As more therapies are able to indicate implantable devices for treatment, incorporating drug delivery into them can be a significant additional benefit. Even when
drug delivery is the primary function, implantable devices can be preferable. This
article reviews some representative applications that device designers can leverage
in developing new products for the implantable drug delivery market.
implants, conversely, provide long-term, “passive”
release without the need for replenishment. Typically found as thin flexible rods or “matchsticks,” these
delivery systems are particularly effective for the
delivery of highly potent drugs, such as hormones.
Commercial examples include histrelin implants for
the palliative treatment of prostate cancer and uterine fibroids, and early puberty in children, levonorgestrel and etonogestrel implants for family planning,
and buprenorphine for the treatment of opioid
addiction (pending FDA approval). Additional
indications in development include subcutaneous
implants for treatment of schizophrenia, breast
cancer, photosensitivity, and Parkinson’s disease.
A number of promising solid implant applications can be found in ophthalmology for
the treatment of macular edema and retinal vein
occlusion using corticosteroids, with products in
development for the treatment of glaucoma and
age-related macular degeneration.
By James Arps, Ph.D., Director, ProMed Pharma
Implantable devices are called upon to serve a variety of functions, from vascular stents that preserve blood flow to electrostimulation
devices that regulate heart rhythm or block spurious signals in the brain to orthopedic devices that
mechanically reinforce the spine or restore range
of motion of hips and knees. For over a decade,
there has been an increasing convergence between
implantable devices and drug therapies, including
devices that deliver drugs as a primary action.
Why Implantable Devices for Drug Delivery?
Implantable drug delivery devices offer several
advantages over conventional oral or parenteral
dosage forms. First, implantable devices allow site
specific drug administration where the drug is
needed most. Examples include implants used in
the treatment of brain tumors or prostate cancer.
This may also allow for
significantly lower doses of
the drug, which can minimize potential side effects.
Second, implantable devices
allow for sustained release
of a therapeutic agent (
Figure 1). The last and perhaps
most important advantage
is patient compliance, as the
treatment regimen associated with an implantable device is generally less
burdensome than pills or injections.
Figure 1: Idealized comparison of tissue drug levels for injections compared
with an implantable drug delivery device. Clearance of the drug after an
injection may result in significant time outside of the therapeutic window.
Types of Drug Delivery Devices
Implantable drug pumps are used to deliver insulin
in the treatment of diabetes and to administer
pain medications directly to the spine (intrathecal
pumps). These are typically programmable “active”
devices that require regular resupply of the medication through an access port. Subcutaneous solid
Opportunities in Women’s Health
In addition to subcutaneous implants, novel drug
delivery forms, such as intrauterine devices (IUDs)
and intravaginal rings (IVRs), are finding increasing applications in the area of women’s health. For
more than two decades after serious safety issues
were encountered with the Dalkon shield, no IUDs
were marketed in the U.S. In 2000, the FDA approved a levonorgestrel eluting IUD providing contraception for up to five years of use. Later, use of
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Medical Design Technology®
May 2013 / 23