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 injection device is less prone to failure than prior art devices and is safer should failure occur.

Description:
BACKGROUND TECHNOLOGY 
       [0001]    The present invention relates to an injection device of the type that receives a syringe, extends it, discharges its contents and then retracts it automatically. 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. 
         [0002]    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. The substantial force produced by the drive spring is applied to the piston of the syringe. This force is transferred to the housing and return spring, via the flange. The flanges are not precision moulded and consequently have low manufacturing tolerances. They are not sufficiently flat or consistent to be used as a satisfactory support means for the syringe through which the force of the drive spring is transferred to the housing and return spring. 
         [0003]    In practice, these flanges have been seen to fail when the drive spring is employed and the force produced by the drive spring is applied, via the piston of the syringe, to the flange. In particular, these flanges have been seen to break off from the syringe, resulting in the syringe body being propelled from the front of the injection device, and the whole needle being inserted into the user&#39;s body. Consequently, when the injection device is taken away from the user&#39;s body, a full, broken syringe is left dangling from the user&#39;s body. This is clearly dangerous because the user is left with a broken syringe, and consequently broken glass, dangling from their body. The user is also left without having had their correct dose of drug. Such a syringe failure is also, of course, unpleasant for any user, particularly those that are squeamish. 
       SUMMARY OF THE INVENTION 
       [0004]    The injection devices of the present invention are designed to deal with these problems. 
         [0005]    An injection device according to the present invention comprises:
       a housing adapted to receive a syringe having a relatively wide reservoir portion and a relatively narrow discharge nozzle, so that the syringe is 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 and restraining its advancement beyond its extended position, wherein the syringe carrier is adapted to support the syringe between the reservoir portion and the discharge nozzle.       
 
         [0009]    The syringe carrier may provide an interface between the syringe and the housing. 
         [0010]    The syringe carrier may comprise an annular collet having an internal diameter that is smaller than an outer diameter of the reservoir portion of the syringe. The annular collet may be adapted to support the syringe between the reservoir portion and the discharge nozzle. The annular collet may be a split annular collet. 
         [0011]    The syringe carrier may further comprise a sheath for surrounding the reservoir portion of the syringe, having a first internal diameter along its length, and further having a first end with a second internal diameter which is smaller than the first internal diameter so that the first end of the sheath is adapted to support the syringe between the reservoir portion and the discharge nozzle. The sheath may be split. 
         [0012]    By supporting the syringe close to its first end with the syringe carrier, any force applied to the housing by the drive spring is transferred to the housing via the first end of the syringe. No force is transferred via any flange of the syringe. The first end of the syringe has been found to be stronger than the flange of the syringe, and to be less prone to failure. In particular, tests have been carried out in which impact loads have been applied to the piston of a filled syringe. In tests where the syringe was supported in a rubber buffer under the flange, a mass of 1.6 kg dropped from 50 mm would almost always result in a broken syringe. In tests where the syringe was supported on a conical collet under the end of the syringe nearest to the discharge nozzle, the syringes would almost always withstand the same mass being dropped from 75 mm. Generally, when the syringe was supported on a conical collet under the end of the syringe nearest to the discharge nozzle, multiple impacts were required for failure. 
         [0013]    By surrounding the syringe with the syringe carrier close to its first end, if the syringe does fail, it will not be propelled from the end of the device because it will not be able to fit through the part of the syringe carrier which has a reduced diameter. 
         [0014]    By providing a sheath that is split, the syringe can be inserted into the syringe carrier through the split of the sheath. Generally, syringes are provided with a boot which covers the discharge nozzle. The boot is generally of larger diameter than the body of the syringe. By providing a split sheath, the syringe can be inserted into the sheath, without having to remove the boot from the syringe. This is advantageous because it is a requirement that the discharge nozzle of the syringe remains sterile for as long as possible before the injection device is used. 
         [0015]    The injection device may further comprise means for biasing the syringe from its extended position to its retracted position and a support for carrying the means for biasing the syringe. The syringe carrier may further comprise means for bearing against the support. The means for bearing may comprise a portion having an external diameter which is greater than the external diameter of any portion of the syringe carrier situated between the means for bearing and the discharge nozzle. 
         [0016]    The syringe carrier may further comprise a ramped surface, and the support may further comprise a corresponding locking surface, wherein the ramped surface is adapted to communicate with the locking surface so as to lock the syringe carrier relative to the support. 
         [0017]    The injection device may further comprise a drive element and the syringe carrier may further comprise an annular portion which is adapted to act as part of a release mechanism and couple with the drive element in order to disconnect the drive element from the drive and allow the return spring to move the syringe from its extended position to its retracted position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0019]      FIG. 1  shows a cross-sectional view of an injection device according to the present invention; and 
           [0020]      FIG. 2  shows an enlarged part of the injection device shown in  FIG. 1 . 
           [0021]      FIG. 3  shows a perspective view of a syringe carrier for use in the present invention from a first direction; 
           [0022]      FIG. 4  shows a perspective view of the syringe carrier of  FIG. 3  from a second direction. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIGS. 1 and 2  show an injection device  110 , having an injection device housing  112 . The end of the housing  112  has an exit aperture  128 , through which the end of a sleeve  119  can emerge. 
         [0024]    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  118  and at the other in a flange  120 . 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  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  124  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. 
         [0025]    As illustrated, the syringe is housed within a syringe carrier  150 . The syringe carrier is best seen in  FIGS. 3 and 4 . The syringe carrier  150  has a first end  151  which has a reduced diameter. The first end  151  of the syringe carrier supports the end of the syringe  114  nearest to the hypodermic needle. Close to the other end of the syringe carrier  150 , are provided a pair of ramped projections  152 . The pair of ramped projections  152  communicate with a corresponding pair of locking apertures on a return spring support  160  so that the syringe carrier  150  cannot move relative to the return spring support  160 . The syringe carrier  150  also comprises a bearing surface  153  close to its second end, against which a corresponding bearing surface of the return spring support  160  is biased by a return spring  126 . The return spring  126 , via the return spring support  160  and 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 . 
         [0026]    The syringe carrier  150  comprises a sheath  154  which is split along its length so that the syringe  114  can be clipped into the syringe carrier  150 . The syringe  114  is provided with a boot (not shown). By providing a syringe carrier  150  in the form of a split sheath  154 , the syringe  114  can be inserted into the syringe carrier  150  and in turn into the injection device  110  without having to remove the boot from the syringe  114 . Furthermore, if the syringe were to fail or break, the sheath  154 , 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. 
         [0027]    The housing is further provided with a resilient latch member  161  that is biased into a position in which it engages a locking surface  163  on the return spring support  160 . Before engaging the locking surface  163 , the latch member  161  also extends through a latch opening  165  in the sleeve  119 . The latch member  161  includes a ramped surface  167  against which an edge of the latch opening  165  acts in the manner of a cam acting on a cam follower. 
         [0028]    The housing also includes an actuator, 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 to the piston 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 drug  124  and the syringe  114 . Static friction between the drive element  134  and the syringe body  116  initially ensures that they advance together, until the return spring  126  bottoms out or the syringe body  116  meets some other obstruction (not shown) that retards its motion. 
         [0029]    The multi-component drive between the drive spring  130  and the syringe  114  consists of three principal components. A drive sleeve  131  takes drive from the drive spring  130  and transmits it to a first drive element  132 . This in turn transmits drive to the drive element  134  already mentioned. 
         [0030]    The drive element  132  includes a hollow stem  140 , the inner cavity of which forms a collection chamber  142  in communication with a vent  144  that extends from the collection chamber through the end of the stem  140 . The second drive element  134  includes a blind bore  146  that is open at one end to receive the stem  140  and closed at the other. As can be seen, the bore  146  and the stem  140  define a fluid reservoir  148 , within which a damping fluid is contained. 
         [0031]    A trigger (not shown) is provided on the housing  112  remote from the exit aperture  128 . The trigger, when operated, serves to decouple the drive sleeve  131  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. 
         [0032]    Initially, the return spring carrier  152 , and consequently the syringe carrier  150  and syringe  114 , are prevented from movement by the resilient latch member  161 . By moving the sleeve  119  in a direction into the housing  112 , the edge of the latch opening  165  is brought into contact with the ramped surface  167  of the latch member  161 , causing the latch member  161  to move outwards and thus to disengage from the return spring support  160 . Once the latch member  161  has disengaged from the locking surface  163 , the syringe is free to move. 
         [0033]    The actuator is then depressed and the drive spring  130  is released. The drive spring  130  moves the drive sleeve  131 , the drive sleeve  131  moves the first drive element  132  and the first drive element  132  moves the second drive element  134 . The second drive element  134  moves and, by virtue of static friction and hydrostatic forces acting through the drug  124  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 in turn moves the return spring support  160  and 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  124  begins to be discharged. Dynamic friction between the second drive element  134  and the syringe body  116  and hydrostatic and hydrodynamic forces now acting through the drug  124  to be administered are, however, sufficient to retain the return spring  126  in its compressed state, so the hypodermic needle  118  remains extended. 
         [0034]    Before the second drive element  134  reaches the end of its travel within the syringe body  116 , so before the contents of the syringe have fully discharged, flexible latch arms linking the first and second drive elements  132 ,  134  reach a constriction within the housing  112  formed by an annular portion  155  at the end of the syringe carrier which is nearest to the flange  120  of the syringe  114 . The constriction moves the flexible latch arms to a position so that they no longer couple the first drive element  132  to the second drive element  134 . Once this happens, the first drive element  132  acts no longer on the second drive element  134 , allowing the first drive element  132  to move relative to the second drive element  134 . 
         [0035]    Because the damping fluid is contained within a reservoir  148  defined between the end of the first drive element  132  and the blind bore  146  in the second drive element  134 , the volume of the reservoir  146  will tend to decrease as the first drive element  132  moves relative to the second drive element  134  when the former is acted upon by the drive spring  130 . As the reservoir  148  collapses, damping fluid is forced through the vent  144  into the collection chamber  142 . Thus, once the flexible latch arms have been released, some of the force exerted by the drive spring  130  does work on the damping fluid, causing it to flow though the constriction formed by the vent  144 ; the remainder acts hydrostatically through the fluid and through friction between the first and second drive elements  132 ,  134 , thence via the second drive element  134 . Consequently, the second drive element  134  continues to move within the syringe body  116  and the drug  124  continues to be discharged. Losses associated with the flow of the damping fluid do not attenuate the force acting on the body of the syringe to a great extent. Thus, the return spring  126  remains compressed and the hypodermic needle remains extended. 
         [0036]    After a time, the second drive element  134  completes its travel within the syringe body  116  and can go no further. At this point, the contents of the syringe  114  are completely discharged and the force exerted by the drive spring  130  acts to retain the second drive element  134  in its terminal position and to continue to cause the damping fluid to flow though the vent  144 , allowing the first drive element  132  to continue its movement. 
         [0037]    Before the reservoir  148  of fluid is exhausted, flexible latch arms linking the drive sleeve  131  with the first drive element  132  reach another constriction within the housing  112 . The constriction moves the flexible latch arms so that they no longer couple the drive sleeve  131  to the first drive element  132 . Once this happens, the drive sleeve  131  acts no longer on the first drive element  132 , allowing them to move relative each other. At this point, the forces developed by the drive spring  130  are no longer being transmitted to the syringe  114 . The only force acting on the syringe will be the return force from the return spring  126  which acts on the end of the syringe  114  nearest to the needle  118  via the return spring support  160  and the syringe carrier  150 . Consequently, the syringe is returned to its retracted position and the injection cycle is complete.