Surgery – Controlled release therapeutic device or system – Osmotic or diffusion pumped device or system
Reexamination Certificate
1999-11-16
2002-08-20
Casler, Brian L. (Department: 3763)
Surgery
Controlled release therapeutic device or system
Osmotic or diffusion pumped device or system
C604S891100
Reexamination Certificate
active
06436091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of drug delivery. In particular, the present invention relates to methods, devices and systems adapted to sub-chronic implantation (less than or equal to 12 months and typically less or equal to about 6 months) in the patient's body to deliver a drug or other pharmaceutical agent at a sustained rate.
2. Description of the Related Art
Since the beginning of modern medicine, drugs have been administered orally. Patients have taken pills as recommended by their physician. The pills must pass through the digestive system and then the liver before they reach their intended delivery site (e.g., the vascular system). The actions of the digestive tract and the liver often reduce the efficacy of medication; furthermore, medications delivered systemically sometimes cause undesirable side effects. Over the course of the past few decades, drug delivery technology and administration has evolved from oral delivery to site-specific delivery. In addition to the oral route of administration, drugs are also routinely administered via the vascular system (intravenous or IV). Intravenous drug delivery has the advantage of bypassing the acidic and enzymatic action of the digestive system. Unfortunately, IV administration requires the use of a percutaneous catheter or needle to deliver the drug to the vein. The percutaneous site requires extra cleanliness and maintenance to minimize the risk of infection. Infection is such a significant risk that IV administration is often limited to a number of weeks, at most. In addition, the patient must wear an external pump connected to the percutaneous catheter.
The next step in the evolution of drug delivery was the implanted pump. The implanted pump is a device that is completely implanted under the skin of a patient, thereby negating the need for a percutaneous catheter. These implanted pumps provide the patient with a drug at a constant or a programmed delivery rate. Constant rate or programmable rate pumps are based on either phase-change or peristaltic technology. When a constant, unchanging delivery rate is required, a constant-rate pump is well suited for long-term implanted drug delivery. If changes to the infusion rate are expected, a programmable pump may be used in place of the constant rate pump. Fully implanted constant rate and programmable rate infusion pumps have been sold in the United States for human use since the late 1970s and early 1980s, respectively. Two problems associated with such 1970s and 1980s vintage constant rate and programmable rate infusion pumps relate to their size and their cost. Current implantable constant rate and programmable pumps are about the size and shape of hockey pucks, and they typically are sold to the hospital for $5,000-$9,000. The current implantable pumps must be implanted in the Operating Room under general anesthesia, which further increases costs, as well as the risk, and discomfort to the patient. The size and cost of such pumps has proven to be a substantial barrier to their use, and they are rarely used to deliver medication. An added drawback of phase-change and peristaltic pumps is that they must be refilled with drug every 3-8 weeks. Refills constitute an added burden to the caregiver, and add further costs to an already overburdened healthcare system. The burden associated with such refills, therefore, further limits the use of phase-change and peristaltic pumps.
In the 1970s, a new approach toward implanted pump design was commercialized for animal use only. The driving force of the pumps based upon this new approach utilized the principle of osmosis. Osmotic pumps may be much smaller than other constant rate or programmable pumps, because their infusion rate can be very low. An example of such a pump is described listed in U.S. Pat. No. 5,728,396. This patent discloses an implantable osmotic pump that achieves a sustained delivery of leuprolide. The pump includes an impermeable reservoir that is divided into a water-swellable agent chamber and a drug chamber. Fluid from the body is imbibed through a semi permeable plug into the water-swellable agent chamber and the drug is released through a diffusion outlet at a substantially constant rate.
A limitation of the osmotic pump disclosed in the above-identified patent, however, is that its infusion rate cannot be adjusted once it is implanted. This is acceptable for medications that do not need rate adjustment, but often physicians desire to adjust the infusion rate based on the clinical status of the patient. One example of when a physician would want to increase the infusion rate is in the field of pain management. Implanted pumps can be used to deliver medication to treat pain lasting over an extended period of time. Pain, however, often increases with time, and sometimes patients become tolerant to pain medications; therefore, more medication is needed to effectively treat the pain. The system disclosed in the above-identified patent does not allow a rate increase after implantation, so the physician must either replace the current implant or implant an additional pump to replace or supplement the system. However, the prospect of yet another surgical procedure may cause many patients to forego the potential benefits of the larger dose and may also cause their physicians to advise against the initial procedure altogether. For such patients for whom the implantable pump no longer delivers an adequate dosage of medication, the physician may opt to supplement the dosage delivered by the implantable device by other means, such as by intravenous delivery, in which case the same side effects discussed above may again occur.
Pain management medications are only one example of medications that need to be increased in dosage over time. Other applications may include but are not limited to hypertensive medications, other cardiovascular medications, and medications to treat disorders of the brain and endocrine system.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to provide methods and implantable devices and systems for long-term delivery of a pharmaceutical agent at selectable rates. It is another object of the present invention to provide implantable devices and systems for long term delivery of a drug that are small in size and that may be readily implanted in a physician's procedure room or a radiology suite.
In accordance with the above-described objects and those that will be mentioned and will become apparent below, an implantable osmotic pump for delivering a pharmaceutical agent to a patient comprises a pump housing; a moveable partition disposed within the housing, the partition dividing the housing into an osmotic driving compartment having an open end and a pharmaceutical agent compartment having a delivery orifice; a first semi permeable membrane disposed in the open end of the osmotic driving compartment, the first semi permeable membrane being exposed to the patient; a second semi permeable membrane disposed in the open end of the osmotic driving compartment, and a first impermeable barrier disposed over the second semi permeable membrane, the second semi permeable membrane being sealed from the patient until the first barrier is breached, wherein breaching the first barrier increases the surface area of semi permeable membrane exposed to the patient and increases a delivery rate of the pharmaceutical agent through the delivery orifice.
According to further embodiments, the first impermeable barrier may include titanium and/or stainless steel. A saturated solution including NaCl may be present between the first impermeable barrier and the second semi permeable membrane. The first and second semi permeable membranes may the same composition and/or may have the same thickness. Alternatively, the first and second semi permeable membranes may have mutually different compositions and/or mutually different thickness. The pump may further include a third semi permeable member, and a second impermeable barrier may be n
Harper Derek J.
Milo Charles F.
Casler Brian L.
MicroSolutions, Inc.
Serke Catherine
Young Law Firm P.C.
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