Abstract:
A medicament delivery device includes a housing having proximal and distal ends; a hollow piston plunger within the housing; a telescopic dose drum concentric between the housing and the plunger; and a plunger driver to drive the plunger toward the proximal end having a hollow drive drum sleeve movable within and coupleable to the piston plunger and fixed to the dose drum; an actuator operably connected to the drive drum sleeve; and a stop body for inhibiting rotation of the dose drum and drive drum sleeve when a set dose equals a remaining dose in a medicament container. The drive drum sleeve and piston plunger are operatively coupled such that axial movement of the actuator toward the proximal end forces the drive drum sleeve and piston plunger to couple, whereby the piston plunger and dose drum are displaced toward the proximal end for delivering the set dose.

Description:
This application is a national-phase entry under 35 U.S.C. §371 of International Application PCT/EP2013/057376. 
     TECHNICAL FIELD 
     The present invention relates to a medicament delivery device and in particular a device capable of delivering a dose of medicament set by user before delivery. 
     BACKGROUND 
     There are numerous devices for delivering medicament on the market and also patented where the medicament is arranged in a container, such as a syringe, cartridge and the like, and wherein the medicament is exposed to pressure when it is to be delivered. A very common design is a generally tubular compartment having a stopper in one end of the compartment and a delivery member attached to the opposite end of the compartment, such as, e.g., a needle, a nozzle or the like member capable of delivering medicament to a patient. 
     In order to deliver a quantity of medicament, the stopper is exposed to pressure, i.e. pushed into the compartment by a plunger rod, which could be done manually by a finger, which is the case for simple handheld syringes, or by pressure means such as springs, which is common in automatic or semi-automatic injectors. In this context, the so called pen-injectors are becoming quite common, where the injection is performed by manually pushing at a distal end of the device. With this type of injector there has also been a development regarding delivering different dose quantities with the same device, i.e. to be able to set a certain prescribed dose before delivery. 
     A number of such devices have been developed, such as the device disclosed in EP-A-1 601 395. Here the device is arranged with a dose setting drum that can be rotated in relation to a housing and a drive sleeve that, upon manual operation by a user, drives a plunger rod to deliver a set dose of medicament. In order to provide the function of setting a dose with the dose setting drum and delivering a dose with the drive sleeve, there has to be some sort of connection/disconnection mechanism between them. Thereby a clutch or uni-directional connection mechanism has been developed for providing the desired function. This solution entails a number of components that are to interact with each other as well as a number of threaded engagement and connection mechanisms that require careful design in order for the manually applied force by a user not to be too large, or the device otherwise will not function properly. There is also a question whether the solution according to EP-A-1 601 395 can provide the possibility of resetting a set dose in a simple and efficient manner. 
     Another feature with the device of EP-A-1 601 395 is that the setting of a dose larger than the remaining quantity should be prevented in that when a nut reaches the end of a helical thread of the connection mechanism, the nut stops rotating of a dose dial sleeve and the drive sleeve will thus become locked together preventing rotation of the dose dial sleeve and setting of a larger dose. This direct action between threads is not so precise in that there is no distinct stop between the components. Rather, the components could be turned in relation to each other quite a turning distance before the friction becomes so high that it is difficult to turn them relative each other any longer. Thus, a user could then erroneously believe that he/she is receiving a larger dose than the actual dose received. 
     Further, the components, such as the dose setting drum and the drive sleeve as well as the plunger rod are elongated and positioned inside each other. In order to not risk a jamming between the components, a certain play is necessary. Then, such play and gaps between components increase the risk of lack of support and therefore rattling and other noises that may negatively affect a potential user. 
     SUMMARY 
     An object of the present invention is to provide a medicament delivery device wherein the drawbacks of the state of the art devices are remedied. 
     In order to overcome one or several of the above-mentioned problems, a medicament delivery device according to independent claim  1  is provided. 
     Further aspects, improvements and variations are disclosed in the dependent claims, the figures and the description. 
     In the present application, when the term “distal” is used, this refers to the direction pointing away from the dose delivery site. When the term “distal part/end” is used, this refers to the part/end of the delivery device, or the parts/ends of the members thereof, which under use of the medicament delivery device is/are located furthest away from the dose delivery site. Correspondingly, when the term “proximal” is used, this refers to the direction pointing to the dose delivery site. When the term “proximal part/end” is used, this refers to the part/end of the delivery device, or the parts/ends of the members thereof, which under use of the medicament delivery device is/are located closest to the dose delivery site. Further, the term “longitudinal”, with or without “axis”, refers to a direction or an axis through the device or components thereof in the direction of the longest extension of the device or the component. In a similar manner, the term “transversal”, with or without “axis”, refers to a direction or an axis through the device or components thereof in a direction generally perpendicular to the longitudinal direction. Also, if nothing else is stated, in the following description wherein the mechanical structure of the device and the mechanical interconnection of its components is described, the device is in an initial non-activated or non-operated state. 
     The invention provides a medicament delivery device having a housing with a proximal end and a distal end. A hollow piston plunger is arranged within the housing. The piston plunger has a longitudinal axis generally corresponding with the longitudinal direction of the medicament delivery device. 
     The device of the invention comprises a hollow piston plunger being arranged within the housing and a telescopic dose drum being concentrically arranged between the housing and the piston plunger. The telescopic dose drum being bidirectional movable in relation to the housing and in relation to the piston plunger when setting a dose and delivering a dose. 
     A piston plunger driving means is also arranged in the device for driving the hollow piston plunger towards the proximal end. The piston drive means may comprise a hollow drive drum sleeve that is movably arranged within the hollow piston plunger. It may further be fixedly connected to the telescopic dose drum such that the hollow drive drum sleeve and the hollow piston plunger are coupleable to each other. In this context it is to be understood that the coupling may be of many designs providing the desired function. 
     Further, the device comprises a resilient spinning element having a longitudinally rod being movable arranged within the hollow drive drum sleeve, wherein the longitudinally rod and the hollow drive drum sleeve are releasably coupleable to each other; such that after a dose is set, axial movement of the resilient spinning element towards the proximal end forces the longitudinally rod and the hollow drive drum sleeve to couple together and thereby the hollow drive drum sleeve and the hollow piston plunger also to couple together whereby the hollow piston plunger and the telescopic dose drum are displaced towards the proximal end for delivering the set dose, and such that after a set dose is delivered, axial movement of the resilient spinning element towards the distal end forces the longitudinally rod and the hollow drive drum sleeve to decouple and thereby the hollow drive drum sleeve and the hollow piston plunger also to decouple for setting a new dose. 
     According to preferable feature of the invention, the device further comprises a stop body being connected to the hollow piston plunger such that said stop member is rotatable but not slidable in relation to said hollow piston plunger, and being also connected to the telescopic dose drum such that said stop member is slidable but not rotatable in relation to said telescopic dose. With this solution it is not possible to set a dose that is larger than the remaining quantity in the medicament container. In this manner, the user is alerted that the dose that is to be delivered is smaller than the prescribed dose. Preferably also the quantity of the last dose is indicated to the user such that he or she may have a complementary dose delivery with the missing quantity when the medicament container has been replaced with a new or that the user takes another medicament delivery device. 
     According to one preferable solution, said stop body is configured to interact with a stop member on said telescopic dose drum when the set dose equals the remaining dose in the medicament container such that rotation of the telescopic dose drum is inhibited. In that context, said stop body is a generally ring-shaped body comprising at least one protrusion, rib or ledge on its outer surface and the telescopic dose drum comprises a first, distal, part and a second, proximal, part being slidably arranged relative to each other wherein said second, proximal, part is a tube shaped body comprising at least one longitudinally extending groove on in its inner surface and wherein said stop member is an end surface of said at least one groove. With this design a purely mechanical stop mechanism is obtained. Also, when a ring-shaped member is used, which is rotatable, a radial support for the piston plunger is also obtained, thereby minimizing the play between components and still minimizing friction between them. 
     Further a dose setting knob may be arranged, the dose setting knob configured to be grasped by a user for setting a dose when being rotated in a first direction. The dose setting knob may preferably be arranged at a distal area of the device, for easy access. 
     Further, the dose setting knob may preferably be a separate component connected with the first part of the dose drum at its distal end. As an alternative, the dose setting knob may be integral with the first part, whereby the first part of the telescopic dose drum is configured to rotationally move distally in the first direction relative to the housing during dose setting by the dose setting knob. 
     As a further alternative, the dose setting knob may be a separate component connected with the drive drum sleeve at its distal end. As another alternative, the dose setting knob is integral with the drive drum sleeve, whereby the drive drum sleeve is configured to rotationally move distally in the first direction relative to the housing during dose setting by the dose setting knob. 
     Furthermore, the device may comprise an unidirectional means for preventing movement of the piston plunger in the distal direction during setting a dose. 
     The medicament delivery device may be an injection device, preferably a pen injector. 
     Other aspects, features, and advantages will be apparent from the summary above, as well as from the description that follows, including the figures and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures below disclose an embodiment of the invention for illustrational purposes only. In particular, the disclosure within the figures is not meant to limit the range of protection of the invention. The embodiment shown may be modified in many ways within the scope of the claims. 
         FIG. 1  shows a perspective view of a medicament delivery device according to a preferred embodiment of the invention, shown in the initial state; 
         FIG. 2  shows a perspective view of a medicament delivery device according to the preferred embodiment of  FIG. 1 , shown in the state when a dose is set; 
         FIG. 3  shows a perspective view of a medicament delivery device according to the preferred embodiment of  FIG. 1 , shown after a set dose has been delivered; 
         FIG. 4  shows a perspective view of a medicament delivery device according to the preferred embodiment of  FIG. 1 , shown in a state having all medicament delivered; 
         FIG. 5  shows an exploded view of the medicament delivery device according to the preferred embodiment of  FIG. 1 ; 
         FIG. 6  shows a partly exploded view of the medicament delivery device according to  FIG. 1 ; 
         FIG. 7  shows another partly exploded view of the medicament delivery device according to  FIG. 1 ; 
         FIG. 8  shows a cross-sectional view of the medicament delivery device according to  FIG. 1 , shown in the initial state; 
         FIG. 9  shows a detailed cross-sectional view taken from marked area IX of  FIG. 8 ; 
         FIG. 10  shows a detailed cross-sectional view taken from the marked area X of  FIG. 9 ; and 
         FIG. 11  shows a detailed cross-sectional view taken from the marked area XI of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Mechanical Structure of an Embodiment 
       FIG. 1  shows a perspective view of a medicament delivery device according to a preferred embodiment of the invention. The medicament delivery device has a proximal end and a distal end and comprises a housing  10  having a proximal part or end  11  and a distal part or end  12 . In the assembled state of the medicament delivery device, the housing  10  forms part of the outer surface or appearance of the medicament delivery device. It is however to be understood that the housing may be designed in many other ways. 
     The medicament delivery device further comprises a medicament container holder  80  which accommodates a medicament container. The medicament container holder  80  also forms part of the outer surface or appearance of the medicament delivery device. The proximal part of the container holder  80  is further arranged with a neck  82  at its proximal end for attaching a per se known and conventional injection needle (not shown). It is however to be understood that other types of connection members, such as bayonet fitting luer-lock fittings and the like may be arranged. Also, the medicament container may have an injection needle integrated in its body whereby the neck portion  82  may be omitted. 
     A cap (not shown) may be provided for releasably covering the proximal end of the device, and thereby the proximal end of the medicament container holder  80 , when not in use. 
     The medicament container holder  80  of the medicament delivery device comprises a window  81  that allows the user to view the progress of medicament delivery, i.e. whether the medicament delivery device is still in its initial stage with the medicament not yet being injected, or whether the medicament container is already emptied. Through window  81 , the user can see the medicament container accommodated at least in the medicament container holder  80  (the distal part of the medicament container may reach into the proximal part of the housing  10 ). In a preferred embodiment, two such windows are provided located at opposite sides of the medicament container holder  80 . 
     Furthermore, at the proximal end  12  of the housing  10 , a further window  13  is provided that is used to indicate a set dose to a user, as described in more detail below. At the proximal end  12  of housing  10 , a dose setting knob  41   a  for dose setting projects distally. 
       FIG. 1  shows the medicament delivery device in the initial state. When the user grasps the dose setting knob  41   a  and rotates it in a first direction, for example in clockwise direction, the dose setting knob  41   a  and other components move distally, as will be explained in detail below, in order to set a dose.  FIG. 2  shows a perspective view of the medicament delivery device in such state, i.e. when a dose is set. 
       FIG. 3  shows a perspective view of the medicament delivery device after a set dose has been delivered. As can be seen, the dose setting knob  41   a  and the components linked therewith were moved proximally and the dose setting knob  41   a  is again in its initial position. However, as can be seen at window  81 , the piston plunger  20  of the medicament delivery device has been displaced in proximal direction and a stopper  29  within the medicament container can now be seen through the window(s)  81 . 
       FIG. 4  then shows a perspective view of the medicament delivery device in a state having all medicament, i.e. several individual doses delivered. The stopper  29  is now located at the proximal end of the medicament container  85 , and part of the piston plunger  20  with its threaded surface  21  can be seen through windows  81 . 
     The medicament container holder  80  is arranged with attachment means for connecting or attaching it to the proximal housing part  11 . In the embodiment shown the attachment means comprise a protrusion  83  (see  FIG. 5 ) fitting into a corresponding recess  14 . It is however to be understood that other attachment members may be utilized, such as bayonet fittings, threads, or the like for attaching the medicament container holder  80  with the housing  10 . 
     An elongated piston plunger  20  (see  FIGS. 5 to 7 ) is arranged inside the housing  10  and has a longitudinal axis generally corresponding with the longitudinal direction of the medicament delivery device. The piston plunger  20  is arranged with threads  21  ( FIG. 6 ) on at least part of its outer surface. In the preferred embodiment shown in the drawings, a proximal part of the piston plunger  20  comprises a threaded structure  21 . On its outer surface, the piston plunger  20  comprises at least one longitudinal groove  25  ( FIG. 6 ) (in the shown embodiment, two such grooves  25  are provided). The proximal end of the piston plunger  20  is arranged with a washer or spinner  28 , ( FIG. 5 ) adapted to abut the stopper  29 . The stopper  29  is intended to be movably received inside the medicament container  85 . 
     The piston plunger  20  fits into an insert  50  arranged with a central passage  51 , ( FIG. 7 ) the center of which generally coincides with the longitudinal axis of the medicament delivery device. The central passage  51  of the thread insert is arranged with threads  52  of complementary design as the threads  21  of the piston plunger  20 . The outer surface of the insert  50  comprises at least one protrusion  53  or the like, fitting into corresponding recesses  15  ( FIG. 5 ) on the inner surface of the housing  10 , whereby the insert  50  is locked to the proximal housing part  10 . As shown in  FIG. 5 , recess  15  in the housing may be formed as a through hole. 
     The insert  50  further comprises a central bore  54  at the distal side of the thread insert  50 . The diameter of the central bore  54  is larger than the diameter of the central passage  51  so that a stepped configuration is provided. The inner circumferential surface of the central bore  54  is arranged with a circumferentially extending ratchet  55  arranged with saw-tooth shaped teeth. 
     The ratchet  55  cooperates with a ring-shaped back rotating blocking element  60  ( FIG. 7 ) which is arranged with two oppositely positioned arms  62 , extending on the outer circumferential surface  61  generally in the circumferential direction of the blocking element  60 . Although two such arms  62  are shown in  FIGS. 5 and 7 , a single arm may as well suffice, or more than two arms may be provided, depending on the size of the blocking member  60 . The one or more arms  62  are flexible in the generally radial direction. On the outwardly directed surfaces of the arm(s)  62 , a ledge  63  is arranged. Each ledge  63  has a shape complementary to the ratchet  55  of the thread insert  50 . The back rotating blocking element  60  is further arranged with a central passage  65  ( FIG. 7 ) through which the piston plunger  20  extends. The central passage  65  is arranged with radially inwardly directed protrusions or ribs  66 , which protrusions  66  fit into the elongated grooves  25  on the outer surface of the piston plunger  20 . This structure provides a rotational lock of the piston plunger  20  but allows a movement of the piston plunger  20  in the longitudinal direction. 
     The piston plunger  20  is further arranged with a plurality of longitudinal splines or ribs  23  provided on the inner circumferential surface  22  of the hollow piston plunger  20  ( FIG. 7 ). A drive drum sleeve  30  ( FIG. 5 ) of generally tubular shape is arranged radially inside the piston plunger  20 . The drive drum sleeve  30  is provided with a distal end wall  31  transversal to the longitudinal axis of the drive drum sleeve  30 . The distal end wall  31  has central opening and the drive drum sleeve is hollow in order to receive a resilient spinning element  70  therein, as will be described below. The proximal end of the drive drum sleeve  30  comprises one or more, preferably two, flexible arms  33  extending in the proximal direction. The arms  33  are flexible in that their proximal ends are radially deflectable upon application of a radial force thereon, as will be describe below. The outer surface of each flexible arm  33  comprises a radially projecting piston plunger engagement surface  34  ( FIG. 8 ) for selectively engaging with the longitudinal splines  23  on the inner surface  22  of the piston plunger  25 . The shape of the surface  34  may generally correspond to the shape of the circumferentially arranged ribs  23  on the piston plunger  20 . The inner surface of each flexible arm  33  comprises a radially engagement protrusion  37  ( FIG. 8 ) for selective engagement with the resilient spinning element  70  located within the hollow drive drum sleeve  30 . 
     The distal end wall  31  forms a coupling element by means of two proximally extending locking arms  35  ( FIG. 5 ). The locking arms  35  comprise at their respective outer surface a locking structure  36  for locking the drive drum sleeve  30  to the inner surface of a dose drum  40 . 
     Outside the piston plunger  20  as seen in a radial direction, a telescopic dose (setting) drum  40  is arranged ( FIGS. 5 and 6 ). The dose drum  40  has a generally tubular shape and is positioned coaxial with the piston plunger  20  as well as the housing  10 . The dose drum  40  comprises a first, distal, part  41  and a second, proximal, part  42  being slidably arranged relative to each other. The distal part  41  is located coaxially radially outside of the proximal part  42  of the dose drum  40 . 
     The distal part  41  comprises a helically or spirally extending groove  49  ( FIG. 6 ) on its outer side surface  41 . The groove  49  extends all the way from the proximal end to the distal end of the distal part  41  of the dose drum  40 . The groove  49  is intended to cooperate with at least one protrusion or spirally extending ledge segment  16  ( FIG. 5 ) arranged on the inner surface of the housing  10  such that the dose drum  40  is rotationally connected to the housing  10 , whereby mutual rotation causes movement in the longitudinal direction of the parts. The distal end area of the first part  41  of the dose drum  40  is further arranged with a locking structure that engages with the locking structure  36  of the drive drum sleeve  30  when the drive drum sleeve  30  is moved into the piston plunger  20  during assembly of the medicament delivery device. 
     At the distal end of the first part  41  the dose setting knob  41   a  is arranged ( FIG. 6 ). The dose setting knob  41   a  comprises a proximally directed generally tubular part having a diameter somewhat larger than the outer surface of the first part  41  of the dose drum  40 . The outermost diameter of the dose setting knob  41   a  is preferably flush with the outer diameter of housing  10 . The first part  41  of the telescopic dose drum  40  is thus configured to rotationally move distally in the first direction relative to the housing  10  during dose setting by the dose setting knob  41   a.    
     The inner circumferential surface  44  of the second part  42  of the telescopic dose drum  40  is threadedly connected to the threaded outer circumferential surface  21  of the piston plunger  20 . In particular, the proximal end of the second part  42  comprises a threaded structure  45  ( FIG. 6 ). The threaded connection between the first part  41  of the telescopic dose drum  40  and the inner circumferential surface of the housing  10  has a pitch different to the pitch of the threaded connection of the inner circumferential surface  44  of the second part  42  of the telescopic dose drum  40  and the threaded outer circumferential surface  21  of the piston plunger  20 . 
     According to the invention the device further comprises a stop body  26  being connected to the hollow piston plunger  20  such that said stop member is rotatable but not slidable in relation to said hollow piston plunger  20 , and being also connected to the telescopic dose drum such that said stop member is slidable but not rotatable in relation to said telescopic dose. Said stop body  26  is configured to interact with a stop member  97  on said telescopic dose drum  40  when the set dose equals the remaining dose in the medicament container such that rotation of the telescopic dose drum  40  is inhibited. The stop body  26  is a generally ring-shaped body ( FIG. 6 ) comprising at least one protrusion, rib or ledge  94  on its outer surface. Further, the second, proximal, part  42 , which is a tube shaped body, comprises at least one longitudinally extending groove  96  on in its inner surface and wherein said stop member  97  is an end surface of said at least one groove. The stop body is arranged to fit in a circumferential groove  90  on the piston plunger, where the groove is arranged at the distal end area of the threads  21  on the outer surface of the piston plunger  20 . In order to fit the ring-shaped body in the groove of the piston plunger, the stop body is arranged with a slit  92  and being made of an elastic material, thereby enabling the widening of the gap of the slit  92  such that the body  26  may be pushed onto the piston plunger. When in place, the body  26  is rotatable in relation to the piston plunger, but locked in the longitudinal direction. The rib(s)  94  of the stop body  26  is/are intended to fit into the longitudinally extending grooves  96  ( FIG. 6 ) arranged on the inner circumferential surface  44  of the second part  42 , whereby the stop body  26  is rotatably locked to the second part  42 , but slidable in the longitudinal direction relative the second part  42 . 
     The resilient spinning element  70  comprises a longitudinal rod  71  and a distal push button  72 . The push button is intended to act as a contact surface for a finger of a user during drug delivery, as will be described. As described above, the longitudinal rod  71  of the resilient spinning element  70  is accommodated within the hollow drive drum sleeve  30 . At its proximal end, the longitudinal rod  71  comprises an engagement structure comprising a circumferential groove  73  ( FIG. 9 ). Adjacent the groove and in the proximal direction is a protrusion  74  and in the distal direction an inclined surface  77 . The size of the groove  73  and the location on the longitudinal rod  71  is such that the radially inwardly directed protrusion  37  on the flexible arms  33  of the drive drum sleeve  30  is initially received in the groove  73 . In such initial stage, the flexible arms  33  are not deflected radially outwards but are in a tension-free state. 
     The axial length of the resilient spinning element  70  in comparison to the drive drum sleeve  30  is such that in the initial state of the medicament delivery device, i.e. with the engagement protrusion  37  being received in the groove  73 , the proximal surface of the push button  72  is spaced from the distal surface of the coupling element  31  by a gap  76  (see, e.g.,  FIG. 10 ). This gap  76  is maintained when a dose is set by a user and the first part  41  of the dose drum  40 , the drive drum sleeve  30  and the resilient spinning element  70  are moved distally. However, as soon as the push button  72  is pushed towards the proximal direction, the push button  72  first bridges the gap  76  thereby moving the longitudinal rod  71  in proximal direction relative to the drive drum sleeve  30 . Due to such relative displacement, the inclined surface  77  is moved in contact with, and is pressed against, the engagement protrusion  37  on the flexible arms  33 , thus deflecting the arms  33  outwardly and into engagement with the longitudinal splines on the inner surface  22  of the piston plunger  20 . 
     Description of the Function and Operation of the Embodiment 
     Setting Operation for a Dose to be Delivered 
       FIG. 8  shows a cross-sectional view of the medicament delivery device in the initial state. 
     In order for a dose to be delivered, the device must be operated to set a dose. In order to set a dose to be delivered the user grips the housing  10  and the distally arranged dose setting knob  41   a  and turns them in relation to each other, where the dose setting knob  41   a  is turned in the clockwise direction, for example. The turning of the dose setting knob  41   a  will cause the first part  41  of the dose drum  40  to be rotated. The connection between the helical groove  49  of the dose drum  40  and the spiral ledge segment of the housing  10 , the rotation will cause the first part  41  of the dose drum  40  to move in the distal direction in relation to the housing  10 . Inside the dose setting drum  40  the drive drum sleeve  30  will also rotate because of the rotational lock both at the distal end  31  of the drive drum sleeve  30  with the dose drum  40 . Thus the drive drum sleeve  30  is rotationally connected to the dose drum  40 . 
     The longitudinal ribs  48  on the inner surface of the first part  41  of the dose drum  40  are in contact with the longitudinal grooves on the outer surface of the second part  42  of the dose drum  40 . Thus, the first part can slide relative to the second part. Furthermore, the second part  42  is also rotated and due to the threads  45  engaging into the threaded surface of the piston plunger  20 , the second part  42  also moves distally, albeit at a lower speed than the first part  41  due to the different pitches. Rotation of the second part  42  also causes a certain turning force on the piston plunger  20 , which also urges the back rotating blocking element  60  to turn due to the rotational lock between the blocking element  60  and the piston plunger  20  because of the protrusions  66  of the back rotating blocking element  60  fitting into the longitudinal grooves  25  of the piston plunger  24 . However, the arms  62  of the back rotating blocking element  60  are directed such and cooperating such with the ratchet  55  of the thread insert  50  that any rotation of the back rotating blocking element  60  is prevented. Thus the piston plunger  20  is prevented from rotating. During rotation, preferably indicia (not shown) on the dose drum  40  are shown through the window or opening  13  at the distal end  12  of the housing  10 . The patient thus rotates the dose setting knob  41   a  until the prescribed dose quantity is displayed. 
     If the user by mistake has set a too large dose, he/she simply turns the dose setting knob  41   a  in the opposite direction, whereby both the dose drum  40  and the drive drum sleeve  30  are turned in the opposite direction until the correct dose has been reached. 
       FIG. 10  shows a cross-sectional view of the medicament delivery device in the state when a dose is set. In particular, it can be seen that the gap  76  still exists. 
     Delivery Operation of a Pre-Set Dose of Medicament 
     In order to deliver a dose of medicament, the user presses the proximal end of the device against a dose delivery site, and in particular an injection site when the medicament delivery member is an injection needle. The next step is to press on the activator button  72  at the distal end of the device. This causes the gap  76  to close due to the force applied by the user and the button  72  contacts the distal coupling member  31  of the drive drum sleeve  30 . 
     The force on the activator button  72  will first bring the drive drum sleeve  30  into engagement with the inner surface of the piston plunger  20 , as already described above. Secondly, once the gap  76  has been bridged, the force on the activator button  72  urges the dose activator knob  41   a  in the proximal direction. This proximal force will be transferred to the dose drum  40  and due to the threaded connection with the housing  10 , the dose setting drum  40  will rotate, now in the anti-clockwise direction, and move in the proximal direction. Because of the rotational lock between the dose drum  40  and the drive drum sleeve  30 , the latter will also rotate. Due to the radial flexing of the arms  33  of the drive drum sleeve  30 , the radially outwardly directed surface  34  of the drive drum sleeve  30  firmly engage the splines  23  of the piston plunger  20 . 
     Thus when now the dose drum  40  and the drive drum sleeve  30  rotate, the latter will urge the piston plunger  20  to rotate as well. This rotation in the anti-clockwise direction will be allowed by the back rotating blocking element  60  due to the design of its arms  62  in contact with the ratchet  55  of the thread insert  50 . The piston plunger  20  will thus rotate together with the back rotating blocking element  60 , and the arms  62  of the back rotating blocking element  60  sliding over the ratchet  55  of the thread insert  50  will provide audible and tactile information. Further the rotation of the piston plunger  20  will cause it to be moved in the proximal direction due to the threaded connection with the thread insert  50 , whereby the movement of the piston plunger  20  will urge the stopper  29  in the proximal direction, thereby expelling a dose of medicament through the dose delivery member. The dose has been delivered when the dose drum  40  has moved back to its initial position, which could be limited by some sort of blocking member (not shown) preventing further movement or rotation of the dose drum. 
     The device may now be removed from the dose delivery site, and the medicament delivery member discarded. If the medicament container  85  still contains a large enough dose to be delivered, the above steps may be repeated from the step “Setting operation for a dose to be delivered”. 
     If the medicament container however contains a dose that is smaller than the prescribed dose, the present invention prevents setting a dose that is larger than the remaining dose. When the dose setting knob  41   a  is rotated as described above the second part  42  of the dose setting sleeve is also rotated in relation to the piston plunger  20  and due to the threaded connection between the second part  42  and the piston plunger  20 , the second part  42  is moved in the distal direction. The ribs  94  of the stop body  26  will slide in the grooves  96  of the second part  42  during rotation, but when the maximum dose is set, the ridges  94  will come in contact with the end surface of the groove  96  ( FIG. 11 ), which is the stop member  97 , thereby preventing any further setting of a dose. Thus, the stop body  26  prevents any further turning of the dose setting knob  41   a , thereby preventing setting a dose that is larger than the remaining dose. 
     Preferably the device is arranged with some indicia or other information means that indicates the quantity of the last, inferior, dose so that the user may take a subsequent complementary dose with the missing volume. In this manner, also all medicament is used in the medicament container, whereby no medicament will go to waste because the remaining dose is smaller than the prescribed. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. 
     Furthermore, in the claims the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfill the functions of several features recited in the claims. The terms “essentially”, “about”, “approximately” and the like in connection with an attribute or a value particularly also define exactly the attribute or exactly the value, respectively. Any reference signs in the claims should not be construed as limiting the scope.