Abstract:
The present invention relates to injectors, such as pen-type injectors, that provide for administration of medicinal products from a multidose cartridge and permit a user to set the delivery dose. The injector may include a housing, a cartridge containing medicinal product, the cartridge being retained within the housing, means for selecting a dose of medicinal product to be expelled, and means for expelling the selected dose of medicinal product. The housing may be a unitary housing within which the means for selecting a dose and the means for expelling the selected dose are moveably retained. Alternatively, the injector may include a housing, a piston rod, an insert located in the housing and through which the piston may rotate, ratchet means, a dose dial sleeve, a drive sleeve, a button located on the drive sleeve and rotatable with respect to the drive sleeve, and clutch means which upon depression of the button prevents rotation between the dose dial sleeve and the drive sleeve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/208,486, filed on Aug. 12, 2011, which is a divisional of U.S. patent application Ser. No. 12/900,725, filed Oct. 8, 2010, which is a continuation of U.S. patent application Ser. No. 10/790,025, filed on Mar. 2, 2004, now U.S. Pat. No. 7,905,867, which claims priority to Great Britain Patent Application No. 0304823.8, filed on Mar. 3, 2003, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to pen-type injectors, that is to injectors of the kind that provide for administration by injection of medicinal products from a multidose cartridge. In particular, the present invention relates to such injectors where a user may set the dose. 
         [0003]    Such injectors have application where regular injection by persons without formal medical training occurs. This is increasingly common amongst those having diabetes where self-treatment enables such persons to conduct effective management of their diabetes. 
         [0004]    These circumstances set a number of requirements for pen-type injectors of this kind. The injector must be robust in construction, yet easy to use both in terms of the manipulation of the parts and understanding by a user of its operation. In the case of those with diabetes, many users will be physically infirm and may also have impaired vision. Where the injector is to be disposable rather than reusable, the injector should be cheap to manufacture and easy to dispose of (preferably being suitable for recycling). 
       SUMMARY 
       [0005]    It is an advantage of the present invention that an improved pen-type injector is provided. 
         [0006]    According to first aspect of the present invention, a pen-type injector comprises a housing; 
         [0007]    a cartridge containing medicinal product, the cartridge being retained within the housing; 
         [0008]    means for selecting a dose of medicinal product to be expelled; means for expelling the selected dose of medicinal product; 
         [0009]    characterised in that the housing comprises a unitary housing within which the dose selecting means and the dose expelling means are moveably retained. 
         [0010]    It is an advantage of this aspect of the invention that it affords a more robust construction of a pen-type injector. 
         [0011]    According to a second aspect of the present invention, a pen-type injector comprises 
         [0012]    a piston rod having a screw thread; 
         [0013]    an insert located in the housing and through which the piston may rotate; ratchet means associated with the insert to ensure the piston only rotates in a single direction through the insert; 
         [0014]    a dose dial sleeve rotatable with respect to the housing and the insert; 
         [0015]    a drive sleeve which is axially displaceable but not rotatable with respect to the piston rod; 
         [0016]    a button located on the drive sleeve and rotatable with respect to the drive sleeve; and 
         [0017]    clutch means which upon depression of the button prevents rotation between the dose dial sleeve and the drive sleeve. 
         [0018]    Preferably, the injector further comprises a nut rotatable with respect to the drive sleeve and axially displaceable but not rotatable with respect to the dose dial sleeve. 
         [0019]    Preferably, the insert comprises a web having an opening, a first cylindrical portion extending from a first side of the web, a second cylindrical portion extending from a second side of the web and a third cylindrical portion extending from a second side of the web. 
         [0020]    Alternatively, the insert comprises a web having an opening, a first cylindrical portion extending from a first side of the web, a boss provided on a second side of the web and a cylindrical portion extending away from the web about a periphery of the boss. 
         [0021]    In a second alternative, the insert comprises a web having an opening, a first cylindrical portion extending from a first side of the web, a boss provided on a second side of the web, a radial flange extending from the boss, the radial flange being spaced from the web, and a cylindrical portion extending away from the web about a periphery of the radial flange. 
         [0022]    Preferably, the dose dial sleeve comprises a first section of first diameter and a second section of second diameter, the insert and an inner surface of the first section being provided with inter-engaging features to provide a helical thread between the insert and the dose dial sleeve. 
         [0023]    Alternatively the dose dial sleeve comprises a first cylindrical portion rigidly connected to a second generally cylindrical portion, an inner surface of the first section and an outer surface of the cylindrical portion of the insert are provided with inter-engaging features to provide a helical thread between the insert and the dose dial sleeve. 
         [0024]    More preferably, the second generally cylindrical portion comprises a first cylindrical section and a second cylindrical section connected by a shoulder, the first section being rigidly keyed to an inner surface of the first portion of the dose dial sleeve, and the second section being of the same outer diameter as the housing. 
         [0025]    Alternatively the second generally cylindrically portion comprises a first cylindrical section and a second cylindrical section connected by a radial flange extending from a part of the second section, the first section being rigidly keyed to an inner surface of the first portion of the dose dial sleeve, and the second section being of the same outer diameter as the housing. 
         [0026]    Preferably, an outer surface of the dose dial sleeve is provided with graphics and the housing is provided with an aperture or window through which a portion of the graphics may be viewed. 
         [0027]    Preferably, the drive sleeve comprises a first part of first diameter located between the insert and the piston rod and a second part of second diameter located between the piston rod and the dose dial sleeve, an internal surface of the drive sleeve being splined to the piston rod such that no relative rotation may occur between these parts, only longitudinal displacement. 
         [0028]    More preferably, the central receiving area includes at a first end a centrally located domed part. 
         [0029]    Preferably, the nut is provided on a helical thread provided on the drive sleeve and is located between the drive sleeve and the dose dial sleeve, the dose dial sleeve and the nut being splined together by spline means to prevent relative rotation between the nut and the dose dial sleeve. 
         [0030]    Preferably, the drive sleeve further comprises a central receiving area having a peripheral recess, the button being of generally “T” shaped configuration has a stem that is retained within the receiving area by co-operation between a peripheral bead provided on the stem retained in a peripheral recess provided in the central receiving area. 
         [0031]    More preferably the second end of the piston rod is generally U-shaped, each of the limbs of the U-shape being received within a second part of the drive sleeve. 
         [0032]    Preferably, the clutch means comprises a plurality of radially extending longitudinally directed teeth provided respectively on the dose dial sleeve and the drive sleeve. 
         [0033]    Preferably, clicker means are provided between the dose dial sleeve and the drive sleeve, the clicker means comprising a plurality of longitudinally extending teeth and a flexible toothed member, one of the plurality of teeth and the toothed member being provided on the dose dial sleeve, the other being provided on the drive sleeve, relative rotation between the dose dial sleeve and the drive sleeve causing the flexible toothed member to ride over the teeth to produce a series of clicks. 
         [0034]    According to a third aspect of the present invention, a pen-type injector comprises a housing; 
         [0035]    a piston rod having a screw thread; 
         [0036]    an insert located in the housing and through which the piston may rotate; 
         [0037]    a dose dial sleeve rotatable with respect to the housing and the insert; and 
         [0038]    a drive sleeve which is axially displaceable with respect to the housing; 
         [0039]    characterized in that a maximum angular displacement of the dose dial sleeve with respect to the housing is determined by abutment of a radially directed lug on the dose dial sleeve with a catch means on the insert. 
         [0040]    Preferably, the radially directed lug extends parallel to a longitudinal axis of the dose dial sleeve. 
         [0041]    Preferably, the catch means comprises a groove extending about a central land, the central land being wedge shaped such that a first edge extends radially less far than a second opposite edge to define a sloping surface between the first edge and the second edge. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0042]    The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0043]      FIG. 1  shows a sectional side view of a first embodiment of an injector in accordance with the present invention in a first position; 
           [0044]      FIG. 2  shows a sectional side view of the injector of  FIG. 1  in a second position; 
           [0045]      FIG. 3  shows a sectional side view of the injector of  FIG. 1  in a third position; 
           [0046]      FIG. 4  shows a sectional side view of the injector of  FIG. 1  in a fourth position; 
           [0047]      FIG. 5  shows a sectional side view of the injector of  FIG. 1  in a second position; 
           [0048]      FIG. 6  shows a sectional side view of a second embodiment of an injector in accordance with the present invention; 
           [0049]      FIG. 7  shows a sectional side view of a third embodiment of an injector in accordance with the present invention; 
           [0050]      FIG. 8  shows a perspective view of a dose dial sleeve for use in conjunction with the present invention; 
           [0051]      FIG. 9  shows a perspective view of an insert for use with the dose dial sleeve of  FIG. 8 ; and 
           [0052]      FIG. 10  shows a sectional side view of a fourth embodiment of an injector in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    Referring first to  FIGS. 1 to 5  there may be seen an injector in accordance with a first embodiment of the present invention. The injector comprises a housing  2  within which are located a cartridge  4  containing a medicinal product, means for setting or selecting the dose of medicinal product to be expelled and means for expelling the selected dose of medicinal product. The housing  2  is generally cylindrical in shape and is divided into two compartments by a web  6  to be described in more detail below. The cartridge  4  is located within a first part of the housing  2 . The dose setting means and the means for expelling the selected dose of medicinal product are retained, that is held, within a second part of the housing  2 . An advantage of a one piece housing enclosing the cartridge  4  together with the dose setting and dose expelling means lies in the ease of assembly of the product. This is in part due to the reduced number of components in the pen-type injector. Also, the unitary nature of the housing  2  means that the pen-type injector is more robust. 
         [0054]    The cartridge  4  may be secured in position in the first part of the housing  2  by any suitable means. A needle unit may be secured to a first end of the cartridge  4 . A temporary covering  8  is shown in this position in the Figures. The cartridge  4  further comprises a displaceable piston  10 . 
         [0055]    Advancing the piston  10  towards the first end of the cartridge  4  causes the medicinal product to be expelled from the cartridge  4  through the needle unit. A cap  12  is provided to cover the needle unit when the injector is not in use. The cap  12  may be releasably secured to the housing  2  by any suitable means. 
         [0056]    The dose setting means and the means for expelling the selected dose of medicinal product will now be described in more detail. The web  6  dividing the housing  2  is a part of an insert  14  located within the housing  2 . The insert  14  comprises a first cylindrical portion  16  extending from a first side of the web  6  and second and third cylindrical portions  18 , 20  extending from a second side of the web  6 . The web  6  is provided with a circular opening  22  extending through the web  6 . 
         [0057]    The first cylindrical portion  16  extends from a periphery of the web  6 . The insert  14  is secured to the housing  2  by way of the first cylindrical portion  16  by any suitable means. In the illustrated embodiment features  24  are provided within the housing  2  and on an outer surface of the first cylindrical portion  16  to enable the insert to be a snap fit to the housing  2 . 
         [0058]    The second cylindrical portion  18  extends a small distance from the second side of the web  6  about a periphery of the opening  22 . An internal surface of the second cylindrical portion is provided with a screw thread  26 . 
         [0059]    The third cylindrical portion  20  extends substantially within the housing  2  from the second side of the web  6 . The diameter of the third cylindrical portion  20  is such that a first channel  28  is formed between an outer surface of the second cylindrical portion  20  and an inner surface of the third cylindrical portion. A second channel  30  is formed between an outer surface of the third cylindrical portion  20  and the housing  2 . 
         [0060]    A piston rod  32  is provided extending through the opening in the web  6 . The piston rod  32  is generally elongate and is provided with a screw thread  34  extending from a first end of the piston rod  32 . The screw thread  34  of the piston rod  32  engages the screw thread of the inner surface of the second cylindrical portion  18  of the insert  14 . The first end of the piston rod  32  is provided with a pressure foot  36 . In use the pressure foot  36  is disposed on the first side of the web  6  to abut the cartridge piston  10 . 
         [0061]    Ratchet means  40  are located adjacent the web  6  on the first side of the web  6 . The ratchet means  40  serve the purpose of allowing the piston rod  32  only to rotate through the insert  14  in a single direction. Due to the one piece construction of the housing, the ratchet means can be made larger than in known devices and so is stronger (more rigid). 
         [0062]    A dose dial sleeve  50  of generally cylindrical form comprises a first section of first diameter and a second section of second diameter. The first section is located within the second channel  30 . An inner surface of the first section and the outer surface of the third cylindrical portion  20  are provided with inter-engaging features to provide a helical thread  52  between the insert  14  and the dose dial sleeve  50 . Conveniently as in the illustrated embodiment, this is achieved by a helical track provided on the outer surface of the third cylindrical portion  20  within which a helical rib provided on the inner surface of the dose dial sleeve  50  may run. This enables the dose dial sleeve  50  to rotate about and along the third cylindrical portion  20  of the insert  14 . 
         [0063]    An outer surface of the first section of the dose dial sleeve  50  is provided with graphics  53 . The graphics are typically a sequence of reference numerals. The housing  2  is provided with an aperture or window  54  through which a portion of the graphics, representing a dosage value selected by the user, may be viewed. 
         [0064]    The graphics  53  may be applied to the dose dial sleeve  50  by any suitable means. In the illustrated embodiment, the graphics  53  are provided in the form of a printed label encircling the dose dial sleeve  50 . Alternatively the graphics may take the form of a marked sleeve clipped to the dose dial sleeve  50 . The graphics may be marked in any suitable manner, for example by laser marking. 
         [0065]    It is an advantage of this arrangement that the helical thread  52  is formed within the dose dial sleeve between the dose dial sleeve and the insert, As can be seen this means there is no direct route from outside the injector to the working surfaces of the helical thread. Should dust or dirt enter the pen this will tend to occur between the housing and the dose dial sleeve where there are no working parts with which to interfere. This is not the case for known devices in which a helical thread is formed between the housing and an interior moving surface. In addition because of the narrower diameter of the helical thread  52  formed between the dose dial sleeve and the drive sleeve in comparison to a similar thread formed between the housing and the dose dial sleeve, the helical thread  52  is more efficient and easier to overhaul. This arrangement also produces an improvement in the dose size that can be delivered for a particular linear travel of the dose expelling means. 
         [0066]    The second section of the dose dial sleeve  50  is preferably of the same outer diameter as the housing  2 . Within the dose dial sleeve  50  there is a shoulder  56  between the first section of the dose dial sleeve  50  and the second section of the dose dial sleeve  50 . 
         [0067]    A drive sleeve  60  of generally cylindrical form comprises a first part of first diameter and a second part of second diameter. A first end of the first part is located within the first channel  28  of the insert  14  in the position shown in  FIG. 1 . The first part of the drive sleeve  60  may be considered as comprising a first portion aligned with a second portion. More generally in the position shown in  FIG. 1  the first portion of the drive sleeve  60  is located between the insert  14  and the piston rod  32  while the second portion is located between the piston rod  32  and the dose dial sleeve  60 . 
         [0068]    A second end of the piston rod  32  and an internal surface of the drive sleeve  60  are splined together such that no relative rotation may occur between these parts, only longitudinal displacement. 
         [0069]    The outer surface of the second portion of the first part of the drive sleeve  60  is provided with a helical thread  62 . A nut  64  is provided on the helical thread  62  between the drive sleeve  60  and the dose dial sleeve  50 . The dose dial sleeve  50  and the nut  64  are splined together by spline means to prevent relative rotation between the nut  64  and the dose dial sleeve  50 . 
         [0070]    The second part of the drive sleeve  60  is of larger diameter than the first part of the drive sleeve  60 . There is a step  66  between the first part of the drive sleeve  60  and the second part. The second part of the drive sleeve  60  is seated within the second section of the dose dial sleeve  50 . The shoulder  56  of the dose dial sleeve  50  and the step  66  of the drive sleeve  60  are adapted to be releasably engagable with one another to form a clutch means. When, as in  FIG. 1 , the dose dial sleeve  50  and the drive sleeve  60  are not in engagement the dose dial sleeve  50  is able to rotate with respect to the drive sleeve  60 . Conveniently, the clutch means comprises a plurality of radially extending longitudinally directed teeth provided respectively on the shoulder  56  of the dose dial sleeve  50  and the step  66  of the drive sleeve  60 . When the dose dial sleeve  50  and the drive sleeve  60  are not forced together the respective teeth will ride over one another. Preferably, the radial separation of the respective teeth corresponds to a unit dosage. 
         [0071]    The second part of the drive sleeve  60  further comprises a central receiving area  68  having a peripheral recess. A button  70  of generally “T” shaped configuration is provided, the stem of which is retained within the receiving area. The stem of the button  70  is provided with a peripheral bead  71  that is retained in the peripheral recess, the button  70  being able freely to rotate with respect to the drive sleeve  60 , but being retained axially therewith. 
         [0072]    Clicker means are provided between the second section of the dose dial sleeve  50  and the second part of the drive sleeve  60 . In the illustrated embodiment, the internal surface of the second section of the dose dial sleeve  50  is provided with a plurality of longitudinally extending teeth. The radial separation of the teeth preferably corresponds to a unit dosage. The second part of the drive sleeve  60  carries a flexible toothed member  72 . Relative rotation between the dose dial sleeve  60  and the drive sleeve  60  will cause the flexible toothed member  72  to ride over the teeth to produce a series of clicks. 
         [0073]    In  FIG. 1 , the injector is provided with a filled cartridge  4 . To operate the injector a user must first select a dose. To set a dose the dose dial sleeve  50  is rotated by manipulating the second section of the dose dial sleeve  50  with respect to the housing  2  until the desired dose value is visible through the window  54 . This action draws the dose dial sleeve  60  along the second cylindrical portion of the insert  14 , The drive sleeve  60  cannot rotate since it is splined to the piston rod  32 . The piston rod  32  does not rotate due to the action of the ratchet means  40 . The drive sleeve  60  is carried away from the web  6  along the piston rod  32  by the dose dial sleeve  50  as the dose dial sleeve  50  moves out from the housing  2 . The relative rotation between the dose dial sleeve  50  and the drive sleeve  60  causes the flexible toothed member  72  to ride over the ridges in the drive sleeve  60  to create a series of clicks. This is an audible confirmation of the dose being dialed. 
         [0074]    Since the nut  64  is splined to the dose dial sleeve  50 , the relative rotation between the dose dial sleeve  50  and the drive sleeve  60  causes the nut  64  to progress along the helical thread  62  of the drive sleeve  60 . 
         [0075]    Once a desired dose has been set (as shown for example in  FIG. 2 ), to deliver the dose the user depresses the button  70  to urge the button  70  towards the first end of the housing  2 . When the button  70  is depressed the second part of the drive sleeve  60  is driven into the second section of the dose dial sleeve  50  to engage the clutch means therebetween to prevent relative rotation between the dose dial sleeve  50  and the drive sleeve  60 . The drive sleeve  60  may still rotate with respect to the button  70 . Further longitudinal movement of the button  70  causes the dose dial sleeve  50  (together with the drive sleeve  60 ) to rotate towards the first end of the injector. Since the piston rod  32  is splined to the drive sleeve  60 , the piston rod  32  is also rotated through the insert  14  and the ratchet means  40  towards the first end of the injector, thereby to advance the cartridge piston  10  and expel the desired dose of medicinal product. The piston rod  32  continues to advance until the drive sleeve  60  and dose dial sleeve  50  have returned to their initial positions ( FIG. 3 ). 
         [0076]    It can be seen that the dose selecting means and the dose expelling means extend beyond a second end of the housing  2  as the dose is selected and are returned within the housing  2  as the selected dose is expelled. 
         [0077]    Further dosages may be delivered as required.  FIG. 4  shows an example of a subsequently selected dosage. It will be noted that the nut  64  has advanced further along the helical thread  62  of the drive sleeve  60 . The position of the nut  64  along the helical thread  62  corresponds to the amount of medicinal product remaining in the cartridge  4 , such that when the nut  64  reaches the end of the helical thread  62  (in the illustrated embodiment adjacent to the step  66  of the drive sleeve  60 ) and can rotate no further this corresponds to no medicinal product remaining in the cartridge  4 . It will be seen that if a user seeks to select a quantity of medical product greater than that remaining in the cartridge  4 , this cannot be done since when the nut  64  stops rotating the dose dial sleeve  50  and the drive sleeve  60  will become locked together preventing rotation of the dose dial sleeve  50  and setting of a larger dose.  FIG. 5  shows an injector according to the present invention in which the entire medical product within the cartridge  4  has been expelled. 
         [0078]    A second embodiment of the present invention is disclosed in  FIG. 6 . Like reference numerals are used to refer to like parts as between the first and second embodiments. 
         [0079]    The piston rod  32 ′ shown in  FIG. 6  has a dual start thread. The piston foot  36 ′ is reversible. This has advantages in manufacture. As can be seen the structure of the insert  14 ′ has been revised. The first side of the web  6 ′ is substantially unchanged. The other side of the web is now provided with a boss  80 . A cylindrical portion  20 ′ extends away from the web  6 ′ about a periphery of the boss  80 . Threaded opening  22 ′ extends through the web  6 ′ and the boss  80 . An end of the cylindrical portion  20 ′ of the insert  14 ′ remote from the web  6 ′ is provided with a stop in the form of a land  104 . 
         [0080]    The dose dial sleeve  50 ′ is of modified construction. The dose dial sleeve comprises a first cylindrical portion  84  rigidly connected to a second generally cylindrical portion  86 . An inner surface of the first cylindrical portion  84  and the outer surface of the cylindrical portion  20 ′ of the insert  14 ′ are provided with interengaging features to provide a helical thread  52 ′ between the insert  14 ′ and the dose dial sleeve  50 ′. An outer surface of the first cylindrical portion  84  is provided with the dose graphics. The housing  2 ′ is provided with an aperture or window  54 ′ through which a portion of the graphics may be viewed. 
         [0081]    The second generally cylindrical portion  86  comprises a first cylindrical section  88  and a second cylindrical section  90 . The first section  88  is rigidly keyed to an inner surface of the first portion  84  of the dose dial sleeve  50 ′. The second section  90  is preferably of the same outer diameter as the housing  2 ′. Within the dose dial sleeve  50 ′ there is a shoulder  56 ′ between the first section  86  and the second section  90 . 
         [0082]    A nut  64 ′ is provided on the helical thread  62 ′ between the drive sleeve  60 ′ and the first cylindrical section  88  of the dose dial sleeve  50 ′. The first cylindrical section  88  and the nut  64 ′ are splined together by spline means to prevent relative rotation between the nut  64 ′ and the dose dial sleeve  50 ′. 
         [0083]    The shoulder  56 ′ of the dose dial sleeve  50 ′ and a step  66 ′ of a drive sleeve  60 ′ are adapted to be releasably engagable with one another to form a clutch means. When, as in  FIG. 6 , the dose dial sleeve  50 ′ and the drive sleeve  60 ′ are not in engagement the dose dial sleeve  50 ′ is able to rotate with respect to the drive sleeve  60 ′. Conveniently, the clutch means comprises a plurality of radially extending longitudinally directed teeth provided respectively on the shoulder  56 ′ of the dose dial sleeve  50 ′ and the step  66 ′ of the drive sleeve  60 ′. When the dose dial sleeve  50 ′ and the drive sleeve  60 ′ are not forced together the respective teeth will ride over one another. 
         [0084]    It will be seen that the structure of the drive sleeve  60 ′ has also been modified. The second end of the piston rod  32 ′ is provided with a scooped surface within which a domed part  90  of the drive sleeve  60 ′ may extend. The domed part  90  is centrally located within a second part of the drive sleeve  60 ′ at a first end of the receiving area. 
         [0085]    The button  70 ′ is of generally “T” shaped configuration. The stem of the button  70 ′ is retained within the receiving area. The stem of the button  70 ′ is provided with a peripheral bead  71 ′ that is retained in the peripheral recess, the button  70 ′ being able freely to rotate with respect to the drive sleeve  60 ′, but being retained axially therewith. 
         [0086]    When the button  70 ′ is depressed the drive sleeve  60 ′ is urged into contact with the dose dial sleeve  50 ′ such that the clutch means are engaged. At the same time, the scooped surface of the piston rod  32 ′ and the domed surface of the drive sleeve approach but do not contact one another. The advantage of this structure is that it enables the overall length of the device to be reduced thereby enabling easier operation of the device when expressing fluid from a cartridge. 
         [0087]    A further embodiment of the button  70 ″ and the dose dial sleeve  50 ″ can be seen in  FIG. 7 . Again like reference numerals are used to refer to like parts. In the embodiment of  FIG. 7 , the overall length of the device may be reduced still further. The second end of the piston rod  32 ″ is generally U-shaped. The limbs of the U-shape are received within a second part of the drive sleeve  60 ″. A central receiving area of the drive sleeve  60 ″ is defined by limbs (not shown) located in use between the limbs formed on the second end of the piston rod  32 ″. The button  70 ″ is of generally “T” shaped configuration. The stem of the button  70 ″ is retained within the receiving area. The stem of the button  70 ″ is provided with a peripheral bead  71 ″ that is retained in the peripheral recess, the button  70 ″ being able freely to rotate with respect to the drive sleeve  60 ″, but being retained axially therewith. 
         [0088]    The second generally cylindrically portion  86 ″ of the dose dial sleeve  50 ″ comprises a first cylindrical section  88 ″ and a second cylindrical section  90 ″ connected by a radial flange  92  extending from a part of the second section, the first section  88 ″ being rigidly keyed to an inner surface of the first portion  84 ″ of the dose dial sleeve  50 ″, and the second section  90 ″ being of the same outer diameter as the housing  2 ″. 
         [0089]    In each of  FIGS. 6 and 7 , there is a further modification to each of the dose dial sleeve and the insert. This may be seen more clearly with reference to  FIGS. 8 and 9 . 
         [0090]    At a first end of the dose dial sleeve there is located on an internal surface a radially directed lug  100  extending generally parallel to a longitudinal axis of the sleeve. At a second end of the insert on an external surface thereof there is provided a catch means. The catch means comprises a groove  102  extending about a central land  104 . The central land  104  is generally wedge shaped such that a first edge  106  nearer the start of the thread extends radially less far than a second opposite edge  108  located further along the thread. A sloping surface  110  is defined between the first edge  106  and the second edge  108 . Thus, when the dose dial sleeve is assembled to the insert, by threading the dose dial sleeve onto the insert, the lug  100  passes over the first edge  106  and over the sloping surface  110 . As the lug  100  passes fully over the land  104  some elastic deformation of the respective elements, the dose dial sleeve and the insert occurs. Once the lug  100  is over the land  104 , the second edge  108  of the land  104  acts as a stop to prevent removal of the dose dial sleeve from the insert. 
         [0091]    The location of the second edge  108  of the land  104  is conveniently chosen at a radial location corresponding to 80 units of medicinal product, that is the maximum dose available is 80 units when the dose dial sleeve is wound from the initial position shown in any of  FIG. 1, 6 or 7  to a fully extended position with the second edge  108  of the land  104  contacting the lug  100 . 
         [0092]    A fourth embodiment of the present invention is disclosed in  FIG. 10 . Like reference numerals are used to refer to like parts. 
         [0093]    As can be seen the structure of the insert  14 ′″ has been revised. The first side of the web  6 ′″ is substantially unchanged. The other side of the web is now provided with a boss  80 ′″. A radial flange  112  extends outwardly from the boss  80 ′″, the radial flange  112  being spaced from the web  6 ′″, and a cylindrical portion  20 ′″ extending away from the web  6 ′″ about a periphery of the radial flange  110 . A threaded opening  22 ′″ extends through the web  6 ′″ and the boss  80 ′″. 
         [0094]    The dose dial sleeve  50 ′″ is of modified construction. The dose dial sleeve  50 ′″ comprises a first cylindrical portion  84 ′″ rigidly connected to a second generally cylindrical portion  86 ′″. An inner surface of the first portion  84 ′″ and the outer surface of the cylindrical portion  20 ′″ of the insert  14 ′″ are provided with inter-engaging features to provide a helical thread  52 ′″ between the insert  14 ′″ and the dose dial sleeve  50 ′″. An outer surface of the first cylindrical portion  84 ′″ is provided with the dose graphics. The housing  2 ′″ is provided with an aperture or window  54 ′″ through which a portion of the graphics may be viewed. 
         [0095]    The second generally cylindrical portion  86 ′″ comprises a first inner cylindrical section  88 ′″ and a second outer cylindrical section  90 ′″. The first section  88 ′″ is rigidly keyed to an inner surface of the first portion  84 ′″ of the dose dial sleeve  50 ′″. The second section  90 ′″ is preferably of the same outer diameter as the housing  2 ′″. Within the dose dial sleeve  50 ′″ there is a radial flange  94  extending between the outer section  90 ′″ and an intermediate part of the inner section  88 ′″. 
         [0096]    A nut  64 ′″ is provided on a helical thread  62 ′″ formed on the drive sleeve  60 ′″. The nut  64 ′″ is disposed between the drive sleeve  60 ′″ and the second cylindrical section  88 ′″ of the dose dial sleeve  50 ′″. The second cylindrical section  88 ′″ and the nut  64 ′″ are keyed together by spline means to prevent relative rotation between the nut  64 ′″ and the dose dial sleeve  50 ′″. 
         [0097]    An upper surface of the radial flange  94  of the dose dial sleeve  50 ′″ and a step  66 ′″ of the drive sleeve  60 ′″ are adapted to be releasably engagable with one another to form a clutch means. When, as in  FIG. 10 , the dose dial sleeve  50 ′″ and the drive sleeve  60 ′″ are not in engagement the dose dial sleeve  50 ′″ is able to rotate with respect to the drive sleeve  60 ′″. Conveniently, the clutch means comprises a plurality of radially extending longitudinally directed teeth provided respectively on the radial flange  94  of the dose dial sleeve  50 ′″ and the step  66 ′″ of the drive sleeve  60 ′″. When the dose dial sleeve  50 ′″ and the drive sleeve  60 ′″ are not forced together the respective teeth will ride over one another.