Surgery – Controlled release therapeutic device or system – Osmotic or diffusion pumped device or system
Reexamination Certificate
1998-07-24
2001-09-11
Mendez, Manuel (Department: 3763)
Surgery
Controlled release therapeutic device or system
Osmotic or diffusion pumped device or system
Reexamination Certificate
active
06287295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to osmotic delivery systems for delivering beneficial agents, and more particularly, to osmotic delivery system semipermeable body assemblies which control the delivery rate of a beneficial agent from an osmotic delivery system incorporating one of the semipermeable body assemblies.
2. Description of the Related Art
Controlled delivery of beneficial agents, such as drugs, in the medical and veterinary fields has been accomplished by a variety of methods. One method for controlled prolonged delivery of beneficial agents involves the use of osmotic delivery systems. These devices can be implanted to release beneficial agents in a controlled manner over a preselected time or administration period. In general, osmotic delivery systems operate by imbibing liquid from the outside environment and releasing corresponding amounts of the beneficial agent.
FIG. 1
illustrates a cross sectional view of a known osmotic delivery system
20
. The osmotic delivery system
20
, commonly referred to as an “osmotic pump,” generally includes some type of a capsule or enclosure
22
having a semipermeable portion which may selectively pass water into an interior of the capsule which contains a water-attracting osmotic agent
24
. In the known osmotic delivery system illustrated in
FIG. 1
, the walls of the capsule
22
are substantially impermeable to items within and outside the capsule, and the plug
26
acts as the semipermeable portion. The difference in osmolarity between the water-attracting agent
24
and the exterior of the capsule causes water to pass through the semipermeable portion of the capsule which in turn causes the beneficial agent
23
to be delivered from the capsule
22
through the delivery port
29
. The water-attracting agent
24
may be the beneficial agent delivered to the patient; however, in most cases such as that illustrated in
FIG. 1
, a separate osmotic agent is used specifically for its ability to draw water into the capsule
22
.
When a separate osmotic agent
24
is used, the osmotic agent may be separated from the beneficial agent
23
within the capsule
22
by a movable dividing member or piston
28
. The structure of the capsule
22
is such that the capsule does not expand when the osmotic agent
24
takes in water and expands. As the osmotic agent
24
expands, it causes the beneficial agent
23
to be discharged through the orifice
29
at the same rate as the liquid, which is typically water, enters the osmotic agent
24
by osmosis. Osmotic delivery systems may be designed to deliver a beneficial agent at a controlled constant rate, a varying rate, or in a pulsatile manner.
In the known osmotic delivery system
20
illustrated in
FIG. 1
, an osmotic tablet is used as the osmotic agent
24
and is placed inside the capsule
22
. The membrane plug
26
is placed in an opening in the capsule
22
through which the tablet
24
and piston
28
were inserted. Known membrane plugs
26
are typically a cylindrical member with ribs, and operate in the same manner as a cork. These membrane plugs
26
seal the interior of the capsule from the exterior environment, essentially permitting only certain liquid molecules from the environment of use to permeate through the membrane plug into the interior of the capsule
22
. The rate that the liquid permeates through the membrane plug
26
controls the rate at which the osmotic agent
24
expands and drives a desired concentration of beneficial agent
23
from the delivery system
20
through the delivery orifice
29
. The rate of delivery of the beneficial agent from the osmotic delivery system
20
may be controlled by varying the permeability coefficient of the membrane plug
26
.
By varying the permeability coefficient of the membrane plug
26
, the liquid permeation rate through the membrane is controlled. Osmotic delivery systems requiring a high beneficial agent delivery rate typically use membrane plugs having high permeability coefficients. Osmotic delivery systems requiring a low beneficial agent delivery rate use membrane plugs having low permeability coefficients. The permeability coefficient is dependent on the particular material or combination of materials used in each membrane plug
26
. Thus, the known osmotic delivery system
20
illustrated in
FIG. 1
, which includes a membrane plug
26
, may control the delivery rate of the beneficial agent
23
by forming the same configuration plug
26
from different semipermeable materials having permeability coefficients corresponding to the desired beneficial agent delivery rate. One problem associated with obtaining different permeation rates in this manner is that a different membrane material must be used for every system which has a different desired beneficial agent delivery rate, requiring the purchase of many different membrane materials and manufacture of many different membrane plugs
26
.
Although the osmotic delivery device illustrated in
FIG. 1
delivers consistent and reproducible beneficial agent delivery rates, it is not possible to easily alter the beneficial agent release rate from the osmotic delivery device; a new membrane plug must be manufactured and incorporated into the device for each application. In many instances, it is desirable to easily increase or decrease the beneficial agent release rate from the osmotic delivery device. For example, the release rate for some drugs should is be increased or decreased for osmotic delivery devices that are to be implanted if the patient is overweight or underweight. Additionally, many disease treatment regimens require dose titration to optimize therapeutic response to the beneficial agent, requiring that the beneficial agent release rate be adjusted in accordance with the patient's efficacious response. It is not possible to easily adjust the beneficial agent release rate from current osmotic delivery devices, such as that illustrated in FIG.
1
.
Many osmotic delivery systems which use membrane plugs, such as that illustrated in
FIG. 1
, must administer beneficial agents at rapid delivery rates over a short period of time. These known systems use membrane materials having high permeability coefficients. i.e., high liquid uptake semipermeable materials. In general, high liquid uptake semipermeable materials are those that have greater than 60% water uptake, where % water uptake=100×(wet weight—dry weight)dry weight. Thus, low uptake semipermeable materials have equal or less than 60% water uptake.
A dramatic problem associated with membrane plugs made from high liquid uptake semipermeable materials is that the membrane plug material has a tendency to absorb liquid and swell as the liquid from the surrounding environment permeates through the membrane. This is problematic because when the membrane plug overly swells, it exerts forces on the walls of the enclosure. Such forces may rupture the enclosure and allow the beneficial agent, osmotic agent or other items within the interior of the enclosure to escape to the environment of use. Furthermore, the membrane plug may become dislodged from the system, which is especially hazardous with implantable delivery systems. Because of biocompatibility and delivery rate considerations, high liquid uptake membrane materials often must be used in osmotic delivery systems destined for human implantation; consequently, there is a need for osmotic delivery systems having membrane plugs which remain intact in the capsule during all phases of delivery.
Even if the membrane plug does not dislodge from the capsule, some high liquid uptake membrane plugs permit the osmotic agent to leak from the capsule because the membrane materials are biologically unstable. For instance, some semipermeable membranes having high permeability coefficients, such as organic polymer membranes, are unstable in biological environments and may degrade over time, permitting fluids, crystals, or powder within the interior of the capsule to leak to the environment of use. In some instan
Ayer Rupal
Berry Steve A.
Chen Guohua
Dionne Keith E.
Jordan Scott D.
ALZA Corporation
Clarke Pauline A.
Lynch Cindy A.
Mendez Manuel
Miller D. Byron
LandOfFree
Osmotic delivery system, osmotic delivery system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Osmotic delivery system, osmotic delivery system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Osmotic delivery system, osmotic delivery system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2525313