Abstract:
An injection apparatus includes a counter wheel ( 54 ) that is incremented by the dose delivery mechanism each time the device is fired. The apparatus includes a final dose disabling mechanism that prevents further usage once the final dose has been delivered. An anti-tamper feature is provided to prevent inadvertent or premature initialisation of the apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to injection apparatus, and in particular, though not exclusively, to injection apparatus designed to allow a number of doses to be delivered from a single cartridge or syringe over a period of time. 
     2. Description of the Related Art 
     In many therapies a drug needs to be injected at daily or other periodic intervals. A potential problem arises because the user may not recall clearly whether they have taken a particular dose. There is therefore a need in such apparatus to provide an increment counter, or day of the week indicator, which indicates whether they have taken the dose for a particular period. Also, where a fixed volume dose is delivered each time, it is highly desirable to be able to signal to the user when all useable doses have been taken from the device to prevent a user from inadvertently taking a nil or incomplete dose. Although it is common on variable dose devices to provide a counter display to allow a user to dial in the number of units of medicament they wish to inject, these displays only indicate the magnitude of the dose to be delivered, and return to zero on completion of an injection. They do not indicate a dose application count i.e. the accumulated number of injections that have been performed by the device. 
     In EP-A-1463550, we describe a dose application counter for an injection device having a dose counter member which has a lost motion connection to the dose setting element, so that, as a user sets the amount of the dosage volume prior to firing the device, the dose application counter is incremented by one count, irrespective of the number of units making up the dose. Although this is a good design, it increments the count on setting of the dose rather than actual delivery of the dose. It is possible therefore that if a user is distracted between the setting dose and delivering it, the dose application counter suggests that the dose for that period has already been taken. Also, after the device has been fired to deliver the final available dose, the dose setting knob can still be rotated to set a further dose even though subsequent firing of the device will not deliver a proper dose. 
     SUMMARY OF THE INVENTION 
     Accordingly, we have designed an injection device in which a counter member is incremented in response to movement of the drive member that delivers the does and which is therefore incremented by dose delivery rather than dose setting. 
     In one aspect this invention provides an injection apparatus including a drive arrangement actuatable to allow movement of a drive member to deliver a dose upon each such actuation, and a counter member drivingly connected to said drive member for being incremented by each dose delivery. 
     In this arrangement, a cumulative dose count may be kept by incrementing the counter by a single uniform amount indicative of a usage, irrespective of the dose magnitude. 
     Although the movement could be linear it is preferred for said drive member to be mounted for rotary movement and to rotate to deliver a dose. Thus the drive arrangement may include an elongate drive plunger threadedly engaged with said drive member and adapted to be advanced longitudinally to deliver a dose upon corresponding rotary movement of said drive member. 
     There are numerous ways in which actual delivery of a dose increments or trips or counter mechanism to increment by suitable motion transfer. For example, the counter member may comprise a counter wheel having a toothed surface meshing with an idler cog, with said drive member carrying one or more cog teeth for engaging the teeth of the idler cog to increment the counter wheel during each dose delivery. Although the drive member cog teeth could be in continuous engagement with the idler cog, or the counter wheel itself, said drive member cog teeth preferably engage the idler cog intermittently, once per dose delivery. It will be appreciated that incrementing may occur at any time during a dose delivery cycle, but it is preferred for said counter member to be incremented part way through the cycle. Alternatively, other arrangements may be used where movement of the dose delivery mechanism or a component thereof is used to increment a counter by one unit during or on completion of dose delivery. This could be tripped by interaction of the plunger with a counter, or by similar interaction between any one or more of the components in the dose delivery mechanism. 
     Conveniently, said drive mechanism includes a dose setting element for being manually twisted to energise an energy storage device associated with said drive member, and a releasable trigger for holding and releasing said drive member in and from its energised condition. 
     The injection apparatus may conveniently include a final dose arrangement for blocking movement of said dose setting element after said drive plunger has advanced to a final dose position, thereby to prevent further dose setting. 
     Where said drive arrangement includes a drive transfer element that rotates with, or is integral with, said dose setting element and is connectable to said drive member by a latching arrangement, the drive transfer element and the plunger may have associated therewith respective abutments that move into a blocking configuration when the drive plunger advances towards its final dose position, thereby substantially preventing rotational movement of the dose setting element and thus further dose setting movement. 
     The apparatus may be designed to deliver fixed volume doses, or it may be adapted to deliver doses of adjustable volume. 
     The final dose disabling feature may be used on devices that do not have a dose delivery counter. The invention therefore extends to an injection apparatus including a drive arrangement having
         a rotary drive gear threadedly engaged with an elongate threaded plunger to advance said elongate plunger to deliver a dose,   a rotary dose setting element angularly movable against a bias from a rest position to an energised position in which it is in latching engagement with or latches with said rotary drive gear,   a trigger arrangement adapted to hold and release the drive gear for rotary movement,   wherein respective abutments associated with the drive plunger and the dose setting element move into a blocking configuration when said elongate plunger advances after successive doses to a final dose position, thereby preventing return of said rotary dose setting element to its latched, energised condition.       

     The abutments may comprise respective cooperable lugs on the drive plunger and on the dose setting element, which cooperate to constrain or limit rotation of said dose setting element. 
     Where the injection apparatus includes a housing having two relatively movable parts required to be moved relative to one another in an initialisation step prior to actuation to deliver a dose, for example to mix a multi-component drug, or to cock or to prime a device, it may include an anti-tamper arrangement to prevent said relative movement prior to release of the anti-tamper arrangement. 
     Said anti-tamper arrangement may typically comprise a removable package for containing at least part of said device and adapted to hold said movable parts against initialisation movement, prior to removal of said package. 
     Alternatively said anti-tamper arrangement may comprise a spacer element disposed to prevent said initialisation movement and removable from the apparatus. 
     The removable spacer element may comprise a tear off band, a tear off label, or a removable spacer element is integrally formed with one of said housing parts e.g. by moulding. 
     The invention also extends to an injection device comprising a housing having two relatively movable parts required to be moved relative to one another in initialisation step, prior to actuation to deliver a dose, and including an anti-tamper arrangement to prevent said relative movement prior to release of said anti-tamper arrangement. 
     The invention also extends to an injection device that is set or primed and which includes an externally visual indicator that displays a change in colour or other visual characteristics when said device is set or primed. 
     Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description, claims or drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       By way of example only, various embodiments of the invention will be now be described in detail, reference being made to the accompanying drawings in which: 
         FIG. 1  is a perspective view of an injection device in accordance with an embodiment of this invention in its as supplied form, prior to retraction of the housing to reconstitute the drug; 
         FIG. 2  is a view similar to  FIG. 1  but showing the device after reconstitution of the drug and once two doses have been delivered; 
         FIG. 3  is a detailed view on the front end of the device of  FIGS. 1 and 2  showing the collar in a forward position; 
         FIG. 4  is a view of the drive mechanism removed from the remainder of the device, with certain parts removed; 
         FIG. 5(   a ) is an exploded view of the drive mechanism, and  FIGS. 5(   b ) and (c) are details thereof; 
         FIG. 6  is a detailed view on the plunger and ratchet drive shaft; 
         FIG. 7  is a detailed view on the aft end of the plunger; 
         FIG. 8  is a cross-sectional view through the ratchet drive shaft, drive plunger and the drive gear; 
         FIGS. 9 to 12  are views of various embodiments of an anti-tamper device that need to be removed prior to moving the housing from its extended position shown in  FIG. 1  to that of  FIG. 2 ; 
         FIG. 13  is a detailed view on another form of anti-tamper feature; 
         FIG. 14  is a detailed exploded view of part of the arrangement of  FIG. 13 , and 
         FIGS. 15(   a ) to ( c ) are detailed views showing the anti-tamper feature of  FIGS. 13 and 14  at various stages of operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiment of injection device illustrated in the drawings is designed for use with a medicament which is supplied as two components in unmixed form in a dual chamber cartridge of known type as described, for example, in our earlier application WO2007/132191. As supplied, the cartridge has two spaced bungs which define two separate chambers and the drug is mixed by driving the rearward bung forwardly so that it causes the forward bung to move forwardly to reveal and open a bypass slot and thereafter to force the fluid in the rear chamber into the front chamber to mix with the substance. In such devices an initial longitudinal movement is required to reconstitute the drug whereafter the normal metered doses are required. In the embodiment described below the doses are all of a uniform volume but it will be appreciated that the device may easily be modified to provide a facility to deliver doses of variable volume. 
     Referring to  FIG. 1 , the injection device comprises a housing made up of a rear part  10  and a forward part  12  telescopically mounted on a reduced diameter position of the rear part. A drive unit  14  is secured to the rear end of the rear housing part  10 , and has a rotatable dial  16  at its rear end which is twisted to cock the device, and an actuator button  18  is slid forwardly to fire the device. The rotatable dial has a forward flange  11  that underlies the rear rim  13  of the outer shell  15  of the drive body. The rear rim is opaque apart from three transparent windows  17 . The flange  11  of the dial has coloured patches  11 ′ disposed so that, when the dial  16  is in the cocked position, the patches  11 ′ align with the windows  17  to indicate a colour change to show readiness. 
     At the front end of the forward housing  12  there is a sprung loaded collar  20  having a bayonet interlock which allows it to be twisted and released forwardly under the influence of a spring  21  to reveal an inspection window through which the contents of the cartridge  19  may be viewed. The collar  20  also shrouds a needle hub (not shown) when attached to the threaded portion  22  at the front end of the cartridge. 
     Referring now to  FIGS. 4 to 8 , the drive mechanism will now be described in more detail. The dial  16  is fixed to the rear end of a ratchet drive shaft  24  for rotation therewith. At its forward end, the ratchet drive shaft carries a ratchet tooth  26  (see  FIGS. 5(   a ), ( c ) and  6 ) that cooperates with corresponding inwardly facing latch teeth or recesses  30  on a drive gear  32  (see  FIG. 8) . A torsion spring  34  is anchored at its rear end to the dial  16  and at its forward end to a fixed support collar  36  which is fixed to the housing of the device. The ratchet drive shaft  24  is free to rotate inside the fixed support collar  36  but is limited to less than one turn of rotation by the interaction of an external rib  37  carried by the ratchet drive shaft  24  and internal ribs  39  carried within the support collar  36 . The body  10  has a pair of inwardly directed splines (not shown) that cooperate with corresponding longitudinal grooves  40  formed in the threaded portion  42  of a plunger  44  to hold the plunger against rotation but to allow longitudinal movement thereof. 
     The drive gear  32  carries at 120° intervals around its surface three pairs of teeth  46  for incrementing a dose counter mechanism as to be described below. Forwardly of the teeth  46 , the drive gear has a plurality of latching recesses  48  which cooperate with latching splines  50  on the forward end of the actuator button  18 . The actuator button  18  is angularly fixed with respect to the housing and axially movable between a rear position in which the splines  50  engage the latch recesses  48  to prevent rotation of the drive gear to a forward position in which the drive gear is released. 
     The drive gear carries a threaded bore  52  that is threadedly engaged with the threaded portion  42  of the plunger  44  and so rotation of the drive gear advances the plunger by a preset amount. The threads on the plunger and the bore are multi-start, for example, 4-start threads. 
     In use, the device is cocked or energised by twisting the dial  16  through a third of a turn to wind up the torsion spring  34  and to rotate the ratchet drive shaft  24  until the ratchet tooth  26  locks in the respective latching recess  30  on the drive gear  32 . The drive gear  32  in this position is held against rotation by the splines  50  on the actuator button. 
     In this condition the change in status is registered by the colour change in windows  17  adjacent the dial  16 . Pushing the actuator button  18  forwardly releases the drive gear  32  so that it rotates with the ratchet drive shaft  24  under the influence of the torsion spring  34 , advancing the plunger  44 . 
     A counter wheel  54  is mounted concentrically with the drive gear  32  by means of spaced mounting plates  56  which also mount an idler gear  58  which meshes with an inner toothed track  59  on the inside of the counter wheel  54 . The plates  56  are angularly fixed with respect to the housing and, as the drive gear  32  rotates, the teeth  46  trip the teeth of the idler cog  58  which in turn rotates the wheel by a uniform increment to register delivery of a dose and to keep a cumulative count. 
     As in seen in  FIG. 7 , the rear end of the plunger is formed with two lugs  60  which, as the plunger reaches its fully extended position engage or move between lugs  62  on the inside of the ratchet drive shaft  24  thereby restricting or preventing further rotation of the ratchet drive shaft relative to the plunger. This not only blocks further forward movement of the plunger, but also prevents the ratchet drive shaft from rotating relative to the housing. This means that the dial  16  is locked against rotational movement, subject to a small amount of backlash. 
     As can be seen from  FIGS. 1 and 2 , in order to prepare the device for injection, the forward housing part  12  needs to be slid rearwardly to be snap locked to the rear housing  10 . In doing so, this causes the plunger to act on the rear bung (not shown) in the dual chamber cartridge  21  to effect mixing of the medicament. In order to provide a tamper evident feature and also to prevent inadvertent or premature mixing or reconstitution, the device of  FIGS. 1 to 8  may be provided with an anti-tamper arrangement. Thus, in  FIG. 9 , the injection device is enclosed in plastics or similar removable casing halves  72 ,  74  which provide a recess  76 , the opposed edges of which prevent telescopic movement of the forward and rearward housing parts. 
     In  FIG. 10 , a separate plastic component  76  is heat staked around the rear housing part  10 , preventing telescopic movement of the housing parts until removal of the plastic component. 
     In  FIG. 11 , a peelable stick on label  78  is wrapped around the device to prevent the telescopic movement. 
     In  FIG. 12 , a moulded-end tear-off part  80  is integrally moulded with the front housing  12  and designed to be ripped off. The adjoining region between the tear-off part of the front housing may have recesses  82  to prevent sharp edges from being exposed. 
     Turning now to  FIGS. 13 to 15 , in this arrangement a raised leg  84  is formed on the rear housing part  10  and cooperates with a profiled slot  86  in the rim of the forward housing part  12 . In this arrangement the slot  86  is profiled so as to have a camming surface  88  up which the forward part of the leg  84  rides during initial turning movement to provide a resilient detent action ( FIGS. 15(   a ) to  15 ( b )). Having ridden up the cam surface  88  the forward part of the leg  84  is aligned with the main portion of the slot  86  so that the forward housing part  12  can be slid telescopically back to meet an opposed surface of the rear housing part. The leg  84  widens towards its rear end so that, having moved to the telescoped position shown in  FIG. 2  ( FIG. 15(   c )) it snaps irreversibly into the slot so it is not then possible to slide the forward housing part  12  forwardly.