COMPOSITE DRUG DELIVERY CATHETER

Abstract: The present invention features a composite catheter comprising an elongate outer member and an elongate inner member positioned within the outer member so that the inner and outer members define an interstitial space. The outer member has a size and other characteristics that facilitate handling and implantation of the composite catheter, while the inner diameter of the inner member has the size and other characteristics suitable for delivery of a drug through a lumen of the inner member. The interstitial space imparts flexibility to the composite catheter by, for example, removing material from the cross-sectional area that would otherwise provide additional stiffness to the catheter, and/or by accommodating movement of the outer member relative to the inner member.

Description: WO 00/78385 PCT/USOO/l 2087 the size and other characteristics suitable for delivery of a drug through a lumen of the inner member. The interstitial space imparts flexibility to the composite catheter by, for example, removing material from the cross-sectional area that would otherwise provide additional stiffness to the catheter, and/or by accommodating movement of the outer member relative to the inner member. In one aspect the invention features a catheter comprising an elongate outer member and an elongate inner member, where the inner member is positioned within a lumen defined by the outer member so as to define an interstitial space between an outer wall of the inner member and an inner wall of the outer member, and where a lumen defined by the inner member is suitable for delivery of drug at a low volume rate. In specific embodiments the catheter further comprises a support member positioned wit-hin the interstitial space. In one embodiment, the catheter of the invention comprises a flexible distal portion. The flexible distal portion can be provided as an extension of a distal end of the outer member beyond the inner member distal end, or as an additional component attached to the distal end of the catheter. The flexible distal portion is flexible relative to a portion of the catheter comprising the outer member and the inner member. In specific embodiments, the distal extension is substantially hollow, and the inner member lumen and a lumen defined by the flexible distal portion form a drug delivery conduit. In other specific embodiments, the drug delivery outlet is defined by an opening at a distal end of the flexible distal portion. In still other specific embodiments, the drug delivery outlet is defined in a sidewall of the flexible distal portion, or the inner member lumen terminates in a drug delivery outlet at a sidewall of the catheter proximal to the flexible distal portion In another aspect the invention features a drug delivery system comprising a drug delivery- device and a composite catheter of the invention. In another aspect the invention features a method for low volume rate delivery of a drug to a treatment site in a subject comprising the steps of: 1) implanting a catheter of the invention into a subject to provide a drug delivery pathway from a proximal end of the catheter, through a lumen defined by a catheter inner member to a distal end of the catheter, and out a drug delivery outlet positioned at a treatment site in a subject; and 2) introducing a drug into the inner lumen of the catheter to deliver drug to the treatment site in the subject. A primary object of the invention is to provide a catheter useful in accurate and reliable delivery of very small volume of a drug, e.g., microliter quantities of a liquid or semisolid drug formulation, which catheter is biocompatible, flexible, and readily handleable to facilitate implantation. Another object of the invention is to provide a catheter that can be used with a variety of drug delivery systems to accomplish site-specific drug delivery. WO 00/78385 PCT/USOO/l 2087 COMPOSITE DRUG DELIVERY CATHETER FIELD OF THE INVENTION This mvention relates generally to catheters for use m delivery of drug, particularly m the context of site-specific drug delivery BACKGROUND OF THE INVENTION Delivery of drug to a specific treatment site represents a substantial challenge in the design of drug delivery systems Site-specific drug delivery can be particularly challenging when the drug is to be delivered long-term (e g , several hours to several days, weeks, or months) One approach to accomplish site-specific drug delivery involves the use of a catheter, which can be positioned at a treatment site to facilitate localized delivery of drug from a drug reservoir that may be some distance from the treatment site Long-term drug delivery requires that such catheters be biocompatible, drug non-reactive, impermeable, and flexible (e g , not sharp or easily breakable while implanted m the body) The combination of required characteπstics of drug delivery catheters limits the mateπals available for their design For example, while a variety of biocompatible mateπals have sufficient flexibility, these mateπals may not have the required impermeability and drug non-reactive characteπstics Similarly, while many mateπals may be both drug non-reactive and impermeable, they may not be sufficiently biocompatible and flexible The problem is further complicated where it is desirable to deliver drug in relatively small amounts, and thus requires a small drug delivery lumen Catheters having a small inner lumen for drug delivery are often extremely difficult to handle due to. for example, their fragility and their small outer diameters Adapting a catheter having a larger outer diameter to have a smaller inner lumen can provide a catheter that is handleable, but too stiff for implantation through tortuous bends m the implantation pathway that leads to the treatment site There is thus a need in the field for a drug delivery catheter that is biocompatible, flexible, handleable (even when designed for delivery of microquantities of drug), and sufficiently impermeable and drug non-reactive The present invention addresses these problems SUMMARY OF THE INVENTION The present mvention features a composite catheter compπsmg an elongate outer member and an elongate inner member positioned within the outer member so that the inner and outer members define an interstitial space The outer member has a size and other characteπstics that facilitate handling and implantation of the composite catheter, while the inner diameter of the inner member has -1- It is another object of the mvention to provide a catheter that is suitable for delivery of drug to a distal treatment site within a subject, particularly sites that are highly sensitive or fragile (e g , the spinal cord) An important advantage of the mvention is that the interstitial space defined by the inner wall of the outer member and the outer wall of the inner member accommodates movement of the outer and inner members relative to one another, e g , m a plane perpendicular to a sidewall of the catheter, and further can make the catheter less stiff by removmg material from the catheter cross-sectional area Furthermore, the interstitial space can be designed to provide for varying degrees of flexibility of the catheter, e g , by varying the dimensions of the space (e g , the distance between the outer member inner wall and the inner member outer wall) The interstitial space can also be designed to accommodate other desirable catheter elements For example, the space can be designed to accommodate one or more support members, which support members can enhance the tensile strength or compression strength of the composite catheter In addition or alternatively, desirable charactenstics can be imparted to the catheter by filling the interstitial space with a gas, liquid, semi- solid, or polymer (mcludmg cross-linked polymers) that is under substantially constant or regulatable pressure, and that optionally compπse antimicrobial (e g , bacteπostatic or bactencidal) agents Another important advantage of the mvention is that the composite catheter facilitates delivery of extremely small volumes of drug (e g , submicrohter volumes), yet is easily handled, e g , by a clinician duπng implantation This advantage of the catheter is provided by the combmed characteπstics of the inner member, which provides the drug delivery conduit, and the outer member, which provides for the biocompatibihty and ease of handling of the composite catheter Furthermore, by facilitating delivery of small volumes of drug, the catheter reduces the economic costs as well as the nsks associated with systemic dosmg Another advantage of the mvention is that the mateπal used for the outer member need not be drug impermeable, smce at most only the inner member need be substantially drug impermeable Thus any available biocompatible and implantable grade material (e g . silicone rubber) can be used for the outer member Thus the catheter can take advantage of a wider range of biocompatible mateπals for the outer member than can conventional catheters m which the material of the outer catheter wall is contact with the drug formulation to be delivered Another advantage of the mvention is that the catheter inner member and the catheter outer member can have distinctly different characteπstics in terms of. for example, relative flexibility, dimensions, biocompatibihty, etc, which characteπstics can be varied and selected accordmg to any of a variety of factors, e g , the drug to be delivered, the desired flow rate, the treatment site, etc For example, the matenal of the outer member can be selected to provide for biocompatibihty, size, flexibility, and other catheter characteπstics important for implantation and retention m the subject WO 00/78385 PCT/USOO/l 2087 without significant constraint imposed by the properties important for delivery of drugs, while the inner member of the composite catheter can be selected to provide the size, non-permeability to drug, non-reactivity to drug, and other charactenstics optimal for delivery of drug without significant constramt imposed by biocompatibihty, flexibility, and other charactenstics important to handlmg and implantation m a subject This combmation allows for use of a wider vaπety of mateπals m the manufacture of the drug delivery conduit defined by the inner member smce the outer member will protect the subject from the inner member material, e g , the inner member may compπse mateπals that would be too sharp, stiff, or otherwise unsuitable for implanting in a subject Similarly, the outer member can be provided m dimensions that facilitate ease of handlmg and implantation, while the inner member can be of relatively smaller dimensions, e g , to define an extremely small inner lumen for delivery of drug at a relatively low volume rate In addition, the use of the outer and inner member allows for more design flexibility, e g , varying the inner and outer diameters to provide dimensions suitable for drug delivery and handleability, respectively, varying the mateπals for the outer member and the inner member to provide for biocompatibihty and drug-impermeability, respectively, etc The mvention is also advantageous m that the inner lumen of the inner member can be designed to provide a drug delivery conduit with a small lumen size to, for example, minimize start-up time, . e , the time for delivery of drug from a drug reservoir of a drug release device, through the catheter, and to the treatment site Still another advantage of the mvention is that the catheter can be designed to have an extremely floppy (flexible) distal portion that can serve as a means for anchormg the catheter at a treatment site, and can be cut to a desired length by the clinician to provide for tailoring the catheter to the present needs of the subject and/or treatment site Furthermore, the drug delivery outlet can be positioned within a sidewall of the catheter to provide for delivery of drug at or about the anchormg point at a treatment site (e g , at or about the point at which the floppy distal portion begms, see, e g , These and other objects, advantages and features of the present mvention will become apparent to those skilled m the art upon readmg this disclosure in combmation with drawings wherem like numerals refer to like components throughout BRIEF DESCRIPTION OF THE DRAWINGS Figs 1 and 2 are cross-sectional and cut-away views, respectively, of an exemplary composite catheter of the mvention Fig 3 is a cut-away view showing a composite catheter havmg a support member incorporated mto the catheter interstitial space Fig 4 is a cut-away view of a catheter compπsmg a tapered support member compπsmg a braid around a portion of smaller diameter Figs 5A, 5B, 5C, 5D, and 5E are cross-sectional views of exemplary composite catheters of the mvention compπsmg a plurality of drug delivery conduits by compnsmg a plurality of inner members (Figs 5A, 5B, and 5C), an inner member defimng a plurality of inner lumen (Fig 5D), or Fig 6 is a cut-away view of a composite catheter of the mvention compπsmg a lumen havmg a closed distal end Fig 7A is a partial cut-away view of an exemplary catheter of the mvention, where the catheter compπses a floppy distal section and is positioned for use with a controlled drug release device Figs 7B and 7C are perspective views of exemplary, alternative embodiments of the catheter floppy distal end Fig 8 illustrates the catheter and drug delivery device of Fig 7 positioned for use in delivery of drug to the spinal cord of a subject Fig 9 is a partial cut-away view of an exemplary catheter of the mvention positioned for use with a controlled drug release device, where the catheter compnses a floppy distal section and a side exit through which drug is delivered Fig 10 is an exploded view of the side exit of the catheter of Fig 9 Fig 11 illustrates the catheter and controlled drug release device of Fig 9 positioned for use m delivery of drug to the spinal cord of a subject Fig 12 is a cut-away view of a composite catheter of the mvention compπsmg an attachment element and attached for use with a drug delivery device DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the present composite catheter, method of drug delivery, and specific devices and formulations used in connection with such are descπbed, it is to be understood that this mvention is not limited to the particular embodiments descπbed, as such methods, devices, and formulations may, of course, vary It is also to be understood that the terminology used herein is for the purpose of descnbing particular embodiments only, and is not mtended to limit the scope of the present mvention which will be limited only by the appended claims It must be noted that as used herein and m the appended claims, the singular forms "a," "an," and "the" mclude plural referents unless the context clearly dictates otherwise Thus, for example, reference to "a formulation" includes mixtures of different formulations, and reference to "the method WO 00/78385 PCT/USOO/l 2087 of delivery" mcludes reference to equivalent steps and methods known to those skilled in the art, and so forth Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill m the art to which this mvention belongs Although any methods and matenals similar or eqmvalent to those descπbed herem can be used m the practice or testmg of the present invention, the prefeπed methods and mateπals are now descπbed All publications mentioned herein are incorporated herem by reference to disclose and descπbe the specific methods and/or mateπals m connection with which the publications are cited The publications discussed herem are provided solely for their disclosure pπor to the filing date of the present application Nothing herein is to be construed as an admission that the present mvention is not entitled to antedate such publication by virtue of pπor mvention Further, the dates of publication provided may be different from the actual publication dates which may need to be mdependently confirmed Definitions The term "low volume rate drug delivery" as used herein generally refers to delivery of a liquid or sermsohd drug at a volume rate of from about 0 01 μl/day to about 200 μl/day, usually about 0 04 μl/day to about 20 μl/day, more usually about 0 1 μl/day to about 8 0 μl/day "Drug delivery device" as used herem is meant to encompass any device that compπses a drug reservoir and that facilitates movement of drug from the drug reservoir to a site external to the drug delivery device "Drug delivery device" thus encompasses controlled drug release devices, as well as devices that release drug in an unpatterned (e g , substantially unregulated) manner Controlled drug release devices are particularly prefeπed for use with the catheter of the present mvention "Controlled release" as used herem (e g . in the context of "controlled drug release") is meant to encompass release of substance (e g , a drug) at a selected or otherwise controllable rate, mterval, and/or amount "Controlled release" thus encompasses, but is not necessaπly limited to, substantially contmuous delivery, patterned delivery (e g , intermittent delivery over a peπod of time that is interrupted by regular or lπegular time intervals), and delivery of a bolus of a selected substance (e g , as a pre-determined, discrete amount of a substance over a relatively short period of time (e g , a few seconds or minutes) The term "controlled drug release device" is meant to encompass any device that provides for controlled release of a drug or other desired substance, and that can be adapted for use with a catheter of the mvention, e g , a drug delivery device that provides for controlled release of drug through a catheter of the mvention. and at a rate that is suitable to accomplish delivery of a therapeutically effective amount of drug to a treatment site accordmg to the methods of the invention WO 00/78385 PCT/USOO/l 2087 The term "treatment site" as used herem is meant to refer to a desired site for delivery of drug from a drug delivery device of the invention, and/or a site from which fluid sampling is desired, e g , for diagnosis and/or prognosis "Treatment site" is thus meant to mclude, although is not necessaπly limited to. a subcutaneous, percutaneous, intravenous, mtrathecal, intramuscular, intra-artenal, mtravascular, lπtrapentoneal, intraspinal, epidural, lntracranial, peπtumoral, or intratumoral (/ e , within a cancerous growth) site within a subject, as well as sites within or near a selected organ or tissue (e g , central nervous system (e g , spmal fluid, brain, etc ), peπpheral nervous system, kidney, liver, pancreas, heart (e g , mtrapeπcardial), lung, eye, ear (e g , inner ear), lymph nodes, breast, prostate, ovaπes, testicles, thyroid, spleen, etc ), digestive system (e g , stomach, gastromtestmal tract, etc ), skeletal muscle, bone, uπnary bladder, gall bladder, adrenal gland, adipose tissue, parathyroid gland, uterus, fallopian tube, skin, to a vessel associated with the circulatory system (e g , artery, arteπole, blood vessel, vein, capillary bed, lymph vessel, particularly artenes that feed a selected organ or tissue)), a tumorous growth (e g , cancerous tumor (e g , solid tumor), cyst, etc ), at a site associated with a microbial infection (e g , bactenal, viral, parasitic or fungal infection), or to an autologous or synthetic graft (e g , a vascular graft) The term "access site" or "implantation site" is used to refer to a site on or in a subject at which a catheter of the mvention is introduced for implantation and positioning within the subject's body, e g . for delivery of drug to a desired treatment site For example, where a catheter is implanted m a subject for delivery of drug to the spmal cord, the access site or implantation site can be a subcutaneous site at which a proximal end of the catheter is substantially retamed, and the treatment site is a position within or adjacent the spmal cord (treatment site) at which a distal end of the catheter is positioned for delivery of drug "Drug delivery system" as used herein is meant to refer to a combmation of a catheter of the mvention and a drug delivery device suitable for use in delivery of a drug to a treatment site, preferably a controlled drug release device The term "subject" is meant any subject, generally a mammal (e g , human, canine, felme, equine, bovine, etc ), to which drug delivery is desired The term "impermeable" means that the material is sufficiently impermeable to environmental fluids as well as ingredients contained within the dispensing device such that the migration of such matenals mto or out of the device through the impermeable device is so low as to have substantially no adverse impact on the activity or function of the drug retained within the device duπng the delivery penod The term "semipermeable" means that the mateπal is selectively permeable, e g , permeable to external fluids but substantially impermeable to other ingredients contained within the dispensing device and the environment of use WO 00/78385 PCT/USOO/l 2087 The term "drug" as used herem is meant to encompass any substance suitable for delivery to a treatment site of a subject, which substances can mclude pharmaceutically active drugs, as well as biocompatible substances that do not exhibit a pharmaceutical activity m and of themselves, but that provide for a desired effect at a treatment site, e g , to flush or lrπgate a treatment site (e g , saline) "Pharmaceutically active drug," "therapeutic agent," "therapeutic drug," and the like are used interchangeably herem to refer to any chemical compound which, when provided to a subject (e g , a mammal, preferably a human), facilitates a therapeutic effect Such drugs may optionally be provided in combmation with pharmaceutically acceptable earners and/or other additional compositions such as antioxidants, stabilizing agents, permeation enhancers, etc In general, "drug" and the like are used to refer to any drug that is conventionally administered by parenteral injection (e g , intravascularly, intramuscularly, subcutaneously, lntrathecally, etc ) Drugs compatible for delivery usmg the devices and methods of the mvention are discussed below, and are readily apparent to the ordmanly skilled artisan upon reading the disclosure provided herem The term "therapeutically effective amount" is meant an amount of a therapeutic agent, or a rate of delivery of a therapeutic agent, effective to facilitate a desired therapeutic effect The precise desired therapeutic effect will vary according to the condition to be treated, the drug to be administered, and a variety of other factors that are appreciated by those of ordinary skill m the art Determinations of precise dosages are routine and well within the skill in the art The term "treatment" is used here to cover any treatment of any disease or condition m a mammal, particularly a human, and includes a) preventmg a disease, condition, or symptom of a disease or condition from occurring in a subject which may be predisposed to the disease but has not yet been diagnosed as having it, b) lnhibitmg a disease, condition, or symptom of a disease or condition, e g , arresting its development and/or delaymg its onset or manifestation in the patient, and/or c) relieving a disease, condition, or symptom of a disease or condition, e g , causmg regression of the disease and/or its symptoms Composite Catheter The present mvention features a composite catheter compπsmg an elongate outer member, and an elongate inner member positioned witl m the outer member either concentπcally (e g , substantially coaxial) or non-concentrically (ι e , off-center) with respect to the outer member The inner and outer members can be any suitable shape mcludmg, but not limited to, tubular, elliptical, cylindrical, etc , and may be either smooth on the composite catheter outer surface, or may compπse ndges (e g , longitudinal, axial, or circumferential) or other surface vaπations as will be desirable for the specific applications for which the composite catheter is used The inner and outer members are configured to define an mterstitial space between an inner wall of the outer member and an outer wall of the inner member The mterstitial space imparts flexibility to the composite catheter by, for example, accommodatmg movement of the outer member relative to the inner member and/or by virtue of havmg less mateπal m the catheter cross-sectional area The mterstitial space can also be designed to accommodate a support member, e g , to provide tensile or compression support to the catheter In general, the inner member defines at least a portion of a drug delivery conduit, which conduit normally extends at least the length of the inner member and terminates m a drug delivery outlet The outer member provides for the handleable and implantable characteπstics of the catheter, while the inner member has an inner diameter optimized for delivery of a liquid or semiso d drug through the lumen of the inner member The composite catheter can also be designed with a smgle outer member and one or a plurality of drug delivery condmts, which conduits can be defined by a smgle inner member or by a plurality of inner members and which can be designed for delivery of the same or different drugs to a treatment site In use, the distal end of the catheter is positioned at a treatment site within the subject, while the proximal end of the catheter is associated with, for example, a drug delivery device While the composite catheter of the mvention is pπmaπly mtended for use m drug delivery, it may also be used m the course of other medical procedures (e g , to facilitate samplmg of fluid (e g , spmal fluid) from the treatment site, etc ) The inner member, the outer member, and vaπous exemplary embodiments of the composite catheter will now be described m more detail Catheter Inner Member Matenals And General Charactenstics As noted above, the catheter inner member defines at least a portion of the catheter drug delivery conduit, and m particular defines that portion of the catheter drug delivery conduit that is charactenzed by an inner diameter suitable for delivery of drug at a desired rate, e g , low volume rate delivery, e g , 0 01 μl/day to about 200 μl/day In general, the inner diameter of the catheter inner member is from about 0 0002" (about 0 005 mm) to about 0 025" (about 0 6 mm), usually from about 0 0005 " (about 0 013 mm) to about 0 015" (about 0 4 mm), generally from about 0 001 " (about 0 025 mm) to about 0 010" (about 0 25 mm), and preferably from about 0 002" (about 0 05 mm) to about 0 006" (about 0 15 mm) The thickness of the inner member walls will vary with a vaπety of factors, such as the stiffness and permeability of the mateπal selected, e g , a. metal-based mateπal may have a very thin wall section (e g , less than 0 001"), while a glass- or polymer-based matenal may have a thicker wall) The catheter inner member is preferably produced from any of a vaπety of suitable drug impermeable mateπals Preferably, drug impermeable mateπals suitable for use m production of the catheter inner member do not react m an unintended manner with the active agent formulation Suitable mateπals for the catheter inner member can compπse a drug non-reactive polymer or a WO 00/78385 PCT/USOO/l 2087 biocompatible metal or alloy Exemplary matenals from which the catheter inner member can be manufactured include, but are not necessanly limited to, polymers, metals, glasses, polyolefins (high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), and the like), nylons, polyethylene terephtholate, urethanes, PEBAX™, HYTREL™, TEFLON™, fluorenated polymers (e g , polytetrafluoroethylene (PTFE), PFA), poly(methyl) methacrylate) (PMMA), polyvmyhdme chloπde, laminates of hydrophilic polymers and hydrophobic polymers, acrylonitnle, mckel titanium, superelastic nickel titanium, multilaminates or polymer, metals, and/or glass, and the like In a particularly preferred embodiment, the inner member is manufactured from mckel titanium, particularly superelastic mckel titanium (NITINOL™) Further specific exemplary polymers suitable for use m production of the catheter inner member include, but are not necessarily limited to, acrylonitnle polymers such as acrylomtπle-butadiene-styrene polymer, and the like, halogenated polymers such as polytetrafluoroethylene, polychlorotπfluoroethylene, copolymer tetrafiuoroethylene and hexafluoropropylene, polyrmide, polysulfone, polycarbonate, polyethylene, polypropylene, polyvmylchlonde-acryhc copolymer, polycarbonate-acrylomtπle-butadiene-styrene, polystyrene, and the like Further exemplary polymers are descπbed m Plastics Matenals 6 th ed , May 1995, J A Brydson, Butterworth-Hememann, publishers Metallic matenals suitable for use m production of the catheter inner member include stainless steel, titanium, platinum, tantalum, gold and their alloys, gold-plated feπous alloys, platinum-plated titanium, stainless steel, tantalum, gold and their alloys as well as other fenous alloys, cobalt-chromium alloys, and titanium mtnde-coated stainless steel, titanium, platinum, tantalum, gold, and their alloys The catheter inner member can compnse additional matenals or agents For example, the inner member can compnse a coatmg on an internal wall to facilitate transport of drug through the inner lumen, or to impart other desirable charactenstics to the catheter The catheter can also compnse coatmgs that reduce the risk of infection, e g , a silver coatmg, a coatmg or treatment with an antimicrobial agent(s), etc Catheter Outer Member Mateπals and General Characteristics The catheter outer member is generally a substantially sheath-like structure compnsmg a proximal end, a distal end, and an outer member body The catheter outer member can be positioned around, either concentncally or non-concentncally (. e , off-center) relative to a catheter inner member (see, e g , Figs 1, 2, and 5A-5C) The thickness of the outer member wall will vary dependmg on, for example, the mateπal selected and the desired flexibility, permeability, etc The dimensions of the outer member (e g , inner diameter, outer diameter, thickness of the outer member wall etc ) can be substantially the same throughout the length of the catheter, or can be vaπed For example, the outer member can be tapered at the distal end to dimensions similar to that of the inner member The outer diameter of the outer member, which generally defines the outer diameter of the composite catheter, is of a size that provides for ease of handlmg the composite catheter In general, the diameter of the outer member is from about 0 01" (about 0 25 mm) to about 0 200" (about 5 mm), usually from about 0 020" (about 0 5 mm) to about 0 100" (about 2 5 mm), generally from about 0 025" to about 0 080", preferably from about 0 030" (about 0 75 mm) to about 0 060" (about 1 5 mm) In one embodiment, the outer member outer diameter is from about 0 040" to about 0 050" The outer member is preferably made of a biocompatible mateπal, more preferably an implantable grade biocompatible mateπal Exemplary materials suitable for the outer member mclude, but are not necessanly limited to, biocompatible polymers and/or elastomers Suitable biocompatible polymers mclude, but are not necessanly limited to, mateπals such as, for example, polyethylene, homopolymers and copolymers of vinyl acetate such as ethylene vmyl acetate copolymer, polyvmylchlondes, homopolymers and copolymers of acrylates such as polymethylmethacrylate, polyethylmethacrylate, polymethacrylate, ethylene glycol dunethacrylate, ethylene dimethacrylate and hydroxymethyl methacrylate, polyurethanes, polyvinylpyπohdone, 2-pynohdone, polyacrylonitπle butadiene, polycarbonates, polyamides. fluoropolymers such as polytetrafluoroethylene and polyvmyl fluoπde, polystyrenes, homopolymers and copolymers of styrene acrylonitnle, cellulose acetate, homopolymers and copolymers of acrylomtnle butadiene styrene, polyvmylchloπde, silicone rubber, polymethylpentene, polysulfones, polyesters, polyimides, polyisobutylene, polymethylstyrene and other similar compounds known to those skilled m the art Suitable, biocompatible elastomers mclude, but are not necessarily limited to, biocompatible elastomers such as medical grade silicone rubbers, polyvmyl chloπde elastomers, polyolefin homopolymeπc and copolymenc elastomers, urethane-based elastomers, and natural rubber or other synthetic rubbers, fluorenated polymers (e g , PTFE). and the like It should be understood that these possible biocompatible matenals are mcluded above for exemplary purposes and should not be construed as limiting The outer member can be made of a mateπal that is relatively softer than the matenal of the inner member, e g , the outer member can have a relatively lower flexural modulus, and the inner member can have a relatively higher flexural modulus For example, the outer member can have a flexural modulus mthe range from about 10,000 to 50,000 psi (703 to 3,515 kg/cm 2 ), while the inner member has a flexural modulus within the range from about 50,000 to 300,000 psi (3,515 to 21,100 kg/cm 2 ) Examples of matenals with lower flexural modulus suitable for the outer member mclude urethanes. PVC, low density polyethylenes, and silicone rubbers It should be noted that one mtent of the mvention is to design a more flexible outer member relative to the inner member Smce flexibility is imparted by the product of member wall thickness times the flex modulus of the material of the wall, these two parameters can be varied to provide an outer member havmg a desired flexibility In WO 00/78385 PCT/USOO/l 2087 general, a low flex modulus is desired However a relatively higher flex modulus times a thm wall thickness can also results m such an overall flexible outer member The catheter outer member can compnse additional mateπals or agents For example, the outer member can comprise a coatmg or be treated (e g , on an external wall) to facilitate implantation of the catheter withm the subject, to reduce the risk of infection (e g , antmucrobial agents), and/or to impart other desirable charactenstics to the catheter Exemplary Specific Embodiments of the Composite Catheter of the Invention Referring generally to one non-limiting embodiment of the catheter of the mvention illustrated m Fig 1, the catheter 10 of the invention compnses an inner member 50 and an outer member 70, where the inner member 50 is positioned withm the outer member 70, i e , inner member 50 is inside outer member 70 The inner wall of the outer member 70 and the outer wall of the inner member 50 define mterstitial space 60 that extends the length of the catheter inner member 50 The dimensions of the catheter 10 outer diameter (which is generally defined by the outer diameter of the outer member 70) is of a size that facilitates handlmg of the catheter duπng implantation, and can be of any diameter suitable for mtroduction mto a wide range of implantation sites (e g , arteπes, capillanes, ducts of organs, etc ) The catheter outer diameter can be substantially the same throughout the entire length of the catheter, or can vary along the catheter's length (e g , the catheter can be tapered or nanowed at any pomt along the catheter body, e g , tapered at a distal end) The dimensions of the catheter and its components can be vaπed accordmg to a vanety of factors such as the treatment site with which the catheter is to be used, desired physical charactenstics of the catheter, etc For example, the outer member diameter and/or wall thickness can be greater over those portions of the catheter where increased relative stiffness is desired and less over those portions of the catheter where increased relative flexibility is desired In general, the drug delivery conduit 90 of the catheter 10 is defined by the inner member 50 inner lumen (see, e g , Fig 1), or a combmation of the inner member 50 inner lumen and the inner lumen of a floppy distal portion of the outer member (see, e g , Fig 7A, m which the drug delivery pathway is extended beyond the inner member distal end by a portion of the outer member distal end) Where the drug delivery conduit is defined by a combination of the inner member lumen and a lumen of a distal extension, the lumen of the inner member can be the same or substantially smaller than the lumen of the distal extension of the outer member The portion of the drug delivery conduit defined by the inner member 50 is of an inner diameter compatible with the desired delivery charactenstics for the drug, e g , delivery at a relatively low volume rate As with the catheter outer diameter, the catheter inner diameter can be substantially the same throughout the entire length of the catheter, or can vary along the catheter's length For example, the drug delivery conduit catheter can be tapered or WO 00/78385 PCT/USOO/l 2087 narrowed at any pomt along the catheter body, e g , tapered at a distal end, or can be widened at any pomt along the catheter body, e g , widened over a distal portion of the catheter The mterstitial space 60 defined by the inner and outer members enhances the flexibility of the composite catheter, e g , by removmg mateπal from the cross-sectional area of the catheter (e g , material that would otherwise impart some stiffness to the catheter shaft), and/or by accommodatmg movement of the inner and outer members relative to each other The cross-sectional width of the catheter mterstitial space (e g , the distance from the outer member inner wall to the inner member outer wall) will vary with a variety of factors such as the degree of flexibility desired, the total desired outer diameter of the catheter, the thickness of the outer member wall, the thickness of the inner member wall, and the total outer diameter of the inner member The desired width of the interstitial space can be vaned to accommodate other catheter elements, such as a support member positioned within the interstitial space, radiopaque markers, etc The mterstitial space width can be substantially the same or varied over the length of the catheter In general, the elements of the composite catheter can be designed so that the catheter is sufficiently flexible to pass through any tortuous bends m the implantation pathway (e g , mtncate bends m a vessel or duct mto which the catheter is implanted Catheters of varying stiffness and/or flexibility can be produced by, for example, varying the mateπals used to produce the catheter components (e g , by using matenals havmg a relatively high or low flexural modulus), and/or by varying the matenal or elements within the mterstitial space For example, the mterstitial space 60 can be substantially empty, or partially or substantially filled with mateπals that impart a selected flexibility Alternatively or in addition, a support member (e g , compression or tensile support member, e g , a sheath or guidewire) may be provided either around the outside of the catheter body and/or positioned within the interstitial space The use of such a support member(s) can allow for use of less stiff matenals for all or a portion of the catheter body Various embodiments of the support members are descnbed below m more detail In general, the dimensions of the catheter (e g , overall length, outer diameter, inner diameter, wall thickness, etc ) can be vaned as required or desired, and will vary accordmg to a vanety of factors (e g , the treatment site for delivery, the drug delivery device used m connection with the catheter, etc ) For example, the inner diameter of the drug delivery conduit 90 of catheter 10 can be equal to, or can be greater or less than, the diameter of an onfice from which drug flows from a drug reservoir of a drug delivery device that is to be used with the catheter In one embodiment, the proximal end of the catheter can compnse an inner diameter that is equal to or greater than the diameter of the onfice of a drug release device to be used with the catheter, and then taper over its length to a relatively smaller inner diameter, e g , to provide a drug delivery outlet at the distal end In WO 00/78385 PCT/USOO/l 2087 general, the inner and outer diameters of at least the proximal end of the catheter is preferably of a size sufficient to provide a leak-resistant or leak-proof drug flow path from a drug reservoir of the drug delivery device through the catheter drug delivery conduit Where the controlled drug release system used m the drug delivery device dispenses drug by convection (as e g , penstaltic or osmotic drug delivery systems), the drug delivery device onfice size as well as the inner diameter of the catheter drug delivery conduit can be designed as descπbed by Theeuwes (1975) J Phαrm Set 64 1987-91 In general, the catheter has an overall length m the range from about 1 cm to about 200 cm, usually from about 5 cm to about 150 cm, normally 10 cm to about 50 cm, more usually from about 15 cm to about 40 cm The outer member 70 and inner member 50 can be made from the same matenals or from different matenals The inner member 50 is preferably made from a matenal that allows for production of a small diameter lumen (e g , a lumen of a diameter suitable for accomplishing low volume rate delivery of drug) and is preferably substantially impermeable to drug The outer member 70 is made of a biocompatible matenal that preferably provides for long-term rmplantability m a subject (e g , for a penod of days to weeks to years) In one prefened embodiment, the composite catheter of the invention is composed of a silicone outer member and a mckel titanium alloy inner member The inner diameter of the inner member is about 0 003" to 0 006," and the outer diameter of the inner member is about 0 005" to about 0 012" The outer member 70 and inner member(s) 50 can be associated m a vaπety of ways to provide the catheter 10 of the invention For example, the inner and outer members may be jomed by connecting walls 15 at the proximal 11 and/or distal 12 ends of the catheter 10, which walls can serve to substantially isolate the mterstitial space from the external environment Alternatively or m addition, the inner and outer members can be jomed together at their ends by crimping, heat fusion, ultrasonic welding, radiofrequency weldmg, heat bondmg, solvent bondmg, soldering, etc The outer and inner members can be jomed by a mechanical element, such as a press fit or locking element Alternatively or m addition, the outer and inner members can be connected by an adhesive matenal, which may be placed withm the mterstitial space, minimally at the extreme proximal and distal ends of the inner member so as to hold the inner member m place withm the outer member Suitable adhesives mclude. but are not necessanly limited to, epoxy resms, ethylene vmyl acetate-based adhesives, polyurethane, cyanoacrylates, UV curable adhesives. RTV silicone adhesives, as well as other sihcone- based adhesives, solvent bonding adhesive substances, polyiosbutylene (PIB)-based adhesives, and the like Additional suitable adhesives are well known m the art, see, e g , Handbook of Adhesive Technology. A Pizzi and K L Mittal, Jan 1994. Marchel Dekker, publisher Elements withm the Interstitial Space The mterstitial space can compnse one or more elements to enhance or provide the catheter with desirable charactenstics In one embodiment, the mterstitial space is filled or substantially filled with one or more of a liquid, semi-solid, polymer, cross-linked polymer, air or other gas (e g , an inert gas), etc Where the walls of the mterstitial space 60 (i e , the inner wall of outer member 70, the outer wall of inner member 50, and the connectmg walls 15) are made of a substantially impermeable mateπal, the mterstitial space can be filled with gas or liquid, and permanently sealed so as to maintain a relatively constant pressure (e g , at least greater than atmospheπc pressure) m the mterstitial space Alternatively, the connectmg wall at the catheter proximal end can be made of a relatively gas permeable matenal (e g , a gas-permeable membrane), or the proximal connectmg wall can define an opening through which gas or liquid can be mtroduced mto the mterstitial space The catheter proximal end can then be permanently or mtermittently connected to a source of gas or liquid (e g , a pressunzed gas or pressunzed liquid source) so that the pressure within the mterstitial space can be maintained at a desired level or regulated The pressure of the gas or liquid m the mterstitial space 60 can provide a means to regulate the stiffness of the otherwise very flexible catheter For example, where it may be desirable to mcrease the catheter's overall stiffness, e g , while pushing the catheter through a vessel duπng implantation, the pressure of the gas m the mterstitial space can be mcreased to make the catheter more stiff or can be decreased to render the catheter more flexible upon reachmg a tortuous bend m the implantation pathway This embodiment of the mvention can also be adapted to substitute a semi-solid, liquid, or liquid-gas mixture for the gas in the mterstitial space as descπbed above Support members In another embodiment, the mterstitial space compnses a support member The support member can provide the catheter with tensile strength (e g , to absorb longitudinal stress on the catheter) or with compression strength (e g , to facilitate pushing of the catheter to an implantation site) and can facilitate implantation of the catheter As used herem, support members that impart tensile strength to the catheter are refened to as "tensile support members," while support members that impart compression strength to the catheter are refened to as "compression support members " The characteπstιc(s) confened on the catheter by the support member can be vaned by, for example, varymg the matenals from which the support member is made, varymg the structure of the support member (e g . a coil-like structure to provide compression strength, or a braid-like structure to provide tensile strength), varymg the thickness of the support member, varying the association of the support member with an element of the catheter (e g , attaching the support member to the inner wall of the outer member, the outer wall of the inner member, or both), and/or varymg the position of the support member (e g , proximity of the support member to the outer member or inner member walls) The support member can be provided m a vaπety of configurations (e g , geometπcal shapes, e g , substantially straight or in a pre-set shape to give all or a portion of the catheter a desired configuration to facilitate access to a specific region) and a vanety of dimensions (e g , length, diameter, etc ) as suitable to provide the desired tensile or compression strength For example as shown m Fig 3, the support member 85 can extend through the mterstitial space 60 for substantially the entire length of the inner member (e g , from the inner member proximal end 11 to at least the inner member distal end 52) and, m other embodiments, may extend the entire length of the catheter, e g , the entire length of both the inner and outer members The support member diameter can be substantially the same throughout its length, or may vary, e g , the support member diameter can be greater over those portions of the catheter where increased relative stiffness is desired and less over those portions of the catheter where mcreased relative flexibility is desired The dimensions and/or configuration of the support member can be vaned with the dimensions of the inner member, the outer member, or both For example, where the inner and/or outer member dιameter(s) taper or are otherwise altered to provide a relatively floppy portion of the catheter (e g , a floppy distal end), the support member diameter can be relatively smaller at the portion of the catheter where flexibility is desired In some embodiments it may be desirable to use a support member havmg a combmation of structural configurations For example, as shown m Fig 4, the support member 85 can be associated with a coil or braid 29 positioned around the outer diameter of the support member 85 over the region of smaller support member diameter, e g , a Teflon-coated stainless steel wire of from about 0 012" to 0 018" Matenals for support members can be selected accordmg to the desired design, e g , to provide for tensile strength or for compression strength Exemplary matenals for use m the support member mclude, but are not necessanly limited to, metals (e g , stainless steel wire, parylene-coated or Teflon- coated stainless steel), metal alloys (e g , mckel titanium (NITINOL™)), polymers (e g , particularly polymers of relatively high modulus, e g , carbon fiber,) and the like Compression support members Where the support member is a compression support member, the support member can be substantially permanently positioned withm the catheter mterstitial space, or can be provided as a removable member, e g , the support member can be withdrawn from the catheter after implanting Where the support member is removable from the catheter, it may be preferable to enhance the slideabihty of the surfaces of the support member, outer member inner wall, and inner member outer wall, e g , by Teflon or parylene coating of the support member, etc Where the compression support member is substantially permanently positioned m the mterstitial space, the support member 85 can be held m place by adhesive 80 at the proximal and/or distal ends of the support member 85 Exemplary solid compression support member mateπals mclude, but are not necessanly limited to, carbon fiber, metal, polycarbonate, plexiglass, etc A prefeπed compression support member is a wire-like element, preferably teflon-coated stainless steel, havmg a diameter withm the range of from about 0 006" to about 0 020" (see, e g , Fig 3) The dimensions of the support member can be substantially the same throughout its length or may vary, e g , the support member diameter can be greater over those portions of the catheter where mcreased relative stiffness is desired and less over those portions of the catheter where mcreased relative flexibility is desired Tensile support member Where the support member is a tensile support member, the support member is generally permanently positioned withm the mterstitial space The tensile support member can be attached to the catheter at its proximal and distal ends, or at any of at least two pomts along its length Exemplary tensile support members include, but are not necessanly limited to, a wire, a braid (e g , a braid that is positioned on the inner wall of the outer member, and which may form a spiral along the outer member inner wall for at least a portion of the length of the catheter that encloses the inner member), an inner lmer layer (e g , that is positioned adjacent the inner wall of at least a portion of the outer member, or positioned m the mterstitial space between the outer member inner wall and the inner member outer wall), a sheath (e g , suπoundmg the outer wall of the inner member) and other tensile support- providing elements The support member is held m place withm the catheter mterstitial space by any suitable means, e g , adhesive, insertion and retention within a portion of the outer member wall (e g , through use of a mechanical press fit or nut and bolt action), etc The support member can be molded m an outer wall of one or more members The inner member may be longer than the support member to avoid tensile load Exemplary Vaπations of the Composite Catheter of the Invention A number of vanations on this basic catheter design are contemplated by the present mvention For example, although a substantially cylindrical catheter shape is descnbed herein as exemplary, the catheter can be formed mto any of a vaπety of dimensions and geometnes, which are selected to be most suitable for the mtended use of the drug delivery device (e g , the desired treatment site, the amount of drug to be delivered, the drug delivery device to be used m conjunction with the catheter, the desired means of attachment of the catheter to the drug delivery device to facilitate flow of drug from the drug delivery device to the catheter, etc ) The catheter may compnse a smgle drug WO 00/78385 PCT/USOO/l 2087 outlet at the distal end for delivery of drug at or near a treatment site, or may compnse a plurality of such drug outlets (e g , m the form of side holes along a portion of the distal end of the catheter that communicate with a drug delivery conduit defined by the inner diameter of the inner member, the outer member, or both) The catheter may compnse a smgle drug delivery conduit (e g , defined by a smgle inner member), or may compnse a plurality of drug delivery conduits (e g , defined by one or more inner members positioned withm a smgle outer member) The catheter of the mvention can also be modified by varymg the relative lengths of the inner and outer members For example, Figs 2 and 3 depict a catheter havmg an inner member 50 and an outer member 70 that are of substantially equal lengths, and that are positioned so that the inner member is substantially completely enclosed withm the inner walls of the outer member (t e , the proximal and distal ends of the inner and outer members terminate substantially withm a smgle plane perpendicular to the proximal and distal ends) However, the mvention also contemplates catheters compπsmg inner and outer members that terminate m different perpendicular planes at the catheter proximal end, the catheter distal end, or both For example, m one embodiment the distal end of the catheter outer member extends distally beyond the distal end of the catheter inner member The catheter 10 of the mvention can be further modified by providmg a radiopaque marker 75 at one or more locations along its length (see, e g , Fig 3) In one embodiment, radiopaque markers are positioned withm the catheter mterstitial space 60 at or near the catheter distal end As exemplified m Fig 3, a radiopaque marker 75 can be provided m connection with a support member 85 (e g , positioned at the distal end of a support member) and can further provide a surface for placement of adhesive 80 to hold the support member 85 the radiopaque marker 75, and the inner member 50 m place withm the outer member 70 Suitable radiopaque markers can comprise metal rings (e g , platmum, palladium, gold, etc ) as exemplified m Fig 3, or can be provided by impregnating or coatmg all or a portion of the catheter body (e g , the body of the outer member or inner member) with appropπate radiopaque dyes or other radiopaque matenals The provision of radiopaque markers is well known m the art In other vanations contemplated by the mvention, the distal end of the catheter is shaped so as to allow for smooth passage through such tortuous bends For example, the distal end of the catheter can be provided as a rounded tip that allows for the catheter to move smoothly around such bends ( g , where a square-ended catheter tip might catch on the sidewalls of a vessel or duct, thus frustrating implantation or placing the subject at nsk of injury) In other vanations, the distal end of the catheter optionally ends m a one-way valve such as a duck bill valve to prevent retrograde flow mto the catheter, with external pressure at that distal end Alternatively or m addition, the distal end may compnse a porous plug that serves as a filter element preventing particulate matter (mcludmg bacteria) from exiting from the catheter and mto the treatment site The catheter can also be provided as a multi-lumen catheter, e g , a. composite catheter compπsmg an outer member with a plurality of inner members, where at least one inner member lumen serves as a drug delivery conduit (see, e g , Figs 5A, 5B, and 5C). a composite catheter compnsmg an outer member and an inner member defining a plurality of inner lumen, where at least one lumen can serve as a drug delivery conduit (see, e g , Figs 5D), or a combmation of multiple inner members compnsmg one or multiple inner lumen (see, e g , Figs 5E) In the multi-lumen embodiment, one of the lumen can define a space through which a guidewire or support member is threaded to facilitate positioning of the catheter In one embodiment, a lumen having a closed distal end is defined by the catheter (e g , the catheter outer member or by a relatively large catheter inner member) to provide for shdeable insertion of a pushing element (e g , a mandrel) to facilitate implantation of the catheter (see, e g , Fig 6) In this embodiment, the pushing element is inserted mto the catheter, and used to position the catheter withm the subject's body during implantation Once the catheter is positioned where desired, the pushing element is withdrawn The empty lumen can then be filled with a matenal (e g , liquid, solid, or semi-solid), which matenal preferably compnses an antimicrobial agent (e g , bacteπostatic or bactencidal agent) Composite Catheter Compnsmg a Distal Extension In specific embodiments of the mvention, the catheter comprises a distal extension, which is positioned adjacent the distal end of the inner member Preferably the distal extension is floppy (z e , flexible, e g , has a low flexural modulus relative to the flexural modulus of the body of the catheter compπsmg both the inner and outer members, or relative to the flexural modulus of the mner member) Where the distal extension is floppy, this portion may be refened to herem as a floppy distal extension or floppy distal portion The flexibility of the floppy distal extension facilitates the catheter's negotiation of curves and tortuous bends (e g , m vessels, ducts, or arteπes) duπng implantation, and further reduces the risk of damage to the sunoundmg tissue The catheter distal extension can be of any desired length, generally from about 1 cm to about 20 cm, usually from about 2 cm to about 10 cm The distal extension of the catheter can be provided m any of a vaπety of configurations For example, the distal extension can be an extension of the distal end of the outer member beyond the distal end of the inner member The extension of the outer member can compnse the same or different materials as the body of the outer member Alternatively, the distal extension can be provided as an additional element that can be permanently attached to the catheter distal end One exemplary embodiment of a composite catheter having a floppy distal extension is illustrated m Figs 7 and 9 In this embodiment, the catheter 10 compπses a floppy distal extension 18, which portion is pπmanly composed of an extension of the distal end of the outer member 70, and compnses a thicker wall over a substantial part of its length The extended distal end of the outer member 70 is composed of a matenal that provides for the desired flexibility of the catheter floppy distal extension 18, which matenal may be the same or different from the mateπal of the remaining portion of the outer member In the embodiment illustrated m Fig 7 A, the distal extension of the outer member defines a lumen 74 that extends from the distal end of the inner member lumen 53 (e g , at the pomt where the inner member 50 terminates within the outer member 70) to the distal end of the catheter 10, and communicates with the inner lumen 53 of inner member 50 The drug delivery conduit 90 is thus composed of both the mner member lumen 53 (from the proximal catheter end to the distal end of the inner member) and the lumen 74 of the extended outer member distal extension 74 (from the distal end of the inner member to the distal end of the catheter) and facilitates flow of drug (mdicated by arrow 93) out a drug delivery outlet 91 at the catheter distal end 12 The distal extension 18 of the catheter 10 m this embodiment is floppy (flexible), thus facilitating placement of the catheter at a treatment site, anchormg at the treatment site, and/or adjustment of the catheter length pnor to implanting (e g , by cutting the catheter's floppy distal end to length) The drug delivery conduit of the exemplary catheter of Fig 7A can extend to the extreme catheter distal end 12 to define a smgle drug delivery outlet 91 Alternatively or m addition, the distal extension can compnse a plurality of drug delivery outlets 91. which can be defined by the wall of the distal extension 18 (see, e g , Fig 7C) Alternatively, or m addition, the drug delivery outlet 97 can be defined by one or more slits m the wall of the catheter distal extension 18 (see, e g , Fig 7B) In use, the distal extension 18 is positioned withm or adjacent a treatment site, and drug is delivered through the drug delivery conduit and out the drug delivery outlet(s) Use of this embodiment of the catheter of the mvention for delivery of drug to the central nervous system (e g . to the spme 5 for intraspmal delivery) is exemplified in Fig 8 In another embodiment, drug delivery conduit terminates at a pomt pnor to the proximal end of the catheter distal extension As exemplified m Fig 9, drug delivery conduit 91 exits out a side of the catheter 10, which may be accomplished by providing an exit through both a side wall of the inner member 50 and outer member 70, or by onentmg the distal end 52 of the inner member 50 toward an opening defined m a wall of the outer member 70 (see. e g , Fig 10) The distal extension 18 of catheter 10 may be substantially solid, or may be substantially hollow with a barner wall 20 positioned at a pomt near or at the distal end of the distal extension 18 In contrast to the embodiment above, the drug delivery conduit 90 is defined substantially only by the inner member lumen This WO 00/78385 PCT/USOO/l 2087 embodiment of the catheter thus mamtams the smaller mner lumen defined by the inner member for the entire drug delivery conduit, and provides for shorter drug residence time m the catheter In use, drug is delivered from the catheter at a pomt just proximal to the beginning of the distal extensιon(see, e g , Fig 11, which illustrates use of the catheter in delivery of drug to the central nervous system (e g , to the spme 5 for mtraspinal delivery) Drug Delivery Devices Suitable for Use with the Composite Catheter of the Invention The catheter of the mvention can be provided m connection with a drug delivery device In this embodiment, it may be desirable to mclude a component that facilitates attachment of the catheter to the drug delivery device and/or stabilize such attachment, e g , substantially dimmish movement of the catheter m a direction perpendicular to the longitudinal axis of the drug delivery device (e g , to provide strain relief), so as to reduce risk of breakage of the catheter at the attachment site As exemplified m, for example, Figs 7 and 9, the drug delivery device 100 minimally compπses a controlled drug release device, such as an osmotic pump, havmg a proximal end and a distal end, which distal end defines a drug delivery onfice The drug delivery onfice provides a drug flow pathway from a drug reservoir withm the drug delivery device, and may be provided as a distmct opening or as a series of openings, e g , as m the context of a rate-limiting membrane, which membrane defines a plurality of openmgs through which drug may flow from the drug reservoir The distal end of the drug delivery device is attached to a proximal end 11 of the catheter so that the drug flow pathway from the drug delivery device reservoir contmues through the drug delivery device onfice and into the drug delivery conduit 90 of the catheter 10 The catheter 10 thus communicates with the drug delivery device in a manner that facilitates movement of drug from the drug delivery device 100, through the catheter 10, and out the drug delivery outlet 91 of the catheter 10 In general, drug delivery devices suitable for use with the catheter of the present invention are those devices that can provide for delivery of the drug from a drug reservoir at a selected or otherwise patterned amount and/or rate, preferably at a low volume rate In general, dependmg on the concentration of drug, the amount of drug delivered can range from about 0 01 μg/day to about 100 mg/day Controlled release of drug can be accomplished m any of a vaπety of ways accordmg to methods well known m the art, e g , by incorporation of drug mto a polymer that provides for substantially controlled diffusion of drug from withm the polymer, by incorporation of drug m a biodegradable polymer, by providing any of a vanety of pumpmg mechanisms (e g , an osmotically- dπven device), etc Drug can be delivered through the catheter to the treatment site as a result of capillary action, as a result of pressure and fluid flow generated from the drug delivery device, or by diffusion through the device and/or the catheter WO 00/78385 PCT/USOO/l 2087 The drug reservoir of the drug delivery device is preferably made of an impermeable matenal that is sufficiently strong to ensure that it will not leak, crack, break or distort so as to expel its active agent contents under stresses it would be subjected to during use, e g , due to physical forces exerted upon the controlled drug release device as a result of movement by the subject or physical forces associated with pressure generated withm the reservoir associated with drug delivery through the catheter The drug reservoir must also be chemically inert (e g , does not react with the active agent formulation) and is preferably biocompatible (e g , is non-reactive with respect to a subject's body or body fluids) Controlled drug release devices suitable for use in the drug delivery devices of the mvention may be based on any of a vanety of drug delivery systems For example, the controlled drug release device can be based upon a diffusion-based delivery system, e g , erosion-based delivery systems (e g , polymer-impregnated with drug placed withm a drug-impermeable reservoir m commumcation with the drug delivery conduit of the catheter of the mvention), electrodiffusion systems, and the like In other embodiments, the controlled drug release device is based upon a convective drug delivery system, e g , systems based upon electroosmosis, vapor pressure pumps, electrolytic pumps, effervescent pumps, piezoelectric pumps, osmotic pumps, etc Controlled drug release devices based upon a mechanical or electromechanical infusion pump, may also be suitable for use with the present mvention Examples of such devices mclude those described m. for example, U S Pat Nos 4,692,147, 4,360,019, 4,487,603, 4,360,019, 4,725,852, and the like In general, the present mvention can be used m conjunction with refillable, non- exchangeable pump systems that are normally used to deliver a substance through a relatively impermeable catheter In this latter context the present mvention provides several advantages, mcludmg improved and repeated access to a treatment site, as well as the elimination of fluid coupling issues normally assocrated with the conventional use of such devices In a prefeπed embodiment, the controlled drug release device is an osmotically-dπven device Exemplary osmotically-dπven devices suitable for use m the mvention include, but are not necessarily limited to, those descnbed m U S Pat Nos 3,760,984, 3,845,770, 3,916,899, 3,923,426, 3,987,790, 3,995,631, 3.916,899, 4,016,880, 4.036.228, 4,111,202, 4,111,203, 4,203,440, 4,203,442, 4,210,139, 4.327,725, 4,627,850, 4,865.845, 5,057,318, 5,059,423, 5,112,614, 5,137,727, 5,234,692, 5.234,693, 5,728.396, and the like In a preferred embodiment, the controlled drug release device is an osmotic pump, more preferably an osmotic pump similar to that descnbed m U S Pat No 5,728,396 In a particularly prefened embodiment, the osmotic pump is a DUROS™ osmotic pump In general, osmotic pumps operate by imbibing fluid from the outside environment and releasmg conespondmg amounts of the therapeutic agent The reservoirs of osmotic pumps can be a smgle chamber, or can be divided into two chambers (e g , a piston can separate the two chambers) Where the pump compnses two chambers, the first chamber (which lies withm one portion of the controlled drug release device reservoir) contams a fluid-imbibing agent, and the second chamber (which lies within a second portion of the controlled drug release device reservoir) contams a therapeutic agent The fluid-imbibmg agent m the first chamber is isolated from the active agent m the second chamber Where a piston serves to separate the two chambers, the piston is capable of sealably moving under pressure withm the reservoir Although controlled release of drug is described above as bemg pnmaπly attributed to characteristics of the drug delivery device (e g , the type of controlled drug release device mcorporated mto the drug delivery device), other aspects, features, or embodiments of the mvention can facilitate controlled release of drug, and are withm the scope of and contemplated by the present mvention For example, charactenstics of the catheter (e g , dimensions of the drug delivery conduit, particularly the inner diameter of the inner member defimng at least a portion of the drug delivery conduit) can facilitate or further facilitate controlled release of drug from a drug reservoir to the treatment site In another example, the catheter can be loaded with polymer that provides for controlled diffusion of drug from the drug reservoir Drugs for delivery using the drug delivery system of the invention Any of a wide vanety of drugs can be delivered usmg the drug delivery system of the mvention Drugs suitable for delivery are preferably provided as flowable formulations, and are generally provided as liquids or semisohds The drugs may be anhydrous or aqueous solutions, suspensions or complexes, and may be formulated with pharmaceutically acceptable vehicles or earners, as well as additional inert or active mgredients The drugs of formulations suitable for delivery usmg the mvention may be in various forms, such as uncharged molecules, components of molecular complexes or pharmacologically acceptable salts Also, simple deπvatives of the agents (such as prodrugs, ethers, esters, amides, etc ) that are easily hydrolyzed by body pH. enzymes, etc , can be employed Preferably the agents are formulated so as to remam stable for long peπods of storage on the shelf or under refrigeration, as well as for long penods stored m an implanted drug delivery system of the invention Of particular mterest is the treatment of diseases or conditions that require long-term therapy, e g , chrome and/or persistent diseases or conditions for which therapy involves treatment over a peπod of several days (e g , about 3 days to 10 days), to several weeks (e g , about 3 or 4 weeks to 6 weeks), to several months or years, up to mcludmg the remaining lifetime of the subject Subjects who are not presently suffering from a disease or condition, but who are susceptible to such may also benefit from prophylactic therapies usmg the devices and methods of the mvention WO 00/78385 PCT/USOO/l 2087 Attachment of a drug delivery device to a catheter of the invention The catheter of the mvention can be modified to be permanently fixed to a drug delivery device (e g , the catheter can be an extension of a drug delivery device component (e g , outer sheath of a drug delivery device) or can be attached by weldmg, adhesive bondmg, etc ) Alternatively, the catheter of the mvention can comprise an attachment element 25 for attaching the catheter to a drug delivery device (see, e g , Figs 7, 9, and 12) The attachment element 25 facilitates and mamtams a connection between a drug delivery device and a catheter of the mvention, and thus mamtams a drug flow pathway from a drug reservoir of a delivery device to a treatment site, duπng use m drug delivery to a treatment site Such an attachment element may provide for permanent or reversible attachment of the drug delivery device to the catheter, and preferably provides for a leak-proof seal between the catheter and the drug delivery device Any of a vanety of attachment elements are compatible for use m the drug delivery system of the mvention The attachment element can be provided as a portion of or component associated with the catheter proximal end, the drug delivery device distal end, or a combmation of both The attachment element can be fashioned from or attached to a proximal portion of the catheter outer member, which proximal portion is extended beyond the proximal end of the catheter inner member For example, the attachment element can be a press fit lock fashioned from or attached to a portion of such an extended catheter outer member In another example, the attachment element is a combmation of a threaded connector elements, luer lock elements, bayonet connectors, etc Alternatively, the attachment element can be provided by a catheter receivmg element positioned at the distal end of the drug delivery device, e g , the proximal end of the catheter can permanently or removably inserted mto the body of the drug delivery device In this latter embodiment, the proximal end of the catheter may not require any additional elements to accomplish attachment to the drug delivery device Use of the Catheter of the Invention in Drug Delivery The catheter of the invention can be used m a wide vaπety of subjects For example, the catheter can be implanted with an associated drug delivery device at any convenient site withm the subject's body and onented for delivery to any desired treatment site In one embodiment, the catheter and the associated drug delivery device are partially or completely implanted, with at least portion of the drug delivery device retained at an accessible, external or subcutaneous site withm the subject's body (e g , under the skin of the arm, shoulder, neck. back, or leg) or within a body cavity (e g , withm the mouth) The site of implantation can be at a site close (e g , withm a few centimeters, e g , within about 2 cm), or at a site relatively distant (e g , more than about 30 cm, generally greater than about 50 cm to 100 cm) from the treatment site, and thus the ultimate site of drug delivery A smgle catheter WO 00/78385 PCT/USOO/l 2087 and/or drug delivery device, or two or more catheters and/or drug delivery devices can be implanted in a subject during the course of a therapeutic program In one embodiment, the catheter is primed with drug prior to implantation, e g , the drug delivery conduit is substantially pre-filled with drug Priming of the catheter reduces delivery start-up time, z e , time related to movement of the drug from the drug delivery device to the distal end of the catheter This feature is particularly advantageous where the drug delivery device releases drug at or below a low or very low volume rate (e g , 0 4 μl/day) The drug used to prime the catheter may be the same drug that is delivered from the drug delivery device, or may be a different drug or different formulation of the drug, e g , the catheter itself may provide for a component of the therapeutic regimen The catheter can be designed for temporary use, or to remain implanted m the subject for an extended period, e g , from several days, to several weeks or months, and can be designed to be substantially permanently implanted in the subject (e g , for the subject's remaining hfespan) The drug delivery devices can be removably attached to the catheter, or may be permanently affixed Where the drug delivery device is removably attached, the drug delivery device can be removed followmg a desired drug administration penod. and. where desirable replaced with a similar or different drug delivery device The devices of the present mvention (e g . catheter, drug delivery device, drug delivery system compπsmg a drug delivery device and catheter) are preferably rendered sterile prior to use This may be accomplished by separately sterilizing each component, e g , by gamma radiation, steam stenhzation or sterile filtration, etc , then asepticalh assemblmg the final system Alternatively, the devices may be assembled, then terminally stenhzed using any appropnate method Insertion of the catheter and/or drug delivery device can be accomplished usmg methods and tools that are well known in the art Insertion of the catheter is generally accomplished m a manner similar to insertion of any of a vanety of catheters, e g , under aseptic conditions with at least some local or general anesthesia administered to the subject Where the catheter compπses radiopaque matenal, insertion of the catheter can be momtored by X-ray or other means of visualization of the insertion process Where desired, the drug delivery device and or catheter can be anchored withm the subject by any suitable conventional means For example, sutures can be used to secure a proximal end of the drug delivery device and or catheter at or near an implantation site Followmg implantation, the catheter defines a drug delivery conduit that provides for transport of drug from a proximal catheter end to a distal catheter end, where the catheter proximal end is preferably maintained at the initial access site or implantation site and the catheter distal end is positioned so a drug delivery outlet of the catheter is positioned at, withm, or adjacent the desired treatment site WO 00/78385 PCT/USOO/l 2087 The catheter (or complete drug delivery device/catheter assembly) can be implanted for delivery of drug to a desired treatment site, the drug delivery device coupled to the catheter (e g , where the drug delivery device is removably attached to the catheter), and, optionally, the drug delivery device and any remaining portion of the catheter completely implanted m the subject The drug delivery device, and generally at least a portion of the catheter, are retamed at a an access site as descnbed above The drug delivery device can be removed from the subject by locatmg the drug delivery device, e g , by fingertip palpation of the subcutaneous implantation or access site After anesthetizing the subject at least locally, an incision is made through the skin and any fibrous capsule tissue sunoundmg the area of implantation The end of the device opposite the incision is pushed so that the proximal end of the drug delivery device is urged out of the incision The drug delivery device can then be released from the catheter and withdrawn, or the entire drug delivery system (drug delivery device with catheter) withdrawn Where the drug delivery device is released from the catheter, a replacement drug delivery device, which device may compnse the same or different drug and drug formulation, can then be attached to the catheter, and re-implanted substantially without withdrawmg the catheter from the treatment site The drug delivery device and/or catheter can be optionally anchored, e g , by suturmg a proximal end of the catheter or a portion of the drug delivery device in place at the access site This procedure can be designed so that removal and replacement of drug delivery devices can be performed on an outpatient basis, and with minimal discomfort to the subject The mvention as shown and descnbed is considered to be the one of the most practical and prefeπed embodiments It is recognized, however, that the departures may be made therefrom which are withm the scope of the mvention and that obvious modifications will occur to one skilled m the art upon reading this disclosure

Claims: WO 00/78385 PCT/USOO/l 2087 WHAT IS CLAIMED IS 1 A composite catheter compnsmg an outer member compnsmg a proximal end, a distal end. and an outer member body defimng an outer member lumen, and an inner member compnsmg a proximal end, a distal end, and an inner member body defining an inner member lumen, wherem the inner member is interposed within the outer member lumen so as to define an mterstitial space between the inner member and the outer member, and wherein the inner member lumen defines a drug delivery conduit suitable for delivery of a drug from the inner member proximal end to the inner member distal end 2 The composite catheter of claim 1 , wherem the inner member defines at least two drug delivery condmts 3 The composite catheter of claim 1, wherem the catheter compnses at least two inner members 4 The composite catheter of claim 1 , wherem the inner member body compπses a substantially impermeable mateπal 5 The composite catheter of claim 4, wherem the matenal of the inner member body is selected from the group consistmg of a polymer, metal, glass, a polyolefin, nylon, polyethylene terephtholate, urethane, a fluorenated polymer, poly(methyl)methacrylate, polyvmyhdine chlonde, laminous hydrophilic polymer, laminous hydrophobic polymer, acrylomtnle, mckel titanium, superelastic mckel titanium, and laminates of hydrophilic and hydrophobic polymers 6 The composite catheter of claim 1, wherem the outer member body compnses a substantially biocompatible mateπal 7 The composite catheter of claim 6, wherem the mateπal of the outer member body is selected from the group consistmg of silicone, polyethylene, an ethylene vmyl acetate copolymer, a polyvmylchlonde, polymethylmethacrylate, polyethylmethacrylate, polymethacrylate, ethylene glycol dimethacrylate. ethylene dimethacrylate, hydroxymethyl methacrylate, polyurethane, polyvinylpyπolidone, 2-pynohdone, polyacrylorntnle butadiene, a polycarbonate, polyamides, a fluoropolymers, a polystyrene, a styrene acrylomtnle homopolymer, a styrene acrylomtnle copolymer, cellulose acetate, an acrylomtnle butadiene styrene homopolymer, acrylomtnle butadiene styrene WO 00/78385 PCT/USOO/l 2087 copolymer, polyvmylchlonde. silicone rubber, polymethylpentene. a polysulfone, a polyester, a polyimide, polyisobutylene, polymethylstyrene, a polyvmyl chloπde elastomer, a polyolefin homopolymenc elastomer, a polyolefine copolymenc elastomer, a urethane-based elastomer, a natural rubber, and a synthetic rubber 8 The composite catheter of claim 1, wherem the catheter further compnses a support member positioned withm the mterstitial space 9 The composite catheter of claim 8, wherem the support member comprises a material selected from the group consistmg of metal, a metal alloy, carbon fiber, a polycarbonate, a polymer, plexiglass, stainless steel, parylene-coated stainless steel. Teflon-coated stainless steel, and mckel titanium 10 The composite catheter of claim 8, wherem the support member is a compression support member 11 The composite catheter of claim 10, wherem the compression support member is shdable withm the interstitial space 12 The composite catheter of claim 8, wherem the support member is a tensile support member 13 The composite catheter of claim 1, wherem the mterstitial space comprises a liquid, solid, semi-solid, or pressunzed gas 14 The composite catheter of claim 1, wherem the mterstitial space compnses an antimicrobial agent 15 The composite catheter of claim 1 , wherem the inner member and the outer member are of different lengths 16 The composite catheter of clam 1, wherem the catheter further compπses an distal extension at a distal end of the catheter WO 00/78385 PCT/USOO/l 2087 17 The composite catheter of claim 16. wherem the distal extension is flexible relative to a proximal portion of the catheter 18 The composite catheter of claim 16. wherein the distal extension is an extension of the outer member distal end 19 The composite catheter of claim 16, wherem the distal extension is substantially hollow, and wherem the mner member lumen and a lumen defined by the distal extension form a drug delivery conduit 20 The composite catheter of claim 16. wherem the distal extension defines an opening that provides a drug delivery outlet 21 The composite catheter of claim 20, wherem the drug delivery outlet is defined m a sidewall of the distal extension 22 The composite catheter of claim 16. wherem the inner member lumen termmates m a drug delivery outlet at a sidewall of the catheter proximal to the distal extension 23 The catheter of claim 1 , wherem the inner member lumen is suitable for delivery of drug at a low volume rate 24 The catheter of claim 1. wherem the inner diameter of the inner member lumen is from about 0 001" to 0 025" 25 The catheter of claim 1, wherem the catheter has an outer diameter of from about 0 030" to 0 060" 26 The catheter of claim 1, wherem the catheter further compπses a radiopaque marker 27 The catheter of claim 1, wherem the catheter compnses a valve at a catheter distal end 28 The catheter of claim 1, wherem the catheter compnses an attachment element for attaching a drug delivery device to the catheter 29 A drug delivery system compnsmg the composite catheter of claim 1, and a drug delivery device. wherem the drug delivery device is attached to the catheter to facilitate delivery of a drug from the drug delivery device and through the inner member lumen of the composite catheter 30 The drug delivery system of claim 29, wherem the catheter is detachably attached to the drug delivery device 31 The drug delivery system of claim 29. wherem the drug delivery device is a convective drug delivery device 32 The drug delivery system of claim 29, wherein the drug delivery device is a diffusive drug delivery device 33 The drug delivery system of claim 29, wherem the drug delivery device facilitates controlled release of drug at a volume rate of from about 0 01 μl/day to about 200 μl/day 34 A method for delivery of a drug to a treatment site in a subject, the method compnsmg the step of implantmg the composite catheter of claim 1 mto a subject, wherem said rmplantmg provides a drug deliver}' pathway from a proximal end of the catheter, through the inner member lumen to a distal end of the catheter, and out a drug delivery outlet positioned at a treatment site m a subject, and mtroducmg a drug mto the inner lumen of the catheter, wherem the drug is delivered to the treatment site m the subject 35 The method of claim 34. wherem the inner member lumen is suitable for delivery of the drug at a low volume delivery rate 36 The method of claim 35. wherem the low volume delivery rate is from about 0 01 μl/day to about 200 μl/day 37 The method of claim 34. wherem the catheter is substantially filled with the drug pnor to implantmg WO 00/78385 PCT/USOO/l 2087 38 The method of claim 34, wherem the catheter further compπses a distal extension at the distal end of the catheter, wherem the distal extension is flexible 39 The method of claim 34, wherem the treatment site is subcutaneous, percutaneous, mtravenous, mtrathecal, intramuscular, lntra-artenal, mtravascular. mtrapeπtoneal, mtraspmal, epidural, mtracramal, intracardial, peπtumoral, or lntratumoral 40 The method of claim 35, wherem the treatment site is a site withm a kidney, liver, pancreas, heart, lung, eye, ear, lymph node, breast, prostate, ovary, testicle, thyroid, spleen, central nervous system, skeletal muscle, bone, lymph vessel, artery, artenole, capillary bed, blood vessel, vem, peπpheral nervous system, digestive system, gastromtestmal tract, uπnary bladder, gall bladder, adrenal gland, adipose tissue, parathyroid gland, uterus, fallopian tube, skin, tumorous growth, autologous graft, synthetic graft, or site of microbial lnfeciton

Inventors: GILLIS EDWARD M, THEEUWES FELIX, GILLIS, EDWARD, M., THEEUWES, FELIX
Applicants: DURECT CORP, GILLIS EDWARD M, THEEUWES FELIX, DURECT CORPORATION, GILLIS, EDWARD, M., THEEUWES, FELIX
Application year: 2000
Main classification: A61M25
IPC codes: A61M25