Abstract:
Auto-injector for delivering a liquid medicament (M), the auto-injector comprising an elongate housing having a loading bay configured to receive a packaged syringe, wherein the loading bay is configured to be laterally accessible for inserting or removing the packaged syringe, wherein a sliding door is slidably arranged over the housing in a manner to reveal the loading bay in a distal position and to cover the loading bay in a proximal position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a U.S. National Phase Application pursuant to 35 U.S.C. §371 of International Application No. PCT/EP2011/073514 filed Dec. 12, 2011, which claims priority to European Patent Application No. 10196078.9 filed Dec. 21, 2010 and U.S. Provisional Patent Application No. 61/432,235 filed Jan. 13, 2011. The entire disclosure contents of these applications are herewith incorporated by reference into the present application. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to an auto-injector for administering a dose of a liquid medicament according to the preamble of claim  1 . 
       BACKGROUND 
       [0003]    Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical. 
         [0004]    Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors. 
         [0005]    In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems. 
         [0006]    The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves. 
         [0007]    Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc. 
         [0008]    Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient&#39;s skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Injection forces/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring. 
         [0009]    US 2002/0095120 A1 discloses an automatic injection device which automatically injects a pre-measured quantity of fluid medicine when a tension spring is released. The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston forward inside the ampoule. After the fluid medicine has been injected, torsion stored in the tension spring is released and the injection needle is automatically retracted back to its original storage position. 
       SUMMARY 
       [0010]    It is an object of the present invention to provide an improved auto-injector. 
         [0011]    The object is achieved by an auto-injector according to claim  1 . 
         [0012]    Preferred embodiments of the invention are given in the dependent claims. 
         [0013]    In the context of this specification the term proximal refers to the direction pointing towards the patient during an injection while the term distal refers to the opposite direction pointing away from the patient. 
         [0014]    An auto-injector for delivering a liquid medicament according to the invention comprises an elongate housing having a loading bay configured to receive a packaged syringe, wherein the loading bay is configured to be laterally accessible for inserting or removing the packaged syringe, wherein a sliding door is slidably arranged over the housing in a manner to reveal the loading bay in a distal position and to cover the loading bay in a proximal position. 
         [0015]    The packaged syringe may comprise a syringe with a hollow injection needle and a stopper for sealing the syringe and displacing the liquid medicament. A drive spring is arranged in the housing for advancing the syringe and the needle in proximal direction for needle insertion into an injection site and for injecting the medicament through the needle. The sliding door may exhibit a door rack gear in mesh with a drive gear which is also in mesh with a drive reset rack such that the sliding door and the drive reset rack translate in opposite directions, wherein the drive reset rack is arranged to compress the drive spring on translation in distal direction. 
         [0016]    When a new packaged syringe has been loaded into the loading bay a user translates the sliding door into the proximal position thereby translating the drive reset rack in distal direction and resetting the drive spring. Conventional re-usable auto-injectors are reset prior to the loading and are in a primed state when an unused syringe is loaded. The advantage of resetting the auto-injector after the syringe has been loaded is that the user is less likely to incur an injury as they load an unused syringe. 
         [0017]    The auto-injector is reset by translating the sliding door along the longitudinal axis of the auto-injector. The sliding door does preferably not protrude beyond either end of the auto-injector regardless of its position within the reset motion. Conventional re-usable auto-injectors are reset by translating a part along their longitudinal axis, but the part frequently extends beyond the ends of the auto-injector. If the auto-injector is released by the user before having been fully reset the part quickly returning into its extending position may cause uncontrolled motion of the auto-injector. The advantage of the sliding door not protruding beyond the auto-injector length is that releasing the auto-injector prior to complete resetting will not result in a projectile and hence the user is less likely to incur an injury as they reset the auto-injector. 
         [0018]    The compression drive spring that provides the axial motion for needle insertion and emptying of the syringe is reset by translation of the sliding door. The motion of the sliding door is coupled to the compression spring through two rack and pinion gear pairs, i.e. the door rack gear to the drive gear and the drive gear to the drive reset rack. By using a different number of teeth on two pinion gears, the translating force can be increased by the ratio of the number of gear teeth. This has the advantage of reducing the user effort required to reset the auto-injector. 
         [0019]    A plunger may be arranged for transferring load from the drive spring to the syringe and/or to the stopper, wherein the plunger comprises a plunger rack gear, wherein a plunger gear is in mesh with the drive gear and the plunger rack gear in such a manner that the plunger translates in distal direction on translation of the sliding door in distal direction wherein a sprag clutch allows translation of the plunger in proximal direction without interference with the sliding door. The sprag clutch may be arranged in the plunger gear. As the plunger is translated into the syringe for injection it has to be re-translated out of the syringe in order to be able to remove the used syringe post injection. The engagement to the sliding door causes the plunger to translate in distal direction out of the syringe when the sliding door is moved into the distal position for revealing the loading bay. The sprag clutch ensures that the plunger can be advanced for needle insertion and injection without interfering with the sliding door. 
         [0020]    The drive spring may be distally grounded in the housing and proximally bearing against a drive collar arranged to be engaged by the drive reset rack for compression of the drive spring. The drive collar is arranged to be latched to the housing when reaching a reset position during compression so as to prevent release of the drive spring from the reset position. An activating means such as a trigger button is arranged to de-latch the drive collar from the housing for starting an injection cycle. 
         [0021]    The trigger button may be arranged at a distal end of the housing biased in distal direction so as to protrude from the housing and arranged for de-latching the drive collar from the housing on depression in order to release the drive spring. Alternatively the trigger button may be arranged laterally or in the shape of wrap-over sleeve button extending over a substantial length of the auto-injector. 
         [0022]    A plunger shuttle may be slidably arranged in the housing, the plunger shuttle having a boss arranged to abut against a proximal stop on the plunger on translation of the plunger shuttle in proximal direction, wherein a rib on the sliding door is arranged to abut against the plunger shuttle on translation of the sliding door in proximal direction. The plunger shuttle is arranged to abut against the packaged syringe on translation in proximal direction in such a manner that near the end of translation of the sliding door into the proximal position the sliding door translates the plunger shuttle, the plunger shuttle translates the packaged syringe into an actuate position and the plunger shuttle translates the plunger in such a manner that a distal head of the plunger passes through the drive collar and is latched to the drive collar for coupling the drive spring to the plunger. 
         [0023]    The packaged syringe may comprise a package housing with the syringe slidably arranged in the package housing. At least one resilient snap arm in the package housing may be arranged to prevent translation of the syringe relative to the package housing for preventing inadvertent exposure of the needle during handling of the packaged syringe. The plunger shuttle may comprise at least one ramp arranged to deflect the snap arm for releasing the syringe on further translation of the plunger shuttle when the packaged syringe is in the actuate position. Thus the syringe and needle are only released for needle insertion when the sliding door has been closed and the auto-injector is ready to fire. 
         [0024]    A skin contact interlock sleeve may be slidably telescoped in the housing and biased in proximal direction so as to protrude from the proximal end of the housing in a proximal position, wherein the skin contact interlock sleeve is arranged to interact with the trigger button in a manner to prevent depression of the trigger button when the skin contact interlock sleeve is in the proximal position, i.e. not pressed against the injection site and wherein the skin contact interlock sleeve is arranged to disengage from the trigger button on depression of the interlock sleeve in the distal direction, i.e. on contact to the injection site thus allowing depression of the trigger button. Hence, the user is required to perform a sequence of operations in order to trigger the injection cycle thus reducing the risk of inadvertent triggering. 
         [0025]    A retraction spring may be arranged in the packaged syringe in a manner to be compressed on translation of the syringe for needle insertion and to retract the syringe and the needle on de-latching of the distal head from the drive collar. 
         [0026]    Hence, once the trigger button has been pressed the auto-injector will insert the needle, fully empty the syringe and then retract the needle to a safe position with no user intervention. 
         [0027]    The housing may comprise a reduced diameter section arranged to prevent de-latching of the drive collar from the distal head of the plunger when the drive collar is between the reset position and a decoupling position where the stopper has at least nearly bottomed out in the syringe. As the drive spring keeps pushing the drive collar while the stopper and plunger have bottomed out the distal head de-latches from the drive collar in a manner to allow it to translate in distal direction out of the syringe independently from the drive collar. The plunger will be translated out of the syringe on translation of the sliding door into the distal position as described above. 
         [0028]    Reliably triggering the retraction of the syringe and needle at the end of an injection normally has to be traded off against an incompletely emptied syringe, which is undesirable. Due to manufacturing tolerances of the syringe and stopper the exact position of the stopper at the end of its travel is not repeatable. Consequently, in some cases the stopper will prematurely bottom out so the retraction will not be triggered at all. In other cases the retraction will be triggered before the stopper bottomed out so residual medicament remains in the syringe. 
         [0029]    This problem may be addressed by releasing the retraction sleeve from the housing a certain amount of time or travel before the stopper bottoms out in the syringe. 
         [0030]    For this purpose the distal head may be telescoped with the plunger and biased against the plunger by a plunger spring. As the plunger is advanced for injection the plunger spring is compressed. 
         [0031]    A viscous damper may be arranged for being contacted by the drive collar on translation of the drive collar during injection just before the stopper bottoms out in the syringe. The viscous damper is arranged to slow down the speed of the drive collar allowing the plunger spring to extend and translate the stopper until it bottoms out. The position of the viscous damper is selected relative to the reduced diameter section in a manner to allow de-latching of the distal head from the drive collar shortly before the viscous damper is fully compressed by the drive collar. 
         [0032]    Thus both problems are solved, reliably retracting the needle to a safe position and fully emptying the syringe which is particularly desirable with expensive drugs. Emptying the syringe is also important for dosage accuracy. 
         [0033]    The auto-injector may preferably be used for subcutaneous or intra-muscular injection, particularly for delivering one of an analgetic, an anticoagulant, insulin, an insulin derivate, heparin, Lovenox, a vaccine, a growth hormone, a peptide hormone, a protein, antibodies and complex carbohydrates. 
         [0034]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0036]      FIG. 1  is an isometric view of a reusable auto-injector with sliding door loading during insertion of a packaged syringe, 
           [0037]      FIG. 2  is the auto-injector during closing of the sliding door, 
           [0038]      FIG. 3  is the auto-injector with the sliding door almost completely closed and the syringe in a loading position, 
           [0039]      FIG. 4  is the auto-injector with the syringe being translated from the loading position into an actuate position, 
           [0040]      FIG. 5  is a detail view showing a plunger shuttle before contacting the syringe, 
           [0041]      FIG. 6  is a detail view with the plunger shuttle having contacted the syringe, 
           [0042]      FIG. 7  is a distal end of the auto-injector with the drive collar being driven in proximal direction, 
           [0043]      FIG. 8  is another longitudinal section of the auto-injector of  FIG. 5  in a different section plane, 
           [0044]      FIG. 9  shows details of the distal end and the proximal end of the auto-injector during skin contact of the proximal end, 
           [0045]      FIG. 10  is the distal end with the trigger button being depressed, 
           [0046]      FIG. 11  is the auto-injector during needle insertion into an injection site, 
           [0047]      FIG. 12  is the auto-injector during injection, 
           [0048]      FIG. 13  is a detail view of a drive collar travelling past a plunger head, 
           [0049]      FIG. 14  is the auto-injector during needle retraction, and 
           [0050]      FIG. 15  is the auto-injector during removal of the packaged syringe after injection. 
       
    
    
       [0051]    Corresponding parts are marked with the same reference symbols in all figures. 
       DETAILED DESCRIPTION 
       [0052]      FIG. 1  shows an isometric view of a reusable auto-injector with sliding door loading during insertion of a packaged syringe. The auto-injector  1  comprises an elongate housing  2  and a sliding door  3  which may be axially translated by a user in order to reveal a loading bay  12  into which a disposable packaged syringe  4  may be inserted. Translation of the sliding door  3  also resets the auto-injector  1  for further operations. 
         [0053]    The packaged syringe  4  comprises a syringe  5  with a hollow injection needle  6  and a stopper  7  for sealing the syringe  5  and displacing a liquid medicament M for injection (see  FIG. 2  for details). The packaged syringe  4  shown in the embodiments further comprises a package housing  11  surrounding the syringe  5  and arranged to allow relative axial translation between the syringe  5  and the syringe housing  11 . The needle  6  is equipped with a protective needle sheath (not illustrated) for keeping the needle  6  sterile and preventing it from being mechanically damaged. 
         [0054]    At a distal end of the package housing  11  resilient snap arms  29  are arranged (see  FIG. 5  for details). An internal stop  30  on each snap arm  29  is arranged to abut against a distal flange  31  on a syringe carrier sleeve  32  in a manner to prevent it from translating in proximal direction P. The syringe carrier sleeve  32  is arranged for holding the syringe  5 , i.e. the syringe carrier sleeve  32  and the syringe  5  always translate together. 
         [0055]    A drive means  8  in the shape of a compression spring  8  is arranged in a distal part of the housing  2 . The drive means  8  is arranged to cause an axial translation for inserting the needle  6  through an orifice  13  at a proximal end P into an injection site, e.g. a patient&#39;s skin and for advancing the stopper  7  in proximal direction P for injecting the dose of medicament M. Another compression spring is arranged as a retraction spring  9  for retracting the needle  6  to a safe position after the end of the injection. The retraction spring  9  is part of the packaged syringe  4  in the embodiment shown, however it could equally be part of the reusable auto-injector  1 . 
         [0056]    The axial motion from the drive means  8  to the syringe  4  or the stopper  7  is transmitted by a plunger  16  having a plunger rack gear  17 . A drive collar  18  is arranged around the plunger  16 . The drive means  8  is grounded in the distal end of the housing  2  and bearing against the drive collar  18 . 
         [0057]    A skin contact interlock sleeve  37  is slidably telescoped in the housing  2  and biased in proximal direction P by an interlock spring  38  so as to protrude from the proximal end P of the housing  2 . The skin contact interlock sleeve  37  extends almost through the entire housing  2  to the distal end D (see  FIG. 8 ). 
         [0058]    A sequence of operation of the auto-injector  1  is as follows: 
         [0059]    The sliding door  3  is axially translated in distal direction D in order to reveal the loading bay  12 , i.e. an aperture in the housing  2 . The user inserts a packaged syringe  4  into the loading bay  12  (see  FIG. 1 ). The protective needle sheath may be removed from the needle prior to insertion of the packaged syringe  4  into the loading bay  12 . Likewise the auto-injector  1  could be arranged to allow removal of the protective needle sheath through the orifice  13  after insertion of the packaged syringe  4 . 
         [0060]    The user translates the sliding door  3  in proximal direction P in order to close the auto-injector  1  (see  FIG. 2 ). A door rack gear  14  on an internal surface of the sliding door  3  meshes with a drive gear  15  pivoted in the housing  2 . On an opposite side the drive gear  15  is also in mesh with a drive reset rack  10  arranged inside the housing  2  so the sliding door  3  and the drive reset rack  10  are arranged to travel in opposite directions. Therefore as the sliding door  3  is moved in proximal direction P the drive reset rack  10  moves in distal direction D. Near a distal end of the drive reset rack  10  a catch  19  is arranged which engages an outer latch arm  20  at the drive collar  18  so the drive reset rack  10  travelling in distal direction D takes the drive collar  18  with it and compresses the drive means  8 . 
         [0061]    A plunger gear  21  is in mesh with the drive gear  15  and the plunger rack gear  17  however a sprag clutch (not illustrated) prevents transmission of torque from the drive gear  15  through to the plunger rack gear  17  when the sliding door  3  is being translated in proximal direction P. The drive gear  15  consists of two gears of differing teeth number. One is in mesh with the plunger gear  21  and the other in mesh with the door rack gear  14 . The two gears of the drive gear  15  are coupled together by the sprag clutch allowing transmission of torque in one direction only—from the sliding door  3  to the plunger  16 . 
         [0062]    When the sliding door  3  is approaching a fully closed position (see  FIG. 3 ), the outer latch arms  20  on the drive collar  18  snap past internal first ribs  22  in the housing  2 . If the sliding door  3  is released in this position, the force of the drive means  8  on the drive collar  18  will be resolved through the housing  2 . The drive collar  18  is now in a reset position. If the sliding door  3  is released prior to this stage, i.e. before the drive collar  18  has snapped past the internal first ribs  22 , the sliding door  3  will be driven open by the drive means  8  and thus does not present a finger trap hazard to the user. As the sliding door  3  approaches the end of travel the outer latch arms  20  are deflected inwards by trigger button arms  35  on a trigger button  36  arranged at the distal end D of the auto-injector  1 . The trigger button  36  is biased in distal direction D by a trigger spring  47  bearing against the housing  2  and against the trigger button  36 . 
         [0063]    On inward deflection the outer latch arms  20  come clear from the catch  19  (see  FIG. 4 ). The drive collar  18 , no longer restrained by the catch  19 , translates in proximal direction P under load of the drive spring  8  until the outer latch arms  20  abut against the first rib  22  (see  FIG. 4 ) returning into the reset position. The trigger button  36  cannot yet be depressed in this situation due to its trigger button arms  35  abutting against outward stops  39  on the skin contact interlock  37  (see  FIG. 8 ). 
         [0064]    In parallel, as the sliding door  3  is being closed, a second rib  23  on the sliding door  3  comes into contact with a plunger shuttle  24  taking the plunger shuttle  24  with it in proximal direction P (see  FIG. 4 ). The plunger shuttle  24  contacts the package housing  11  and moves the packaged syringe  4  from the loading bay  12  to an actuate position (see  FIG. 4 ). A boss  25  on the plunger shuttle  24  is engaged within a longitudinal groove  26  in the plunger  16 . As the boss  25  abuts against a proximal stop  27  at a proximal end of the groove  26  during the translation the plunger  16  is caused to move with the sliding door  3 . The plunger  16  moves towards the stopper  7  reducing the motion required from the drive spring  8  in a later stage. Further movement of the plunger shuttle  24  enables ramps  28  (see  FIG. 5 ) on the plunger shuttle  24  to deflect the snap arms  29  on the package housing  11  outwards. As the snap arms  29  are outwardly deflected the stops  30  in the package housing  11  are also deflected thus releasing the syringe carrier sleeve  32  with the syringe  5  for translation in proximal direction P relative to the package housing  11  (see  FIG. 6 ). 
         [0065]    In parallel, a distal head  33  telescoped in the plunger  16  and biased against the plunger  16  by a plunger spring  42  is drawn through the drive collar  18 . Inner latch arms  34  on the drive collar  18  are deflected outwards by a shoulder  44  on the distal head  33  and allow the distal head  33  to be pulled through the drive collar  18 . This enables the drive force from the drive spring  8  to be transferred to the plunger  16  (see  FIG. 7 ). 
         [0066]    With the final motion of closing the sliding door  3 , the outer latch arms  20  on the drive collar  18  are driven against the trigger button arms  35  deflecting the outer latch arms  20  inwards for de-latching the drive reset rack  10  from the drive collar  18  (see  FIG. 4 ). 
         [0067]    The drive collar  18  is then returned to the reset position with the outer latch arms  20  abutting against the first rib  22  through the force of the drive spring  8 . The auto-injector  1  is now fully reset (see  FIG. 4 ). 
         [0068]    In order to trigger an injection the user presses the auto-injector  1  against the injection site, e.g. a patient&#39;s skin. This causes the skin contact interlock  37  to translate in distal direction D within the housing  2 . As the skin contact interlock  37  translates, the outward stops  39  preventing depression of the trigger button  36  are deflected inwards by ramps  40  within the housing  2  allowing depression of the trigger button  36  (see  FIG. 9 ). This feature prevents the user from accidentally actuating the auto-injector  1  when it is not in contact with the injection site. 
         [0069]    The user depresses the trigger button  36  translating it in proximal direction P into the housing  2 . As the trigger button  36  moves, the trigger button arms  35  contact the ramped outer latch arms  20  on the drive collar  18  deflecting them inwards out of engagement with the first ribs  22  allowing the drive collar  18  to move freely with respect to the housing  2  (see  FIG. 10 ). The force from the drive spring  8  is transferred through the drive collar  18 , to the plunger  16  and on to the stopper  7 . An inward third rib  43  on the inner latch arms  34  is arranged to bear against the shoulder  44  on the distal head  33 . The inner latch arms  34  are funnelled into a section  45  of the housing  2  with a reduced diameter preventing outward deflection of the inner latch arms  34 . Grooves in the reduced diameter section  45  are arranged to allow translation of the outer latch arms  20 . Friction opposing motion of the stopper  7  with respect to the syringe  5  is greater than the force of the retraction spring  9  and the needle insertion force and hence the syringe  5  is advanced and the needle  6  is inserted into the injection site. An insertion depth is controlled by the flange  31  contacting a fourth rib  41  on the housing  2  extending through an aperture the package housing  11  (see  FIG. 11 ). 
         [0070]    Once the flange  31  contacts the fourth rib  41 , the force from the drive spring  8  causes the plunger spring  42  to be compressed. Once compressed, the force on the stopper  7  is sufficient to overcome friction and emptying of the syringe contents (see  FIG. 12 ). 
         [0071]    If the auto-injector  1  is removed from the injection site at any point during the injection, the skin contact interlock  37  will be sprung forwards preventing access to the needle (not illustrated). 
         [0072]    Towards the end of the dose (i.e. just before the stopper  7  bottoms out in the syringe  5 ) the outer latch arm  20  of the drive collar  18  contacts a viscous damper  46  arranged near a proximal end of the reduced diameter section  45 . The load from the drive spring  8  is now shared between the stopper  7  and the viscous damper  46 . This allows the plunger spring  42  to extend and complete the dose. The reaction force offered by the viscous damper  46  is speed dependent and hence an appropriate damping coefficient must be selected to ensure the full dose is delivered. The viscous damper  46  could be implemented with a visco-elastic foam material (see  FIG. 12 ). 
         [0073]    Once the viscous damper  46  is fully compressed, the position of the drive collar  18  is such that the inner latch arms  34  transmitting the force to the distal head  33  are no longer constrained in de reduced diameter section  45 . The inner latch arms  34  are deflected radially outward enabling the distal head  33  to pass through the collar (see  FIG. 13 ). Now the only force resolving the force of the retraction spring  9  is the friction of the needle  6  within the skin, which is in the range of 2 N and hence the retraction spring  9  withdraws the needle  6  from the skin. The syringe  5  is finally positioned in a retracted location within the package housing  11  of the packaged syringe  4  (see  FIG. 14 ). This prevents user access to the needle  6  once removed from the re-usable auto-injector  1 . Only when the sliding door  3  is fully opened is the syringe  5  locked in this retracted position. The injection is now complete. 
         [0074]    The user then removes the auto-injector  1  from the skin and slides open the sliding door  3  in distal direction D to reveal the used packaged syringe  4 . As the sliding door  3  is opened, the door rack gear  14  on the internal surface of the sliding door  3  meshes with the drive gear  15  which rotates with translation of the sliding door  3 . 
         [0075]    The drive gear  15  is in mesh with the plunger gear  21  which transmits a force to the plunger rack gear  17  on the plunger  16 . Therefore, as the sliding door  3  is opened the plunger  16  is withdrawn from within the syringe  5 . The drive gear  15  is also in mesh with the drive reset rack  10  and therefore as the sliding door  3  is moved the drive reset rack  10  moves in the proximal direction P. When the sliding door  3  is nearly fully open, the catch  19  on the drive reset rack  10  snaps proximally past the outer latch arms  20  (see  FIG. 15 ). 
         [0076]    In parallel, as the sliding door  3  approaches a fully open position, the boss  25  on the plunger shuttle  24  that is engaged in the longitudinal groove  26  on the plunger  16  reaches the end of free travel. Further movement of the plunger  16  is coupled to the plunger shuttle  24 . The plunger shuttle  24  is frictionally coupled to the packaged syringe  4  by the ramps  28 . Hence, the packaged syringe  4  is moved from the firing position to the loading bay  12 . Once the packaged syringe  4  is positioned in the loading bay  12  the syringe shroud may contact the fourth rib  41  within the casework. The fourth rib  41  is arranged to define an end stop/limit of motion of the packaged syringe  4  in the distal direction D. As the packaged syringe  4  couples the fourth rib  41 , the friction coupling of the ramps  28  on the plunger shuttle  24  is overcome and the syringe carrier sleeve  32  stops moving while the plunger shuttle  24  and plunger  16  continue to be withdrawn from the syringe  5  driven by the motion of the sliding door  3 . 
         [0077]    Once the sliding door  3  is fully opened, the packaged syringe  4  is returned to the loading bay  12 , and the plunger  16  and plunger shuttle  24  are withdrawn sufficiently to enable removal of the used packaged syringe  4 . The drive spring  8  is not compressed at this time. 
         [0078]    A resilient feature beneath the packaged syringe  4  may be contacted by a proximal end of the drive reset rack  10  at the end of its travel in the proximal direction P as shown in  FIG. 15 . Thus the packaged syringe  4  may be lifted to facilitate removal. 
         [0079]    The auto-injector  1  may preferably be used for subcutaneous or intra-muscular injection, particularly for delivering one of an analgetic, an anticoagulant, insulin, an insulin derivate, heparin, Lovenox, a vaccine, a growth hormone, a peptide hormone, a protein, antibodies and complex carbohydrates.