Surgery – Controlled release therapeutic device or system – Osmotic or diffusion pumped device or system
Reexamination Certificate
2000-02-15
2003-09-09
Casler, Brian L. (Department: 3763)
Surgery
Controlled release therapeutic device or system
Osmotic or diffusion pumped device or system
Reexamination Certificate
active
06616652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of drug delivery systems. In particular, the present invention relates to osmotic pump systems, devices, kits and associated methods for shortening the time interval between implantation of the osmotic pump system and delivery of a pharmaceutical agent to the patient.
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. A recent 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.
Once implanted, however, conventional osmotic pump systems do not begin infusing drug into the patient immediately. Indeed, the semi permeable plug, initially dry before implantation, must first become thoroughly hydrated with the patient's bodily fluids after implantation before the pump will deliver the drug at the intended and designed infusion rate. This time interval between implantation and full hydration of the semi permeable plug is non-trivial, and is usually on the order of several hours to 2-4 days. In the case wherein the pump contains pain medication, this means that the patient must endure a long delay before the pump begins to work as designed (i.e., at its steady state infusion rate) and.provides the expected relief. Often, therefore, the surgeon must provide the patient with additional medication to bridge the gap between implantation of the osmotic pump system and full operation thereof. Patients, therefore, would be well served with osmotic pump delivery systems that would begin infusing drug at the intended rate immediately or soon after implantation.
Further adding to this delay is the catheter attached to the osmotic pump. The catheter is designed to carry the drug from the osmotic pump to the intended delivery site within the patient, whether a subcutaneous, epidural, subdural, subarachnoid, intravenous or intraventricular location, for example. The infusion lumen of the catheter defines an internal volume called the dead volume of the catheter. Upon first implantation of a osmotic pump system, the drug pushed out of the pump's drug compartment must flow the entire length of the catheter before reaching the intended delivery site. The time required for the drug to do so further adds to the already long hydration delay and further delays any benefit to be derived from using an implantable pump system. Patients would also be well served, therefore, with methods, devices and systems to shorten or eliminate the delay in delivery of the drug attributable to the dead volume of the catheter.
A conventional osmotic pump system, however, does start to infuse some amount of drug as the semi permeable plug hydrates. However, the amount of drug that is infused as the plug hydrates is often unknown and unpredictable. Indeed, the rate at which the plug hydrates may vary upon many factors, such as the composition and thickness of the semi permeable plug, as well as the hydration levels of the implantation site of the system within the patient. Therefore, it becomes difficult for the surgeon to estimate the effective drug delivery rate in the first few hours and days after implantation. This may render the surgeon overly conservative or unduly aggressive when administering pain medication to bridge the aforementioned gap between initial implantation and full hydration of the semi permeable plug. Indeed, the surgeon may administer less (or more) drug than the therapeutically optimal amount. This is because the surgeon has no way of reliably estimating the current amount of drug being infused into the patient soon after implantation of the osmotic device, as the semi permeable plug thereof typically does not hydrate at a constant or predictable rate in all situations.
There is believed to have been a long felt need for osmotic pump systems, devices and associated methods in which the initial delivery rate of pharmaceutical agent is predictable, and occurs at substantially the designed steady state infusion rate.
SUMMARY OF THE INVENTION
It is an object of the present invention, therefore, to provide osmotic pump delivery systems that begin infusing a pharmaceutical agent at the intended rate immediately or soon after implantation. It is a further object of the present invention to provide methods, devices and systems to shorten or eliminate the delay in deliver
Harper Derek J.
Milo Charles F.
Casler Brian L.
DeSanto Matthew
Microsolutions, Inc.
Young Law Firm P.C.
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