Abstract:
A pharmaceutical cartridge piston including a rigid core to resist compression of the piston. The resistance to compression contributes to the piston providing dose accuracy and dynamic recovery advantages.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention pertains to medication delivery devices, and, in particular, to a piston of a pharmaceutical cartridge for a medication delivery device.  
         [0002]     A variety of medication delivery devices, such as injector pens and infusion pumps, employ pharmaceutical cartridges that include a movable piston and contain a multi-dose quantity of liquid medication. In an injector pen, a drive member, extending from within a base of the injector pen and operably connected with typically more rearward mechanisms of the pen that control drive member motion, is movable forward to advance the piston in the cartridge in such a manner to dispense the contained medication from an outlet at the opposite cartridge end, typically through a needle that penetrates a stopper or septum at that opposite end. In disposable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the entire pen is discarded by a user, who then begins using a new replacement pen. In reusable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the pen is disassembled to allow replacement of the spent cartridge with a fresh cartridge, and then the pen is reassembled for its subsequent use.  
         [0003]     While these types of medication delivery devices with cartridges offer a number of advantages to their users, such devices are not without their limitations. For example, possible compression of the cartridge piston during an injection can have a negative effect on the overall operation of the device. For an injector pen, such piston compression can result in the pen&#39;s medication drooling from the needle after an injecting force has been removed and the needle has been prematurely withdrawn from the user, and/or the pen delivering a dose that is less than anticipated.  
         [0004]     Thus, it would be desirable to provide an apparatus that can overcome one or more of these and other shortcomings of the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In one form thereof, the present invention provides a piston for a pharmaceutical cartridge including a tubular barrel extending in an axial direction, the piston being advanceable by a separate drive member of a medication delivery device equipped with the cartridge. The piston includes a body and a core. The body has a distal end, a proximal end and a sealing periphery, which distal end is in contact with a medication disposed within the cartridge barrel, which sealing periphery is in sealing contact with an interior surface of the barrel, and the distal end and the sealing periphery are unitarily constructed from a material having a first hardness. The core is within the body and sealed within the cartridge barrel between the distal end and the proximal end. The core is constructed from at least one material having a second hardness greater than the first hardness to limit axial compressibility of the piston.  
         [0006]     One advantage of the present invention is that a pharmaceutical cartridge piston can be provided which resists axial compression during an injection.  
         [0007]     Another advantage of the present invention is that a pharmaceutical cartridge piston can be provided which may enhance dose accuracy.  
         [0008]     Still another advantage of the present invention is that a pharmaceutical cartridge piston can be provided which may reduce injection hold time. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above-mentioned and other advantages and objects of this invention, and the manner of attaining them, will become more apparent, and the invention itself will be better understood, by reference to the following description of embodiments of the invention taking in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a front perspective view of a pharmaceutical cartridge including a first embodiment of a piston of the present invention;  
         [0011]      FIG. 2  is a longitudinal cross-sectional view of the cartridge of  FIG. 1 , which cartridge is further shown loaded in one form of an abstractly shown medication delivery device;  
         [0012]      FIG. 3  is a rear perspective view of the piston of  FIG. 1  removed from the rest of the cartridge;  
         [0013]      FIG. 4  is a front perspective view in longitudinal cross-section of the piston of  FIG. 3 ;  
         [0014]      FIG. 5  is an exploded, front perspective view of the piston of  FIG. 3 ; and  
         [0015]      FIG. 6  is a longitudinal cross-sectional view of a second embodiment of a pistoin of the present invention. 
     
    
       [0016]     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale, and certain features may be exaggerated or omitted in some of the drawings in order to better illustrate and explain the present invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring now to  FIG. 1 , there is shown a perspective view of a pharmaceutical cartridge, generally designated  10 , including a first embodiment of a piston of the present invention, which piston is generally designated  20 .  FIG. 2  shows the cartridge of  FIG. 1  loaded in one type of a medication delivery device, such as an injector pen or injection pen. The present invention alternatively may be utilized in other medication delivery devices.  
         [0018]     With additional reference to  FIGS. 3-5 , cartridge piston  20  has an axially extending, generally cylindrical, main body  21  that includes a distal end face  22  and a proximal end face  24 . Along its radial periphery, body  21  is formed with a first sealing rib  26  that is immediately adjacent to the distal end face  22 , a second sealing rib  28  immediately adjacent to the proximal end face  24 , and an axially shorter rib  30  centrally disposed therebetween. Circumferential recesses  27  and  29  are disposed between ribs  26  and  30 , and ribs  30  and  28 , respectively. Sealing ribs  26 ,  28  and  30  each extend continuously around the circumference of body  21  to form rings that provide a fluid tight seal with the interior surface of the cartridge tubular barrel to prevent passage of materials out from and into the medicine reservoir. A plurality of protuberances  32  project from the planer distal end face  22  and the planer proximal end face  24  to limit adhesion between multiple pistons when in, for example, a hopper during assembly line production of multiple pharmaceutical cartridges.  
         [0019]     Main body  21  is formed of a material, such as halo butyl rubber, that is chemically and biologically compatible with the not shown medication contained within cartridge  10 . A silicone emulsion coating may be provided on body  21  to provide lubrication. One particularly suitable elastomeric formulation for body  21  is available from West Pharmaceutical Services of Lionville, Pa. and is known as West Formulation PH 4002/50 Red. This elastomeric formulation has a hardness, or resistance to deformation by indentation, using the Shore A Durometer scale, of between 45 and 55.  
         [0020]     Piston  20  also includes a relatively rigid core or insert  40  that is fixedly disposed within a cylindrical hollow or bore  35  of piston body  21 . Core  40  is shown as being cylindrical in overall form, with a planer distal face  42 , a planer proximal face  44 , and an outer periphery  46 . Core  40  is axially centered within the axial or longitudinal length of body  21 , and further is radially centered within body  21  so as to be in alignment with and symmetrical with respect to the central axis of cartridge tubular barrel  55 .  
         [0021]     Core  40  results in piston  20  being less compressible in the axial direction, while not compromising the ability of the piston via its sealing ribs  26 ,  28  and  30  to seal the medicine reservoir. This lesser compressibility not only may improve dose accuracy, but also may shorten the dynamic response, and therefore the injection hold time, during which the piston&#39;s elastic properties cause the piston to return toward its original shape to account for any piston compression during injection. In one form, core  40  is a solid aluminum casting, having a hardness which is greater than the hardness of the elastomeric formulation of body  21  so as to provide a stiffening effect to the piston. Although aluminum is described as being used, one or more other relatively stiff materials, such as various plastics or other polymeric materials, may be used to form the rigid core in alternate embodiments. The hardness or resistance to deformation of these other possible core materials is greater than the hardness of the piston main body material, regardless of, for example, numerical values that are dependent on the type of hardness test, such as Brinell, Rockwell, Shore or other method, by which the hardness is measured. Furthermore, the shape of the rigid core need not be cylindrical to provide advantageous piston properties. For example, cores which have an overall shape more hour-glass in design, or cores having protruding ribs or molding features, may be used within the scope of the invention.  
         [0022]     Core  40  can be of various axial lengths as well as various diameters, while still performing its stiffening function. For a standard piston body having an axial dimension of about 0.32 inch, and a diameter of the sealing ribs  26 ,  28  and  30  of about 0.39 inch, the axial length of core  40  extending between distal face  42  and proximal face  44  is within the range of about 0.08 inch-0.24 inch, more preferably within the range of about 0.16 inch-0.24 inch, and most preferably about 0.24 inch. The diameter of the core may be of various size, such as in the range of about 0.08 inch-0.31 inch.  
         [0023]     Plug  50  covers the proximal face of core  40  and is secured to the piston body  21 , such as via adhesives. Plug  50  is cylindrical and sized to completely fill the piston hollow  35  not filled by core  40 , and seals core  40  within body  21 . The proximal face of plug  50  is coplanar with proximal end face  24 . Plug  50  is made of the same elastomeric formulation as is piston body  21 . Consequently, core  40  is completely encapsulated within the elastomeric formulation that is chemically and biologically compatible with the medication contained within the pharmaceutical cartridge. In alternate embodiments, core  40  may be encapsulated within a one-piece piston body molded completely thereover, in that the plug/piston body combination shown separately formed in the embodiment of  FIGS. 1-5  is integrally molded and formed as a single encapsulating piece.  
         [0024]     The remainder of cartridge  10  may be of standard form, including a tubular barrel  55 , made of glass or other suitable material, which has an inner surface  52 . The inner surface  52  along the larger diameter section of the barrel is sealingly engaged by sealing ribs  26 ,  28  and  30  of piston  20 . The distal end of tubular barrel  55  includes an inwardly sloping shoulder portion  56 , a reduced diameter neck  58 , and a rim  60 . Rim  60  provides a circumferential flange having a larger outer radius than that of neck  58 . The distal, outlet end of barrel  55  is sealed by septum  62  held by cap  64  that is secured to rim  60 . The medicine-filled reservoir  54  is of variable volume due to the movability of piston  20 , and is defined by septum  62 , the interior surface  52 , and the distal end face  22  of piston  20 . In alternate embodiments, the larger diameter section of the tubular barrel can have other than the cylindrically shaped interior surface shown, provided the exterior of the piston is appropriate modified so as to provide the fluid tight seal therewith.  
         [0025]     With reference again to  FIG. 2 , cartridge  10  including piston  20  is shown loaded in an abstractly shown injection pen. The injection pen is equipped with a pen-needle assembly of known design, generally designated  70 , a drive member, generally designated  80 , having an enlarged foot  81  that directly contacts piston  20 , a manually accessible input member, such as the shown plunger, generally designated  90 , and an injecting mechanism, generally designated  100 . The needle of assembly  70  punctures cartridge septum  62  during mounting of the needle assembly to the medication delivery device as is conventional to provide an outlet for the pharmaceutical within the reservoir  54 . As is conventional, injecting mechanism  100  is operatively connected with the drive member  80  and plunger  90  to produce appropriate motion of the drive member that shifts piston  20  distally within barrel  55  during plunger operation. A variety of different known injecting mechanisms are suitable to convert an input, such as a plunging force, into an advancement of a drive member to force medication from the pharmaceutical cartridge.  
         [0026]     Referring now to  FIG. 6 , there is shown an axial cross-sectional view of an alternate cartridge piston  20 ′ of the present invention. In this embodiment, rigid core  100  has a larger axial length than core  40 , so as to have its proximal face  101  coplanar with the annular proximal end face  24 ′ of the piston body  21 ′. Such a construction may facilitate molding, but may require either proper orientation of the piston during its assembly to the cartridge barrel during manufacture, or a suitable material selection for core  100  along with sufficient testing to satisfy any requirements related to the core material possibly being in contact with the medicine should the piston be inadvertently inverted during cartridge/piston assembly.  
         [0027]     Piston  20  and  20 ′ are well suited to be axially advanced, without rotation, via an abutting contact with a foot  81  that merely translates, without rotation, during drive member  80  advancement. In alternate embodiments, piston  20  or  20 ′ c an be screwed into the cartridge barrel during piston advancement via, for example, a foot that contacts, and does not slip relative to, the piston, which foot and drive member screw distally as a unit during injecting operations. Such a screwably advancing piston may provide even better dose accuracy, but likely requires larger forces being generated to so move that piston during its advancement. Still further, the core and/or piston body can include a hollow for accommodating a portion of the drive member that inserts thereinto. In such a construction, the hollow may be keyed in the case of a torque-transmitting engagement between a screwing drive member and the screwable piston.  
         [0028]     While this invention has been shown and described as having preferred designs, the present invention may be modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.