as it travels through the circulatory
system, followed by subsequent diffusion through various tissue before it
reaches the intended location.
In the case of injectible administration, the exposure to the harsh intestinal
environment and drug loss in the lumen are certainly avoided, however, reduction
of drug availability as a result of its path through the circulatory system and
subsequent tissues until reaching the intended location still represents a significant
limitation. Further, patient compliance for injectible regiments is generally low, an
overwhelming preference being given to oral administration which does not re-
quire a regular hospital/physician’s office visit or pain associated with intravenous
administration.
7.1.2 The BioMEMS Solution
The current drug therapy limitations are being addressed through the devel-
opment of medical devices, such as MEMS, which can protect labile active in-
gredients, precisely control drug release kinetics, deliver multiple doses, and
eliminate frequent injections.
1
Traditionally, BioMEMS represent the family of
medical devices manufactured using microfabrication techniques and materials
similar to those used by the semiconductor industry. Presently, the BioMEMS
definition has been broadened to include medical devices manufactured using
adapted microfabrication techniques and alternative materials to those employed
by the semiconductor industry. These techniques and materials usually fall outside
of the traditional micromachining of silicon which has defined the semiconductor
industry focus.
The field of controlled release has emerged to particularly address the short-
comings of oral and injectible routes of administration. It initially focused on
developing systems which would lead to a nearly constant release of drug over
an extended period of time, independent of local biological factors such as pH.
4
Much of this work involved the manipulation of biodegradable polymers sys-
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