Patent Publication Number: US-2010121274-A1

Title: Prefillable constant pressure ambulatory infusion pump

Description:
BACKGROUND 
     The present disclosure relates generally to portable infusion devices and more specifically to portable prefillable infusion devices. Infusion pumps are used commonly to deliver a wide variety of medication to medical patients. Infusion pumps are used to deliver, for example, intravenous fluids and solutions for medical therapies such as chemotherapy, antiviral and antibiotic therapy. Infusion pumps are used also to intravenously introduce blood, saline solutions, glucose solutions and other medical fluids including drugs and pharmaceuticals. 
     Besides a single infusion of medication to a patient, a patient may require multiple infusions on a daily basis, intermittent infusion over a time period, or even a slow, continuous introduction of medication into a patient. Specifically, certain medicinal therapies require the infusion of medication over a particular period of time that can range from a short period (about 30 minutes) to an extensive period (several days). It is important, therefore, to administer these medication doses completely and accurately. Accurate administration requires, for example, a consistent and controllable flow rate. 
     There is an increasing reliance on outpatient and home care treatment. Different infusion devices, however, have different drawbacks. Many existing infusion pumps do not offer the portability required to meet the needs of an ambulatory patient because these devices generally require a patient confined to a bed while others are too bulky to be an option for the ambulatory patient. 
     High-end infusion pumps contain sophisticated electrical components and mechanisms that are expensive. Other ambulatory infusion pumps use mechanical members that impart a dispensing force that is often inconsistent and inaccurate. 
     Still other infusion devices are single, self-contained units, such that the device, though refillable, must be disposed after the single medication therapy is complete. It is common practice to dispose fluid contacting components in medication infusion. In most single use infusion pumps, the container of the solution is integrated into the pump unit or the container itself serves as the energy source, especially in elastomer devices. Therefore, the fluid contacting components are inseparable from the pump unit, which consequently results in disposing the whole unit after the single medication therapy is complete. 
     A need accordingly exists for an ambulatory infusion pump device that operates simply and inexpensively. A need also exists for an ambulatory infusion pump device that dispenses a uniform flow rate of medication and that can dispense multiple types of medication without disposal of the entire device. 
     SUMMARY 
     The infusion devices of the present disclosure provide portable, reusable, non-electrical, infusion devices that can consistently dispense medications with a uniform flow rate multiple times to a patient. In one embodiment, for example, the device includes an inflatable cartridge that secures a bellows inside of a housing. The housing has a piston that applies a constant force to the bellows to dispense medical fluid to a patient at a uniform flow rate. 
     The infusion device can include a cylindrical housing and an inflatable cartridge sized to fit within the housing. The cartridge includes an inlet and an outlet and an end configured to be releasably secured to an end of the housing when the cartridge is inserted into the housing. The cartridge end is also connected to an inflatable portion of the cartridge. The infusion device also includes a piston that is located within the housing. The piston includes at least one biasing device or spring positioned to apply a constant force to the inflatable portion of the cartridge to expel a medical fluid from the cartridge. 
     In a further embodiment the cartridge may be placed in a barrier over-wrap containing a desired gas to increase the shelf life or performance of the infusion device. 
     In another embodiment of the present disclosure, a portable infusion device is provided. 
     In still another embodiment of the present disclosure, a portable infusion kit is provided. The infusion kit includes a portable infusion device and a retracting tool. The infusion device can have a cylindrical housing and an inflatable cartridge filled with medical fluid. The inflatable cartridge includes an inflatable portion, which is sized to fit within the housing, while an end of the cartridge is releasably secured to the housing when a bellows is inserted into the housing. The infusion device further includes a piston located within the housing. The piston includes at least one biasing device or spring positioned to apply a constant force to the inflatable portion of the cartridge to expel the medical fluid from the cartridge. 
     The retracting tool includes a threaded rod, which includes a handle on one end and a nut configured to be releasably secured to the housing. 
     It is, accordingly, an advantage of the present disclosure to provide a portable infusion device that is refillable with the same medication for the same patient. 
     It is another advantage of the present disclosure to provide a portable infusion device that administers medication at a uniform flow rate. 
     It is a further advantage of the present disclosure to provide a portable infusion device that can be reused to administer different medications. 
     It is yet another advantage of the present disclosure to provide a portable infusion kit for administering different medications within a single housing. 
     It is yet a further advantage of the present disclosure to provide a portable infusion kit with prefillable cartridge having a reloading kit. 
     It is still a further advantage of the present disclosure to provide a ambulatory infusion device that is significantly smaller and lighter than existing reusable ambulatory infusion pumps. 
     It is another advantage of the present disclosure to provide adequate compatibility with most of the drugs currently administered with ambulatory infusion pumps. 
     It is a further advantage of the present disclosure to provide an a prefilled ambulatory infusion pump which maintains an extended shelf life. 
     It is a further advantage of the present disclosure to provide an accurate means of estimating the remaining volume or the dispensed volume of the medication during infusion. 
     It is yet another advantage of the present disclosure to provide a flow indicating device, especially for viewing very slow flow rate infusion. 
     It is yet a further advantage of the present disclosure to allow the device to be prefilled. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a cross-section view of a disassembled embodiment of an infusion device of the present disclosure. 
         FIG. 2  is a cross-section view of the cartridge embodiment of  FIG. 1  with a compressed bellows. 
         FIG. 3  is a perspective view of the cartridge cap embodiment of  FIG. 2 . 
         FIG. 4  is a perspective view of the piston embodiment of  FIG. 1  that contains two negator springs. 
         FIGS. 5A to 5C  are partial cross-section views illustrating the connection of the pump and the cartridge and expansion of the bellows according to one embodiment of the present disclosure, in which the pump is in cross-section and the cartridge is in full view. 
         FIG. 6  is a perspective view of one embodiment of a portable infusion device of the present disclosure. 
         FIG. 7  is a perspective view of the portable infusion device embodiment of  FIG. 6  with multiple cartridges. 
         FIG. 8A  is a perspective view of one embodiment of an infusion device with a flow indicator of the present disclosure.  FIGS. 8B and 8C  are enlarged front views of the flow indicator of  FIG. 8A . 
         FIG. 9  is a top view of the pump embodiment of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings,  FIG. 1  illustrates one embodiment of a portable infusion device  10 . Infusion device  10  includes a compressible cartridge  20  and a reusable pump  50 . As will be described in more detail below, cartridge  20  is configured to fit inside pump  50  such that pump  50  can dispense medical fluid contained in cartridge  20 . 
     Compressible cartridge  20  is generally cylindrical, disposable and includes a compressible bellows  22  and an end or cap  24 . Bellows  22  includes a top surface  26 . Bellows  22  has an accordion-like structure as shown in an expanded configuration in  FIG. 1 , in which a hollow interior of bellows  22  is filled with a drug or pharmaceutical composition. When not filled with a medication or after expelling medication, bellows  22  assumes a compressed configuration as shown in  FIG. 2 . 
     Bellows  22 , in one embodiment, is made of low-density polyethylene (“LDPE”), which is known to be chemically inert and compatible with most drugs. The material used to make bellows  22  can also be multi-layered to provide increased moisture barrier properties and/or for mechanical strength enhancement to cartridge  20  when pre-filled with medication. 
     The angle of each corrugation of expanded bellows  22  is about 60° in the illustrated embodiment. Narrowing the corrugation angle provides bellows  22  with more corrugations, which therefore provides bellows  22  with more resistance against bursting or buckling when expanded. If the corrugation angle is too narrow, however, then bellows  22  requires significantly more corrugations to achieve the same volume as that shown in the illustrated embodiment. Consequently, the height of bellows  22  increases when fully compressed, which increases the potential dead volume, and the length of the device. 
     The diameter of bellows  22  is sized as needed to provide sufficient stability to maintain rigidity and straightness of bellows  22  and to prevent buckling or bending of expanded bellows  22  when under pressure. Increasing the diameter improves buckling resistance, but necessitates a greater force to compress bellows  22  to expel fluid at a required flow rate. The wall thickness of bellows  22  is provided to prevent bursting or flattening of the corrugation under maximum positive pressure. If the wall thickness is too thick, the height of the compressed bellows will increase, which increases the potential dead volume within the compressed bellows. 
     Bellows  22  may also be made of other flexible materials such as polyolefin or an elastomer or rubber. If the bellows is made of a material such as an elastomer capable of being inflated or stretched to the filled configuration, use of the corrugations may not be needed. 
     Cap  24  connects cartridge  20  to pump  50  and closes bellows  22  to hold medication contained in the interior of bellows  22 . Cap  24 , in one embodiment, is injection molded from high-density polyethylene (“HDPE”) to provide welding compatibility with the mating bellows (made of “LDPE”) while providing structural strength. Cap  24  is made alternatively from a polyolefin, such as polypropylene. 
     Cap  24  includes three main portions: an outer rim  32 , a bottom surface  34  and a center boss  36 . A flange  30  on bellows  22  is affixed to cap  24  at center boss  36  as illustrated in  FIG. 1 . Outer rim  32  provides a handle on cartridge  20  for assembling (connecting) and disassembling (disconnecting) cartridge  20  to and from reusable pump  50 . The exterior surface of outer rim  32  is corrugated to prevent slippage when rotating cartridge  20 . The interior surface of outer rim  32  includes, for example, three or four cylinder shaped lugs  46  (shown in  FIG. 3 ) extending in and from the interior surface. Lugs  46  have the size and shape necessary to engage mating locking grooves  64  on pump  50  when connecting cartridge  20  to pump  50 . 
     Center boss  36  of cap  24  includes an inlet  38  having a check valve  44  (best seen on  FIG. 3 ), an outlet  40  and an associated tube  42  with a flow restrictor  43  and an inline air eliminating filter  45 . Flow restrictor  43  is configured to restrict flow out of outlet  40  to a desired flow rate over the course of an infusion. When opened, restrictor  43  has a small diameter opening permitting fluid flow between outlet  40  and the outlet of tubing  42 . Illustrated inlet  38  is a female luer port that can accept a syringe or male luer for the injection of medication. Illustrated outlet  40  is a flow channel communicating with tube  42 . Filter  45 , located in tube  42  upstream from flow restrictor  43 , eliminates the potential for air bubbles and the generation and migration of particulate matter during the filling procedure. 
     Center boss  36  extends from the bottom surface  34  of cap  24  to the height of a fully compressed bellows  22  (shown in  FIG. 2 ) such that bellows  22 , when fully compressed, contacts center boss  36  at a cap head  28 . Center boss  36  fills the dead volume of fully compressed bellows  22  to minimize the residual volume of, for example, an expensive drug at the completion of infusion when bellows  22  is at maximum compression. The diameter of center boss  36  is slightly smaller than the inner diameter of compressed bellows  22 , so that bellows  22  can be compressed and expanded freely without any interference from center boss  36 . 
     Cartridge  20 , including bellows  22 , cap  24  and outlet tube  42  are all part of the fluid contacting portion of infusion device  10 . These portions generally are not refilled after use and, instead, are discarded after use. However, for the same patient using the same medication, cartridge  20  can be refilled multiple times when a large volume therapy is preferred. For example, a cartridge of 60 mL size can be refilled five times for 300 mL total therapy when only 60 mL size device is available, thereby providing a pump that consistently dispenses fluid during repeated use. 
     Reusable pump  50  as illustrated in  FIG. 1  includes a generally cylindrical housing  52  having an open end  54 , a top end  56  and a piston  60  located within housing  52 , which is operated by two constant force springs  62  (or negator springs). Housing  52  can be injection molded from a rigid plastic like polycarbonate, polyester or acrylonitrile butadiene styrene (“ABS”), which provide structural integrity to withstand a high-tension force exerted by negator springs  62 , while being sufficiently clear to see inside the device through a provided window. 
     The cylindrical shape of housing  52  extends from open end  54  to top end  56 , and has an inner diameter that is slightly bigger than the outer diameter of bellows  22 , so that piston  60  (with springs  62 ) and bellows  22  can slide along the inside wall of housing  52  with minimal resistance. The clearance space between the inside wall of housing  52  and piston  60 /bellows  22  is minimized, however, to prevent buckling of bellows  22  or wiggling of piston  60  as each moves up and down along housing  52 . 
     Housing  52  also includes a spring path  58  having a rectangular shape extending outward from the main cylindrical portion of housing  52 . Spring path  58  provides a path for the coiling and uncoiling of negator springs  62  as discussed in detail below. The height and the width of the rectangular shape spring path  58  are determined by the thickness and the width of the strap of the negator springs. Open end  54  also includes mating grooves  64  located on the edge of open end  54 . Mating grooves  64  are configured to mate with inserted cartridge  20  as described herein. 
     Housing  52  can be opaque or translucent, for example, via colored plastic or textured surface treatment. Two viewing windows  74  may be installed on both walls of housing  52  so that the fluid content within bellows  22  and the movement of bellows  22  can be seen from the outside of housing  52 . One of the illustrated viewing windows  74  includes fine graduation marks  76  printed to estimate the residual medicament volume during infusion of medication by compression of the bellows. By providing an indicating line (not shown) on the side wall of piston  60 , the pump&#39;s residual volume can be estimated accurately to the milliliter by noting the indicating line&#39;s location relative to the graduation marks during the linear movement of bellows  22  within pump  50 . 
     Referring again to  FIG. 1 , piston  60  includes a bottom surface  66  and two parallel ribs  68  (best seen on  FIG. 4 ) extending upward from bottom surface  66  of piston  60 . The railroad-shaped ribs minimize piston surface contact with the surface of the negator springs, which consequently allows a free movement of negator springs  62  as they coil and uncoil. The size and shape of bottom surface  66  of piston  60  is such that top surface  26  of bellows  22  can snap-fit to bottom surface  66 . For example, the flat portion of bottom surface  66  may have a width and length that is slightly larger than the length and width of top surface  26  of bellows  22  such that the top surface  26  snap-fits into bottom surface  66  of piston  60 . The diameter of piston  60  is slightly larger than the diameter of compressed bellows  22  so bellows  22  can be compressed and expanded with no interference with springs  62 . Piston  60 , including bottom surface  66  and ribs  68 , can be injection molded from a plastic of low friction coefficient like Polyacetal, or any thermoplastic material that can provide rigid structural integrity. The piston can also include a lubricant or coating for minimizing friction. 
     The two negator springs  62  made, for example, of stainless steel, lie within piston  60  on two parallel protruding ribs  68  (better shown in  FIG. 4 ). Negator springs  62 , when uncoiled, exert a constant compression force on bellows  22  regardless of the displacement of the springs. Ribs  68 , protruding upwardly from surface  66  of piston  60 , allow springs  62  to rotate or slide freely within piston  60  with minimal frictional resistance. Each spring  62  also includes a spring tip  70  that is fixed to housing  52  at an attachment portion  72 . Attachment portions  72  reside on the inside surface of housing  52 , specifically in spring path  58  of housing  52 . Moreover, in one embodiment, low friction material such as Teflon™ lubricates or coats the outside surface of negator spring  62  to promote unimpeded coiling and uncoiling of springs  62  and unimpeded movement of springs  62  within piston  60  or, at minimum, movement and coiling/uncoiling with minimal frictional resistance. Other low friction materials include, for example, PTFE coating (FluroMed®) or vapor deposition Parylene. 
     The dimension (strength) of spring  62  is determined by the required pressure of the solution retained within bellows  22  of cartridge  20 . The required pressure is based on the desired flow rate and viscosity of the medication, and the pressure differential between the upstream pressure of flow restrictor  43  and the downstream physiological backpressure provided by the medication within bellows  22 . The tension (or retracting) force of each negator spring  62  is determined by multiplying the required pressure by the cross-sectional area of bellows  22 , and dividing that value by the number of springs, which is two in the embodiment illustrated in  FIG. 1 . The width and diameter of the coiled spring are optimally determined from a table of values from the spring supplier, or can be custom designed if necessary. Currently, most of the disposable ambulatory infusion pumps are designed to exert the pressure from about 4 psig to about 9 psig. With these fixed pressures, flow rate is adjusted by the dimension (bore diameter and the length) of the outlet or tubing instead of varying the pressure of the pump. To overcome a high backpressure, the present disclosure advantageously provides a higher pressure using a stronger spring. 
     Reusable pump  50 , including housing  52 , springs  62  and piston  60 , are part of the non-fluid contacting portion of infusion device  10 . Therefore, these non-fluid contacting portions are reusable, and do not need to be disposed after use for contamination reasons. 
     Springs  62 , and corresponding piston  60 , reciprocate between a resting, coiled position adjacent attachment portion  72  of housing  52 , and a non-resting, uncoiled position near top end  56  of housing  52 .  FIG. 1  illustrates springs  62  in a non-resting, uncoiled position, in which springs  62  have uncoiled, due to positive fluid pressure within bellows  22 , via spring tips  70  held to housing  52 .  FIG. 5A , on the other hand, shows springs  62 , and piston  60 , in a resting, coiled position. 
     In the resting, coiled position of  FIG. 5A , piston  60  and springs  62  rest inside housing  52  adjacent attachment portion  72  of the housing. In this resting position, the springs are not stretched and therefore have no stored kinetic energy. In  FIG. 5A , cartridge  20  is shown outside of and not connected to pump  50 . Bellows  22  of cartridge  20  is fully compressed because no medication is contained within the bellows. 
     To place infusion device  10  in a position to dispense medication to a patient, cartridge  20 , with compressed bellows  22 , is first engaged to pump  50  as illustrated in  FIG. 5B . To engage cartridge  20  with pump  50 , bellows  22  is inserted into pump  50  through open end  54  of pump  50 . Bellows  22  is inserted into pump  50  until open end  54  of pump  50  contacts bottom surface  34  of cap  24  on cartridge  20 . After contact, the user rotates cap  24  until lugs  46  (shown in  FIG. 3 ) on cap  24  align with the entrance of mating grooves  64  (shown in  FIG. 5A ) on housing  52 . Further rotation and slight pushing of cap  24  locks lugs  46  into place in mating grooves  64 , thereby locking cartridge  20  to pump  50 . When lugs  46  pass the peak of the mating groove (illustrated in  FIG. 5A ), the lug is snapped in a secure lock position. Slight tension is generated in this position, which enhances secure ‘lock’ without possibility of loosening of the cap. In this locked position, compressed bellows  22  and center boss  36  on cap  24  reside within housing  52  of pump  50 . Top surface  26  of bellows  22  may contact bottom surface  66  of piston  60  or snap-fit to bottom surface  66  depending on (a) the location of piston  60  relative to bellows  22  and, as discussed previously, (b) the size and shape of piston bottom surface  66  relative to bellows  22 . Other than the slight tension described above, bellows  22  does not impart any force on piston  60 , nor does bellows  22  push piston  60  from its resting, coiled position illustrated in  FIGS. 5A and 5B . 
     To inflate bellows  22  as shown in  FIG. 5C , a user inputs medication into bellows  22  through inlet  38  using, for example, a syringe or filling machine (not shown). Fluid dispensed from the syringe or filling machine through the inlet applies sufficient pressure to open check valve  44  and allow the fluid to pass check valve  44  into bellows  22 . 
     As medication is dispensed into collapsed bellows  22 , bellows  22  inflates and applies pressure to piston  60 . As bellows  22  inflates, springs  62  uncoil along spring paths  58  of housing  52 . As springs  62  uncoil, piston  60  moves upward through housing  52  while spring tips  70  stay fixed to housing  52  at attachment portions  72 . As springs  62  uncoil, piston  60  applies downward pressure to bellows  22 . However, no fluid will dispense through outlet  40  as long as an end clamp or slide clamp (not shown) on tube  42  is activated. Moreover, as long as the infusion of fluid into bellows  22  continues, piston  60  will continue to move upward and springs  62  will continue to uncoil until piston  60  reaches top end  56  of housing  52  or filling of specified volume is completed, which can be smaller than the volume of the infusion device. 
     Once filling of medication is stopped, check valve  44  closes to prevent a backflow of fluid from escaping cartridge  20  through inlet  38 . The infusion device is now ready to dispense drug through outlet  40 . To commence dispensing, the end cap or slide clamp (not shown) is removed from tube  42 , thereby allowing medication to flow. Springs  62  impart a constant recoiling force on bellows  22 , dispensing medication at a constant flow rate. The flow rate should remain constant regardless of how far bellows  22  displaces piston  60  from its resting position illustrated in  FIG. 5A . To allow for this constant force by springs  62 , the springs rest on ribs  68 , and uncoil and recoil along spring path  58 , which allow springs  62  to rotate and slide freely with minimal frictional resistance. 
     Alternatively, a locking mechanism located at top end  56  of housing  52  may control dispensing of the drug. In this case, once infusion of medication into bellows  22  forces the piston to top end  56  of housing  52 , a built-in latch  57  on piston  60  has two outward-protruding fingers that snap into a mating slot  59  at top end  56  of the housing and lock piston  60  to housing  52  with springs  62  fully uncoiled. Locked piston  60  prevents application of force on expanded bellows  22  even though springs  62  are uncoiled. To dispense the medication contained in bellows  22 , a releasing mechanism disconnects built-in piston latch  57  from housing  52  to allow springs  62  to compress bellows  22  and dispense the medication. The releasing mechanism can include, for example, two sliding tabs  61  formed on the outside of housing  52  that is easily accessible by the user as illustrated in  FIG. 1  and configured to slide toward each other to press the fingers of latch  57  towards each other to unlock and activate piston  60 . 
     After dispensing the medication from bellows  22 , the user discards cartridge  20  by rotating cap  24  in a direction opposite the initial engagement rotation direction to release lugs  46  of cartridge  20  from mating grooves  64  on housing  52 . This motion releases cartridge  20  from pump  50  and allows pump  50  to accept a new cartridge  20 . 
     In the cases where fluid flow out of infusion device  10  is slow (e.g., 0.5 mL/hr), it can be difficult for a patient or a caretaker to check whether the solution is flowing or stopped by blockage. In those cases, portable infusion device  10  may also include a flow indicator mechanism as illustrated in  FIG. 8A . The flow indicator includes a sticker label  77  attached to the side wall of piston  60  and a plurality of half cylinder shaped magnifying lenses  78  formed on a window  81  of housing  52 . Sticker label  77  can include, for example, a color spectrum. A plurality of color bars  79  on sticker label  77  represent the color spectrum, with the width of each color bar  79  being as small as about 0.010″. The width of the sticker label is approximately 0.5″ and the length of the sticker is slightly bigger than the width of window  81 . 
     The plurality of magnifying lenses  78  are installed across the length of window  81 , which is installed on the opposite side of viewing window  74 . Each magnifying lens  78  can have dimensions measuring, for example, 0.080″ in thickness and 0.75″ in length. Distance between each magnifying lens  78  is approximately 0.5″. The distance from the bottom surface of the lens to the sticker determines curvature of the magnifying lens, so the color spectrum of 0.010″ is magnified to fill entire width of lens, 0.080″. Magnifying lenses  78  are injection molded and have a clear appearance while the surrounding body of housing  52  are textured or colored opaque. 
     As piston  60  moves slowly downward along housing  52 , sticker label  77  and corresponding color bars  79  pass underneath magnifying lenses  78 . Magnifying lenses  78  magnify color bars  79  on sticker label  77 , indicating clearly which of the color bars  79  lie beneath a respective magnifying lens  78 , as illustrated in  FIG. 8B . As piston  60  advances further down housing  52 , sticker label  77  also advances along the same magnifying lens  78 , indicating clearly a different color bar  82  or combination of color bars  79  lying beneath the same lens  78 , as illustrated in  FIG. 8C . For a flow rate of 5 ml/hr, for example, the color changes every 3 minutes to reflect the movement of piston  60 . Further, for a flow rate of 0.5 ml/hr, the color changes about every 30 minutes. Therefore, these color changes provide a relatively inexpensive visual indicator that flow is occurring. 
     In another embodiment illustrated in  FIG. 9 , the side of piston  60  includes a pair of primary rails  65  and a pair of secondary rails  67 . Each primary rail  65  is sized to fit into a primary groove  69  on housing  52  such that piston  60  can slide vertically through housing  52  without tilting off of vertical. Each secondary rail  67  is sized to fit into a secondary groove  71  on housing  52  such that piston  60  cannot rotate or slide horizontally within housing  52 . By providing two sets of rails and corresponding grooves, piston  60  can slide smoothly and vertically within housing  52  and negator springs  62  can coil and uncoil within spring path  58  without any non-vertical movement. 
     In an alternative embodiment illustrated in  FIG. 6 , a portable infusion kit  100  is provided. Kit  100  includes infusion device  10  and a retractor  80 . Infusion device  10 , as described above, includes compressible cartridge  20  and reusable pump  50 . Alternatively, kit  10  may include a plurality of compressible cartridges  20  as illustrated in  FIG. 7 . Since cartridge  20  is fluid contacting and is therefore discarded after a single use, kit  10  provides a plurality of compressible cartridges  20  to allow for multiple uses of reusable pump  50  over multiple treatments. 
     Referring to  FIG. 6  in an alternate embodiment, the cartridge  20  may be filled with a medication or other fluid and stored for a period of time before use. It has been found that the performance of the infusion device  10  may be affected by long-term storage. Some possible reasons are the transmission of water vapor through the wall of the bellows  22  or outlet tube  42  ( FIG. 1 ) that may lead to some deterioration of the material of the bellows or may increase the concentration of the drug in the tube to where the drug will fall out of solution and crystallize to form a blockage. Other performance factors include the potential that oxygen or other atmospheric gas may migrate through the bellows  22  and have a detrimental effect on the fluid contained in the cartridge  20 . A still further performance factor may be the affect that an atmospheric gas such as oxygen may have on the material of the cartridge  20 . If the material of the bellows  22  is in a stressed state, such as when the material is an inflated elastomer, the effect of oxidation may be pronounced. 
     To protect the cartridge  20  and/or the contents and provide increased shelf life the cartridge may be packaged in an overwrap barrier container (not shown) to encase the cartridge in an enclosure which forms a gas barrier. Such a container may comprise aluminum film or foil or a polymeric film such as the outer envelope film described in U.S. Pat. No. 6,007,529, the disclosure of which is incorporated herein. 
     The atmosphere within the barrier container may be an atmosphere or an inert gas such as nitrogen or other gas that is more compatible with the contents of the cartridge or the material of the bellows  22  or a mixture thereof. In addition the moisture level of the atmosphere within the container may be selected to increase the performance characteristics of the infusion device  10 . In an alternate embodiment the entire infusion device  10  may be stored within the overwrap barrier container. 
     In  FIG. 6 , retractor  80  includes a threaded rod  82 , a contact surface  84 , a mating nut  86  and a handle  88 . Mating nut  86  includes a hex nut  87 , hex nut housing  89  sized to fit hex nut  87 , rim  90  and plurality of nut lugs  92  provided on the inside surface of rim  90 . Nut lugs  92  have the same features and design as lugs  46  on cap  24 , illustrated in  FIG. 3 , such that nut lugs  92 , like lugs  46 , can be locked to mating grooves  64  on housing  52  of pump  50 . Handle  88  includes a rod fitment  91  with a hole sized to fit and hold threaded rod  82 . Retractor  80 , like pump  50 , is non-fluid contacting and reusable. Rod  82  and mating nut  86  can be made from anodized aluminum, and can be made from a polyacetal material or any thermoplastic materials that provide sufficient mechanical strength with low friction coefficient. Handle  88  and contact surface  84  is made of acrylonitrile butadiene styrene (“ABS”). 
     If cartridge  20  is pre-filled with medication, springs  62  on pump  50  need to be retracted and locked at top end  56  of housing  52  so that cartridge  20  can be loaded into pump  50  without having to retract piston  60  using the already expanded bellows  22  of cartridge  20 . To retract springs  62 , retractor  80  engages pump  50 , and forces springs  62  open (retracts the springs) to lock piston  60  in the forced-open or retracted position before inserting pre-filled cartridge  20 . 
     Retractor  80  is fixed to housing  52  in much the same way as cap  24  on cartridge  20 , illustrated in  FIG. 5B . Specifically, mating nut  86  has substantially the same configuration as cap  24  such that, with threaded rod  82  in a fully retracted position, nut lugs  92  lock to mating grooves  64  on housing  52  as mating nut  86  is rotated onto housing  52 . 
     Once retractor  80  is fixed to pump housing  52 , the operator turns handle  88  to extend retracted threaded rod  82  into housing  52  such that contact surface  84  engages and pushes piston  60  up towards top end  56  of housing  52  while mating nut  86  remains fixed to mating grooves  64  on housing  52 . At top end  56 , built-in latch  57  on piston  60  snaps into a mating slot  59  located at top end  56  to lock piston  60  to housing  52  with springs  62  fully uncoiled. The operator then turns mating nut  86  of retractor  80  in the opposite direction to disengage the retractor from pump  50  by unlocking from mating grooves  64 . The operator then fits pre-filled cartridge  20  into pump  50  and locks it into position by engaging lugs  46  on cartridge cap  24  with mating grooves  64  on housing  52 . The threaded rotation to translational motion of retractor  80  provides even a weak patient with the requisite mechanical power to retract piston  60  and load cartridge  20 . 
     Alternatively, retractor  80  can retract piston  60  by pressing pump  50  onto retractor  80 , which is fixed to a flat surface, causing contact surface  84  to face upward. Using body weight, a user presses pump  50  down on contact surface  84  of retractor  80  to allow contact surface  84  to contact bottom surface  66  of the piston to translate piston  60  and uncoil springs  62  to top end  56  of housing  52 , locking piston  60  to housing  52  as described above. Here, a user with sufficient strength does not need to lock retractor  80  to pump  50  and rotate handle  88  to move the piston. 
     To dispense the medication contained in bellows  22 , releasing mechanism  61  previously discussed disconnects the built-in latch  57  from housing  52  to allow springs  62  to compress bellows  22  and dispense the medication. After dispensing the medication from bellows  22 , the user discards cartridge  20  as discussed above because it is the fluid-contacting part of infusion device  10 , or the user can refill the cartridge with the same medication for longer and larger infusions. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.