Patent Publication Number: US-9849243-B2

Title: Substance delivery devices

Description:
FIELD OF THE INVENTION 
     The present invention relates to substance delivery devices (e.g. injection devices) and parts thereof, in particular an adjustment mechanism for use in such devices. 
     SUMMARY OF THE INVENTION 
     Although not limited thereto, the present invention finds particular application in substance delivery devices (in particular drug delivery devices) which are intended to house, or include, a container which, during the delivery process, is moved in distal direction so that the container is moved towards the skin of a patient, whereby the movement of the container is followed by a substance contained in the container being expelled. The container can for example be a syringe so that, when the container (syringe) moves in distal direction, the needle of the syringe penetrates the skin of the patient so that the substance in the syringe is subsequently injected into the patient. As used in the present specification, the term “distal” is intended to designate a location or direction towards the (injection site of the) patient&#39;s skin, and the term “proximal” is intended to designate a location or direction away from the (injection site of the) patient&#39;s skin. 
     The substance to be expelled will in most cases be a fluid, in particular a liquid. It is however conceivable that the substance could comprise a powder, suspension or similar, or a mixture of any of these substances. The container can also comprise a dual chamber cartridge, e.g. with a liquid in one chamber and a powder in the other which are mixed just prior to being expelled. For the sake of simplicity the description will proceed using fluid as an example of the substance to be expelled, and a syringe with needle will be used as an example of a container, but it will be appreciated that the invention encompasses applications without needle. 
     BACKGROUND OF THE INVENTION 
     Many injection devices of the above type (i.e. where a syringe is moved in distal direction during the injection operation) are particularly easy to use since the entire injection process (causing the needle of the syringe to penetrate the skin and the dose to be injected) can be triggered simply by pushing one button. One example of such an injection device is disclosed in WO 03/011378, which is incorporated herein by reference in its entirety. Whilst this device works well, the present inventors have appreciated at least two drawbacks with this device: there is no provision for adjusting the dose to be injected, and there is also no provision for priming the syringe. By way of explanation, “priming” refers to the process of expelling from the syringe any air and perhaps a small amount of fluid which is initially contained in the syringe. The present invention has been made with a view to overcoming these drawbacks. However, it will be appreciated, on consideration of the present specification, that the various aspects of the invention find application also in other types of injection/substance delivery devices. 
     Whilst dose adjustment and a priming function are generally known (the attention of the reader is directed to WO 2005/044346 and WO 2005/046770, also incorporated herein by reference in their entirety), it will be appreciated that thus far there has not been any attempt to provide the injection device of e.g. WO 03/011378 with an adjustment and/or priming function. As will be appreciated, the way in which the adjustment and the priming function pursuant to the present invention work is quite different from any adjustment or priming function disclosed in WO 2005/046770 and WO 2005/044346. This is why in particular the dose adjustment mechanism is useful in its own right, that is, it can be used with a range of other injection devices, not limited to injection devices in which a syringe is moved in distal direction during the injection process. 
     Aspects of the invention are set out in the independent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG. 1  shows a longitudinal section through an injection device according to a first embodiment of the present invention. 
         FIG. 2  shows a longitudinal section through the injection device shown in  FIG. 1 , whereby the section plane of the  FIG. 2  view is perpendicular to the section plane of the  FIG. 1  view. 
         FIG. 3  shows a perspective view of an injection device according to a second embodiment of the present invention. 
         FIG. 4  shows a side view of the embodiment shown in  FIG. 3 . 
         FIG. 5  shows a top view of the embodiment shown in  FIG. 3 . 
         FIG. 6  shows a longitudinal section through the embodiment shown in  FIG. 3 . 
         FIG. 7  shows a perspective view of the sectional view of  FIG. 6 . 
         FIG. 8  shows a longitudinal section through the proximal portion of the embodiment shown in  FIG. 3 . 
         FIG. 9  shows a perspective view of the embodiment shown in  FIG. 3 , after priming. 
         FIG. 10  shows a longitudinal section through the proximal portion of the embodiment shown in  FIG. 3 , after priming. 
         FIG. 11  shows a perspective view of a sub-assembly of the embodiment shown in  FIG. 3 . 
         FIG. 12  is a perspective view of a longitudinal section through the sub-assembly shown in  FIG. 11 . 
         FIG. 13  shows a perspective view of a longitudinal section through part of the body of the embodiment shown in  FIG. 3 . 
         FIG. 14  shows a perspective view of a longitudinal section through part of the body of the embodiment shown in  FIG. 3 . 
         FIG. 15  shows a perspective view of a syringe carrier assembly for use in the embodiment shown in  FIG. 3 . 
         FIG. 16  shows a longitudinal section through part of the embodiment of  FIG. 3 . 
         FIG. 17  shows a perspective view of a longitudinal section through the proximal portion of an injection device according to a third embodiment. 
         FIG. 18  shows a longitudinal section through the portion shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The injection device  1  shown in section in  FIG. 1  is shown in a condition before use.  FIG. 2  shows the same device, also before use, but sectioned at 90° to the  FIG. 1  view. 
     Referring both to  FIGS. 1 and 2  (not all reference numbers are shown in both Figures), 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 in turn carries a syringe  20 . Syringe  20  comprises a generally cylindrical container portion  24  for accommodating a fluid  22 , and a needle  26 . The needle is in communication with the interior of container portion  24  so that the fluid  22  may be expelled through needle  26 . A bung  28  is inserted in the container portion  24  at the proximal end. This prevents leakage of the fluid  22  out of the proximal end of container portion  24 . Syringe  20  is biased towards the proximal end by means of spring  23 . This spring is however relatively weak. Needle  26  is initially protected by a needle sheath  29 . 
     A safety cap or needle sheath remover  30  is provided at the distal end of injection device  1 . This safety cap is carried by a shroud retainer  15  of housing  2 . Towards its proximal end the safety cap 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. 
     The distal end of injection device  1  is also provided with a needle guard  32  or “lockout shroud”. This needle guard is movable along the longitudinal axis of the injection device over a limited range. The needle guard  32  is however 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  30  move. 
     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 . 
     At the very proximal end of injection device  1  there is provided a firing button assembly  51 . Its structure and function will be explained below. 
     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 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 needle  26  does not project beyond the distal end of needle guard  30 . 
     As in the earlier-disclosed technique, when the firing button is depressed the plunger 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 needle  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 needle  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. 
     In contrast to the earlier-disclosed injection device, the injection device shown in  FIGS. 1 and 2  has several additional features. Most notably these additional features are an adjustment means for adjusting the dose to be injected, and a priming function. 
     The adjustment means primarily comprises a stop member  44  which is carried by the distal plunger portion  41 . Stop member  44  is, in the preferred embodiment, 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 threadibly 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. 
     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 distal portion  41  of 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 . 
     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. 
     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 . 
     In order to adjust the dose to be injected the user can rotate adjustment ring  48 , thereby rotating the distal portion  41  of 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 . 
     While  FIGS. 1 and 2  show the injection device  1  generally in the same state, it will be noted that the position of stop member  44  is different in these two Figures. Stop member  44  has been moved in proximal direction in  FIG. 1  so as not to obscure any details. 
     Turning now to the priming function of injection device  1 , two priming buttons  70  are provided in the distal housing portion  12  (it is to be noted that the priming function could be achieved with only one priming button, but two priming buttons are preferred). Priming buttons  70  can be slid parallel to the longitudinal axis of injection device  1  over a small distance determined by the length of window  18 . A projection  72  is provided on the radially inner side of each priming button  70 , which projection engages with engagement formations  80  of the syringe carrier  82  around container portion  24 . The co-operation between projection  72  and engagement formations  80  means that, initially, the syringe carrier  82  is locked against axial movement with respect to priming buttons  70 . Container portion  24  in turn is sufficiently firmly attached to syringe carrier  82 , which means that syringe  20  is also locked against axial movements with respect to priming buttons  70 . The priming buttons may be formed such that accidental priming can be prevented. For example, priming buttons  70  may be formed with a catch or similar (not shown) so that they must be depressed before they can be moved in proximal direction. 
     In order to prime syringe  20  a user would hold injection device  1  upright so that the distal end points upwards. The user then moves priming buttons  70  in proximal direction (i.e. downward) until the priming buttons  70  contacts the proximal ends of windows  18 . Syringe carrier  82  and syringe  20  perform the same proximal movement. As a result of this proximal movement the bung  28  is pushed in distal direction with respect to container portion  24  as its proximal end contacts the distal end  45  of the distal plunger portion  41 . Any air contained in container portion  24  is thus expelled through needle  26  (and perhaps also a small amount of fluid  22 ). 
     As syringe  20  and syringe carrier  82  move in proximal direction the syringe carrier  82  is pivoted slightly about the axis of the syringe. This pivoting movement is achieved by a camming arrangement at the proximal end of syringe carrier  82 . The camming arrangement comprises cam surfaces at the proximal end of syringe carrier  82  and a corresponding cam surface provided at the distal end of projections or ribs  90  which are provided on the inside of distal main body portion  12 . As these cam surfaces contact and slide along each other the syringe carrier  82  is pivoted. This pivoting movement has the effect that syringe carrier  82  (and therefore also syringe  20 ) is no longer locked against axial movement with respect to priming buttons  70  since internal projections  72  and the engagement formations  80  on the syringe carrier  82  are limited in circumferential direction. This means that, once syringe carrier  82  has turned, the engagement formation  80  can freely move past internal projection  72  so as not to impede or prevent the injection operation. The syringe  20  may turn with syringe carrier  82  during priming, although this is not essential. 
     The way in which the priming function is implemented means that the injection operation cannot normally be performed without the priming operation having been performed first since without the priming operation having been performed the syringe  20  cannot move in distal direction since it is locked with respect to priming buttons  70 , which in turn are prevented from moving in distal direction as they contact the distal ends of windows  18 . 
     In preferred embodiments the projections or ribs  90  and most of the structure of priming buttons  70  (preferably all of the structure of priming buttons  70 , apart from their internal projections  72 ) are accommodated in an enlarged diameter portion of the distal main body portion  12 . This can ensure that, once the priming operation has been completed, the projections or ribs  90  and the priming buttons  70  do not interfere with stop member  44  when plunger  40  moves in distal direction. 
     However, in alternative embodiments no such enlarged diameter portion of distal main body portion  12  is provided and the projections or ribs  90  and much of the structure of priming buttons  70  project into distal main body portion  12 . In those embodiments the stop member  44  is provided with recesses at the circumferential positions of projections  90  (and priming buttons  70 ) so that stop member  44  can move past projections  90  and priming buttons  70  when plunger  40  and stop member  44  move in distal direction. Interference between plunger  40  and projections  90  or priming buttons  70  can thus be avoided. The recesses (not shown) in stop member  44  could conveniently be used as part of a recess and spline arrangement for keying stop member  44  with respect to main body  10 . 
     Mid body  13  is provided with two viewing windows  9  on opposite sides so as to permit a user to view container  24 . In the preferred embodiment the viewing windows  9 , the windows  14  and the windows  16  are all provided on the same side(s) of the housing  2 . Whilst it is preferred that two opposing ones of each type of window  9 ,  14  and  16  are provided, the device  1  may also be formed with only one, or more than two of each type of window  9 ,  14  and  16 . 
     The firing button arrangement  51  will now be explained, although it will be appreciated that alternative firing arrangements could be used. The firing button arrangement  51  comprises a firing button  52  carried by, and slidable within, the proximal end of the proximal main body portion  11 . In the initial position however the firing button  52  is not slidable. The reason for this is as follows. At the proximal end of the proximal plunger portion  42  there are provided two or more fingers which are provided with outwardly projecting teeth or plunger retaining barbs indicated by  58 . These outwardly projecting teeth  58  butt against a shoulder  19 , which is firmly attached to proximal main body portion  11  or is formed integrally thereto. This prevents the proximal plunger portion  42  from moving in distal direction. A safety tab  56  is provided at the centre of firing button  52 , and the distal end of the safety tab  56  also butts against shoulder  19 . This prevents safety button  52  from being depressed. When the injection device is to be used the user would tear safety tab  56  off (it is connected to firing button  52  by a thin bridge  57 , which is easily severed) and remove the safety tab  56  from the firing button  52 . This enables firing button  52  to be depressed in distal direction against the bias of spring  54 . Firing button  52  is provided with at least one internal projection  59 , preferably an annular projection  59 , which is arranged to squeeze the fingers at the proximal end of proximal plunger portion  41  together so that teeth  58  have cleared shoulder  19 . Plunger  40  is thus released, which enables it to perform the injection operation. 
     At the end of the injection operation syringe carrier  82  has moved in distal direction such that a set of locking barbs  61  has moved in distal direction past a set of housing barbs  17 . Housing barbs  17  are provided on an internal surface of mid body portion  13  whilst locking barbs  61  are provided on flexible legs  60  formed integrally with syringe carrier  82 . Locking barbs  61  project outwardly so that they can engage housing barbs  17  to prevent syringe carrier  82  from moving in proximal direction after the injection operation has been completed. 
     Locking barbs  61  and housing barbs  17  have the following purpose. When the injection device  1  has been pressed against a patient&#39;s skin the needle guard  32  will have moved in proximal direction (to the position shown in  FIGS. 1 and 2 , since needle guard  32  will have moved in distal direction as soon as safety cap  30  has been removed, due to the bias provided by spring  34 ). During the injection operation, as syringe carrier  82  moves in distal direction, the distal ends  62  of legs  60  move inwardly, using the proximal surface of housing barbs  17  as a ramp. This enables legs  60  to slide between and through guard legs  38  attached proximally to needle guard  32  (guard legs  38  are provided with an opening  37  so that legs  60  can project into/through guard legs  38 ). Eventually, legs  60  come to a halt between guard legs  38  when the syringe carrier  82  has completed its movement in distal direction due to a stop surface  91  of syringe carrier  82  stopping against a stop feature  92  of mid body  13 . After the injection operation, when injection device  1  is withdrawn from the injection site, needle guard  32  moves in distal direction, due to the bias provided by spring  34 . While this happens the guard legs  38  slide in distal direction past the distal ends  62  of legs  60 , and whilst syringe carrier  82  does not move in axial direction legs  60  move outwardly as they are no longer biased inwardly by guard legs  38 . Once legs  60  have moved outwardly the locking barbs  61  are approximately at the same radial position as housing barbs  17  but slightly more distal than housing barbs  17 , which means that syringe carrier  82  cannot be moved in proximal direction beyond a position where locking barbs  61  engage housing barbs  17 . 
     If, once legs  60  have moved outwardly, any attempt is made to move needle guard  32  in proximal direction, then the proximal end of guard legs  38  will butt against the distal end  62  of legs  60 . Because of this (syringe carrier  82  being prevented from movement in proximal direction because of the engagement of locking barbs  61  and housing barbs  17 ) the needle guard cannot be moved any further in proximal direction. This ensures that the needle  26  cannot be caused to project beyond the distal end of needle guard  32  after the injection device  1  has been used. 
     The injection device  1  is particularly easy to use. In order to perform an injection operation a user would “work their way up” along the injection device  1 , starting at the distal end. Initially, the user would remove the safety cap  30 . The user would then prime the syringe by means of priming buttons  70 , then set the desired dose by turning adjustment ring  48 , then remove the safety tab  56 , then press the injection device against the skin and then press the firing button  52 . After the injection operation the user would withdraw the injection device  1  from the skin and dispose of the device. 
     The injection device  1  can also accommodate different syringe diameters (i.e. sizes) with minimal modifications. If a smaller diameter syringe is desired to be used, then syringe carrier  82  should have a relatively small bore in which to accommodate the syringe. If a larger diameter syringe is to be used, then the bore of syringe carrier  82  should be made larger. Accordingly, a range of syringe carriers  82  with different bore diameters can be provided for use with the injection apparatus. All other parts of the injection apparatus may be the same for any syringe diameter (of course, the diameter of the distal plunger portion needs to be sufficiently small so that the plunger can project into container portion  24 ). This enables all parts of the injection device  1  (apart from the syringe carrier  82 ) to be manufactured in large numbers at reduced cost 
     Whilst the present invention has been described using a preferred embodiment as an example, it will be appreciated that the invention is not limited to a device having all of the features of the embodiment described with reference to  FIGS. 1 and 2 . In particular, it will be appreciated that the dose adjustment mechanism may be useful in its own right, and can be used in connection with other kinds of injection devices. 
     A second embodiment of the present invention will now be described with reference to  FIGS. 3 to 16 . Many features, as well as a major part of the principle of operation, of the second embodiment correspond to, or are similar to, those in the first embodiment described with reference to  FIGS. 1 and 2  and will therefore not necessarily be described again in detail. Features in  FIGS. 3 to 16  which are similar to corresponding features in  FIGS. 1 and 2  carry a reference numeral between  100  and  199 , whereas features whose structure or position is not necessarily similar to that in  FIGS. 1 and 2  carry reference numerals from  200  onwards. 
       FIG. 3  shows a perspective view of the injection device according to the second embodiment. This includes a housing with a mid body  113  and a proximal main body portion  111 . Mid body  113  may be held with respect to proximal main body portion  111  by means of unidirectional teeth  450  (shown in  FIG. 13 ) or other “snap features”. A safety cap  130  is located at the distal end of the injection device. A syringe viewing window  109  is formed in mid body portion  113 , and a dose indicator window  116  is provided in proximal main body portion  111 . Both viewing windows can be left open, but are preferably covered by a transparent material so as to protect the interior of the device. 
     The priming, dose adjustment and trigger functions are somewhat different from those of the first embodiment. A combined priming button and dose dial  200  is provided at the proximal end of the injection device. A priming alignment arrow  205  is marked on the priming button  200 . A trigger (or firing button)  300  is mounted to the body, laterally along proximal main body portion  111 . 
       FIGS. 4 and 5  show the injection device according to the second embodiment from the side and from the top. 
     The sectional view of  FIG. 6  shows the interior structure of the injection device. As in the first embodiment, the injection device includes a syringe  120  containing liquid  122 , a needle  126  mounted to the distal of syringe  120 , a bung  128  and a plunger  140 . 
     As shown in  FIG. 7 , a syringe carrier  182  is located within the housing, generally within proximal main body portion  111 . Syringe carrier  182  carries syringe  120  such that syringe  120  can only be moved in distal direction when syringe carrier  182  also moves in distal direction. 
       FIG. 8  shows the structure of the proximal portion of the injection device in more detail. The priming button  200  is held slideably within proximal main body portion  111 . It is prevented from sliding in proximal direction out of the housing by means of snap teeth  260 . For example three of these snap teeth may be provided, spaced equally around the housing. The priming button  200  is however initially also prevented from moving in distal direction, as will be described later. As will also be described later, angular movement of priming button  200  is initially also restricted, for example to a movement of 30°. A spring  150  is compressed between a distal surface of priming button  200  and a proximal surface of plunger  140 . Plunger  140  is thus biased in distal direction. However, plunger  140  is prevented from moving in distal direction since it is firmly connected or integrally formed with two fingers with outwardly projecting teeth  158  (somewhat similar to the two fingers and teeth  58  of the proximal plunger portion  42  shown in  FIG. 2 . Whilst not explicitly shown in  FIG. 8 , teeth  158  are “hooked” over a proximal surface of priming button  200 . 
     At its distal end the priming button  200  forms a non-circular channel  580 , preferably of square cross section. The fingers of the plunger are of a corresponding cross section and pass through channel  580  so that the fingers (i.e. plunger  140 ) substantially cannot rotate with respect to channel  580 . Plunger  140  is thus angularly locked with priming button  200 . 
     A firing block  210  forms part of priming button  200 . In the embodiment shown in  FIG. 8  the firing block is moulded into a trim cap  214  of priming button  200  and connected to the proximal portion of trim cap  214  by means of a flexible leg  215 . 
     Radially inwardly the firing block  210  is provided with a “V” shaped cut out, i.e. in a cross sectional view perpendicular to the axis of the device the firing block has a generally “V” shape. The proximal end of teeth  158  is received within the “V” shape. 
     The trigger  300  is pivotally connected to the housing, as also shown in  FIG. 9 . As shown in  FIG. 9 , the trigger may be provided with a ring  335 , which is attached into a recess around the outside of the device, approximately mid-way along the proximal main body portion  111 . Referring again to  FIG. 8 , a syringe carrier release pin  310  projects from approximately mid-way along trigger  300  radially inwardly. A firing pin  320  projects from near the proximal end of trigger  300 , also radially inwardly. Whilst trigger  300  is formed such that it can in principle be pivoted and/or flexed inwardly, it is initially prevented from doing so by the distal portion of priming button  200 , which blocks the inward path of travel of firing pin  320 . Trigger  300  is held in place by a tooth  330  projecting in proximal direction from the radially inner end of firing pin  320 . 
     The syringe carrier  182  is located within the housing. As is more clearly shown in  FIG. 15 , syringe carrier  182  is provided with an opening or recess  560  near its proximal end. A bridge portion  550  is located proximally adjacent the opening or recess  560 . A tooth  570  formed radially inwardly on proximal main body portion  111  projects into opening or recess  560 , as shown in  FIG. 8 . The distal surface of bridge portion  550  butts against the proximal surface of tooth  570  so that syringe carrier  182  is prevented from moving in distal direction. Whilst it is preferred that syringe carrier  182 , while being held by tooth  570 , cannot move at all in distal direction, it would also be possible to provide a small gap between tooth  570  and bridge portion  550  so that syringe  182  can move over a very limited range in distal direction. 
     As in the first embodiment, plunger  140  has an externally threaded shaft, onto which internally threaded stop member  144  is threaded. As shown in more detail in  FIG. 11 , stop member  144  has at least one projection  410  which is guided by an internal rib  555  extending longitudinally along a portion of syringe carrier  182 . Preferably at least two projections  410  and ribs  555  are provided so that stop member  144  is prevented from rotating with respect to syringe carrier  182 . On rotation of plunger  140  the stop member  144  will thus travel longitudinally along the threaded portion of plunger  140 . 
     Operation of the second embodiment will now be described. Initially, the user would remove the safety cap  130  either by simply pulling it in distal direction, or by rotating it and then pulling it in distal direction. A cam  131  is formed between the proximal end of safety cap  130  and the distal end of mid body portion  113 . This can help to overcome any particular high forces which may occur if the needle sheath (see item  29  in  FIGS. 1 and 2 ) sticks to the syringe  120 . In contrast to the first embodiment, after removal of the safety cap  130  no needle guard moves in distal direction. The needle  126  remains protected by, and within, the shroud  132  shown in more detail in  FIG. 15 . 
     The safety cap  130  should be removed prior to priming so that air can be expelled from syringe  120  during priming. 
     As mentioned above, initially the priming button  200  is prevented from moving in distal direction (as will be explained later). After removing safety cap  130  the user would pivot priming button  200  by about 30°. After this pivoting movement the priming button can be moved to a limited extent in distal direction (details of this movement in distal direction will be explained later). During the movement in distal direction the priming button  200 , which butts against plunger  140 , pushes plunger  140  in distal direction. Assuming that the injection device is held in a generally upright position, with the distal end pointing upwards, the syringe  120  will be primed during the movement of the plunger  140  in distal direction since the plunger moves bung  128  further into the syringe  120 . In order to achieve proper priming it is preferable that, in the initial condition, the distal surface of plunger  140  is close to, or butts against, the proximal surface of bung  128 . During priming the syringe does not move with respect to the housing since syringe  120  is held within syringe carrier  182  which itself is prevented from moving in distal direction, as described above. Instead, the plunger  140  moves with respect to the housing. 
     After priming the injection device is in the condition shown in  FIG. 9 , which shows that safety cap  130  has been removed and that the priming button  200  has moved in distal direction. 
     The user would then set the required dose. Once the device has been primed the user can fully rotate the dose dial  201  (see  FIGS. 10 to 12 ) at the proximal end of priming button  200 . Rotating the dose dial  201  rotates the entire priming button  200 , including the square channel  580 . As plunger  140  is rotationally locked to square channel  580  the plunger will rotate as well. This in turns moves the stop member  144  in longitudinal direction. The closer the stop member  144  is moved towards the syringe  120  the less is the extent to which plunger  140  can project into syringe  120 , i.e. the less will be the dose dispensed. 
     After the dose has been set the user would hold the distal end of the injection device against the desired injection site on the patient&#39;s skin (the patient may be the same as the user). 
     The priming button  200  is formed with a window  250  which needs to be aligned with firing pin  320  so that trigger  300  can be pivoted towards the housing. In order to better indicate to the user that the dose dial is in the “correct” position (i.e. so that window  250  is aligned with firing pin  320 ) the priming button  200  can be provided, as shown in  FIG. 11 , with one or more ribs  220  which is/are accepted in one or more recesses  222  in the proximal main housing portion  111 , as shown in  FIG. 13 . 
     Additionally, markings on the surface of the proximal main housing portion and on the dose dial  201  may be provided which, when aligned, indicate alignment of window  250  and firing pin  320 . 
     Once the window  250  has been aligned with firing pin  320  the user can depress the trigger  300 . As trigger  300  is depressed the syringe carrier release pin  310  presses down bridge portion  550 , which moves radially inwardly so that it is no longer held by tooth  570  of the proximal main housing portion  111 . This means that the syringe carrier (and with it the syringe) can move in distal direction. Further, as trigger  300  is pivoted inwardly it pushes firing block  210  inwardly as well. The inward movement of firing block  210  squeezes the proximal end of fingers  158  together so that they no longer project laterally beyond the internal edge of the square channel  580 , i.e. the plunger  140  is no longer prevented from moving in distal direction. The force stored in compression spring  150  thus propels plunger  140  in distal direction so that the actual injection operation can begin, similar to the first embodiment. As plunger  140  moves in distal direction it acts on bung  128 . Since the force required to move bung  128  with respect to syringe  120  is greater than the force required to move the syringe  120  and syringe carrier  182  in distal direction the movement of plunger  140  initially only moves the syringe and syringe carrier in distal direction, substantially without expelling any drug from syringe  120 . Syringe carrier  182  is free to move in distal direction since the syringe carrier release pin  310  has released it from tooth  570 . The movement of the plunger and syringe carrier in distal direction continues until the distal surface of syringe carrier  182  butts against guide ribs  510  shown in  FIG. 14 . Spring  150  continues to act on plunger  140  and thus on bung  128  so that bung  128  now moves in distal direction with respect to syringe  120  until stop member  144  is stopped by the proximal end of syringe  20 . The drug  122  is thus injected into the patient&#39;s skin. 
     The user would then withdraw the injection device from the skin and dispose of the device. 
     As shown more clearly in  FIGS. 14 to 16 , the needle guard  132  is connected to the syringe carrier  182  by two syringe carrier springs  500 . These two compression springs are located laterally alongside syringe  120 . They are preferably integrally moulded with one, or preferably both, with the needle guard  132  and the syringe carrier  182 . When the syringe carrier  182  moves in proximal direction during the injection operation the syringe carrier springs  500  are compressed and thus bias needle guard  132  in distal direction. Needle guard  132  can however not move in distal direction during the injection operation since it is held against the patient&#39;s skin. However, once the injection device has been removed from the patient&#39;s skin the syringe carrier springs  500  push needle guard  132  in distal direction so that its distal end projects more forward in distal direction than the distal end of needle  126  so that the needle is surrounded by needle guard  132 . Needle guard  132  is laterally provided with lockout legs  520  which are arranged to co-operate with housing barbs  525  ( FIG. 16 ) so that needle guard  132  is prevented from movement in proximal direction once lockout legs  520  have moved past housing barbs  525 . This helps to protect the user from accidental injury. 
     As shown in  FIG. 14 , guide ribs  510  are provided laterally with respect to the syringe carrier springs  500  so as to guide them and to ensure that they reliably move the needle guard  132  in distal direction at the end of the injection operation. 
       FIG. 15  shows two further features of the injection device. Firstly, one or more cut outs  530  are provided laterally in the distal half of syringe carrier  182  which are arranged to accept corresponding ribs formed on the interior surface of the housing. This prevents the syringe carrier from rotating within the housing. 
     Secondly, several dose indicator windows  540  are provided in the syringe carrier  182 . The dose indicator windows  540 , in the embodiment shown in  FIG. 15  consisting of small triangles, are individually “highlighted” if, as is preferred, the lateral surface of stop member (and dose indicator)  144  has an easily distinguishable colour, for example red. Dose indicator  144  may be moulded in that colour, or painted. As the dose indicator  144  passes underneath the triangles  540  the dose is indicated by that dose indicator window  540  which is at the same axial position as the dose indicator  144 . Numbers or other symbols may be marked on the syringe carrier next to the dose indicator windows  540 . 
     With reference to  FIG. 11 , it is particularly preferred that the distal end of plunger  140  is not threaded, i.e. has a non-threaded portion  400 . This helps to achieve a more even pressure distribution at the interface between the distal end of plunger  140  and the proximal surface of bung  128  when compared with embodiments where the distal portion of plunger  140  is threaded as well. 
     It is particularly preferred that dose indicator  144  is moulded (in situ) onto plunger  140 . The composition of dose indicator  144  is preferably different from that of plunger  140  so that the two parts do not bond during the moulding process. Moulding the dose indicator  144  onto the plunger  140  has three advantages. Firstly, with the distal end of plunger  140  being non-threaded, it is essentially impossible to thread dose indicator  144  onto plunger  140  from its distal end. Secondly, even if all of the plunger shaft was threaded, moulding the dose indicator  144  onto plunger  140  may make it easier to place the dose indicator  144  at the correct initial position along plunger  140 . Thirdly, since it is preferred to form the thread of plunger  140  as a multi-start thread it might be more difficult to find the “correct” thread start for dose indicator  144  if it was threaded onto the plunger shaft from the distal end of the plunger  140 . Moulding the dose indicator  144  onto the plunger  140  overcomes this problem. 
     The initial restrictions on the movement of priming button  200  of the second embodiment will now be described. 
     The priming button is provided (see  FIG. 11 ) with a ring  245 , which projects radially outwardly from the priming button  200 . This ring  245  is circumferentially interrupted by a transit lock recess  230  and an adjoining gateway  240 . The extent of the transit lock recess  230  in circumferential direction is larger than that of gateway  240 . In a preferred embodiment the transit lock recess extends over an angle of about 30°. A priming button locking rib  270  (see  FIG. 13 ) is provided on the internal surface of proximal main housing portion  111 . This priming button locking rib  270  can pass through the similarly shaped and dimensioned gateway  240 . The priming button locking rib  270  can, however, only pass through gateway  240  if these are aligned. In the initial condition of the injection device the priming button locking rib  270  is mis-aligned with gateway  240 . However, the proximal end of priming button locking rib  270  is initially positioned within transit lock recess  230 , near that circumferential end of transit lock recess  230  which in  FIG. 11  is uppermost. Since a portion of ring  245  butts against the proximal end surface of priming button locking rib  270  the priming button  200  cannot be moved in distal direction. The priming button  200  can, however, be pivoted over an angle of about 30° (corresponding to the length of the transit lock recess) until the gateway  240  is aligned with priming button locking rib  270 . 
     A priming alignment arrow  205  (see  FIG. 3 ) is provided on the priming button to indicate that the priming button has been pivoted into the correct position for priming. 
     A corresponding mark can be provided on proximal main housing portion  111  with which arrow  205  can be aligned. 
     Once the priming button  200  has been pivoted the priming operation can be performed. 
     During the priming operation the priming button  200  is moved in distal direction up to a fixed stop so that the proximal end of ring  245  passes to a position just distal to the distal end of priming button locking rib  270 . The gateway  240  and the distal portion of priming button locking rib  270  have a generally trapezoidal shape, their extent at their distal end being larger than at their proximal end. In particular, the width of the proximal end of gateway  240  is smaller than the width of the distal end of priming button locking rib  270  so that the priming button  200  cannot be moved in proximal direction towards the initial condition once the priming operation has been performed. As priming button locking rib  270  passes through gateway  240  the gateway  240  widens slightly. To this end the ring  245  is slightly flexible. 
     One or more such transit lock recesses  230 , priming button locking ribs  270  and gateways  240  may be provided around the circumference of the proximal main housing portion  111  and the priming button  200 , for example three. 
     In the second embodiment the trigger including the firing pin  320  and the syringe carrier release pin  310  is preferably a unitary moulded part. The trigger  300  of the second embodiment is arranged such that it releases bridge portion  550  from tooth  570  and (almost) simultaneously fires the device by firing pin  320  pressing down on firing block  210 . While it is preferred that firing block  210  is pressed down substantially simultaneously with syringe carrier  182  being released, this is not essential. The pressing down of firing block  210  may also occur with some delay after release of the syringe carrier  182 . However, in the injection device according to the second embodiment it is ensured that the syringe carrier  182  is released at the latest when compression spring  150  moves plunger  140  in distal direction. 
     It is worth noting that in the second embodiment it is the trigger  300  which both releases syringe carrier  182  and fires the injection device. In contrast to some prior art injection devices, the release of the syringe carrier does not cause plunger  140  to move in distal direction, nor does the movement of the plunger in distal direction cause the release of the syringe carrier  182 . It is the trigger  300  which causes both these actions without these two actions influencing each other. 
     A third embodiment will now be described. This is closely based on the second embodiment, and therefore only the differences will be explained here. The sectional view shown in  FIG. 18  and, perspectively, in  FIG. 17 , is very similar to the view shown in  FIG. 8 . The firing block  210  is again formed with a “V” shaped profile  211  for squeezing together the proximal ends of fingers  158  of the plunger  140 . However, trim cap  214  of the third embodiment is provided with a transversal portion  213  which is attached to firing block  210  and extends transversely across the injection device. A block  212  extends in distal direction from transversal portion  213  and partly projects into the space between the proximal ends of fingers  158  of the plunger  140 . Block  212  thus prevents, in the initial and in the primed condition, the proximal ends of the fingers  158  of plunger  140  from moving towards each other, for example as might happen if the injection device was dropped. When the trigger is pivoted inward and firing pin  320  acts on firing block  210 , block  212  moves with firing block  210  so that it no longer projects into the space between the proximal ends of fingers  158  of plunger  140 . Thus the injection device can be fired properly by means of trigger  300 , but an accidental firing is essentially prevented. 
     Whilst in the description of the preferred embodiment reference has been made to a syringe carrier  82  and  182 , in the claims the term “container carrier” is used. This is to take into account that, as mentioned above, the invention may be equally applicable to devices which deliver a substance from a container which is not necessarily a syringe. 
     Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.