Patent Publication Number: US-10314980-B2

Title: Dispensing mechanism for a medical device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/EP2014/055129, filed Mar. 14, 2014, which claims the benefit of Great Britain application number 1304575.2, filed Mar. 14, 2013 and U.S. provisional application No. 61/782,225, filed Mar. 14, 2013, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     The present invention relates to a dispensing mechanism for administering a dosage of a medicament. The present invention also relates to a medical device comprising a dispensing mechanism, an injection device comprising a dispensing mechanism and an inhaler comprising a dispensing mechanism. 
     Medical devices for administering medicament are known, for example liquid solutions or powders can be delivered to a user or patient using injection devices or powder inhalers respectively. 
     One such medical device for administering a liquid solution is an injection device comprising a dispensing mechanism in which the dosage to be administered may be set by a dosage button moveable by a user or patient. A subsequent further movement of the dosage button, typically in the proximal direction of the device, i.e. in a direction towards an injection site of the device on the patient&#39;s skin, serves to inject the medicament using a ram to displace a plunger in a vial or cartridge of liquid medicament. A needle is typically attached to the cartridge in order to allow a subcutaneous delivery of the medicament. The dispensing mechanism ensures that a controlled and accurate dose may be administered. 
     However, such drive mechanisms often include several interacting component parts and thus packaging the components within a medical device that is optimal in size to carry and simplicity to use can be difficult. In addition, it cannot always be readily determined by a user of the device whether the correct dosage has been fully administered. 
     The present invention aims to alleviate at least to a certain extent at least one of the problems of the prior art. 
     According to a first aspect of the invention, there is provided a dispensing mechanism for administering a dosage of a medicament, the mechanism comprising: a dosage setting means, element, part or parts for setting a dose of medicament to be administered; expelling means, element part of parts for expelling a medicament from a medicament container; a coupling means, element, part of parts operatively coupled with the dosage setting means and the expelling means, wherein the coupling means is arranged to convert displacement of the dosage setting means into a displacement of the expelling means in a first direction, wherein the expelling means or coupling means includes a ratchet means, element, part or parts, and wherein the mechanism includes a first and a second independently moveable resisting pawl means or pawls facing a common side of the ratchet means, the first and the second resisting pawl means being configured to engage with the ratchet means and resist displacement of the expelling means in a second direction opposite to said first direction. 
     Advantageously, such a mechanism provides a compact arrangement and control of the expelling means. The resisting pawl means advantageously prevents movement of the expelling means during dose setting. 
     The dosage setting means may comprise a push button or other component which can be manually manipulated by a user. 
     Optionally, the ratchet means comprises a first and a second set of teeth, the first set of teeth being arranged to engage with the first resisting pawl means and the second set of teeth being arranged to engage with the second resisting pawl means. 
     The first and second sets of teeth are optionally each arranged in rows. The rows are optionally parallel and may be spaced from one another. The teeth preferably comprise peaks and valleys. The ridges of the peaks of each set of teeth are aligned transverse to the longitudinal axis of the expelling means. The teeth are preferably equally spaced in each row of teeth. The heights of the teeth are preferably equal. 
     Each tooth preferably comprises a front planar face and a rear planar face. The front planar face is preferably arranged proximally, i.e. nearer the point of contact with a patient&#39;s skin, in use, in the mechanism. The front face is preferably inclined at a smaller angle to a plane extending parallel to a side of the body of the mechanism or device and the rear face of each tooth being inclined at a relatively larger angle to said plane. 
     The engaging faces are preferably the faces of the teeth against which the pawls may act to resist movement. The engaging faces are preferably the rear faces of the teeth in each row of teeth. 
     The pawls may be orientated with their free, ratchet-engaging ends angled towards a first, proximal end of the mechanism. 
     Optionally, the dosage setting means is linearly displaceable in a direction substantially parallel to the longitudinal axis of the expelling means. 
     Optionally, the dosage setting means is rotationally displaceable about an axis substantially parallel to the longitudinal axis of the expelling means. 
     Optionally, the dosage setting means is displaceable both axially and rotationally about an axis parallel to the longitudinal axis of the expelling means, for example where a screw thread arrangement is provided. 
     Optionally, the first and/or second resisting pawl means comprise(s) or are formed with a part of a body of the mechanism. 
     Optionally, the mechanism may be formed of a plastics material, a metallic material or a combination of both. 
     Optionally, the teeth pitch in each of the first set of teeth and the second set of teeth is substantially equal. 
     Optionally, engaging faces of the second set of teeth are arranged offset from engaging faces of the first set of teeth on the ratchet means. Preferably, the offset is in the longitudinal direction of the expelling means. 
     Optionally, the engaging faces of the teeth in the first set of teeth are offset a distance of half the tooth pitch, i.e. half the distance between adjacent engaging faces from the teeth of the second set of teeth. Preferably, the offset is in the longitudinal direction of the expelling means. 
     Optionally, the resisting pawls are offset in the longitudinal direction of the expelling means. Optionally, the ratchet comprises a single set of teeth engageable with the resisting pawls. This allows for an alternative arrangement in order to achieve fine dosages. Optionally, the offset of the resisting pawls may be, for example, 0.5 or 1.5 times the pitch or distance between adjacent teeth in the ratchet. 
     Advantageously, by arranging the teeth or pawls so that only one pawl engages with an engaging face of one of the two sets of teeth at any one time, finer doses can be dispensed whilst the component features remain the same size. 
     Optionally, the expelling means comprises a longitudinal member. 
     Optionally, the expelling means is formed with ribs, or protrusions to be received in or be guided in corresponding recesses or channels. This ensures smooth motion of the expelling means. 
     Optionally, the first and second resisting pawl means are formed on opposing parts of a body of the mechanism. This reduces the number of components and can provide strength to the resisting pawls. 
     Optionally, the body may be formed of two half-shells. 
     A dispensing mechanism is also provided, wherein the first and the second resisting pawl means are aligned in a substantially common plane. Alternatively, the first and the second resisting pawls means could be aligned offset with the teeth in the ratchet being in alignment. 
     Optionally, the first resisting pawl means is aligned adjacent the second resisting pawl means. 
     Optionally, the coupling means comprises a drive means or driver comprising a pair of drive pawls engageable in said ratchet means for displacing said expelling means. 
     Optionally, the drive pawls are arranged in adjacent alignment or may be offset corresponding to the offset of the resisting pawls. 
     Optionally, the coupling includes a guide slot in which a follower on the drive means is received and configured such that the drive means is moved as a result of movement of the dosage setting means. Optionally, the driver is caused to rotate about a pivot in order to engage the drive pawls with the teeth in the ratchet and produce motion of the expelling means. 
     Alternative coupling means may include gears or thread arrangements in order to produce a displacement of the expelling means upon movement of the dosage means. 
     Optionally, the expelling means comprises a ram means. 
     According to a second aspect of the invention, there is provided a dispensing mechanism for administering a dosage of a medicament, the mechanism comprising: a body; and dosage setting means, element, part of parts for setting the dosage of a medicament to be administered, the dosage setting means being moveable in a first direction for setting the dose and in a second direction for administering the dose, wherein the mechanism further comprises an indication element, the indication element being arranged to be displaced by a predetermined movement of the dosage setting means; and wherein the indication element is arranged such that the indication element remains unmoved relative to said body of the mechanism during at least part of said movement of the dosage setting means. 
     In this way, the indication element can provide a static indication to a user for at least part of the motion of the dosage setting means. This can serve to facilitate operation of the mechanism or device by a user. 
     Optionally, the indication element is movable within a guide channel. Advantageously, this maintains the orientation of the indication element. 
     Optionally, the indication element is slidingly supported in or on the body. 
     Optionally, the dosage setting means is movable in an axial direction substantially parallel to the longitudinal axis of the body. 
     Optionally, the indication element is formed as a planar element, preferably as a generally rectangular plate or element. 
     Optionally, the dosage setting means is rotatable about the longitudinal axis of the body. 
     Optionally, the dosage setting means is operative coupled to a first and a second engagement means, elements or parts, the first engagement means and the second engagement means being engageable with the indication element such that upon engagement, movement of the dosage setting means causes displacement of the indication element. 
     The engagement means are preferably formed to engage with the indication element in order to move it with corresponding movement of the dosage setting means. 
     Optionally, the engagement elements are arranged spaced from one another at a distance greater than a length of the indication element. This then provides a degree of lost motion of the indication element relative to the dosage setting element. 
     Optionally, resisting means, elements or parts are provided, the resisting means being arranged to resist movement of the indication element relative to movement of the dosage setting means. This prevents movement of the indication element until a predetermined movement of the dosage setting means has been made. 
     Optionally, the resisting means comprises a protrusion receivable in a corresponding recess. The protrusion may be provided on the body or dosage setting element or on the indication element or vice versa, for example. This provides a degree of mechanical resistance without additional parts. 
     Optionally, the resisting means comprises a protrusion receivable in a corresponding recess. 
     Optionally, the mechanism includes an aperture through which at least a portion of the indication element is exposed, in use, to a user. 
     Optionally, the indication element comprises tactile and/or visual indications. This may include Braille or other types of tactile indications and/or visual indications such as lights or printed numbers. The indications may indicate the state of the mechanism or device, e.g. whether a dose is ready to be administered or if a dose needs to be set. 
     Optionally, the indication element is moved directly by the dosage setting means. The indication element may be in direct contact with the dosage setting means. 
     Optionally, the indication element is moved indirectly by the dosage setting means. 
     According to a third aspect of the invention, there is provided a dispensing mechanism for administering a dosage of a medicament, the mechanism comprising: a body; dosage setting means, element, part or parts for setting the dosage of a medicament to be administered, the dosage setting means being moveable in a first direction for setting the dose and in a second direction for administering the dose; and an indication element, the indication element being arranged to be displaced by a predetermined movement of the dosage setting means; and wherein the mechanism further includes conversion means, element, part of parts configured, during displacement of the indication element, to convert a movement of the dosage setting means of a first magnitude into a movement of the indication element of a second magnitude, and wherein said first magnitude of movement is different to said second magnitude of movement. 
     In this way, the degree of movement of the indication element can be configured to be different in magnitude to that of the dosage setting means. 
     Optionally, the first magnitude of movement is greater than the second magnitude of movement. In this way, a small movement of the dosage setting means can cause a larger movement of the indication element. 
     Optionally, the first magnitude of movement is smaller than the second magnitude of movement. As such, the indication element can be arranged to move a shorter distance that the movement of the dosage setting means. 
     Optionally, the conversion means is configured to move the indication element during all movement of the dosage setting means. The conversion means may be in constant contact with the dosage setting means or in constantly coupled thereto, for example through an intermediate component. 
     Optionally, the indication element remains unmoved relative to the body of the mechanism during at least part of said movement of the dosage setting means. 
     Optionally, the indication element is movable within a guide channel. 
     Optionally, the indication element is slidingly supported in or on the body. 
     Optionally, the dosage setting means is movable in an axial direction substantially parallel to the longitudinal axis of the body. 
     Optionally, the dosage setting means is rotatable about the longitudinal axis of the body. 
     Optionally, the conversion means comprises a first and a second engagement means operatively coupled to the dosage setting means, the first engagement means and the second engagement means being engageable with the indication element such that upon engagement, movement of the dosage setting means causes displacement of the indication element. 
     Optionally, the engagement elements are arranged spaced from one another at a distance greater than a length of the indication element. 
     Optionally, the conversion means comprises a lever. 
     Optionally, the lever acts about a fulcrum operatively coupled to the dosage setting means. The relative magnitudes of movement of the dosage setting means and indication element may be configured by the relative lengths of the lever either side of the fulcrum. 
     Optionally, the lever is reliantly flexible. In this way dimensional tolerances may be accounted for as the lever may flex if movement of the dosage setting means is greater that the space in which the lever is located. 
     Optionally, the lever is pivotally attached to said body. 
     Optionally, the lever is formed integrally with said body. This can serve to reduce manufacturing costs and reduce the number of parts in the mechanism. The lever could alternatively be any part of the body, indicator or dose setting means, for example. 
     Optionally, resisting means are provided, the resisting means being arranged to resist movement of the indication element relative to movement of the dosage setting means. 
     Optionally, the resisting means comprises a protrusion receivable in a corresponding recess. 
     Optionally, the mechanism includes an aperture through which at least a portion of the indication element is exposed, in use, to a user. 
     Optionally, the indication element comprises tactile and/or visual indications. 
     Optionally, the indication element is moved directly by the dosage setting means. 
     Optionally, the indication element is moved indirectly by the dosage setting means. 
     According to a fourth aspect of the invention, there is provided a dispensing mechanism for administering a dosage of a medicament, the mechanism comprising: a dosage setting means, element, part or parts for setting a dose of medicament to be administered; expelling means, element, part of parts for expelling a medicament from a medicament container; a coupling means, element, part or parts operatively coupled with the dosage setting means and the expelling means, wherein the coupling means is arranged to convert displacement of the dosage setting means into a displacement of the expelling means in a first direction, wherein the coupling means includes a ratchet means, element or part or parts comprises a first and a second ratchet wheels, and wherein the mechanism includes a first and a second independently moveable resisting pawl means facing the ratchet means, the first and the second resisting pawl means being configured to engage with the first and second ratchet wheels respectively and resist displacement of the expelling means in a second direction opposite to said first direction. 
     Advantageously, such a mechanism provides a compact arrangement and control of the expelling means. The resisting pawl means advantageously prevents movement of the expelling means during dose setting. 
     Optionally, the first ratchet wheel comprises a first set of teeth and the second ratchet wheel comprises a second set of teeth, the first set of teeth being arranged to engage with the first resisting pawl means and the second set of teeth being arranged to engage with the second resisting pawl means. 
     Optionally, engaging faces of the second set of teeth are arranged rotationally offset from engaging faces of the first set of teeth on the ratchet means. Each of the first and second ratchet wheels may have teeth provided around their entire circumference. The first and second ratchet wheels preferably share a common rotational axis. 
     Optionally, the dosage setting means is linearly displaceable in a direction substantially parallel to the longitudinal axis of the expelling means. 
     Optionally, the dosage setting means is rotationally displaceable about an axis substantially parallel to the longitudinal axis of the expelling means. 
     Optionally, the first and/or second resisting pawl means comprise(s) a part of a body of the mechanism. 
     Optionally, the angular teeth pitch in each of the first set of teeth and the second set of teeth is substantially equal. 
     Optionally, the engaging faces of the teeth in the first set of teeth are offset by an angle of rotation of half the angle of rotation between adjacent engaging faces from the teeth of the second set of teeth. 
     Optionally, the expelling means comprises a longitudinal member. 
     Optionally, the first and second resisting pawl means are formed on opposing parts of a body of the mechanism. 
     Optionally, the first and the second resisting pawl means are aligned in a substantially common plane. 
     Optionally, the first resisting pawl means is aligned adjacent the second resisting pawl means. 
     Optionally, the coupling means comprises a drive means comprising a pair of drive pawls engageable in said ratchet means for rotation of said ratchet wheel. The drive pawls may be spaced from one another to align either side of the expelling means. 
     Optionally, the drive pawls are arranged in adjacent alignment. 
     Optionally, the coupling includes a guide slot in which a follower on the drive means is received and configured such that the drive means is moved as a result of movement of the dosage setting means. 
     Optionally, the ratchet means comprises a gear wheel engageable with a corresponding set of teeth on the expelling means. The gear wheel preferably shares a common axis of rotation with the ratchet wheels. The teeth on the expelling means are preferably formed as a rack of teeth. The rotation of the gear wheel preferably results in axial movement of the expelling means. 
     Optionally, the first and second ratchet wheels are arranged either side of said gear wheel. 
     Optionally, the diameter of the gear wheel is smaller than the diameter of each of the ratchet wheels. The ratchet wheels may be aligned either side of the expelling means. The gear wheel and ratchet wheel may be formed integrally as a single piece. 
     Optionally, the expelling means comprises a ram means. 
     Any one or more of the first to fourth aspects of the invention or any optional feature thereof may be combined. Advantages of the features are applicable to different aspects and embodiments of the invention. 
     According to a fifth aspect of the invention, there is provided a medical device comprising a dispensing mechanism according to any of the first to fourth aspects of the invention and any optional feature thereof. 
     Optionally, the medical device may comprise a medicament container such glass vial, cartridge or foil pack and/or a receiving part for such a medicament container. 
     According to a sixth aspect of the invention, there is provided an injection device comprising a dispensing mechanism according to any of the first to fourth aspects of the invention and any optional feature thereof. 
     According to a seventh aspect of the invention, there is provided an inhaler comprising a dispensing mechanism according to any of the first to fourth aspects of the invention and any optional feature thereof. 
    
    
     
       The present invention will now be described by way of an exemplary embodiment, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of a medical device with a dispensing mechanism comprising a dosage button in a depressed state; 
         FIG. 2  shows a perspective view of the medical device of  FIG. 1  with a dosage button in a withdrawn state; 
         FIG. 3  shows a first side perspective view of the medical device of  FIG. 1  with part of the outer body removed with the dosage button in a depressed state; 
         FIG. 4  shows a first side perspective view of the medical device of  FIG. 1  with part of the outer body removed with the dosage button in a withdrawn state; 
         FIG. 5  shows a first side perspective view of a drive pawl of the medical device of  FIG. 1 ; 
         FIG. 6  shows a second side perspective view of the medical device of  FIG. 1  with part of the outer body removed with the dosage button in a depressed state; 
         FIG. 7  shows a second side perspective view of the medical device of  FIG. 1  with part of the outer body removed with the dosage button in a withdrawn state; 
         FIG. 8  shows a second side perspective view of a drive pawl of the medical device of  FIG. 1 ; 
         FIG. 9  shows a perspective side view of the medical device of  FIG. 1  without a cartridge holder; 
         FIG. 10  shows a cutaway view through the body of the medical device as shown in  FIG. 9  showing a rear view of a ratchet arrangement; 
         FIG. 11  shows a cutaway view through the body of the medical device as shown in  FIG. 9 , with the ratchet removed and showing the underside of the drive pawl; 
         FIGS. 12 and 14  show cross-sections A-A and B-B respectively of the medical device as is marked in  FIG. 13  with the dosage button in a depressed state; 
         FIGS. 15 and 17  show cross-sections C-C and D-D respectively of the medical device as marked in  FIG. 16  with the dosage button in a withdrawn state; 
         FIG. 18 a    shows a side view of the ratchet of the medical device as shown in  FIG. 1 ; 
         FIG. 18 b    shows a detail view A as circled in the ratchet view shown in  FIG. 18   a;    
         FIG. 19 a    shows a plan view along the length of the ratchet as shown in  FIG. 18   a;    
         FIG. 19 b    shows a detail view B as circled in the ratchet view as shown in  FIG. 19   a;    
         FIG. 20  shows a perspective view of the ratchet as shown in  FIG. 18   a;    
         FIG. 21  shows a perspective side view of a medical device with an indicator window with a dosage button in a depressed state; 
         FIG. 22  shows a perspective side view of the medical device with an indicator window with the dosage button in a withdrawn state; 
         FIG. 23  shows a perspective view of the medical device shown in  FIG. 21  with part of the outer body removed; 
         FIG. 24  shows a side view of the medical device as shown in  FIG. 21  marking cross-section E-E; 
         FIG. 25  shows a cross-sectional view E-E of  FIG. 21  showing the dosage button in an initial depressed state; 
         FIG. 26  shows a cross-section view E-E of  FIG. 21  showing the dosage button in an initial retracted state; 
         FIG. 27  shows a cross-section view E-E of  FIG. 21  showing the dosage button in an intermediate retracted state; 
         FIG. 28  shows a cross-section view E-E of  FIG. 21  showing the dosage button in an fully retracted state; 
         FIG. 29  shows a medical device with an alternative dosage button in a depressed state; 
         FIG. 30  shows the medical device of  FIG. 29  with the dosage button in a rotated and retracted state; 
         FIG. 31  shows the medical device of  FIG. 29  with the dosage button in a rotated and depressed state; 
         FIG. 32  shows an external perspective view of a further medical device with the dosage button in a withdrawn state; 
         FIG. 33  shows a partial cross-section through the device as shown in  FIG. 32 ; 
         FIG. 34  shows an external perspective view of the device of  FIG. 32  with the dosage button on a depressed state; 
         FIG. 35  shows a partial cross-section through the device as shown in  FIG. 33 ; 
         FIGS. 36 to 39  show the medical device of  FIGS. 32 and 33  in partial stages of assembly; 
         FIG. 40  shows a view of a further medical device comprising an alternative dispensing mechanism with part of the body removed with a push button in a depressed state; 
         FIG. 41  shows a further view the medical device of  FIG. 40  with the push button in a retracted state; 
         FIG. 42  shows a view of the coupling means and expelling means of the dispensing mechanism shown in Figures and  41 ; and 
         FIG. 43  shows a view of a rotary ratchet of the expelling means of the dispensing mechanism of  FIG. 42 . 
     
    
    
       FIG. 1  shows a perspective view of a medical device including a dispensing mechanism generally indicated  1 . The medical device  1  comprises an elongate body  2  with a substantially square cross-section with rounded edges between adjacent sides. However, it is envisaged that the body  2  may be formed in any suitable shape, for example with a circular cross-section or with varying cross section along the length of the device  1 . 
     The size and the form of the body  2  may be designed to facilitate being held in a user or patient&#39;s hand. The surface may be provided with surface protrusions or knurling or any other such surface texture to facilitate gripping of the device  1 . 
     At a first, proximal end  3   a  of the body  2 , i.e. the end nearest an injection site of a user in use, a cartridge receptacle  4  is attached, for example by a bonded or clipped engagement, to the body  2 , for holding a medicament cartridge or carpule. The cartridge receptacle  4  is formed generally as a truncated cone and may be made transparent in order that a user may inspect the contents of the medicament cartridge to obtain a visual indication of the quantity of medicament remaining. The medicament cartridge may be filled with a liquid medicament, for example insulin. 
     A removable and disposable needle (not shown) may be attached to the cartridge receptacle  4  or to a threaded engagement  5  provided on the outer surface of a cylindrical part at the proximal end of the cartridge which, as shown in  FIG. 1 , extends through the end of the cartridge receptacle  4 . A typical needle comprises a rear needle part for puncturing a plastic stopper  6  provided at the proximal end of the medicament cartridge. The needle also comprises a forward needle part. In use, the forward needle part may be inserted subcutaneously into a patient so that medicament may be injected from the medicament cartridge into a patient. 
     At a second, distal end  3   b  of the body  2  of device  1 , i.e. the end, in use, furthest from an injection site of a user, a dosage setting means or element is provided in the form of a push button  7 . In the embodiment, the push button has a similar, generally square, cross-sectional shape to that of the body  2  of the device  1 . However, different shapes and arrangements of the dosage means are envisaged. The dosage means  7  is typically sized to be gripped between a finger and thumb of a user.  FIG. 1  shows the push button  7  in a depressed, i.e. pushed-in state relative to the body  2  of the device  1 . 
     The push button  7  may be pulled out away from the body  2  in a first distal direction in order to set a dose and pushed in towards the body  2  in a second proximal direction in order to administer a dose of medicament. 
     In  FIG. 2 , the push button is shown in a first, pulled-out state, with the device ready to deliver a dose. The push button  7  comprises a drive shaft  8  connecting the push button to a drive mechanism within the body of the device. 
     The body  2 , in the embodiment, is formed of two half-shells  2   a ,  2   b . The body  2  is generally formed of a plastics material, which may be injection moulded or produced by any other suitable manufacturing technique. 
       FIG. 3  shows the device  1  with one of the half-shells  2   b  removed to expose the internal drive mechanism of the device  1 . 
     Within the body  2  of the device  1 , an expelling means, element or part is provided in the form of a longitudinal drive rod  15 . The rod  15  is linear in form and serves as a ratchet or ratchet means, with an upper surface comprising two sets of ratchet teeth  18   a ,  18   b  extending along at least part of the length of the rod  15 . The teeth are orientated such that their lands, valleys or ridges of the peaks run transverse to the longitudinal direction of the device. 
     In the exemplary embodiment described herein, the teeth of one of the sets of ratchet teeth are offset from the teeth of the other set of ratchet teeth. However, it should be noted that such an ‘offset’ arrangement is only a preferred embodiment of the present invention. 
     The sets of ratchet teeth in this example are separated by a longitudinal planar divider  24 . The longitudinal rear side of the rod  15  is planar with a central protruding guide rib  20 . Corresponding channels and support rails  23   a ,  23   b  are formed within the body  2  to receive the rod  15  and the guide rib  20  and allow linear movement thereof along the longitudinal axis of the device  1 . 
     At the proximal end of the rod  15 , the rod comprises an engagement ram  16   a  in the form of a circular disc. The ram  16   a  is formed and sized such that, in use, the ram  16   a  can engage with and displace a plunger  17  in a medicament cartridge received in the cartridge receptacle  4 . 
     A coupling means, element, part or mechanism is provided to couple the dosage setting element with the expelling element. In the embodiment, the coupling means includes a first coupling element  22  connected to the push button  5  via a shaft  8 . In the embodiment, the first coupling element  22  is formed integrally with the shaft  8 . However, it is envisaged that the coupling element  22  could be operatively coupled to the push button  7  and/or shaft via a sprung or biased coupling so as to be moveable relative thereto. 
     The coupling element  22  comprises a pair of spaced planar sections of which only the upper planar section  9   a  is visible in  FIG. 3 . However, a corresponding lower planar section is formed with the lower side of the shaft of the push button  7 . The spaced planar sections  9   a  are perpendicular to the plane of the surface on which the ratchet teeth are provided. In the upper planar section  9   a  of the coupling element  22 , a diagonal slot  10   a  is provided. The diagonal slot  10   a  extends diagonally in a direction across the body of the device. 
     The coupling further comprises a drive means or driver  21  which, as shown more clearly in  FIG. 5 , comprises a pair of parallel and spaced planar arms  12   a ,  12   b  connected via a transverse web  16   b  towards a proximal end thereof. Each of the planar arms  12   a ,  12   b  comprises a circular protrusion or follower of which only the upper protrusion  11   a  is visible in  FIGS. 3 to 4 . 
     The circular protrusion  11   a  of the upper planar arm  12   a  is received in the diagonal guide slot  10   a  of the upper planar section  9   a  of the coupling element. Although not shown, a corresponding circular protrusion is formed on the lower planar arm  12   b  and is received in a corresponding diagonal guide slot  10   a  in the lower planar section of the coupling element  22 . 
     The underside of the upper planar section  9   a  of the coupling element  22  is supported on and slides atop of the upper planar arm  12   a  of the driver  21 . 
     The driver  21  comprises a pair of drive pawls  14   a ,  14   b  extending from the web  16   b . A gap is provided between the drive pawls  14   a ,  14   b  which fits around the divider  24  between the two sets of ratchet teeth  18   a ,  18   b . The drive pawls are independently flexible about their connection with the driver  21 . 
     The driver  21  comprises a cylindrical portion  13   a  which is pivotally located in a corresponding hole in the body  2  of the device  1 . The cylindrical portion is rotatably engaged with the hole in the body  2  such that the driver  21  may rotate about the axis of the cylindrical portion, which acts therefore as a pivot axis. 
     The drive pawls  14   a ,  14   b  are arranged such that they can engage with a tooth respectively of each of the sets of ratchet teeth  18 , although due to the offset in the sets of teeth, the drive pawls  14   a ,  14   b  do not necessarily contact the same part of a tooth in a respective set of teeth. For example, with an offset arrangement of the two sets of teeth in the drive rod, one drive pawl may be in engagement with a rear face of a tooth and the other drive pawl may be atop a ridge or peak of a tooth in the adjacent set of teeth. The drive pawls  14   a ,  14   b  of the driver  21  are angled towards the proximal end  3   a  of the body  2  of device  1 . However, embodiments are envisaged where the teeth in each set of teeth are in adjacent alignment. 
       FIG. 4  shows a further view of the device  1  as shown in  FIG. 3  with the push button  7  in a retracted or withdrawn position. 
     As can been in  FIGS. 3 and 4 , in the depressed state of the push button  7 , the engagement protrusion  11   a  of the driver  22  is located at one end, the distal end, of the diagonal slot  10   a  of the coupling element  22 . In the withdrawn position of the push button  7 , the engagement protrusion  11   a  of the driver  22  is located at the other end, the proximal end, of the diagonal slot  10   a  of the coupling element  22 . This change of position is achieved by the engagement protrusion  11   a  sliding in the diagonal slot  11   a  as the push button  7  is moved in a direction along the longitudinal axis of the device. 
     Because of the diagonal orientation of the slot  11   a  in the coupling element, the movement of the engagement protrusion  11   a , which is formed with the driver  21 , causes the driver  21  to rotate about the pivot point formed by the engagement of the cylindrical protrusion  13  of the driver  21  engaged in the body  2  of the device  1 . 
     As the driver  21  is rotated clockwise about the pivot axis  13  by the push button  7  being depressed, one of the pawls  14   a ,  14   b  engages with at least one rear face of a tooth on one of the sets of ratchet teeth  18  a such that the longitudinal rod  15  is displaced in a direction towards the proximal distal end of the device. 
       FIGS. 6, 7 and 8  show reverse side perspective views respectively of the views shown in  FIGS. 3, 4 and 5 . 
     In  FIG. 6 , the device  1  is shown with the push button  7  in a depressed state. The longitudinal drive rod  15  can be seen showing the upper side thereof in which the two sets of ratchet teeth  18   a ,  18   b  are provided separated by divider  24 . The upper and lower drive pawls  14   a ,  14   b  can be engaged with teeth respectively in the first and second sets of ratchet teeth  18   a ,  18   b , although as described above, due to the offset of the teeth in the two sets of teeth  18   a ,  18   b , the drive pawls  14   a ,  14   b  do not necessarily contact the same portion of a tooth in a respective set of teeth. 
       FIG. 7  shows the device  1  with the push button  7  in a withdrawn state. As can be seen from  FIG. 6 , with the push button  7  in a depressed state or position, the driver  21  has been rotated about the pivot axis  13  thus engaging at least one of the drive pawls  14   a ,  14   b  with at least one rear face of a tooth of a set of ratchet teeth  18   a ,  18   b  and causing the drive rod  15  to be displaced in a proximal direction. 
     The drive pawls  14   a ,  14   b  are formed to allow a degree of flexing relate to the web  16   b.    
       FIG. 9  shows a view of the device  1  with the push button  7  in a depressed state. The device  1  is shown with the cartridge receptacle  4  removed. An aperture  25  can be seen in the proximal end  3   a  of the body  2  in which the drive rod  15  may extend in use to engage with the stopper of a medicament cartridge (not shown). 
       FIG. 10  shows a view of the device  1  with a cut-out in the body  2 . Through the cut-out, the drive rod  15  may be seen. Either side of the drive rod  15 , the upper and lower arms  12   a ,  12   b  of the driver are located. The upper and lower drive pawls  14   a ,  14   b  can also be seen. 
     Spaced from the upper and lower drive pawls  14   a ,  14   b , in the proximal direction of the body  2  of the device  1 , a pair of resistance or resisting pawls  26   a ,  26   b  is provided. The resistance pawls  26   a ,  26   b  are formed with or attached to the body  2  of the device  1 . 
       FIG. 11  shows a further cut-away view of the body  2  of the device  1 , but with the drive rod  15  removed. Here, the arrangement of the resistance pawls  26   a ,  26   b  and drive pawls  14   a ,  14   b  can be seen. 
     The resistance pawls  26   a ,  26   b  are angled in a direction towards the proximal end  3   a  of the body  2  of device  1 . The resistance pawls are flexible to a certain degree with respect to the body  2  of the device  1 . 
     The upper resistance pawl  26   a  can engage with the upper set of teeth  18   a  on the longitudinal rod  15 , with the lower resistance pawl  26   b  engageable with the lower set of teeth  18   b  on the longitudinal rod  15 . Due to the offset of the teeth between the teeth in one set of ratchet teeth to the teeth in the other set of ratchet teeth in this embodiment, the resistance pawls  26   a ,  26   b  may not contact the same part of a tooth in each of the first and second sets of ratchet teeth  18   a ,  18   b.    
     The resistance pawls  26   a ,  26   b  serve to resist or prevent movement of the longitudinal rod  15  in a direction away from the proximal end  3   a  of the body  2  of device  1 , by engaging the rear faces of the ratchet teeth  18   a ,  18   b.    
     The operation of the device  1  will now be described with reference to  FIGS. 12 and 14 , which show cross sections A-A and B-B along the parallel longitudinal planes shown in  FIG. 13 . 
       FIGS. 12 and 14  show the device  1  with the push button  7  in a depressed state. A medicament cartridge  27  is shown within the cartridge receptacle  4 . A plunger  17  is provided within the medicament cartridge  27  which can be moved by engagement and displacement of the ram  16   a  of the longitudinal or drive rod  15 , which serves to expel the medicament from the cartridge  27 .  FIG. 14  is a lower side view of the device  1  and the description of the upper side as shown in  FIG. 12  is equally applicable to the lower side. 
     The upper resistance pawl  26   a  and the distal edge thereof can be seen engaged with a rear face of a tooth of the upper set of ratchet teeth  18   a  on the longitudinal drive rod  15 . 
     The upper drive pawl  14   a  can also be seen engaged with a rear face of a tooth of the upper set of ratchet teeth  18   a  on the longitudinal or drive rod  15 . 
     In order to set a dose, a user must withdraw the push button  7  in a direction away from the cartridge receptacle  4 , i.e. in a distal direction with respect to the body  2  of device  1 . 
     As the push button  7  is withdrawn, as has been described in relation to  FIGS. 3 to 8 , the sliding or engagement protrusion  11   a  on the upper drive arm  12   a  of the driver, which is located in the diagonal slot  10   a  of the coupling element  22 , slides in the slot, causing the driver  21  to rotate in an anti-clockwise direction about the pivot axis  13 . During this movement, due to the offset of the sets of ratchet teeth  18   a ,  18   b , one of the resistance pawls  26   a ,  26   b  acts to resist movement of the drive rod  15  in a distal direction by engagement with the rear face of the tooth. 
     As the driver  21  rotates, one of the drive pawls  14   a ,  14   b  slides from between a space or valley between two longitudinally adjacent peaks of two teeth, over the front tooth face and ridge of a tooth such that it proceeds to be located in the longitudinally adjacent space or valley between successive teeth. The other of the drive pawls also moves, but due to the offset in the sets of ratchet teeth  18   a ,  18   b  does not necessarily end up on the same part of a tooth. At this stage, the push button is then in a retracted state as shown in  FIGS. 15 and 17  which show cross sections D-D and C-C along the parallel longitudinal planes shown in  FIG. 16 . 
     Upon the subsequent displacement of the dosage setting means  7  towards the proximal end  3   a  of the body  2  of device  1 , the sliding protrusion  11   a  moves along the slot  10   a  in the coupling  22 . As a result, the driver  21  rotates in a clockwise direction about the pivot point  13 . One of the drive pawls  14   a ,  14   b  on the driver  21 , normally a drive pawl positioned behind a peak of a tooth, engages with the rear face of the tooth in the set of ratchet teeth  18   a ,  18   b  in which it is located such that the longitudinal rod is displaced upon further movement of the dosage setting means in an axial direction in order to administer a dosage of medicament. 
     This operation, i.e. the continued withdrawal and subsequent depression of the push button  7 , serves to move the drive pawls  14   a ,  14   b  successively into subsequent valleys or spaces between the teeth and drive the drive rod  15  towards the proximal end  3   a  of the body  2  of device  1 . After the drive pawl reaches the surface  28   a ,  28   b  after the last tooth of the drive rod  15 , no further displacement can be made. 
     The resistance pawls  26   a ,  26   b  are fixed to the body  2  of the device  1  and serve to resist or prevent movement of the drive rod (“expelling means”)  15  in a direction opposite to the administering direction, i.e. in a direction towards the proximal end  3   a  of the body  2  of device  1 . This ensures a consistent displacement of the drive rod  15  in the proximal direction only and prevents backlash or displacement of the drive rod  15  in the distal direction. 
     All of the sets of ratchet teeth  18   a ,  18   b  are provided on a common side of the drive rod  15  and therefore all the resistance pawls  26   a ,  26   b  and drive pawls  14   a ,  14   b  are arranged to face a common side of the drive rod. 
     As the drive rod  15  is displaced in the proximal direction of the device  1 , the resistance pawls  26   a ,  26   b  slide over the ratchet teeth  18   a ,  18   b  on the drive rod  15 . 
       FIGS. 18 a , 19 a   ,  20 , show more detailed side, plan and perspective views of adrive rod  15  having offset sets of teeth. 
     The drive rod  15  comprises two sets of ratchet teeth  18   a ,  18   b  separated by a divider  24 . The two sets of ratchet teeth  18   a ,  18   b  are offset, i.e. engaging faces of the upper set of ratchet teeth  18   a , are offset from the engaging faces of the lower set of ratchet teeth  18   b  in a direction parallel to the longitudinal axis of the drive rod  15 . This can be more clearly seen in details A and B shown in  FIGS. 18 b    and  19   b.    
     As shown in  FIG. 18 b   , each tooth has a ridge or peak  29   c , a sliding front face  29   a  over which the pawls slide and an engagement rear face  29   d  as well a valley centre  29   b . The teeth in each set of ratchet teeth  18   a ,  18   b  on opposing sides of the expelling means are equally spaced from one another. The offset between the two sets of ratchet teeth  18   a ,  18   b  in the embodiment is equal to half the spacing between adjacent teeth in either of the first or second sets of ratchet teeth  18   a ,  18   b.    
     In the embodiments described, the upper and lower resistance pawls  26   a ,  26   b  are arranged in adjacent alignment. Similarly, the upper and lower drive pawls  14   a ,  14   b  are also arranged in adjacent alignment. Due to the offset of the two sets of ratchet teeth  18   a ,  18   b  on the drive rod  15 , when driving the driver  21 , as described above, during each sequence of withdrawing the push button  7  and subsequently depressing the push button  7 , only one set of resistance pawl  26   a  and drive pawl  14   a  engage fully with one set of the ratchet teeth, i.e. only one of the drive pawls  14   a  causes the drive rod  15  to be displaced and only one of the corresponding resistance pawls  26   a  prevents return movement of the drive rod  15 . During a subsequent sequence, the other set of drive pawl  14   b  and resistance pawl  26   b  fully engages with the other set of ratchet teeth  18   b , and so on. 
     Accordingly, the offset of the ratchet teeth  18   a ,  18   b  provides a ratchet with finer resolution of movement, which is equal to the distance between the valley of one tooth in one of the sets of ratchet teeth  18   a  and the valley of an adjacent tooth in the other of the sets of ratchet teeth  18   b . This offset is shown in  FIG. 19 b    at item  30 . 
     It follows that movement of the drive rod  15  in the embodiment described proceeds in smaller increments than if no offset were to be provided between the two sets of ratchet teeth  18   a ,  18   b . This enables a finer dose or volume of medicament to be administered with the device  1  as a result of movement or displacement of the drive rod  15 . 
     The offset in the case of a drive rod  15  with offset sets of ratchet teeth  18   a ,  18   b  may be adjusted according to requirements. For example, a drive rod  15  may be chosen with a larger tooth pitch in the sets of ratchet teeth in order to administer a large dosage during each cycle of movement. Conversely, a smaller pitch could be chosen. The other components however generally remain the same. 
     As previously mentioned, a drive rod  15  where the sets of ratchet teeth are in alignment is also envisaged. In such an embodiment, both drive pawls and resistance pawls would be in engagement with corresponding parts of teeth in each set of teeth at the same time in order to drive the expelling means and resist movement of the expelling means in the distal direction of the device. 
     With all of these embodiments, providing the ratchet teeth  18   a ,  18   b  on a single, common side of the drive rod  15  enables a more compact and simple device construction to be achieved. 
     As an alternative to offset teeth on the drive rod  15 , the adjacent ratchet teeth may be aligned with the drive pawls offset from one another. Indeed, a single set of ratchet teeth can be provided which can engage with each of the drive pawls and each of the resistance pawls. 
     It is envisaged that other coupling mechanisms may be provided to displace the drive rod and the present invention should not be considered limited to the exemplary coupling mechanism as shown in the Figures. 
       FIGS. 21 and 22  show a further embodiment of the device  1  having an indicator element  34  visible through a display window or aperture  31  provided in a surface of the body  2  of the device.  FIGS. 21 and 22  have drive mechanisms configured to drive a drive rod  15  as described above in relation to  FIGS. 1 to 20 . However, the indicator element  34  and display window  31  arrangement of  FIGS. 21 and 22  may be applied to devices with different drive mechanisms, including inhaler devices (not shown). 
       FIG. 21  shows the device  1  with the push button  7  in a depressed state. In this position of the push button  7 , a first state indicator  32   a  of “0” provided on the indicator element  34  is visible in the window  31 . This first state indicator  32   a  could for example indicate to a user that no dosage has been set by the push button  7 . 
       FIG. 22  shows the device  1  with the push button  7  in a withdrawn or retracted state. In this position of the push button  7 , a second state indicator  32   b  of “5” provided on the indicator element  34  is visible through the window  31 . This second state indicator  32   b  could for example indicate to a user that a dosage of 5 units has been set for administration. Of course, other indications of state could be provided such as arrows or other visual or tactile markers or characters. 
       FIG. 23  shows a view of the device  1  with part of the body removed to show the internal drive mechanism and also the mechanism to move the indicator element  34 . The drive mechanism includes a driver  21  rotatable about a pivot axis  13 . The driver  21  includes a protrusion  11   a  which engages through a diagonal, linear slot in a coupling element  22 . The driver  21  drives a drive rod  15  provided with sets of ratchet teeth  18   a ,  18   b . The drive rod  15  comprises a ram  16   a  which can be extended or displaced through an aperture  25  in order to displace a plunger in a medicament container such an insulin cartridge (not shown). The function of such a mechanism has already been described in relation to  FIGS. 1 to 20  and will not be described further here. 
     The coupling  22  includes a planar surface  9   a , as described above. The surface  9   a  is provided with distal and proximal protrusions  33   a ,  33   b , which are spaced apart a distance greater than the axial length of the indicator element  34 , which is disposed in the body  2  between said protrusions  33   a ,  33   b.    
     A protrusion  35   c  is provided along an edge of the window  31 , the protrusion  35   c  being configured to engage with each of two spaced indents  35   a ,  35   b  located along an edge of the indicator element  34  parallel to the direction of movement of the indicator element  34 . When engaged with either of the indents  35   a ,  35   b , the protrusion  35   c  acts to inhibit free axial linear movement of the indicator element  34 , which in this embodiment is formed as a substantially rectangular planar element. 
     The indents  35   a ,  35   b  and the protrusion  35   c  combine with protrusions  33   a ,  33   b  on the body  2  to form motion conversion means, the function of which will now be described with reference to  FIGS. 25 to 28  which are sectional views through section E-E as shown in  FIG. 24 . 
     When the push button  7  of the device is fully depressed into the body  2  of the device, as shown in  FIG. 25 , the indicator element  34  is positioned with its distal edge engaged with protrusion  33   a  towards the rear or distal end of the device body  2 . The indication “0” is shown in the window  31 , represented by the dashed outline. 
     Upon initial withdrawal of the push button  7 , as shown in  FIG. 26 , the indicator element  34  remains stationary relative to the body  2  of the device thanks to protrusion  35   c  along the edge of window  31  engaging with rearmost indent  35   a  of the indicator element  34 . This engagement acts to resist axial movement of the indicator element  34  relative to the body  2  such that the indicator element  34  slides over the surface of the coupling  22  when during an initial movement of the push button  7  and, as there is no movement of the indicator element  34  relative to the body  2 , the indication “0” remains visible to a user through window  31 , indicating, for example, that the dosage has not yet been set. 
     Upon further withdrawal of the push button  7 , as shown in  FIG. 27 , the proximal protrusion  33   b  engages with the proximal edge of the indicator element  34 , which causes the indicator element  34  to be displaced in a distal axial direction of the body  2  of the device, in doing so overcoming the resistance provided by the engagement of the protrusion  35   c  and distal indent  35   a , such that the indication “0”  32   a  begins to move out of visibility in the window  31 . 
       FIG. 28  shows the fully retracted position of the push button  7 . Here it can be seen that the proximal protrusion  33   b  on the coupling  22  maintains its engagement with the indicator element  34  thereby completing the axial movement of the indicator element  34  to bring indication “5”  32   b  into visibility in the display window  31 . This could for example indicate to a user that the dosage has been correctly set and the push button  7  could be depressed in order to administer the dose. In this final fully withdrawn position of the push button  7 , the protrusion  35   c  along the edge of window  31  becomes engaged with the foremost indent  35   b  on the edge of the indicator element  34 . 
     Upon subsequent depression of the push button  7  in order to administer a dose, the indicator element  34  again initially remains stationary relative to the body  2  due to the resistance of protrusion  35   c  being engaged with the foremost indent  35   b  on the edge of the indicator element  34  such that the indication “5”  32   b  remains visible in the window  31  during an initial movement of the push button  7 . This could, for example, indicate to a user that the dose has not yet been fully administered. 
     Similarly as when the push button  7  is withdrawn, upon continued depression of the push button  7 , the distal protrusion  33   a  on the coupling  22  engages with the corresponding distal edge of the indicator element  34  thereby to move it in the proximal direction relative to the body  2  of the device such that the indication “0”  32   a  is again displayed in the window  31  and protrusion  35   c  again engages with rearmost protrusion  35   a  on the edge of the indicator element  34 . 
     Although in the embodiment, the indicator element  34 , here in the form of a sliding indicator, has been provided with indents  35   a ,  35   b  at each end of travel, it is also envisaged to provide a protrusion on the edge of the sliding indicator  34  which engages with corresponding indents provided on a corresponding edge of the window  31 . 
     It will be understood that the mechanism provides a magnitude of displacement of the indication element  34  which is different to (i.e. less than) the magnitude of displacement of the dosage setting means. In the embodiment, the spacing of the protrusions  33   a ,  33   b  on the surface  9   a  of coupling  22  provides a relative or “lost motion” movement between the push button  7  and the indicator element  34 . This allows the indications  32   a ,  32   b  to remain visible and unchanged during phases of the operation of the device. This can lead to improved operation of the device as the displayed indications  32   a ,  32   b  remain consistent and unchanged. 
     While in the embodiment, an axially moveable push button  7  has been shown to provide drive of the mechanism, other forms of dosage setting means may be provided such as a dial, rotatable about the longitudinal axis of the device while still embodying the above-described arrangement of the indicator element  34 . An example of such a dosage setting means with a rotating dial  36  on a cylindrical body  37  is shown in  FIGS. 29 to 31  in a fully screwed in position in  FIG. 29 , a fully retracted, i.e. screwed-out position in  FIG. 30  and a fully depressed position in  FIG. 31 . 
     A further embodiment of a device  1  is shown in  FIGS. 32 to 39  comprising a different indicator element arrangement. Externally, the device  1  is formed similarly to the embodiments described above, comprising a body  2 , a cartridge receiver  4 , a cartridge with a threaded portion  5  for receiving an injection needle, a push button or dosage means  7  and a window or aperture  31 . Through the window  31 , an indication, here the number “5” is visible, which is on an indicator element  42 . 
       FIG. 33  shows a cross-section through the device shown in  FIG. 32 . The dispensing mechanism is similar to that shown in  FIGS. 1 to 31  and comprises a driver  21  with drive pawl  14   a ,  14   b  and resistance pawls  26   a ,  26   b  arranged to engage with ratchet teeth  18   a ,  18   b  on a drive rod  15 . 
     A coupling element  38  is provided, which comprises a diagonal slot  10   a  within which a protrusion  11   a  is received. These parts function similarly to the coupling element  22  described in relation to  FIGS. 1 to 31  in order to set a dose with the push means  7  and administer a dose. The dosage and administering functions will accordingly not be described further here. 
     In contrast to the device of  FIGS. 1 to 31 , as shown in  FIG. 33 , the coupling element  38  comprises a rectangular aperture  43 . Along one edge of the aperture, an opening  45  is provided in which a conversion means in the form of lever  39  is positioned. The lever  39  extends through the opening  45  into the aperture  43  from a pivoted connection  40  on the body  2  located outside the aperture  43 . 
     The indicator element  42  is provided with a pair of spaced protrusions, represented by the dashed lines  41   a ,  41   b . The protrusions  41   a ,  41   b  extend from the rear surface or underside of the indicator element  42  (not shown in  FIG. 33 or 35 ) and are positioned towards either end of the indicator element  42  in the longitudinal direction of the device. When assembled, the protrusions  41   a ,  41   b  extend into the aperture  43  such that they are positioned either side of the distal end of the lever  39 , i.e. the end of the lever  39  furthest from the pivoted connection  40 , such that the indicator element  42  rests atop the lever  39 . 
       FIG. 33  shows the device with the push button  7  in a retracted position. Here it can be seen that the lever  39  is in contact with the rearmost or distal protrusion  41   b  of the indicator element  42  and is orientated such that the lever  39  is angled towards the distal end of the body  2 . 
       FIG. 34  shows an external view of the device of  FIGS. 32 and 33  when the push button  7  is in a fully depressed position. In this position, the indicator element  42  now shows the indication “0”. As has been described in relation to  FIGS. 28 to 31 , the indication “0” can be used to indicate to a user that no dose has been set and the indication “5” can be used to indicate that a dose of 5 units has been set, for example. 
     As can be seen in  FIG. 35 , with the push button  7  in a fully depressed state, the rectangular aperture  43  has been axially displaced in the proximal direction of the device relative to the position of the rectangular aperture  43  of the device in the state shown in  FIG. 33 . It can be seen that the opening  45  in the side of the aperture  43  has therefore also moved in a corresponding towards the proximal end of the body  2 . As the lever  39  is pivotally attached to a fixed pivot  40  on the body of the device, the movement of the aperture  43  and the opening  45  therein causes rotation of the lever  39  about the pivot  40 . As the distance between the pivot  40  and the opening  45  is less than the distance between the opening  45  and the distal end of the lever  39 , it can be appreciated that a movement of the aperture  43  results in a movement of the distal end of the lever  39  of a greater magnitude, which moves the indicator element  42 , via the protrusions  41   a ,  41   b , a corresponding distance. Thus it can be seen that the opening  45  acts as a fulcrum  43 . 
     The relative lengths of the lever  39  between the pivot  40  and the fulcrum  43  and the length between the fulcrum  43  and the distal end of the lever  39 , or its point of contact with the protrusions  41   a ,  41   b  of the indication element  42 , may be selected to produce a desired magnitude of movement of the indication element  42  relative to the dosage setting means  7 . 
     As shown in  FIG. 35 , in the depressed state of the push button  7 , the distal end of the lever  39  is in contact with the protrusion  41   a  of the indicator element  42  towards the proximal end of the body  2  and has moved the indicator element  42  such that the indication “0” is now visible in the aperture or window  31  as shown in  FIG. 34 . 
     The lever  39  acts to convert a movement of a first magnitude of the push button  7  or coupling  38  into a movement of a second, greater magnitude of the indicator element  42 . In a device with limited space, the lever  39  can provide a greater movement and functionality of the indicator element  42  than if the movement of the indicator element  42  was limited only to the same magnitude or degree of movement of the push button  7 . For example, a 4 mm movement of the indicator element  42  can result from just a 2 mm axial movement of the push button  7 , thereby providing a “gained motion” effect. 
     It will be understood however, that the opening  45  or fulcrum  43  and lever  39  may be arranged with a shorter distance between the opening  45  and the distal end of the lever  39  than the distance between the pivoted end  40  of the lever  39  and the opening  45  such that a smaller magnitude of movement of the indicator element  42  is achieved relative to the magnitude of movement of the push button  7 . 
     As a further alternative, the lever  39  may be formed of a resiliently flexible material such that when the indicator element  42  reaches the limit of its movement, if the lever  39  should be caused to rotate further, for example if the manufacturing tolerances of the lever  39  are such that it is slightly longer or wider than necessary or if the fulcrum  43  or opening  45  position is not precisely located, the lever  39  will flex to prevent damage to itself or to the indicator element  42 . 
       FIGS. 36 to 39  show some assembly steps of the device with the lever.  FIG. 36  shows the body, driver  21  and drive rod  15  located in the body  2 . The body  2  is formed with a circular aperture  40  for receiving a support  44  of the lever  39 . 
       FIG. 37  shows the support  44  of the lever  39  located in the aperture  40 . The lever  39  is pivotable about the axis of the circular aperture  44 . Although shown in  FIG. 37  as a separate part in the embodiment, the lever  39  could be formed integrally with the body  2 , yet still able to pivot. 
       FIG. 38  shows the device with the coupling  38  attached to the push button  7  fitted. The lever  39  can be seen located in the opening  45  provided along one longitudinal side of the rectangular aperture  43 . 
     Finally,  FIG. 39  shows the indicator element  42  positioned atop the coupling  38  and hence lever  39 . The indicator element  42  is formed with the lever-engagable protrusions  41   a ,  41   b  underneath, which were shown and described in relation to  FIGS. 33 and 35 . 
     The indicator element  42  is shown provided with indents  46   a ,  46   b , which have a similar function to the indents  35   a ,  35   b  described in relation to  FIGS. 23 and 25 to 28  to resist free motion of the indicator element  42 . 
     Although not shown in the Figures, it is envisaged that instead of a lever  39 , the conversion means could comprise geared or threaded components, with the gearing or threading being chosen or configured such that a predetermined magnitude of movement of the indicator element  34  is achieved for a predetermined differing magnitude of movement of the push button  7 . 
     In each of the aforementioned embodiments, the dosage setting means  7  could be indirectly or directly coupled to the indication element  34 ,  42 . The indicator element  34 ,  42  is typically constrained within a channel or guide elements to limit the lateral movement thereof. 
       FIG. 40  shows an alternative dispensing mechanism provided in a device  1 . The device  1  includes a medicament container in the form of a cartridge receptacle  4 . Within the cartridge receptacle  4 , a cartridge is contained with a screw thread  5  at the proximal end to receive a needle. 
     Similarly to the embodiments shown in  FIGS. 1 to 39 , the dispensing mechanism comprises a dosage setting means in the form of a push button  7 . The dosage setting means is formed with a shaft  8  connecting the push button  7  with a plate  38  in which a diagonal slot  52   a  is formed similarly to the embodiments of  FIGS. 1 to 39 . Accordingly, this aspect of the embodiment will not be described in further detail. 
     An expelling means  51  is provided in the form of a ram with a circular disc  52  to engage with the plunger of a cartridge in order to dispense a liquid medicament therefrom. 
     A drive element  48  is provided. The drive element  48  comprises an arm  48   a  connected towards the proximal end thereof to a pivot point  49  formed in the body  55  of the mechanism. At the distal end of the drive element of driver, a circular protrusion or follower  52   a  is provided which engages with the diagonal slot  10   a  in the plate  38  of the dosage setting means  7 . 
     The drive element  48  comprises a further pair of arms  48   b  which extend from the distal end of the driver  48  in the proximal direction of the mechanism and device and angled relative the arm  48   a  connected to the pivot point  49 . Each of the pair of arms  48   b  comprises at their proximal, free ends, a drive pawl  48   c.    
     The expelling means  51  comprises a rack of teeth  54  which are formed to engage with the teeth  47   c  of a drive wheel  47 . The drive wheel  47  has a central section  47   c  formed as a gear wheel which engages with the teeth  54  of the rack of the expelling means  51 . 
     The drive wheel  47  is formed with two ratchet wheels  47   a ,  47   b  at either end. The ratchet wheels  47   a ,  47   b  have a larger diameter to the diameter of the central gear wheel  47   c . The teeth of the ratchet wheels are offset relative to one another, i.e. the faces of the teeth in one ratchet wheel are offset from the faces of the teeth in the other ratchet wheel. Similarly to the embodiments described in relation to  FIGS. 1 to 39 , this can provide a finer movement and thus dosage. 
     Biasing pawls  50  are formed with the body  55  and are angled in the proximal direction of the device. Two such biasing pawls are provided. One upper biasing pawl engages with one of the ratchet wheels  47   a  and the other, lower biasing pawl engages with the other of the ratchet wheels  47   b . It can therefore be seen that these biasing pawls  50  serve to prevent anticlockwise (as seen in  FIGS. 40 m   ,  41 ) rotation of the drive wheel and can therefore be seen to act similarly to the biasing pawls described in relation to  FIGS. 1 to 39 . The biasing pawls  50  face a common side of the ratchet wheels provided on the drive wheel. 
       FIG. 40  shows the device  1  with the push button  7  in a depressed position. As can be seen from  FIGS. 40 and 41 , upon withdrawal of the push button  7  into the withdrawn position as shown in  FIG. 41 , the protrusion  52   a  on the driver  48  follows the diagonal slot  10   a  such that the driver  48  is caused to rotate anticlockwise about the pivot point  49 . In so doing, the drive pawls  48   c  slide over the teeth in the ratchet wheels  47   a ,  47   b , thus moving into successive valleys formed by the ratchet teeth. The biasing pawls  50  prevent rotation of the drive wheel in an anticlockwise direction during this movement of the drive pawls. 
     Upon the subsequent depressing of the push button  7  in the axial proximal direction, the driver  48  is caused to rotate about the pivot point  49 . Due to the offset of the ratchet teeth in the ratchet wheels  47   a ,  47   b , only one of the drive pawls  48   c  engages fully with an engaging face of one of the ratchet wheels  47   a ,  47   b  and rotates the ratchet wheel  47  about its axis  56  in a clockwise direction as viewed in  FIG. 41 . 
     As the drive wheel  47  rotates, the gear teeth  47   c , which are engaged with the rack of teeth  54  on the expelling means  51 , rotate causing the expelling means to be displaced in an axial direction to deliver or administer a dose from the cartridge. 
       FIG. 42  shows the expelling means  51 , driver  48  and drive wheel  47 . Due to the larger relative diameters of the ratchet wheels  47   a ,  47   b  to the size of the gear wheel  47   c  on the drive wheel  47 , the expelling means sits between the drive arms  48   c  of the driver  48 . This again allows for a more compact arrangement of components. 
       FIG. 43  shows a view of the drive wheel  47 . Each ratchet wheel  47   a ,  47   b  shares the same axis of rotation as the central gear wheel  47   c  located therebetween. The ratchet wheels  47   a ,  47   b  may be formed integrally with the gear wheel  47   c.    
     As with the embodiments of  FIGS. 1 to 39 , the drive pawls could be offset rather than the ratchets on the drive wheel, with the ratchets of the drive wheel being in alignment. 
     Various modifications may be made to the embodiments described without departing from the scope of the invention as defined in the accompanying claims. Furthermore, a skilled person will note that, though the terms “upper” and “lower” are used throughout the description for ease of reference to the figures, these terms are interchangeable with other differentiating terms for similar or identical features such as “first” and “second”, for example.