Patent Application
20050101943
The invention relates generally to implantable osmotic pumps for delivering beneficial agents. More specifically, the invention relates to an implantable osmotic pump having a semipermeable membrane for controlling the delivery rate of a beneficial agent.
Implantable osmotic pumps for delivering beneficial agents within the body of a patient are known in the art. For illustration purposes,
The rate at which the osmotic pump 100 delivers the beneficial agent to the patient depends on the rate at which fluid is imbibed through the semipermeable membrane plug 108. The rate at which fluid is imbibed depends on the permeability, thickness, exposed surface area, and radial compression of the semipermeable membrane plug 108. Thus, once the osmotic pump 100 is assembled, the rate at which the beneficial agent 120 will be delivered to the patient is already established. This limits use of the osmotic pump in applications such as personalized care, where a caregiver requires the flexibility of administrating dosages to patients using non-standard dosing regimens. For these applications, the ability to adjust the delivery rate of the osmotic pump post-manufacture and pre-implantation could be beneficial. Preferably, the adjustment means does not have an adverse effect on the ability of the osmotic pump to deliver the beneficial agent.
In one aspect, the invention relates to an osmotic pump system which comprises a capsule having at least one delivery port, a membrane plug retained at an open end of the capsule remote from the delivery port, the membrane plug providing a fluid-permeable barrier between an interior and an exterior of the capsule, and a removable imbibition rate reducer attachable to the capsule. The imbibition rate reducer comprises one or more flow controllers selected from the group consisting of an orifice having a selected size smaller than a surface area of the membrane plug and a membrane having a selected thickness, surface area, radial compression, and permeability.
In another aspect, the invention relates to an osmotic pump system which comprises an implantable osmotic pump having a membrane plug at a first end and a delivery port at a second end remote from the first end. The membrane plug forms a fluid-permeable barrier between an interior and an exterior of the osmotic pump. The osmotic pump system further includes a removable imbibition rate reducer that is attachable to the osmotic pump. The imbibition rate reducer is selected from the group consisting of an orifice module having an orifice with a selected size, a membrane module having a membrane with a selected thickness, surface area, radial compression, and permeability, and combinations thereof. The orifice and membrane are configured to decrease an imbibition rate of the osmotic pump.
In another aspect, the invention relates to a method of adjusting a predefined delivery rate of an osmotic pump having a membrane plug forming a fluid-permeable barrier between an exterior and an interior of the osmotic pump. The method comprises reducing an imbibition rate of the osmotic pump by attaching an imbibition rate reducer to the osmotic pump so that fluid enters the membrane plug by passing through the imbibition rate reducer. The imbibition rate reducer comprises one or more flow controllers selected from the group consisting of an orifice having a selected size and a membrane having a selected thickness, surface area, radial compression, and permeability. The orifice is configured to reduce an effective surface area of the membrane plug, and the membrane is configured to increase an effective flow path length of the membrane plug.
In yet another aspect, the invention relates to an osmotic pump kit which comprises an implantable osmotic pump including a semipermeable membrane plug forming a fluid-permeable barrier between an interior and an exterior of the osmotic pump, a membrane module for increasing an effective flow path length of the membrane plug, and an orifice module for decreasing an effective surface area of the membrane plug, wherein the membrane module and orifice module are separately and independently attachable to or detachable from the osmotic pump.
Other features and advantages of the invention will be apparent from the following description.
The invention will now be described in detail with reference to a few preferred embodiments, as illustrated in accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or process steps have not been described in detail in order to not unnecessarily obscure the invention. The features and advantages of the invention may be better understood with reference to the drawings and discussions that follow.
An imbibition rate reducer according to embodiments of the invention may be attached to or detached from an osmotic pump post-manufacture. When the imbibition rate reducer is attached to the osmotic pump, it functions to reduce the imbibition rate of the osmotic pump. In accordance with embodiments of the invention, the imbibition rate reducer includes an orifice to reduce the exposed surface area of a semipermeable membrane plug, which forms a fluid-permeable barrier between the exterior and interior of the osmotic pump, and/or one or more membranes to increase the effective flow path length of the membrane plug. The imbibition rate reducer allows the delivery rate of the osmotic pump to be reduced by an amount corresponding to the reduction in the imbibition rate of the osmotic pump. In one practical application, a caregiver could start with an osmotic pump designed to deliver a larger amount of medicament than what may be required for a particular patient. Based on the actual delivery rate desired by the caregiver, a reduction in exposed surface area and/or an increase in effective flow path length that would give the required imbibition rate can be determined and used to configure the imbibition rate reducer.
The imbibition rate reducer can be configured post-manufacture and pre-implantation using an orifice module and/or one or more membrane modules. For illustration purposes,
It should be noted that the invention is not limited to use of the single orifice 208 to control flow into the semipermeable membrane plug. For example, a cluster of holes can replace the single orifice 208, the combined flow area of the holes being selected to achieve the desired reduction in imbibition rate. Reduction in imbibition rate through the use of the orifice module 200 produces a corresponding reduction in the rate at which a beneficial agent is delivered by the osmotic pump.
The housing 202 is constructed so that it can be attached to an end portion of the osmotic pump including the semipermeable membrane plug. Preferably, the housing 202 can be snap-fitted to the osmotic pump. In one embodiment, an annular lip 212 is provided on an inner surface 214 of the housing 202. The annular lip 212 can engage with an annular groove (not shown) provided on an outer surface of the osmotic pump. Alternatively, the annular lip can be provided on the osmotic pump and the annular groove for engagement with the annular lip can be provided on the housing 202. Basically, any means of coupling tubular members, such as a threaded connection, can be used to affix the housing 202 to the osmotic pump. To maintain the osmotic pump in a sterile condition, the housing 202 should be attached to the osmotic pump using aseptic technique. In general, the cross-section of the housing 202 should be selected such that it can fit on or over an end portion of the osmotic pump. In general, any configuration such that a biofluidic path cannot be formed between the junction of the housing 202 and the end portion of the osmotic pump can be used. For example, if the end portion of the osmotic pump containing the semipermeable membrane plug has a circular cross-section, the housing 202 should preferably have a circular cross-section.
The housing 202 is formed from an inert and, preferably, biocompatible material. The material is “inert” in the sense that it will not react with the materials it will come in contact with during use. Exemplary inert, biocompatible materials include, but are not limited to, metals such as titanium, stainless steel, platinum and their alloys, and cobalt-chromium alloys and the like. Other compatible materials include polymers such as polyethylene, polypropylene, polycarbonate, polymethylmethacrylate (PMMA), and the like.
The exposed surface area of the membrane 304 may be the same as or may be different from the exposed surface area of the semipermeable membrane plug of the osmotic pump. That is, fluid imbibition can be controlled not just by the thickness of the membrane 304 but also by the exposed surface area of the membrane 304. The sleeve 302 radially constrains the membrane 304, exerting an amount of radial compression on the membrane 304. This radial compression along with the thickness, permeability, and exposed surface area of the membrane 304 can be selected to achieve a desired reduction in imbibition rate of the osmotic pump.
The membrane module 300 is constructed so that it can be attached to the osmotic pump post-manufacture and pre-implantation. Preferably, the membrane module 300 can be snap-fitted to the osmotic pump. In one embodiment, this could be accomplished by providing an annular lip 306 on an inner surface 308 of the sleeve 304 that can engage with an annular groove (not shown) on an end portion of the osmotic pump containing the semipermeable membrane plug. Alternatively, the annular lip could be provided on the osmotic pump and an annular groove that can engage with the annular lip can be provided on the sleeve 304. However, the invention is not limited to use of annular lip/annular groove to couple the membrane module 300 to the osmotic pump. In general, any means of coupling tubular members, such as a threaded connection, can be used to affix the membrane module 300 to the osmotic pump. Preferably, any coupling configuration used is such that a biofluidic path cannot be formed between the junction of the sleeve 302 and the end portion of the osmotic pump. The membrane module 300 should be attached to the osmotic pump using aseptic technique.
The membrane module 300 is also constructed so that a plurality of the membrane modules can be coupled together to form a membrane stack. In
The sleeve 302 is formed from an inert and, preferably, biocompatible material. Exemplary inert, biocompatible materials include, but are not limited to, metals such as titanium, stainless steel, platinum and their alloys, and cobalt-chromium alloys and the like. Other examples of compatible materials include polymers such as polyethylene, polypropylene, polycarbonate, polymethylmethacrylate (PMMA), and the like.
The membrane module 300 can be modified in various ways. For example, as shown in
In practice, an imbibition rate reducer can be constructed using any of the modular structures described in
For illustration purposes,
The osmotic pump 402, as illustrated in
The semipermeable membrane plug 412 is made of a semipermeable material that allows water to pass from an exterior of the capsule 404 into the interior of the capsule 404 while preventing compositions within the capsule from passing out of the capsule. Semipermeable materials suitable for use in the invention are well known in the art. Semipermeable materials for the membrane plug are those that can conform to the shape of the capsule upon wetting and that can adhere to the inner surface of the capsule. Typically, these materials are polymeric materials, which can be selected based on the pumping rates and system configuration requirements, and include, but are not limited to, plasticized cellulosic materials, enhanced PMMAs such as hydroxyethylmethacrylate (HEMA), and elastomeric materials such as polyurethanes and polyamides, polyether-polyamind copolymers, thermoplastic copolyesters, and the like.
Two chambers 414, 416 are defined inside the capsule 404. The chambers 414, 416 are separated by a partition 418, such as a slidable piston or flexible diaphragm, which is configured to fit within the capsule 404 in a sealing manner and to move longitudinally within the capsule. Preferably, the partition 418 is formed from an impermeable resilient material. As an example, the partition 418 may be a slidable piston made of an impermeable resilient material and including annular ring shape protrusions that form a seal with the inner surface of the capsule 404. An osmotic agent 420 is disposed in the chamber 414 adjacent the semipermeable membrane plug 412, and a beneficial agent 422 to be delivered to a body is disposed in the chamber 416 adjacent the delivery port 410. The partition 418 isolates the beneficial agent 422 from the environmental liquids that are permitted to enter the capsule 404 through the semipermeable membrane plug 412 such that in use, at steady-state flow, the beneficial agent 422 is expelled through the delivery port 410 at a rate corresponding to the rate at which liquid from the environment of use flows into the osmotic agent 420 through the orifice module 200 and semipermeable membrane plug 412.
The osmotic agent 420 may be in the form of tablets as shown or may have other shape, texture, density, and consistency. For example, the osmotic agent 420 may be in powder or granular form. The osmotic agent may be, for example, a nonvolatile water soluble osmagent, an osmopolymer which swells on contact with water, or a mixture of the two.
In general, the present invention applies to the administration of beneficial agents, which include any physiologically or pharmacologically active substance. The beneficial agent 422 may be any of the agents which are known to be delivered to the body of a human or an animal such as medicaments, vitamins, nutrients, or the like. Drug agents which may be delivered by the present invention include drugs which act on the peripheral nerves, adrenergic receptors, cholinergic receptors, the skeletal muscles, the cardiovascular system, smooth muscles, the blood circulatory system, synoptic sites, neuroeffector junctional sites, endocrine and hormone systems, the immunological system, the reproductive system, the skeletal system, autacoid systems, the alimentary and excretory systems, the histamine system and the central nervous system. Suitable agents may be selected from, for example, proteins, enzymes, hormones, polynucleotides, nucleoproteins, polysaccharides, glycoproteins, lipoproteins, polypeptides, steroids, analgesics, local anesthetics, antibiotic agents, anti-inflammatory corticosteroids, ocular drugs and synthetic analogs of these species. An exemplary list of drugs that may be delivered using the osmotic pump system 400 is disclosed in U.S. Pat. No. 6,270,787. The list is incorporated herein by reference.
The beneficial agent 422 can be present in a wide variety of chemical and physical forms, such as solids, liquids and slurries. On the molecular level, the various forms may include uncharged molecules, molecular complexes, and pharmaceutically acceptable acid addition and base addition salts such as hydrochlorides, hydrobromides, sulfate, laurylate, oleate, and salicylate. For acidic compounds, salts of metals, amines or organic cations may be used. Derivatives such as esters, ethers and amides can also be used. A beneficial agent can be used alone or mixed with other beneficial agents. The beneficial agent may optionally include pharmaceutically acceptable carriers and/or additional ingredients such as antioxidants, stabilizing agents, permeation enhancers, etc.
Materials which may be used for the capsule 404 must be sufficiently rigid to withstand expansion of the osmotic agent 420 without changing its size or shape. Further, the materials should ensure that the capsule 404 will not leak, crack, break, or distort under stress to which it could be subjected during implantation or under stresses due to the pressures generated during operation. The capsule 404 may be formed of chemically inert biocompatible, natural or synthetic materials which are known in the art. The capsule material is preferably a non-bioerodible material which remains in the patient after use, such as titanium. However, the material of the capsule may alternatively be a bioerodible material which bioerodes in the environment after dispensing of the beneficial agent. Generally, preferred materials for the capsule 404 are those acceptable for human implantation.
In general, typical materials of construction suitable for the capsule 404 according to the present invention include non-reactive polymers or biocompatible metals or alloys. The polymers include acrylonitrile polymers such as acrylonitrile-butadiene-styrene terpolymer, and the like; halogenated polymers such as polytetraflouroethylene, polychlorotrifluoroethylene, copolymer tetrafluoroethylene and hexafluoropropylene; polyimide; polysulfone; polycarbonate; polyethylene; polypropylene; polyvinylchloride-acrylic copolymer; polycarbonate-acrylonitrile-butadiene-styrene; polystyrene; and the like. Metallic materials useful for the capsule 404 include stainless steel, titanium, platinum, tantalum, gold, and their alloys, as well as gold-plated ferrous alloys, platinum-plated ferrous alloys, cobalt-chromium alloys and titanium nitride coated stainless steel.
A capsule 404 made from the titanium or a titanium alloy having greater than 60%, often greater than 85% titanium, is particularly preferred for the most size-critical applications, for high payload capability and for long duration applications, and for those applications where the formulation is sensitive to body chemistry at the implantation site or where the body is sensitive to the formulation. In certain embodiments, and for applications other than the fluid-imbibing devices specifically described, where unstable beneficial agent formulations are in the capsule 404, particularly protein and/or peptide formulations, the metallic components to which the formulation is exposed must be formed of titanium or its alloys as described above.
The orifice module 200 is installed by, for example, snapping the annular lip 212 on the housing 202 into an annular groove 424 on the outer surface of the capsule 404. As previously mentioned, other means of installing the orifice module 200 may be used, such as a threaded connection. An optional porous substrate 426, such as a screen or mesh, may be inserted between the orifice 208 and the semipermeable membrane plug 412 to prevent deformation of the membrane 412. That is, the semipermeable membrane plug 412 can bulge out because of pressure inside the capsule 404. The semipermeable membrane plug 412 may extend into the orifice 208 if the bulging is not controlled. If desired, the housing 202 may be sized such that a chamber (not shown) is formed between the semipermeable membrane plug 412 and the capped end 204 of the housing 202 that allows for a degree of movement of the semipermeable 412 into the housing 202 as a result of pressure in the interior of the capsule 404. The capped end 204 can act as a stopper to prevent the semipermeable membrane plug 412 from being separated from the osmotic pump 402.
The invention typically provides the following advantages. The invention provides a means of adjusting the delivery rate of an osmotic pump post-manufacture. A variety of delivery profiles can be achieved without adversely affecting the operation of the osmotic pump. This gives caregivers flexibility in treatment options.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein.
This application claims the benefit of U.S. Provisional Application No. 60/518,111, filed Nov. 6, 2003.
| Number | Date | Country | |
|---|---|---|---|
| 60518111 | Nov 2003 | US |
