Abstract:
A substance delivery device for delivering a substance from a container includes a body, and a plunger movable with respect to the body so as to expel at least a portion of a substance from the container, a trigger mechanism, a latch member latched in a stationary position at least along the longitudinal axis of the device before use, and a lockout shroud movable along the longitudinal axis relative to the latch mechanism. User manipulation of the trigger mechanism causes the latch mechanism to become unlatched and move along the longitudinal axis and to cause movement of a plunger relative to the body, and in a first position of the lockout shroud along the longitudinal axis relative to the latch member, the lockout shroud prevents the trigger mechanism from unlatching the latch member, whereas in a second position the lockout shroud allows the trigger mechanism to unlatch the latch member.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to injection devices with a mechanical interlock and, in particular, though not necessarily, to such injection devices for delivering a single dose of medicament. 
       BACKGROUND 
       [0002]    WO-A-03/011378 discloses an injection device where a syringe is enclosed in a housing of barrel-like form, the syringe being propelled forward by a drive mechanism to project its needle, followed by continued operation of the drive mechanism to push the plunger of the syringe and eject a dose. This procedure will leave the needle sticking-out, unless certain measures are taken. One answer is to have an arrangement for withdrawing the syringe back into the housing, while another is to have a needle shroud that moves out from the housing to enclose the-needle. Of course, this must not interfere with the actual injection operation. It has therefore been proposed that the shroud is normally spring urged forwardly to a needle protecting position, but when the device is pushed against the patient&#39;s skin the shroud is forced to retract against its spring. After injection, the spring pushes the shroud forwards again. A mechanism is provided for automatically locking the shroud at its fully projecting position after the injection but not before. The device of WO-A-03/011378 comprises a housing for the syringe, a needle-shroud captive to the leading end of the housing and movable before use between extended and retracted positions, a drive member releasable from a rearward position within the housing to urge the syringe forwards to project its needle beyond the retracted needle shroud and then to express a dose through the needle, and locating members on the housing for capturing the drive member at its forward position attained after expressing the dose, and wherein the captured drive member is arranged to block retraction of the needle shroud from its extended position. 
         [0003]    EP-A-1968670 discloses a substance delivery device (auto-injector) for use with a container (such as a syringe) containing the substance, the device comprising a body arranged to house or hold the container; a plunger which is movable with respect to at least a portion of the body, the plunger being arranged to act upon the container so as to move the container with respect to said portion of the body; wherein the plunger is also arranged to expel at least a portion of the substance from the container; and wherein the device comprises means for adjusting the amount of substance to be expelled from the container. The device can also have means for priming the container, and can accommodate containers of different size or shape. 
         [0004]      FIG. 6  is a sectional view of an embodiment of the device disclosed in EP-A-1968670. The injection device  1  comprises a body or housing  2 , which has three portions. These are (in the order from the proximal end of device  1  to the distal end): a main body  10 , a mid-body  13  and a shroud retainer  15 , the main body  10  is subdivided into a proximal main body portion  11  and a distal main body portion  12 . These portions can be formed as one piece. The housing  2  carries or houses a sleeve-like syringe carrier  82 , which is an example of a container carrier. The syringe carrier  82  in turn carries a syringe  20  (or other container for a substance). Syringe  20  comprises a generally cylindrical container portion  24  for accommodating a fluid  22 , and a cannula  26 . The needle is in communication with the interior of container portion  24  so that the fluid  22  may be expelled through cannula  26 . A bung  28  is inserted in the container portion  24  at the proximal end. The bung  28  seals the fluid  22  within the container portion  24 . Syringe  20  is biased towards the proximal end by means of spring  23 . This spring  23  is however relatively weak. Cannula  26  is initially protected by a needle sheath  29 . 
         [0005]    A safety cap or needle sheath remover  30  is provided at the distal end of injection device  1 . This safety cap  30  is carried by the shroud retainer  15  of housing  2 . 
         [0006]    Towards its proximal end the safety cap  30  is hooked over the proximal end of needle sheath  29  so that, when safety cap  30  is removed, the needle sheath is removed as well. 
         [0007]    The distal end of injection device  1  is also provided with a needle guard  32  or “lockout shroud”. This needle guard  32  is moveable along the longitudinal axis of the injection device over a limited range. The needle guard  32  is initially covered, and prevented from moving, by safety cap  30 . Only once safety cap  30  has been removed (as will be explained below) can needle guard  32  move. 
         [0008]    Towards the proximal end of injection device  1  there is provided a plunger  40 , which has a distal portion  41  and a proximal portion  42 . The plunger is biased by spring  50  towards the distal direction. This bias is relatively strong, and much stronger than the bias provided by spring  23 . 
         [0009]    At the very proximal end of injection device  1  there is provided a firing button assembly. Its structure and function will be explained below. 
         [0010]    The core principle of operation and much of the structure of the injection device  1  is very similar to the technique disclosed in WO 03/011378. Essentially, as in that earlier document, after removal of the safety cap  30  (and needle sheath  29 ) the needle guard  32  extends in distal direction because of the bias provided by a spring  34 . The distal end of the injection device  1  is then pressed against a patient&#39;s skin. This pushes needle guard  32  in proximal direction against the bias of spring  34 . However, during this action the cannula  26  does not project beyond the distal end of needle guard  32 . 
         [0011]    As in the earlier-disclosed technique, when the firing button is depressed the plunger  40  is released and can move in distal direction. When the front surface  45  of plunger  40  contacts bung  28 , continued movement of the plunger in distal direction initially moves syringe  20  (i.e. not just bung  28 ) in distal direction. This is so because the force required to move bung  28  in distal direction with respect to container portion  24  is greater than the force required to move the entire syringe  20  in distal direction (to this end the interior surface of the container portion  24  can be provided with circumferential ribs or other friction increasing formations). During this movement of syringe  20  the cannula  26  penetrates the skin of the patient. Eventually the movement in distal direction of syringe  20  comes to a halt, but plunger  40  is still able to move further in distal direction. This leads to bung  28  being moved in distal direction with respect to container portion  24 , which means that fluid  22  is expelled from container portion  24  through cannula  26  into the patient. Hence the movement of the syringe  20  (as a whole) and the movement of bung  28  within syringe  20  is brought about by plunger  40  acting on bung  28 . It will be appreciated that the portion of plunger  40  (i.e. distal end surface  45 ) which acts on the syringe  20  to move the syringe is the same as the portion of the plunger which acts on the syringe to move bung  28  so as to expel the fluid. When the plunger  40  has its movement in distal direction stopped the injection operation has been completed. The user can then move the injection device  1  in proximal direction so as to withdraw the needle from the injection site. As the injection device  1  is withdrawn from the skin of the patient the needle guard  32  is moved in distal direction due to the bias provided by spring  34 . The guard  32  then locks in the distal position rendering the device safe. The injection device  1  can then be disposed of. 
         [0012]    In contrast to the earlier-disclosed injection device, EP-A- 1968670  discloses several additional features. Most notably these additional features are an adjustment means for adjusting the dose to be injected, and a priming function. 
         [0013]    The adjustment means of EP-A-1968670 primarily comprises a stop member  44  carried by the distal plunger portion  41 . Stop member  44  may be provided with an internal thread co-operating with an external thread  43  on the circumferential surface of the distal plunger portion  41 . Additionally, stop member  44  is keyed at  46  to the inner surface of distal housing portion  12 . With stop member  44  being threadably engaged with the distal plunger portion  41  and being keyed to distal housing portion  12  (e.g. by means of splines or similar, not shown), the stop member  44  will move in distal or proximal direction when distal plunger portion  41  is rotated about its longitudinal axis. 
         [0014]    Distal plunger portion  41  can be rotated by means of adjustment ring  48 . Adjustment ring  48  is keyed to a relatively large diameter proximal portion  49  of the plunger  40 . This means that, on rotation of adjustment ring  48 , the distal plunger portion  41  will carry out the same rotation, but the distal plunger portion  41  is substantially free to move in a direction parallel to the plunger axis, independently from adjustment ring  48 . The proximal portion  49  of the distal plunger portion  41  is engaged with the distal portion  47  of the proximal plunger portion  42  such that the distal plunger portion  41  can substantially freely rotate with respect to the proximal plunger portion  42  but has to make the same movements in distal or proximal direction as the proximal plunger portion  42 . 
         [0015]    The adjustment ring  48  is located between proximal and distal main body portions  11  and  12 . Windows  14  are provided on opposite sides of main body  10  where the proximal and distal main body portions  11  and  12  meet. 
         [0016]    The injection device  1  has a generally oval cross section. The windows  14  are provided on those “sides” of the oval which have the smaller distance from the centre of the oval. The main body is continuous on those “sides” of the oval which have the greatest distance from the centre of the oval. This means that the main body  10  with proximal and distal main body portions  11  and  12  can be formed (e.g. moulded) in one piece and further that adjustment ring  48  can project through windows  14  whilst being securely held within main body  10 . 
         [0017]    In order to adjust the dose to be injected the user can rotate adjustment ring  48 , thereby rotating the plunger  40 . As mentioned, this sets the axial position of stop member  44  along distal plunger portion  41 . Through setting this axial position the user can determine how far the plunger is allowed to project into container portion  24 . This is so because movement of the plunger in distal direction during the injection process is stopped when stop member  44  makes contact with the proximal end of container portion  24 . The axial position of stop member  44  along distal plunger portion  41  (before the beginning of the injection operation) can be viewed by the user through a further window  16  provided in the distal main body portion  12 . Suitable indications may be provided at window  16  to indicate to the user which dose corresponds to the set position of stop member  44  with respect to window  16 . 
         [0018]    EP-A-2633874 discloses a medicament delivery device comprising a housing, a safety sleeve movable between an extended position and a retracted position relative to the housing, a guide sleeve rotatably disposed in the housing, a plunger slidably disposed in the safety sleeve, and a button coupled to the housing. When the safety sleeve is in the retracted position, translation of the button relative to the housing causes the guide sleeve to rotate relative to the safety sleeve. Rotation of the guide sleeve relative to the safety sleeve allows the plunger to translate a predetermined axial distance relative to the safety sleeve. 
       SUMMARY 
       [0019]    In a first aspect the invention provides a substance delivery device for delivering a substance from a container, the device comprising a body, a plunger which is movable with respect to the body so as to expel at least a portion of a substance from a container, a trigger mechanism, a latch member latched in a stationary position at least along the longitudinal axis of the device before use, a lockout shroud being moveable along the longitudinal axis relative to the latch mechanism, wherein user manipulation of the trigger mechanism causes the latch mechanism to become unlatched and able to move along the longitudinal axis and to cause movement of a plunger relative to the body, and in a first position of the lockout shroud along the longitudinal axis relative to the latch member, the lockout shroud prevents the trigger mechanism from unlatching the latch member, whereas in a second position the lockout shroud allows the trigger mechanism to unlatch the latch member. 
         [0020]    The lockout shroud may comprise one or more members configured, when the lockout shroud is in the first position, to prevent movement of one or more portions of the latch member, which in turn prevents the trigger mechanism from unlatching the latch member. 
         [0021]    A needle guard may be accommodated at one end of the lockout shroud. 
         [0022]    Before use of the device the end of the lockout shroud may stand proud of the needle guard and after the device is fired, the needle guard is retained by the lockout shroud but stands proud of the end of the lockout shroud. 
         [0023]    The degree of movement between the plunger and the body may determine the amount of substance that is delivered and the device may comprises, an instance of one or more co-operating features associated with the plunger, and a corresponding instance of one or more co-operating features associated with the body, whereby co-operation between the two instances of co-operating features determines the degree of movement between the plunger and the body, wherein there is a plural instances of said one or more co-operating features associated with at least one of the plunger and the body, and co-operation between different instances of co-operating features allows different ranges of movement between the plunger and the body. 
         [0024]    There may be a single instance of one or more co-operating features associated with one of the body and the plunger and plural instances of one or more co-operating features associated with the other of the plunger and the body. 
         [0025]    The at least one instance of one or more co-operating features associated with the plunger may be located on an external surface of the plunger. 
         [0026]    The at least one instance of one or more co-operating features associated with the body may be located on an internal surface of the body. 
         [0027]    The plural instances of one or more co-operating features associated with one of the plunger and the body may each comprise one or more tracks, and the or each track of a first instance of the one or more co-operating features may be relatively long compared with the or each track of a further instance of the co-operating features. 
         [0028]    A single instance of one or more co-operating features may comprise an instance of one or more pegs associated with one of the plunger and the body, the or each peg being configured to follow each said track. 
         [0029]    Relative rotation of the plunger and body may determines which instance of one or more co-operating features associated with the body or the plunger is selected for co-operation with the corresponding instance of at least one co-operating feature associated with the other of the body and the plunger. 
         [0030]    The device may further comprise a selector rotatable by a user for causing relative rotation of the plunger relative to the body. 
         [0031]    The substance delivery device may comprise a container carrier housed within the body for receiving a substance container, wherein the container carrier is move-able along a longitudinal axis of the device relative to the body during a substance delivery process, wherein a surface of the container carrier includes at least one visual indicator that can be seen through a window in the body in at least one of the positions of the container carrier. 
         [0032]    The container carrier may carry two visual indicators, at least one of the visual indicators is not visible to a user in at least one position of the container carrier. 
         [0033]    The lockout shroud may be housed coaxially within the body of the device, the container carrier being housed within the lockout shroud and the lockout shroud comprises a cut out portion whereby a portion of the container carrier can be seen through the window of the body. 
         [0034]    In a second aspect the invention provides a substance delivery device for delivering a substance from a container, the device comprising a body, a plunger which is movable with respect to the body so as to expel at least a portion of a substance from a container, a container carrier housed within the body for receiving a substance container, wherein the container carrier is move-able along a longitudinal axis of the device relative to the body during a substance delivery process, wherein and a surface of the container carrier includes at least one visual indicator that can be seen through a window in the body in at least one of the positions of the container carrier. 
         [0035]    The container carrier may carry two visual indicators, at least one of the visual indicators is not visible to a user in at least one position of the container carrier. 
         [0036]    The substance delivery device may further comprise a lockout shroud housed coaxially within the body of the device, the container carrier being housed within the lockout shroud and the lockout shroud comprises a cut out portion whereby a portion of the container carrier can be seen through the window of the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a cross section through an injection device according to the invention; 
           [0038]      FIG. 2  is an exploded perspective view of a proximal portion of the device of  FIG. 1 ; 
           [0039]      FIG. 3  is an exploded perspective view of a distal portion of the device of  FIG. 1 ; 
           [0040]      FIGS. 4 a  and 4 b    are detailed part views of the lockout shroud and latch ring; 
           [0041]      FIG. 5  is a perspective view of the device of  FIG. 1 ; 
           [0042]      FIG. 6  is a cross section through a prior art injector pen; 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    Considering  FIGS. 1 to 5 , an injection device  1  is shown in accordance with the invention.  FIG. 1  is a cross section through the whole device whereas  FIGS. 2 and 3  are exploded perspective views of certain components of the device for ease of description.  FIGS. 4 a  and 4 b    are enlarged view of a portion of a lockout shroud and a latch ring that co-operates with the lockout shroud as described below. 
         [0044]    As can be seen from the exploded views the various part of the device fit together along a common longitudinal axis. The embodiment shown is a specific embodiment and is not intend to limit the manner in which the invention is implemented. For example, where some parts are shown as separate but would function mechanically if they were integral then the skilled person will recognise that both implementations are disclosed herein; similarly where certain parts are shown as integral but could be provided as two or more parts then such an implementation is also envisaged as falling within the present invention. 
         [0045]    The main parts of the device  1  are the housing  2 , including a main body  10 , a mid-body  13 , a shroud retainer  15 , a needle guard  32 , syringe carrier  82 , syringe  20  including a container portion  24 , plunger  40 , a dose adjuster rod  41 , firing spring  50  and trigger button  52 . The dose adjuster rod in the present embodiment is fixed both rotationally and axially to the main body  10 . The device also includes amongst other components, a lock out shroud  100  (shown in  FIGS. 1 and 3 ) and an interlocking latch ring  110  ( FIGS. 1 and 2 ). 
         [0046]    Starting from the proximal end and considering  FIGS. 1 and 2 , a firing or trigger button  52  is received concentrically within the main body  10 , together with the dose adjuster rod  41  and the firing spring  50 . Dose adjuster rod  41  has its proximal end  43  connected to the main body  10 ; in this case the proximal end  43  is received by an opening  44  in a frame  46  formed at the proximal end of the main body  10 . Rotation of the main body causes rotation of the dose adjuster rod  41  around its longitudinal axis. 
         [0047]    The trigger button  52  co-operates with the latch ring  110 . The latch ring  110  is held in place relative to the housing  2 , before use, by shoulder  19  carried by the internal wall of the main body  10  of the housing  2 , which co-operates with co-operating portions in the form of outwardly projecting teeth  58  on flexible fingers  111  of the latch ring  110 . The trigger button  52  has flexible arms  53  with cam surfaces  113  that co-operate with cam surfaces on the flexible fingers  111  of the latch ring  110 , such that movement of the trigger button  52  relative to the latch ring  110  in the distal direction (towards the needle end of the device) will flex the fingers  111  of the latch ring  110  inwardly releasing the co-operating portions  58  from the shoulder  19 . During the process the trigger button moves relative to the main body  10  against the bias of a spring  54 . 
         [0048]    Once the latch ring  110  has been released during the above process, the trigger button  52  is prevented from further, significant, movement, distally relative to the housing  2  by the ends of the flexible arms of the trigger button  52  abutting the shoulder  19 . Alternatively, further co-operating elements can be supplied on the trigger button  52  or housing  2 , or both in order to prevent further movement of the trigger button on release of the latch ring  110 . The latch ring  110  is then urged forcefully by the spring  50  in a distal direction axially of the housing  2 . The latch ring  110  in turn acts on a proximal portion of the plunger  40 . 
         [0049]    In an initial condition the above process is prevented from occurring by the lockout shroud  100 . A proximal end of the lock out shroud cooperates with the latch ring to prevent accidental firing of the device  1 . In other words, there is a two stage firing process, which is described below. 
         [0050]    Turning now to  FIGS. 1 and 3 ; distal end of plunger  40  is received in container portion  24  of syringe  20 . In turn, the container portion  24  is received within syringe carrier  82 , and syringe carrier  82  is received within lockout shroud  100 . The syringe  20 , the syringe carrier  82 , and lockout shroud  100  are all housed within the mid-body portion  13  of housing  2 . 
         [0051]    A safety cap or needle sheath remover  30  is provided at the distal end of injection device  1 . In an embodiment the safety cap  30  is hooked over the proximal end of a needle sheath  29  protecting the needle before use so that, when safety cap  30  is removed, the needle sheath is removed as well. The safety cap  30  may be formed in  2  halves which are assembled around the needle sheath to avoid applying axial force to the needle sheath during assembly. In the present embodiment shown in  FIGS. 1 and 3 , a separate component  15  is provided that is formed as a claim shell or in this case half clam shell which is assembled around the needle sheath allowing the safety cap to be snap fit onto the component  15  without damaging the needle sheath. 
         [0052]    A needle guard  32  is accommodated on the distal end of the lockout shroud  100  and is moveable therewith axially of the mid-body  13 . A spring  34  is included to bias the needle guard  32  in a distal direction and the syringe carrier  82  in a proximal direction. 
         [0053]    In the present embodiment the needle guard  32  has proximally extending legs  33  which engage with axially extending closed-ended grooves  35  within the lockout shroud  100 . The legs  33  have outward protrusions which initially engage within deeper detents within the grooves which hold the guard in position relative to the lockout shroud. This allows the needle guard  32  to move a limited distance in a distal direction only once the detent engagement has been disengaged but to be constrained from becoming detached from the lockout shroud  100 . As can be seen from  FIG. 1 , with the safety cap  30  in place, the lockout shroud stands proud of the needle guard  32  which is located within the lockout shroud. 
         [0054]    Once the safety cap  30  is removed, pressure can be applied to the end of the lockout shroud  100  (in use by pressing the end of the device against the skin of the user), whereby the needle guard  32  and the lockout shroud  100  move axially relative to the housing  2  in the proximal direction. 
         [0055]    As can be seen more clearly in  FIGS. 4A and 4B , the flexible fingers  111  of the latch ring  110  are interspersed by slots which have a generally T-shaped profile, the head of the T-profile being at the proximal end of the latch ring  110 . Before any movement of the lockout shroud  100  in the proximal direction ( FIG. 4 a   ), internally facing lugs  114  located at the ends of the legs  101  of the lockout shroud  100  engage with the flexible fingers  111  of the latch ring  110  in the region of the narrow part of the T-profile. This arrangement prevents inward flexing of the fingers  111  and movement of the trigger button  52  since it is necessary for the fingers  111  to flex inwards for the trigger button to move relative to the latch ring. 
         [0056]    The application of sufficient pressure to the distal end of lockout shroud  100  causes movement of the needle guard  32  and the lockout shroud  100  relative to the housing  2 . The latch ring  110  is prevented from movement in the proximal direction (relative to the housing  2 ) by its engagement with the trigger button  52  and the force of the loaded spring  52 ; thus the lockout shroud  100  also moves relative to the latch ring  110 . The movement of the lockout shroud  100  against the bias of the spring  34  is sufficient to move the lugs  114  into the T-profile slots described by the fingers  111  of the latch ring  110  ( FIG. 4 b   ) allowing fingers  111  to flex inwards. The trigger button can now be pushed axially of the housing  2  in the distal direction causing the cam surfaces  113  to co-operate with the fingers  111  to cause inward flexing of the fingers  111  and disengaging teeth  58  from shoulder  19 . 
         [0057]    When both operations required to trigger the device to fire are performed, the spring  50  then urges the latch ring  110  to move distally relative to the housing  2 , until it contacts the plunger  40  and then the plunger  40  is also urged forcefully in the distal direction relative to the housing  2 . The syringe  20  and syringe carrier  82  also move relative to the housing  2 , the lockout shroud  100  and consequently the needle guard  32 . This movement proceeds a certain distance increasing the pressure on the spring  34  which acts between the syringe carrier  82  and the needle guard  32  until the needle guard  32  is knocked out of position relative to the lockout shroud  100  when sufficient pressure is built up in spring  34  (or the spring  34  is completely compressed becoming solid in which case the entire load from spring  50  then acts to knock the guard out of its detent previously keeping it in place relative to the lockout shroud  100 ). The geometry is chosen to make sure the forward movement of the syringe carrier  82  is subsequently halted before the needle guard  32  is driven into the user under a high force from spring  50 . Forward movement of the syringe carrier  82  is halted when one or more engagement portions  85  on the syringe carrier  82  abut corresponding engagement portions  86  on the internal wall of the lockout shroud  100 . The force of the drive spring  50  is then applied to the plunger  40 , the syringe carrier  82 , and the lockout shroud  100 , whereas the needle guard  32  is biased lightly forward by spring  34  only. Subsequent axial movement of the plunger  40  is then relative to the container portion  24  and causes the substance in the container to be expelled through the cannula  26 . 
         [0058]    Removing the pressure on the distal end of the lockout shroud  100  allows the needle guard  32  to extend beyond the lockout shroud under bias of spring  34  so as to guard the cannula that now extends beyond the lockout shroud  100 . In the present embodiment the syringe carrier  82  is prevented from returning to its original position by the force of the firing spring acting on the latch ring, the plunger, the syringe and the syringe carrier. 
         [0059]    The above described arrangement with the interlocking latch ring  110  and lockout shroud  100  provide a novel arrangement for a device with a two stage firing process. 
         [0060]    Alternatively, or in addition a latch button may be provided external of the housing to allow firing of the device without movement of the lockout shroud if present. Instead of moving a lockout shroud to allow movement of fingers  111 , a latch button can effect movement of the shoulder or shoulders  19  (or a portion of the housing carrying the shoulder  19 ) so as to allow movement of the latch ring  110  relative to the housing. 
         [0061]    The present embodiment will also be used to describe a novel variable dosing selection for an injection device that may be used in conjunction with the above arrangement or may be used in other arrangements where appropriate. 
         [0062]    As most easily seen in  FIG. 2 , the plunger  40  includes a head  102  for receiving the dose adjuster rod  41 . As can be seen the distal end  103  of the dose adjuster rod  41  is shaped so as to prevent rotation of the dose adjuster rod  41  relative to the plunger  40 . The head  102  of the plunger  40  carries pegs  104 , which are shaped to follow tracks  105  in the housing  2 , principally in the mid-body  13 . 
         [0063]    During the firing process the pegs  104  follow the tracks  105  as the plunger  40  travels axially within the housing  2 . The tracks  105  are of a length to provide a specific dose of substance to be expelled from the syringe  20 . The plunger can only travel the length of the tracks  105  before coming to a stop as the pegs  104  abut the end of the tracks  105 . By providing more than one set of tracks  105 —each set of tracks providing a differing specific dose of substance to be delivered by the device—a simple means for selecting the dose to be delivered is provided. 
         [0064]    Before triggering the device  1 , the pegs  104  are located at the start of one set of tracks; that is they are aligned with a particular track pair, for example, long tracks providing a “full” dose of the substance contained in the syringe  20 . Off set from the long track pair around the circumference of the internal surface of the mid-body  13  is another shorter track pair  105  (not shown). Rotating the main body and mid body relative to each other (for example, rotating the main body  10  relative to the mid-body  13  clockwise looking from proximal to distal) will align the line  120  with the small indicator circle rather than the big indicator circle in  FIG. 4 . This equates to selecting a small dose rather than a full dose. Internally, the rotation of the main body portion  10  relative to the mid-body portion  13  causes rotation of the dose adjuster rod  41  and hence rotation of the plunger  40  relative to the mid-body  13  and consequently the pegs  104  are no longer aligned with the long tracks  105  but now with the short tracks  105 . 
         [0065]    In this embodiment, the rotation of the two housing portions  10  and  13  relative to each other causes relative rotation of the plunger head  102  and plunger  40  to the mid-body  13 , whereas the trigger button  52 , and latch ring  110  rotate relative to the main body  10 ; that is the latch ring  110  is fixed relative to the mid-body  13  and does not rotate relative to the lockout shroud  100  and trigger button  52 . Rotation of the main body  10 , relative to the mid-body  13  causes rotation of the plunger  40  since the proximal end  43  of the dose adjuster rod  41  is connected to the frame  46  of the main body  10 . 
         [0066]    In an alternative embodiment, the dose selector could be provided as a separate part of the housing  2 , whereby the rotation of the selector acted directly on the proximal portion of the plunger which then provided rotation of the distal portion of the plunger relative to the housing. 
         [0067]    Of course, the head  102  with the pegs  104  could be provided at any suitable portion of the plunger or a separate component configured to operate on the plunger and move with the plunger relative to the housing  2 —together with appropriate modifications in relation to the co-operating tracks in the housing  2 . Whilst the co-operating tracks in the embodiment are provided in the wall of the mid-body portion of the housing, the tracks could be provided in any convenient manner, for example in a separate component located within the housing. 
         [0068]    In the embodiment of  FIGS. 1 to 4 , the dose selector relies on pegs on the plunger located in one set of co-operating tracks, selected from  2  or more sets of such co-operating tracks. In an alternative embodiment the tracks are located on the plunger and pegs, ribs or other protrusions are located on the housing or otherwise arranged to co-operate with the tracks on the plunger so as to provide the required co-operation with the tracks. Any combination of tracks or protrusions is envisaged. The use of pegs on the plunger and tracks or grooves on the housing wall, provides a compact device. 
         [0069]    When the device is triggered the latch ring  110  and plunger  40  all move axially in the distal direction. This movement also serves to move the syringe carrier  82  and syringe so as to protrude out of the needle guard  32  so that the skin of a user can be punctured by the cannula  26 . 
         [0070]    In a further aspect of the invention, the syringe carrier  82  carries indicator markings to indicate that the injector device is ready to be used or conversely that the device has already been used and should be discarded. Before use the ready-for-use indicator  83  (the tick mark on the distal portion of the syringe carrier shown in  FIG. 3 ) is visible through a window  131  in the mid-body  13 . In particular, the window  131  of the mid-body  13  is located relative to the syringe carrier  82  such that the ready-for-use indicator  83  can be seen through a distal portion of the window  131  before use of the device. A cut out  132  is required in the lockout shroud so that at least a portion of the syringe carrier  82  can be seen through the window  131 . 
         [0071]    Following the two-step procedure described above for firing the device, the syringe carrier  82  has moved relative to the lockout shroud  100  and the mid-body  13 . The ready-for-use indicator  83  can no longer be viewed through the window  131  and/or through the cut-out  132  of the lockout shroud  100 . On the other hand, a “used” indicator  84  can now be seen through a proximal portion of the window  131  and cutout  132 . 
         [0072]    Exemplary embodiments of the invention have been described with reference to the drawings. Modifications will suggest themselves to those skilled in the art without departing from the scope of the invention as defined by the appended claims.