Abstract:
An injection device  110  is described having a housing  112  that receives a syringe  114  having a needle  118 , wherein the syringe is supported in a syringe carrier  150 . The syringe  114  and syringe carrier  150  are biased by a return spring  126  from an extended position in which the needle  118  extends from the housing  112  through an exit aperture  128  to a retracted position in which it does not. A drive spring  130  acts via a drive to advance the syringe  114  from its retracted position to its extended position and discharge its contents through the needle  118  and a return spring  126 , brought into play when the drive has reached a nominal return position, restores the syringe  114  to its retracted position. The syringe carrier  150  is designed to restrict rearward movement of the syringe so that the injection device is less prone to failure and damage to is components than prior art devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an injection device of the type that receives a syringe, extends it through an exit aperture, discharges its contents and then retracts it automatically. 
     BACKGROUND OF THE INVENTION 
     Devices of this general description are shown in WO 95/35126 and EP-A-0 516 473 and tend to employ a drive spring and some form of release mechanism that releases the syringe from the influence of the drive spring once its contents are supposed to have been discharged, to allow it to be retracted by a return spring. 
     Often, such injection devices are required to work with glass pre-filled syringes that were originally designed for manual use. Such glass syringes have a flange at their base to allow a user to grip the syringe and a needle through which the contents of the syringe can be ejected. Prior to use, the needle is generally covered with a needle shield which may be of plastic or rubber material. The needle shield itself may be contained in a rigid housing which is gripped in a cap on the injection device. Thus, when the cap of the injection device is removed by a user, the needle shield is also removed allowing the device to be operated to extend and expose the needle. The needle shield acts to protect the needle from mechanical damage and maintain its sterility. 
     In practice, the syringe may not be held rigidly in place within the injection device due, for example, to manufacturing tolerances in the syringe and injection device. In particular, the syringe may be able to move rearwardly in the injection device, i.e. away from the exit aperture. Since the needle shield is gripped in the device cap which is held rigidly in place on a front end of the injection device, if the device is dropped or subjected to adverse external loading, the syringe may move rearwardly so that the needle shield becomes detached from the syringe needle. This is undesirable because the needle is exposed to an environment which may not be sterile. The needle may also become damaged without the protection of the needle shield. 
     SUMMARY OF THE INVENTION 
     The injection device of the present invention is designed to deal with the aforementioned problems. 
     In accordance with a first aspect of the invention, the present invention provides an injection device comprising:
         a housing adapted to receive a syringe having a discharge nozzle at a first end of the syringe, the syringe being movable between a retracted position in which the discharge nozzle is contained within the housing and an extended position in which the discharge nozzle extends from the housing through an exit aperture;   a drive that acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle; and   a syringe carrier for carrying the syringe as it is advanced, the syringe carrier having a first end through which the discharge nozzle extends and a second end opposite the first end,   wherein the syringe carrier is adapted to restrict movement of the syringe relative to the syringe carrier in a direction from the first end of the syringe carrier to the second end of the syringe carrier.       

     In this way, the syringe and its discharge nozzle can be protected against damage caused by rearward movement within the injection device. 
     The syringe may comprise a flange at a second end of the syringe opposite the first end of the syringe. 
     The syringe carrier may comprise, at its second end, means for restricting movement of the syringe relative to the syringe carrier in a direction from the first end of the syringe carrier to the second end of the syringe carrier. 
     The means for restricting movement may comprise at least one lug on the syringe carrier for preventing movement of the syringe relative to the syringe carrier. The lug may be deformable. 
     In this way, the syringe can be easily inserted into the syringe carrier during manufacture whilst subsequently being rigidly held at its flange to prevent rearward movement. 
     Each lug is adapted to be in juxtaposition to the flange on the syringe. 
     Alternatively, the means for restricting movement comprises at least one damping element. 
     In this way, movement of the syringe in the syringe carrier is damped and restricted such that the shock of an impact force is not transmitted along the syringe causing damage to the syringe. 
     The damping element is arranged to bias the syringe in a direction from the second end to the first end of the syringe carrier. Thus, if the impact force is from an end of the injection device, the rearward movement of the syringe can be absorbed by the damping element. 
     The damping element may comprise resilient biasing means formed from resilient material. In particular, the resilient biasing means could be in the form of an arc of resilient material,
         wherein each end of the arc is attached to the syringe carrier and an outer convex surface of the arc is in juxtaposition with the flange of the syringe.       

     In this way, the biasing means can be integrally moulded with the syringe carrier for ease of manufacture. 
     Preferably, the syringe carrier includes a delatch mechanism for releasing the drive from acting on the syringe after the contents of the syringe has been discharged and wherein each end of the arc is attached to the delatch mechanism. 
     The delatch mechanism may be in the form of an annular portion which is adapted to couple with the drive element in order to disconnect the drive element from the drive. 
     The discharge nozzle comprises a hypodermic needle and the syringe comprises a removable needle shield on the needle. In this embodiment, the syringe carrier is adapted to prevent rearward movement of the syringe so that the needle shield does not become removed from the syringe when an impact force is applied to the injection device. This prevents the discharge nozzle of the syringe becoming exposed to an non-sterile environment if, for example, the device is dropped onto a hard surface. In addition, the integrity seal of the discharge nozzle connecting to the syringe can be disturbed if rearward movement of the syringe occurs. The present invention overcomes this problem. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying drawings, in which: 
         FIGS. 1 a  and 1 b    show a side view of an injection device according to the present invention; and 
         FIG. 2 a    shows an enlarged side view of part of the injection device shown in  FIG. 1  without its external housing; 
         FIG. 2 b    shows an enlarged side view of part of the injection device shown in  FIG. 1  without certain internal components of the injection device being shown; 
         FIGS. 3 a  and 3 b    show a perspective view of the syringe carrier in a first embodiment of the invention; and 
         FIGS. 4 a  and 4 b    show a perspective view of one embodiment of the syringe carrier in a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 a  and 1 b    show an injection device  110 , having an injection device housing  112 . The injection device  110  has a removable cap  190 . With the cap  190  removed, as shown in  FIG. 2 , the end of the housing  112  can be seen to have an exit aperture  128 , through which the end of a sleeve  119  can emerge. The injection device  110  also has a trigger  180 . 
     As shown in  FIGS. 2 a  and 2 b   , the housing  112  contains a hypodermic syringe  114  of conventional type, including a syringe body  116  defining a reservoir and terminating at one end in a hypodermic needle (not shown) and at the other in a flange  120 . The hypodermic needle is covered by a needle shield  118 . The needle shield  118  is fixed inside the cap  190 . 
     The syringe body  116  is of substantially constant diameter along the length of the reservoir, and is of significantly smaller diameter close to the end of the syringe which terminates in the hypodermic needle. A drive element  134  (syringe piston) acts through the bung of the syringe to discharge the contents of the syringe  114  through the needle  118 . This drive element  134  constrains a drug (contained in the syringe) to be administered within the reservoir defined by syringe body  116 . Whilst the syringe illustrated is of hypodermic type, this need not necessarily be so. Transcutaneous or ballistic dermal and subcutaneous syringes may also be used with the injection device of the present invention. 
     The housing  112  comprises a case nose  113  which is integrally formed with a sleeve  160 . The sleeve  160  surrounds a syringe carrier  150  which is moveable within the sleeve  160  along its longitudinal axis. 
     As illustrated, the syringe  114  is housed within the syringe carrier  150 . The syringe carrier  150  has a first end  151  and a reduced diameter section  151   a . The section  151   a  of the syringe carrier supports the end of the syringe  114  nearest to the hypodermic needle. The syringe carrier  150  comprises a bearing surface  153  on which an end of a return spring  126  is located. The return spring  126 , via the syringe carrier  150  biases the syringe  114  from an extended position in which the needle  118  extends from the aperture  128  in the housing  112  to a retracted position in which the needle  118  is contained within the housing  112 . 
     If the syringe were to fail or break, the syringe carrier  150 , which substantially surrounds the syringe  114  along its length, would contain the broken pieces of syringe and reduce the likelihood of them from escaping from the injection device. 
     The housing  112  also includes a trigger  180 , and a drive which here takes the form of a compression drive spring  130 . Drive from the drive spring  130  is transmitted via a multi-component drive ( 118   a ) to the drive element  134  of the syringe  114  to advance the syringe from its retracted position to its extended position and discharge its contents through the needle  118 . The drive accomplishes this task by acting directly on the syringe  114  and the drug in the syringe. Static friction between the drive element  134  and the syringe body  116  initially ensures that both the syringe  114  and bung advance together, until the return spring  126  bottoms out when the bearing surface  153  on the syringe carrier  150  comes up against an opposing bearing surface  161  on the sleeve  160 . 
     The trigger  180  is provided on the housing  112  remote from the exit aperture  128 . The trigger, when operated, serves to decouple a drive sleeve  131  on which the drive spring  130  acts from the housing  112 , allowing it to move relative to the housing  112  under the influence of the drive spring  130 . The operation of the device is then as follows. 
     The cap  190  can be removed by a user with a twist and pull action or simply by pulling the cap. The exact action required depends on the type of syringe  114  being used. In one embodiment, the syringe  114  will comprise a rigid needle shield  118  containing a rubber boot (not shown) in which the needle is contained. In this embodiment, the needle shield  118  simply needs to be removed by pulling the cap  190  along the longitudinal axis of the device  110 . In an alternative embodiment, the syringe  114  comprises a plastic needle shield  118  which is held to the syringe  114  by a frangible connection. In order to break the frangible connection, the cap  190  must be first twisted and then pulled along the longitudinal axis of the device  110 . A guiding element  191  on the end cap  113  serves to guide the removal of the cap  190  in the way that is required to remove the needle shield  118 . 
     Since the needle shield  118  is held inside the cap  190 , removal of the cap  190 , causes the needle shield to be removed, thereby exposing the needle of the syringe  114  within the injection device. At this time, the needle is still enclosed by the housing  112 . 
     Initially, the syringe carrier  150  and syringe  114 , are prevented from movement by a resilient latch member  162 . By moving the sleeve  119  in a direction into the housing  112 , the latch member  162  moves outwards disengaging from the syringe carrier  150 . Once the latch member  162  has disengaged from the syringe carrier  150 , the syringe  114  and syringe carrier  150  are free to move. 
     The trigger  180  can then be depressed by a user and the drive spring  130  is released. The drive spring  130  moves the drive sleeve  131 , the piston  134  and, by virtue of static friction and hydrostatic forces acting through the drug to be administered, moves the syringe body  114  against the action of the return spring  126 . The syringe body  114  moves the syringe carrier  150 , which compresses the return spring  126 . The hypodermic needle  118  emerges from the exit aperture  128  of the housing  112 . This continues until the return spring  126  bottoms out or the syringe body  116  meets some other obstruction (not shown) that retards its motion. Because the static friction between the second drive element  134  and the syringe body  116  and the hydrostatic forces acting through the drug  124  to be administered are not sufficient to resist the full drive force developed by the drive spring  130 , at this point the second drive element  134  begins to move within the syringe body  116  and the drug begins to be discharged. 
     One embodiment of the present invention is depicted in  FIGS. 3 a  and 3 b   . The syringe carrier is shown with two arms  172  extending from a second end  158  of the syringe carrier  150 , opposite its first end  151 . As shown in  FIG. 3 b   , the syringe  114  has a flange  120  on its rear end attached to the syringe body  116 . An underside  175  of the flange  120  is in juxtaposition with one or more supporting lugs  170  located on the arms  172 , wherein each supporting lug provides a supporting interface for the underside  175  of the flange  120  to prevent forward movement of the syringe during device operation. 
     Each arm  172  also includes means for restricting movement of the syringe relative to the syringe carrier in a direction from the first end of the syringe carrier to the second end of the syringe carrier which are restraining lugs  172  which are dimensioned and shaped with a restraining surface  173  to prevent movement in a rearwards direction R (i.e. movement in a direction from the first end  151  to the second end  158  of the syringe carrier  150 ) of the syringe  114  relative to the syringe carrier  150 . Each restraining surface  173  prevents rearward movement by interfacing with an upper surface  176  of the flange. Following insertion of the syringe  114  into the syringe carrier  150  during manufacture, there may be a nominal separation between the restraining surface  173  and the upper surface  176  of the flange  120 . This nominal separation allows some movement of the syringe  114  in a rearwards direction R to buffer the impact of the discharge nozzle as it becomes fully extended during use, thereby reducing pain to a user of the device. 
     During manufacture of the device  110 , the syringe  114  is inserted into the syringe carrier  150  by first inserting its discharge nozzle through the opening at the second end  158  of the syringe carrier  150 . The underside  175  of the flange  120  is nominally prevented from passing over the lugs  171 . The lugs  171  are sloped on their top surface which means that, as the underside  175  of the flange  120  is pushed over the lugs  171 , the arms  172  move apart so that, eventually, the lugs  171  no longer hinder movement of the syringe  114  into the syringe carrier  150  and the restraining surface  173  of the lugs hinders rearward movement of the syringe  114  in the syringe carrier  150 . 
     An alternative embodiment of the invention is shown in  FIGS. 4 a  and 4 b   . In this embodiment, the syringe carrier  150  includes arms  172  and supporting lugs  170  as described above. The syringe carrier also includes a release mechanism  250  that acts to release the drive sleeve  131  from the piston  134  when the drive sleeve  131  moves over the release mechanism  250  when the syringe  114  reaches its extended position. In this way, the force of the drive spring  130  on the syringe  114  is released when it reaches its extended position so that the syringe  114  can then be retracted. 
     The release mechanism  250  is attached to the arms  172  of the syringe carrier  150  by protrusions  260  which engage with openings (not shown) on the arms  172 . 
     The release mechanism  260  includes two damping elements  270  which are each in the form of an arc of material connected at each end of the arc to the release mechanism  250  at pivot points P. The damping elements  270  are on opposing sides of the release mechanism  250 . The damping elements  270  can each resiliently pivot about points P as a result of the resilience of the material and the lever arm formed at the points P. The damping elements  270  can resiliently pivot in a direction R towards the body of the release mechanism  250 , providing bias in the opposite direction. In this way, when the release mechanism  250  is rigidly connected via protrusions  260  to the arms  172 , following insertion of the syringe  114  during manufacture, a convex section C of each arc is in juxtaposition with the upper surface  176  of the flange  120 . Thus, movement of the syringe  114  within the syringe carrier  150  in direction R is damped. 
     In this way, sudden movement of the syringe  114  caused by an impact force is absorbed by the damping elements  270 . Since the damping elements  270  absorb such syringe movement gradually, there is reduced likelihood that the flange  120  can fracture. Moreover, the needle shield  118  remains in place on the discharge nozzle, whilst the integrity seal of the discharge nozzle connecting to the syringe does not get disturbed because sudden rearward movement of the syringe  114  is damped. 
     It will of course be understood that the present invention has been described above purely by way of example and modifications of detail can be made within the scope of the invention.