Abstract:
An autoinjector has a body portion ( 10, 12 ) containing a syringe ( 13 ) or cartridge with a needle at its forward end, the autoinjector having a drive arrangement ( 60  . . . ) for effecting operation of the autoinjector and including a drive element that moves from a first position to a second position during the operation, the body including a first ( 10 ) and a second body portion ( 12 ) connected together by a snap fit arrangement including a resiliently moveable latch finger ( 138 ) on one of the body portions that cooperates with a latch surface ( 142 ) on the other thereof to hold the two portions connected, wherein the drive element in the second position ( 60 ) limits or prevents resilient movement of the moveable latch finger ( 142 ), thereby preventing disconnection of the first and second body portions after operation.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to autoinjectors. 
     DESCRIPTION OF THE RELATED ART 
     Many autoinjectors are assembled by inserting a syringe or cartridge into a front body assembly and then snap-fitting the front assembly containing the syringe or cartridge to a rear body assembly containing a drive arrangement. For safety and other purposes, it is highly desirable to make it difficult if not impossible for the device to be disassembled after use. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect, this invention provides an autoinjector having a body portion containing a syringe or cartridge with a needle at its forward end, the autoinjector having a drive arrangement for effecting operation of said autoinjector and including a drive element that moves from a first position to a second position during said operation, said body including a first and a second body portion connected together by a snap fit arrangement including a resiliently moveable latch finger on one of said body portions that cooperates with a latch surface on the other thereof to hold the two portions connected, wherein said drive element in said second position limits or prevents resilient movement of said moveable latch finger thereby preventing disconnection of said first and second body portions after operation. 
     Preferably first and second body portions comprise front and rearward generally tubular body portions that are snap fitted together during assembly. 
     In many embodiments said snap fit arrangement includes a plurality of respective removable latch fingers and latch surfaces, and said drive element conveniently blocks at least two of said resiliently moveable latch fingers when in said second position. The latch surface may comprise an edge of a latch through hole. Conveniently, said drive element is an elongate plunger having a blocking surface for moving into alignment with the or each resiliently moveable latch finger when in said second position. 
     Whilst the invention has been described above, it extends to any inventive combination or sub-combination of novel features set out above, or in the following description or claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention may be performed in various ways and an embodiment thereof, with various modifications, will now be described by way of example only, reference being made to the accompanying drawings in which: 
         FIG. 1  is a perspective view of an autoinjector in accordance with an embodiment of this invention with the first, front cap removed prior to an injection, but before removal of the second, rear cap; 
         FIG. 2  is a view of the autoinjector with the rear assembly and front assembly separate prior to loading of a syringe in the forward assembly and being snap-fitted together; 
         FIG. 3  is an exploded view of the front assembly; 
         FIG. 4  is an exploded view of the rear assembly; 
         FIG. 5  is an enlarged view of the syringe carrier; 
         FIG. 6  is an enlarged view of the needle shroud; 
         FIG. 7  is an enlarged view of the front body housing; 
         FIG. 8  is an enlarged view of the spring guide; 
         FIG. 9  is a view showing the spring guide and syringe carrier snap-fitted together; 
         FIG. 10  is an enlarged view of the front cap/needle shield remover; 
         FIG. 11  is a horizontal section view taken through the cap of  FIG. 10  on the major axis thereof; 
         FIG. 12  is an enlarged view of the trigger button; 
         FIG. 13  is an enlarged view of the plunger; 
         FIGS. 14( a ) and ( b )  are transverse section views on the major and minor planes respectively of the autoinjector when in its pre-use condition; 
         FIGS. 15( a ) and ( b )  are transverse section views on the major and minor planes respectively of the autoinjector after use, and 
         FIGS. 16( a ) and ( b )  are detail views on the front end of the device showing the forwardly dished skin-contact surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiment of autoinjector illustrated in the Figures and described below is designed automatically to inject a selected dose of medicament when offered up an injection site and fired. Referring initially to  FIGS. 1 and 2 , the autoinjector comprises a rear assembly  10  containing a drive mechanism and a front assembly  12  for receiving a syringe  13  with medicament. The front and rear assemblies are snap-fitted together during manufacture. On the front end of the device is a removable cap  14  that also serves as needle shield remover as to be described below. On the rear end of the rear assembly is a rear cap  16  which includes a safety pin which prevents premature firing of the drive mechanism, the rear cap also covering the firing button  18 . 
     Referring now to  FIG. 3 , the front assembly  12  comprises an outer body housing  20  of generally clear plastic material defining opposed integral viewing windows  22  through which the syringe can be viewed when the device has been assembled. The windows allow the whole of the dose volume of the syringe to be viewed. Apart from the clear plastic material of the windows  22 , the body housing  20  may be opaque. Provision of a transparent window element, instead of the common arrangement of an open aperture or slot, has the advantage of preventing external access to the syringe. Also the provision of twin shroud springs spaced to either side of the longitudinal axis of the device means that the entire length of the dose volume is clearly visible without being obscured by any springs etc. 
     Slideably mounted within the housing  20  is a needle shroud  24  having a chamfered, conical and/or convexly curved domed front face  26  with a central aperture  28  therein to provide a forwardly dished configuration through which the needle of the syringe may project during the injection. The shroud  24  includes two rearwardly extending arms  30  of arcuate cross-section, extending back from a forward tubular section  32 . 
     Slideably coupled to the needle shroud is a syringe carrier  34  having a forward tubular portion  36  capable of sliding telescopically inside the tubular portion  36  of the needle shroud  24 . Extending rearwardly from the tubular portion  36  of the syringe carrier  34  are two arms  38  having opposed inner concave surfaces  40  for slideably receiving the barrel of a syringe and outer concave surfaces  42  for defining with convex inner arcuate surfaces on the arms  30  of the needle shroud  24 , cylindrical containment spaces for a pair of shroud springs  44 . 
     A spring guide  46  has two forwardly extending fingers  48  that pass down the centre of a respective spring  44 . The spring guide  46  has an over-moulded liner  50  surrounding a circular aperture  52  through which a syringe is passed. The liner serves as a shock absorber for the syringe. The spring guide  46  is a snap fit with the rear end of the syringe carrier  34  as to be described below. The spring guide  46  has a rearwardly extending tubular portion in one side wall of which is a recess  53  for captively receiving a disc magnet  54 . 
     Referring now to  FIG. 4 , the rear assembly comprises a rear body housing  56  in which is received the main drive spring  58  which acts on the rear end of a plunger  60 . The plunger has a forward end  62  for engaging the piston  11  within a syringe and an over-moulded coloured indicator strip  64 . To the rear of the indicator strip  64  is a transverse passage  66  in which is mounted for transverse movement a ball magnet  68 . To the rear of the passage  66  is a provided a recess  70  which receives a ferro-magnetic keeper ball  72  which is fixedly disposed on the longitudinal axis of the plunger  60 . The plunger  60  has two rearwardly extending split arrowhead limbs  74  with barbs  76  on the rear ends which seat around the edge of an annular catchment surface  77  in the inside of the rear body housing  56  (see  FIGS. 14 and 15 ) to latch the plunger in a cocked position, with the main spring  58  compressed. 
     The autoinjector is of modular construction designed to allow all except two components to be the same for autoinjectors with syringes of three different fill volumes. The shape and the size of the syringe itself is standard; only the fill volume is different. The two components that vary are the rear body housing  10  and the plunger  60 . The forward end of the rear body housing  52  contains opposed cut outs or slots  78  which are of variable length according to the fill volume contained in the syringe. The axial length of the slots  78  in the rear body housing  56  is proportional to the fill volume. Also the indicator position moves by the same amount so that it arrives at the same place relative to the body at the end of the plunger stroke. The plunger is also modified according to the fill volume of the syringe to locate the magnet-containing passage  66  so that, at the end of its forward stroke, it reaches the same axial position with respect to the rear body housing  56  for each fill volume. In other words, the plunger  60  and the axial length of the slots  78  are designed so that, for each of the plurality of fill volumes, the user will see prior to use in the viewing window  22  just that length of the syringe containing the dose, with the window being framed at the rear end by the slots  78 . After the dose has been delivered, the indicator will be at the same forward position for each fill volume. 
     Referring now to  FIGS. 5 to 9 , the assembly of the principal components of the front assembly will be described in more detail. The syringe carrier  34  has twin linear ribs  82  provided to either side of the forward tubular portion  36 . The ribs  82  run in respective channels  84  on the inside of the tubular portion  32  of the needle shroud. Immediately behind each rib  82  is a live hinge  85  from which extends back a spring finger  86  with a barb  88  with a rearwardly inclined forward surface. When the syringe carrier is assembled telescopically into the needle shroud  24 , the barbs  88  project through slots  90  in the shroud  24  (see  FIG. 6 ) to limit forward movement of the shroud  24  relative to the syringe carrier  34  when the rear ends of the slots  90  contact the barbs  88 . Rearward movement of the shroud  24  relative to the syringe cap is limited by a rearward shoulder  92  of the needle shroud tubular portion abutting a forward facing shoulder  94  upstanding from the rear of the tubular portion  36  of the syringe carrier  34 . Rearwardly of the barbs  88  on the syringe carrier are two rearwardly facing ramp surfaces  96 . 
     At its rear end, the syringe carrier has four lugs  98  that, when the device is assembled, run in respective slots  100  in the front body portion  20  to limit linear movement of the syringe carrier relative to the front body portion  20 . Snap fitted onto the rear of the syringe carrier is the spring guide  46  as shown in  FIG. 8 . This has snap fit tabs  102  that snap fit around walls  104  on the rear end of the syringe carrier. The tabs also form a platen surface for the shroud springs  44 , with the spring guide fingers  48  passing down the centre thereof. The forward ends of the shroud springs are seated on projecting fingers  106  towards the rear of the arms  30  of the needle shroud  24 . About two-thirds of the way back from the front of each slot  90  are two barbs  108  with inclined forward surfaces. Behind each slot  90 , on a live hinge is a rearward barb  110 , again with an inclined forward surface. The barbs  108  and  110  cooperate with respective opposed barbs  112  about a third of the way down the length of the front body housing  20  on the inner walls thereof. 
     The arrangement of the barbs in the pre-use position can be clearly seen in  FIGS. 14 and 15 . In the pre-use position, the barbs  108  on the needle shroud cooperate with the barbs  112  on the front body housing to prevent rearward movement of the needle shroud  24 . The forward faces of the barbs  88  on the syringe carrier also cooperate with the barbs  112  on the front body housing on the forward housing to prevent forward movement of the syringe carrier  34  prior to and during removal of the front cap  14 . Removing the cap removes a bracing on the barbs  88  which initially prevents inward movement of the barbs so that, when fired, the force of the drive spring causes the barbs  88  to cam past the barbs  112  on the front body housing. During operation of the device, when fired, with the needle shroud  24  held against forward movement by its contact with the skin around the injection site, the sub-assembly of the syringe  13  and the syringe carrier  34  is shifted forwardly, relative to the forward housing to a limit position defined by the lugs  98  reaching the forward ends of the slots  100 . After the injection is complete, the needle shroud  24  moves forward as the skin contact pressure is removed from the surface  28  as the device is lifted clear of the skin. This allows the needle shroud to move forwardly under the influence of the shroud springs  46  so that the rear barbs  110  move forwardly and snap past the barbs  112  on the front housing  20  to prevent retraction once the needle shroud has extended. The barbs  110  are braced in this position by the underlying ramp surfaces  96  on the syringe carrier  34 . 
     Referring now to  FIGS. 10 and 11 , the removable front cap  14  has opposed slots  114  which align with the slots  78  on the rear body housing  56 , to frame the window  22  in the front body housing  20  to allow viewing of the dose volume as described above. Referring more particularly to  FIG. 11 , the cap is elliptical in outer section and has an inner central cylindrical portion  116  extending rearwardly from which extend further two fingers  118  of arcuate cross-section disposed on the major axis of the ellipse. On the inner surface of the fingers, towards the rear ends, are respective inwardly directed barbed ribs  120  with inclined rear surfaces. As seen in  FIGS. 14 and 15 , the ribs  120  are designed to snap into a gap formed between the forward shoulder on the barrel of the syringe  13  and the rear surface of the rigid needle shield  15  or an aperture therein. When the syringe  13  is loaded into the front assembly  12  (with the cap  14  attached) during manufacture, the rigid needle shroud  15  snaps past the ribs  120  so that they lodge behind the rear edge of the needle shield  15  (or a rear edge of an aperture in the needle shield) as shown. The front cap  14  also has twin shallow scallops  122  which releasably engage pips  124  on the outer surface of the front body housing when the cap is fitted (see  FIGS. 14 and 15 ). 
     When in the condition as supplied ( FIG. 14 ) the fingers  118  of the cap underlie the spring fingers  86  on the syringe carrier  34  and prevent these from flexing inwardly. In this condition, the fingers  118  thus brace the spring fingers  86  against inward unlatching motion. The forward end of the cylindrical portion  116  of the cap  14  is also provided with inward projections  123  aligned with the minor axis of the ellipse and which prevent forward movement of the rigid needle shield relative to the front cap  14 . In this way, when the front cap  14  is withdrawn from the position shown in  FIG. 15 , the ribs  120  pull the rigid needle shield  15  to ease it off the forward end of the syringe  13 . At the same time the presence of the fingers  118  also temporarily locks the syringe carrier  34  (and thus the syringe  13 ) against forward movement by blocking the fingers  86  against inward movement until the needle shield is off the syringe to prevent the syringe from being pulled forwardly if there is a tight fit between the syringe and the needle shield. When the front cap is free of the device the needle shield  15  is captive in the cap  14 , trapped by the ribs  120  and the inward projections  123 . Orienting the ribs  120  and the inward projections  123  at 90° means that the open ended cap may be injection-moulded in a simple injection mould with a slide rather than requiring a more complex mould design. 
     Referring to  FIGS. 4, 12 and 15 , the firing button  18  is of elliptical form with two split arrowhead tabs  125  aligned with the minor axis, which seat behind respective ribs on the inner rear surface of the rear housing portion  56  to retain the firing button  18  on the rear of the housing and to limit rearward movement thereof. The inner rear surface of the trigger has a firing boss  126  which is of slightly smaller diameter than the outer diameter of the split arrowheads  74  on the rear of the plunger  60  so that, when the firing button  18  is pressed forwardly from the position shown, the boss squeezes the twin arrowheads  74  together to release the barbs  76  from the catchment surface  77  to free the plunger for forward movement. The firing button  18  has an aperture  130  concentric with the boss  126  through which a safety pin  134  on the rear cap  16  passes to hold the split arrowheads apart. Aligned with the major axis of the ellipse are two forwardly extending flexible biasing strips  134  which cooperate with respective bias camming surfaces  136  in the rear end of the rear housing  56 , as shown in  FIGS. 14( a ) and 15( a )  to provide a low friction gliding plastic-to-plastic surface contact. The camming surfaces  136  are shaped to provide a predetermined variation of resistance force with distance. The biasing strips cooperate with the curved rear portion of the camming surfaces to provide a bias force tending to restore the button to its rearmost position as defined by the split arrowhead tabs. It is desirable to provide a tactile resistance to movement and to require a few millimeters of movement before the firing boss  126  releases the plunger, to avoid premature firing. A forward portion of the camming surfaces is of shallower inclination and designed to provide a non-reversible resistance to movement after the device has been fired, thereby to trap or wedge the firing button in its forwardmost position. This gives a further useful visual cue to a user as to whether the device has been fired or not. Of course, if required the camming surface may instead be designed to return the button to its original position after firing. 
     The autoinjector as illustrated includes several safety features to prevent inadvertent firing and to render the device safe after use. It is also highly desirable to resist or prevent disassembly of the device after use. It will be noted from the description and  FIG. 2  above that the device is assembled by inserting a syringe into the syringe carrier in the front assembly and then snap-fitting the front and rear assemblies together. The snap fitting is done by means of outwardly facing sprung tabs  138 ,  140  on the rear of the front body housing  20  which seat simultaneously in respective apertures  142  in the rear body housing  56 . One pair of tabs  138  is aligned with the minor axis and one pair  140  with the major axis of the device. It will be appreciated that, given appropriate dexterity and strength, it would be possible to press in all four of the tabs  138 ,  140  by poking an implement through the recesses  142  from outside and thereby disassemble the device. However, this is prevented in this embodiment by means of two fin formations  144  provided on the plunger  60  as seen in  FIGS. 13 and 15 ( b ). The plunger is designed so that, once the device is fired and the plunger is at its post-firing position, the fin formations  144  underlie the tabs  138  on the minor axis of the ellipse, as shown in  FIG. 15( b ) , thereby bracing them against inward deflection and preventing disassembly. 
     For operation, the user removes the front cap  14  and rear cap  16 , thereby arming the device. The device is then offered up to the injection site to press the conical or curved front face of the needle shroud  26  against their skin. When ready, the firing button  18  is pressed, which releases the plunger  60  for forward movement under the action of the main drive spring  58 . Initially, due to a sprung engagement finger  145  on the plunger, the plunger and syringe move as one forwardly to extend the needle to penetrate the flesh, with this movement continuing until the lugs  98  on the syringe carrier reach the forward end of the slots  100  on the front body housing, thereby inserting the syringe needle to the required depth. Upon arresting movement of the syringe, the sprung engagement finger  145  flexes inwardly into the bore of the syringe and the plunger continues to move, driving the piston  11  down the syringe body to expel a dose. Alternatively, in other designs of the device, the spring engagement finger may yield so that the plunger starts to move into the syringe before forward movement of the latter is arrested. In either design, when the plunger reaches its forwardmost position, the ball magnet  68  which up till now has been held in the passage  66  on the centre line of the plunger by magnetic attraction to the keeper ball  72  is attracted by the greater force provided by the disc magnet  54  held in the recess of the spring guide, accelerating towards it and impacting the magnet and/or spring guide to produce a loud audible click to indicate to the user that the injection is complete. 
     The user then removes the device from their skin and the release of pressure on the front end of the needle shroud  24  means that it can now extend forwardly under the influence of the twin shroud springs  44  to move forwardly to shield the needle. As it nears its forwardmost position, the barbs  110  snap past the barbs  112  on the inside of the front housing  20  thereby to prevent retraction of the needle shroud.