Abstract:
An autoinjector includes a housing ( 10 ) to receive a syringe ( 14 ), and a drive mechanism including first and second springs ( 30, 32 ) operating in tandem via an intermediate member ( 34 ), on a plunger ( 42 ). The plunger is retained in a locked position by a trigger. Release of the trigger causes the first spring to advance the syringe to an arrest point whereafter the second spring extends within the syringe to expel a dose.

Description:
FIELD OF THE INVENTION 
     This invention relates to autoinjectors. 
     BACKGROUND OF THE INVENTION 
     There is a need for autoinjectors which are of compact form so that they can be carried and used unobtrusively and further which are simple to manufacture, assemble and use with consequent savings in manufacturing and assembly costs, and a lower environmental impact. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect, this invention provides an autoinjector for receiving in use a syringe containing a dose of medicament, said syringe comprising a syringe body of generally cylindrical form, a needle at the forward end of the syringe body, and a piston slideably mounted in said syringe body for expressing a dose, said autoinjector comprising:
         a housing for receiving in use said syringe for sliding movement between a retracted position and an extended, injection position in which said needle projects from said housing;   a drive mechanism for being released from an energised condition to drive the syringe forwards to the injection position and to expel a dose;       

     wherein said drive mechanism includes:
         a plunger adapted to drive said piston in use;   an intermediate drive member;   a first compression drive spring disposed between said intermediate drive member and said housing or a part associated therewith to urge said intermediate drive member forwardly, and   a second compression spring acting between said intermediate drive member and said plunger to urge said plunger forwardly,   the intermediate drive member having an internal cylindrical space for receiving the rear end of said second compression spring, whereby following release of said drive mechanism, the second spring, as it expands, is surrounded along at least a major portion of its length by at least one of the cylindrical space and the internal bore of the syringe body.       

     In this arrangement, the external support provided to the second compression spring means that a long spring of relatively narrow diameter may be used without the risk of snaking or the need to provide an internal support along its length. In turn, the ability to use a relatively low diameter spring means that in preferred embodiments, the spring can be designed to fit into the interior of the syringe body rather than expanding exteriorly, and this means that the overall length of the device may be reduced as less of the expansion takes place outside the syringe, thereby providing a compact design. It will be appreciated that the second spring could act directly on the piston if the latter is suitably formed. 
     Preferably the intermediate member comprises a generally cylindrical body, closed at its rear end. In this fashion, the intermediate member provides an internal cylindrical wall surface for externally constraining at least part of the second spring, and an external cylindrical surface for internally constraining at least part of the first spring. 
     Conveniently, the autoinjector is configured so that, upon release of the drive mechanism, the intermediate member is urged close to or in contact with the rear end of the syringe, thereby substantially completely to enclose the second spring to constrain it externally. Preferably, the drive mechanism includes a trigger arrangement adapted releasably to prevent movement of the intermediate member from a cocked position. The trigger arrangement preferably includes a latch member engageable with an abutment surface on said intermediate member. The abutment surface preferably is disposed between the forward end of the intermediate member and the rearward end of the syringe when in said cocked position. Preferably, the trigger arrangement is released by a trigger element, which may be biased away from its release position by one or both of the drive springs. It is common in autoinjectors to provide a small spring to provide a bias or controlled resistance to the firing button, and to prevent free motion or rattling. By using the drive spring to supply a bias, an extra spring is not required for this purpose. This is a significant benefit in automatically assembled devices, where spring handling and detangling can be problematic. 
     Many existing autoinjectors require some system of mechanical sequencing or latch to sequence the syringe advance movement and the syringe plunger movement of the autoinjector. Such mechanisms add to the complexity of the autoinjector and also contribute to its length. Accordingly, we have designed a compact autoinjector which does not require such mechanisms and in which, immediately on release of the drive mechanism, the plunger and the intermediate member are free for relative movement. In the conventional mechanisms described above, the intermediate member and the plunger continue to be actively locked against movement until they have reached a forward position, where they are unlatched. 
     Accordingly, in another aspect, this invention provides an autoinjector for receiving in use a syringe containing a dose of medicament, said syringe comprising a syringe body of generally cylindrical form, a needle at the forward end of the syringe body, and a piston slideably mounted in said syringe body for expressing a dose, said autoinjector comprising:
         a housing for receiving in use said syringe for sliding movement between a retracted position and an extended, injection position in which said needle projects from said housing;   a drive mechanism for being released from an energised condition to drive the syringe forwards to the injection position and to expel a dose;       

     wherein said drive mechanism includes:
         a plunger adapted to drive said piston in use;   an intermediate drive member;   a first compression drive spring disposed between said intermediate drive member and said housing or a part associated therewith to urge said intermediate drive member forwardly, and   a second compression spring acting between said intermediate drive member and said plunger to urge said plunger forwardly,       

     wherein immediately on release of said drive mechanism said intermediate drive member and said plunger are freed for relative movement. 
     In yet another aspect there is provided an autoinjector for receiving in use a syringe containing a dose of medicament, said syringe comprising a syringe body of generally cylindrical form, a needle at the forward end of the syringe body, and a piston slideably mounted in said syringe body for expressing a dose, 
     said autoinjector comprising:
         a housing for receiving in use said syringe for sliding movement between a retracted position and an extended, injection position in which said needle projects from said housing;   a drive mechanism being released from an energised condition to drive the syringe forwards to the injection position and to expel a dose;       

     wherein said drive mechanism includes:
         a plunger adapted to drive said piston in use;   an intermediate drive member;   a first compression drive spring disposed between said intermediate drive member and said housing or a part associated therewith to urge said intermediate drive member forwardly, and   a second compression spring acting between said intermediate drive member and said plunger to urge said plunger forwardly,       

     wherein the second spring is selected such that the spring force it exerts when substantially fully compressed is less than the force required to overcome the static friction between the piston and the syringe body, but greater than the force required to maintain movement of the piston once the static friction has been overcome by the residual force in the first spring when the syringe is in its injection position. 
     Whilst the invention has been described above, it extends to any inventive combination feature disclosed in the description or drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways and several embodiments thereof will now be described in detail, by way of example only, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a section view of a first embodiment of autoinjector of this invention in a pre-use cocked position; 
         FIG. 2  is a section view of the embodiment of  FIG. 1 , with the trigger button depressed and the syringe moved forwardly ready to deliver a dose, 
         FIG. 3  is a section view of the embodiment of  FIGS. 1 and 2 , following expulsion of a dose; 
         FIGS. 4 to 7  are section views of a second embodiment of autoinjector; 
         FIG. 8  is an exploded view of a third embodiment of an autoinjector in accordance with this invention; 
         FIG. 9  is a side section view through the autoinjector of  FIG. 8  assembled and prior to use; 
         FIGS. 10( a ) and ( b )  are respective side and top section views of the autoinjector with the cap in place, and removed; 
         FIGS. 11( a ) and ( b )  are respective side and top section views of the autoinjector with the firing button partially depressed immediately prior to the release of the plunger; 
         FIGS. 12( a ), ( b ) and ( c )  are respective side section views showing the autoinjector with the syringe in its forwardmost position, shortly after breakout of the piston, and at the injection complete stage respectively; 
         FIG. 13  is a view of the device after use, with the shroud extended and locked out by the magnetically enabled latch; 
         FIG. 14  is a side view through a fourth embodiment of an autoinjector, and 
         FIG. 15  is a shaded side view of the fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , the autoinjector comprises an outer housing  10  of cylindrical form in the bore of which is slideably located a syringe  12 . The syringe  12  is of generally conventional form comprising a syringe body  14  having a flange  16  at its rear end with a needle  18  projecting from the front end. A piston  20  is slideably contained in the syringe body for expulsion of a medicament  22 . The syringe  12  can slide in the housing from a rearward position as shown in  FIG. 1 , against a bias provided by a compression spring  24 , to a forward position defined by an internal shoulder  26  on the housing and the compressed spring  24 , in which the needle  18  projects from the housing. The syringe is centrally located in the housing by a rib  28  on the body. 
     In the rear end of the housing  10  is provided a drive mechanism for the autoinjector. This comprises first and second compression springs  30 ,  32  that act in tandem via an intermediate member  34  on a plunger member  42 . At its rear end, the first spring  30  is anchored in an internal bore of a trigger button  38 , which is captive to the housing. The trigger button may be moved from the rearward position shown in  FIG. 1  to the forward position shown in  FIGS. 2 and 3  to fire the device as to be described below. The forward end of the first spring  30  surrounds the closed rear end of the intermediate member  34  and abuts a collar  37  on the outside thereof. The rear end of the second spring  32  engages the inner closed rear end of the intermediate member  34  and is externally constrained thereby. The front end of the second spring abuts a shoulder  40  on a plunger  42  which has a rear stem  44  that fits within the compressed second spring as shown in  FIGS. 1 and 2 . 
     The plunger  42  has a frustoconical latch surface  46  which is latched by a pair of latch fingers  48  pivoted on the housing  10 . The latch fingers  48  are constrained against pivoting movement when the trigger button  38  is in its rear position as shown in  FIG. 1 , but splay outwards to release the plunger  42  when the trigger button is pushed to its forward position. The trigger button has apertures into which the rear ends of the latch fingers  48  can pivot when the button is pushed forwardly. 
     In use, from the position shown in  FIG. 1 , the autoinjector is offered up to the injection site with the front end in contact with the skin. After removing any safety catch, the trigger button  38  is pressed in against a bias afforded by the first spring  30  so that the latch fingers pivot to release the plunger  42  and intermediate member  34  for forward movement. The first spring  30  is stronger than the second spring  32  and so, initially, the intermediate member  34  plunger  42 , piston  20 , and syringe  14  move as one under the influence of the first spring to drive the syringe to its forward position to extend the needle. During this phase, the reaction or resistance to the forward movement of the syringe as the syringe moves forwardly in the housing and the needle penetrates the flesh is relatively low and less than the break out force required to advance the piston down the syringe. Having reached its forward position, the syringe is arrested, and continued expansion of the first spring pushes the intermediate member  34  towards the now stationary syringe until the collar  37  of the intermediate member is butted up against the rear end of the syringe ( FIG. 2 ). As this occurs the intermediate member  34  initially closes towards the plunger  42 , slightly further compressing the second spring  32 , until the second spring is fully compressed, whereupon the intermediate member  34 , the plunger  42  and piston  20  shift forwards relative to the syringe so that, following arrest of the syringe, the more powerful thrust of the first spring  30  is utilised to overcome the static friction or break out force between the piston and the syringe body. Thereafter, the second spring  32  urges the piston forwards to expel a dose, whilst the intermediate member remains butted up against the rear of the syringe. During this latter phase of operation, the second spring is wholly externally enclosed in the internal space defined between the syringe and the intermediate member. In addition, the harnessing of the power of the first spring  30  to overcome the static friction between the piston and the syringe means that the second spring can be less powerful as it only needs to provide a glide force and to pressurise the medicament to exit the needle. 
     Turning now to the second embodiment illustrated in  FIGS. 4 to 7 , this is similar in many respects to the first embodiment and like parts are given like references. The main difference is in the design of the intermediate member  34 . In the second embodiment the intermediate member has a further cylindrical shell section  39  that extends forwardly of the collar  37  and can enter the rear end of the syringe. In this embodiment the cylindrical shell section offers fully enclosed support of the second spring  32  until it expands with the body of the syringe. Without such a shell a forward portion of the spring is exposed in the initial stages, but equally in this case the second spring diameter can be increased to approximately the inner diameter of the syringe, which can be advantageous. 
     Referring now to  FIGS. 8 to 11 , the third embodiment of autoinjector comprises an outer housing  110  of cylindrical form in the bore of which is disposed a syringe  112  of known form with a barrel  114 , a needle  116  extending from the forward end, and a flange  118  at its rear end. A medicament is contained within the syringe and can be expressed through the needle by a piston  120  inside the barrel. The syringe is supported and surrounded by moulded plastics shroud/carrier  122  assembly comprising a forward hollow cylindrical portion  124  integrally formed with diametrically opposed springs  126  to either side, and a collar  128  adapted to engage the forward face of the syringe flange. Extending rearwardly from the collar are two diametrically opposed clearance fingers  130  with barbed teeth  132  that engage the intermediate member, to ensure that the collar  128  and thus the syringe  112  cannot separate by more than a short distance from the intermediate member  142  described below when the needle shield is pulled off the syringe prior to injection. The barbed teeth  132  run in respective diametrically opposed grooves  134  on the inner surface of the rear part of the housing. In the pre-use position, the shroud portion  124  is telescopically received within the forward end of the housing and coterminous therewith. 
     In the rear of the housing is provided a drive mechanism which comprises a first outer spring  136  which acts between the front face of a transverse inner wall  138  at the rear of the housing and a forward flange  140  of a top hat-shaped intermediate member  142 . An inner, second, spring  144  is received within a cylindrical part of the intermediate member  142  and acts between an inner face of the rear end wall thereof and a circumferential rib  146  on the forward part of a plunger  148 . At the rear end, the plunger has a resilient hooked arm  150  (see  FIGS. 8, 11 ( b )) which latches around the edge of an aperture in the transverse inner wall  138  of the housing. Projecting rearwardly from the rear end of the housing is a captive axially slideable trigger button  152  movable against a rearward bias from the position shown in e.g.  FIG. 11( a ) , where a release finger  154  is spaced rearwardly of the hooked arm  150 , to a forward position ( FIG. 11( b ) ) where the finger  154  cams the hooked arm to release its retention by the wall  138 , thereby allowing the springs  136 ,  144  to drive the plunger  148  forwardly. The plunger is shaped and sized so that it can pass into and down the internal bore of the syringe barrel  114 , to urge the piston  120  to express a dose. In the forward end of the plunger is a cylindrical recess in which is located a small powerful magnet  156 . 
     The trigger button  152  is biased rearwardly by means of two integral forwardly extending sprung arms  158  with cam surfaces  160  which ride over respective abutments  162  inside the rear of the housing. However, initially, forward movement of the trigger button is prevented by means of two rearwardly extending locking arms  164  which extend back from the rear end of a cap  166 . The cap covers the whole of the forward end of the housing and has a re-entrant cylindrical portion  168  with claw features  170 . The claw features  170  slip over the rear end of a needle shield  172  which is secured to the front end of the needle during manufacture. Thus the cap  166  fulfils the functions of acting as a safety catch for the trigger button  152 , serving as a shield remover. 
     Anchored inside the forward end of the housing is a latch  174  formed of pressed steel or other ferro-magnetic material to provide two latch arms  176  which extend forwardly from an anchorage normally to sit in an annular space between the shroud  124  and an inner part of the housing wall. 
     In operation, the user pulls the cap  66  off forwardly which removes the needle shield  122  from the syringe and arms the device by rendering the trigger button  152  operational. The user then offers the injection device up to the injection site and presses the trigger button  152 . This releases the hooked arm  150  of the plunger  148  as shown more particularly in  FIG. 12( b ) . Once the plunger is released, the first spring  136  expands to extend the syringe  120  so that the needle penetrates the flesh. During this period ( FIG. 13( a ) ), the second spring  144  remains substantially fully compressed, with the plunger  148  bearing against the piston  210  within the syringe but not moving it relative to the syringe, so that the thrust of the first spring is transmitted via the intermediate member  142 , the compressed second spring and the piston to the syringe. 
     At its extended position, the syringe is arrested by the compression spring portions  126  bottoming out, the shroud  124  being held against movement by contact with the skin surface. When the syringe is arrested, the first spring  136  continues to expand to drive the flange  140  of the intermediate member into engagement with the syringe flange  118  thereby contributing to the force required to initiate movement of the piston down the syringe ( FIG. 12( b ) ). From this position the second spring  144  expands to drive the piston down the barrel of the syringe to express a dose. At the end of its travel, it will be noted that the magnet  156  in the plunger is spaced between the latching arms  176  of the latch  174 , as shown in  FIG. 12( c ) . When the dose has been expressed, the user pulls the device away from the flesh and so the shroud portion  124  is free to expand under the influence of the compression spring portions  126 . The shroud portion is driven by the springs  126  forwardly beyond the front tips of the latching arms  176 . Once this happens, the latching arms are free to move inwardly to the latching positions shown in  FIG. 13 , under the influence of the magnet  120 . The shroud portion  124  is therefore locked out and the device thereby rendered safe. 
     In other embodiments, not shown, further magnets or ferro-magnetic material may be disposed in the front end of the housing around or in front of the syringe in order to provide a magnetic boost effect as the plunger nears the end of its stroke. 
     Referring now to  FIGS. 14 and 15  the fourth embodiment has many of the same components as the third embodiment and which act in a similar fashion. These components are given the same reference numbers and will not therefore be described in detail again. This second embodiment incorporates a magnetic coupling embodiment between the plunger  148  and the syringe designed so that during an initial penetration phase of movement the plunger is coupled magnetically to a thrust collar  180  of ferro-magnetic material that is positioned in contact with the rear face of the syringe flange  118 . Thus the plunger  148  and the syringe  118  are initially held against relative movement and so move as one during this phase, until the syringe is arrested by reaching its forwardmost position, with the needle inserted into the injection site. Upon arrest of the syringe, the spring force acting on the plunger overcomes the magnetic coupling force and the coupling yields so that the plunger is released to move forward relative to the syringe to move the plunger into contact with and to urge the piston forwardly to expel a dose. As previously, as the plunger moves alongside the ferro-magnetic latching arms  176  and they are attracted inwardly. This is enhanced in the embodiment by provision of two magnets  182  on the forward ends of the latching arms. These magnets are aligned so as to be attached towards and to exert a pull on the magnet  156  in the plunger to provide a magnetically influenced forward boost to the plunger toward the forwardmost end of its stroke. Upon completion of the injection and removal of the device from the site, the shroud  124  extends forwardly as the spring portions  126  re-expand, and as a rearward lip on the shroud passes the magnets, the latching arms move inwards to block retraction movement of the shroud and thereby lock it out. The magnets  182  may be housed slideably in through-holes in the housing wall, allowing them also to move inwards with the latching arms as the rearward lip on the shroud passes the magnets, and so provide a visual and tactile confirmation of locking out of the shroud  124 . 
     In either of the embodiments incorporating agnetic latching, the latches may be arranged that they, or a component associated therewith, emits an audible click as the mechanism latches, thereby to confirm that the injection is complete.