Biomedical Engineering Reference
In-Depth Information
area of the drug is not easily controlled. In most cases, the initial drug con-
centration at er administration is above the toxicity level and then gradually
diminishes over time to an insui cient therapeutic level. h is is a very in
ef ective and potentially dangerous way of delivering drugs. Also, the dura-
tion of the therapeutic ei cacy is dependent on the frequency of adminis-
tration and the half-life of the drug. High dosages of non-targeted drugs are
ot en administered to achieve an ef ective blood concentration for treat-
ment which could be damaging to the entire body [89]. Conventional drug
administration methods are also limited in providing long-term treatment,
a narrow therapeutic window, complex dosing schedule, combination ther-
apy, and personalization-based dosing [90]. To overcome these limitations,
development of combination drug and medical device systems that have the
ability to protect active ingredients, precisely control drug release kinetics
(time of dose and the amount administered), and deliver multiple doses
are required. New medical device and drug combination system also need
to have the ability to be controlled and to adjust the release of therapeutic
agents. h is helps to eliminate the need for frequent injection or even sur-
gery for implantable drug release systems [90].
Advances in microfabrication technology of implantable responsive drug
release systems are becoming more realistic for medical applications [88].
Implantable drug delivery devices for administration of a precise amount of
therapeutic agents at a specii c time would be an important tool for treatment
of numerous diseases that require repeat administration of drugs. However,
there are some large limitations to implantable drug delivery devices, e.g.,
the device requires surgery for implantation and needs to have the ability
to release drugs over a long period of time and therefore a large amount of
drugs. Also, if a device needs to have a lifetime of a year, a high concentration
of drug will need to be stored in the device safety. h erefore, the ideal implant
system would protect the drug from the body until it is needed, allowing con-
tinuous or time-specii c delivery of therapeutic agents, and being controlla-
ble externally without surgery. h ese requirements can be achieved by using
individual drug containing reservoir microchips which have one important
advantage over other designs: they have the ability to totally control drug
delivery amount and timing via either continuous or palatial delivery [91].
Also, polymer microchips that are biodegradable are benei cial products
because surgery would not be required to retrieve the device.
2.6.2
Drug Delivery Improved by Devices
Since the 1970s, the FDA has approved over 70 controlled drug-delivery
combination products [92]. During the last twenty years, drug-delivery
