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 injection device  110  has a removable cap  190 . 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. The syringe carrier  150  abuts a surface inside the removable cap  190  which prevents forward movement of the syringe carrier  150  when the cap is in place. The injection device is less prone to failure than prior art devices and is safer should failure occur.

Description:
FIELD OF THE INVENTION 
     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. 
     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. 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 syringe carrier. The syringe carrier is normally sheath which is designed to envelop the syringe and take up forces applied to the syringe to prevent damage to the frangible glass body of the syringe. 
     The syringe is manufactured with a boot which covers its needle. The aim of the boot is to protect the needle and maintain its sterility. The needle is joined to the glass body of the syringe by an integrity seal. With injection devices of the present invention, the syringe boot may be connected to the syringe body via a frangible connection, or, alternatively, the boot may be a tight rubber boot covering the needle. In either case, the boot is gripped by a cap of the injection device so that the boot becomes removed when the cap of the injection device is removed prior to use. 
     In current injection devices, the syringe carrier is nominally biased into the syringe by a return spring. The bias is only overcome when a drive spring is released which forces the syringe carrier against the bias of the return spring to move the syringe into an extended position whilst its contents is ejected. However, before actuation of the drive spring, the syringe carrier is still free to move against the return spring when high loading forces are applied externally to the injection device, for example during impact of the injection device with a hard surface, such as when the device is dropped. In such situations, since the boot is held rigidly in the cap of the injection device, movement of the syringe carrier (and syringe) may disturb the integrity of the needle seal with the syringe or cause the frangible connection between the boot and the syringe to break. Of course, this exposes the needle and its contents to a non-sterile environment which is undesirable. 
     SUMMARY OF THE INVENTION 
     The injection devices of the present invention are designed to deal with the aforementioned problems. 
     An injection device according to the present invention comprises:
         a housing adapted to receive a syringe having a reservoir portion and a 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;   a removable cap adapted to be connected to the housing for closing the exit aperture; and   a syringe carrier for carrying the syringe as it is advanced,   wherein the removable cap is adapted to restrict movement of the syringe carrier in a direction towards the exit aperture when the removable cap is connected to the housing.       

     In this way, the syringe carrier, and, hence syringe is prevented from being moved when an excessive impact force is applied to the syringe. 
     Preferably, the cap provides a first interface for restricting movement of the syringe carrier in a direction towards the exit aperture. The syringe carrier may provide a second interface for engaging the first interface. The first interface and second interface may each comprise a planar surface and the first interface may be located at an edge of on an annular component within the cap. 
     Preferably, the annular component is adapted to extend into the exit aperture when connected to the housing. 
     In a particular embodiment, the annular component is adapted to grip a removable shield on the discharge nozzle of the syringe. 
     In this way, the needle shield can be removed when the cap of the injection device is removed. 
     The syringe carrier may comprise a sheath for surrounding the reservoir portion of the syringe, wherein the sheath has a first internal diameter along its length, and an intermediate section with a second internal diameter which is smaller than the first internal diameter so that the intermediate section of the sheath is adapted to support the syringe between the reservoir portion and the discharge nozzle. 
     The second interface may be located on an annular protrusion at the first end of the syringe carrier which extends over the discharge nozzle. Preferably, the annular protrusion is a split annular protrusion. The injection device may further comprise: a sliding sleeve projecting from the exit aperture; and at least one locking arm which is engageable with the split annular protrusion, wherein the at least one locking arm disengages from the split annular protrusion on movement of the sliding sleeve into the injection device. In this way, engagement of the first and second interfaces when the cap is in place on the injection device prevents the locking arms of the device from being stressed during impact. 
     The annular protrusion may be split on diametrically opposing sides of the protrusion, and each split in the protrusion may comprise a locking surface for contacting with a corresponding locking arm. The injection device may further comprise means for biasing the syringe from its extended position to its retracted position. 
     The injection device may comprise a support for carrying the means for biasing the syringe. 
    
    
     
       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; 
         FIG. 3  shows a perspective cut-through view of the cap of the injection device according to the embodiment of  FIG. 1 ; 
         FIG. 4  shows a perspective view of the syringe carrier and syringe according to the embodiment of  FIG. 1 ; and 
         FIG. 5  shows a perspective view of the cap of the injection device according to the embodiment of  FIG. 1 . 
     
    
    
     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. 
     The cap  190  of the injection device  110  of the present invention is depicted in  FIG. 3 . The cap  190  includes an annular protrusion  191  which extends into the exit aperture  128  when it is attached to the injection device  110 . 
     The annular protrusion  191  includes grip means  191   a  which grip the boot  118  of the syringe  114  so that the boot is removed when the cap  190  is removed from the injection device  114 . 
     At an end of the annular protrusion  191 , where it opposes the exit aperture  128 , there is an edge of the annular protrusion  191  which provides a first planar interface  192  for interfacing with the first end  151  of the syringe carrier  150 , on which resides a second planar interface  151   b . The annular protrusion  191  and syringe carrier  150  are dimensioned so that the first and second planar interfaces  192 ,  151   b  are in juxtaposition with each other when the cap  190  is in place on the injection device  110 . Thus, when the cap  190  is in place, movement of the syringe carrier  150  in a direction F out of the injection device  110  is prevented, for example, when the injection device  110  experiences an external impact force, when it hits a hard surface. Since forward movement is inhibited, damage to an integrity seal  196  and/or needle  197  of the syringe is prevented. 
     The syringe carrier  150  is shown with an intermediate section  151   a  of reduced diameter which acts to prevent forward movement of the syringe  114  in the syringe carrier  150  by gripping the syringe  114  between the discharge nozzle and the syringe body  116 . 
       FIG. 4  shows the first end of the syringe carrier  150 , on which the second planar interface  151   b  is located. The syringe carrier  150  is in the form of a split annular sheath, with a split  193  in each diametrically opposing side of the sheath at the first end  151  of the syringe carrier  150 . Each split  193  provides a restraining interface  194 . When the sleeve  119  is in its extended (unactuated) position, the resilient latch members  161  are in juxtaposition with the restraining interfaces  194 , thereby preventing forward movement of the syringe carrier  150 . When the sleeve  119  is pushed into the injection device  110 , the latch members splay away from the syringe carrier  150 , permitting the syringe carrier  150  to travel forward on actuation of the trigger  180 . 
     When the cap  190  is in place on the injection device  110 , juxtaposition of the interfaces  192  and  151   b  prevents loading of (and hence damage to) the latch members  161  during high loading of the impact of the injection device  110  with, for example, external forces. 
       FIG. 5  shows the cap  190  of the injection device as depicted in  FIG. 3  without the boot  118  of the syringe  114  in place. The grip means  191   a  is seen to comprise rearward protrusions  198   a  which engage the boot  118  such that movement of the boot  118  in a direction out of the cap (i.e. opposite to direction F) is prevented. However, the grip means  191   a  is formed of resilient metallic material so that insertion of the boot  118  into the cap  190  is permitted, following which the protrusions engage the rubber material of the boot  118  to prevent its removal out of the cap  190 . 
     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.