Abstract:
An injection device includes a cap which is withdrawn from the front of the device before use to remove a boot from the needle. The cap has fingers which grip the boot and which pass down a passage through which the needle projects to inject a dose. The passage has projections disposed to reduce the effective bore of the passage, the projections having inwardly inclined resilient portions which allow the boot to be withdrawn forwardly through the passage but prevent a finger being poked into the passage.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to injection devices and, in particular, but not exclusively, to autoinjectors. 
     Description of the Related Art 
     In autoinjectors a syringe or cartridge (both hereinafter referred to generally as a syringe) is mounted in a body and a drive mechanism is provided so that, when the device is held against the flesh and fired, the syringe is moved forwardly to urge the needle into the injection site and thereafter the syringe plunger is advanced to expel a dose. After the dose has been expelled it is common to make the device safe, either by retracting the syringe into the autoinjector body or to extend and lock out a needle shroud from the front of the body, in each case shrouding the needle in a shrouding passage. Prior to use, the needle is usually covered by a boot to keep it sterile to prevent evaporation of the drug, and to facilitate assembly of the autoinjector, with the boot being withdrawn forwardly off the needle to prepare for an injection. In such designs it is necessary to withdraw the boot down the shrouding passage and this places conflicting demands on the designer. In order to allow the boot to be withdrawn, the shrouding passage must be wide enough to accommodate the diameter of the boot and any elements that engage a clasp the boot to remove it. Other design considerations mean that the maximum diameter of the boot is often similar to the outer diameter of the syringe barrel which may typically be 5 mm to 11 mm. Conversely, safety considerations require that the bore of the passage be sufficiently narrow to prevent a small child from pushing a finger into the open end of the shrouding passage surrounding the needle and sustaining a needle stick injury. It is therefore highly desirable to have a reduced effective aperture in the shrouding passage that still allows the boot to be withdrawn. Although particular reference is made to designs in which a boot is withdrawn axially from the needle, some similar considerations apply in general where access to the needle is to be obstructed in instances where there is no boot. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, in one aspect of this invention, there is provided an injection device comprising: 
     a body portion; 
     a syringe having a needle at its forward end; 
     one or more walls defining an elongate passage relative to which said syringe may pass between a rearward, retracted, position in which a forward tip of the needle is shrouded by said passage and a forward, extended, position in which said forward tip projects from the forward end of said passage, 
     wherein said passage includes a plurality of transverse projections projecting inwardly from the wall of the passage to reduce the effective cross-section of the passage and at least some of the projections include resiliently deflectable portions inclined inwardly towards the forward end of the passage. 
     In this manner the resiliently deflectable portions reduce the effective bore of the passage and their angle of inclination means that an attempt to force access to the passage from the front end is met with resilient deflection of the projections thereby further reducing the effective diameter of the passage, whereas movement of an object in the opposite direction may deflect the projections outwardly to increase the effective bore of the passage. The term ‘effective’ bore is used to mean the maximum diameter of an object that may be passed down the passage in a given direction. 
     It is preferred for the effective bore to be slightly less than the diameter of the barrel of a syringe whereby at least some of the projections engage and exert a braking effect on the syringe, should the syringe move forwards beyond a predetermined forward position. For example, in an autoinjector, it may be required to make provision for the unlikely event that the syringe shoots forwardly beyond its intended forward position during the penetration phase, for example if the flange on the rear of the syringe barrel breaks off. 
     There are many various configurations for the passage; in a design where the syringe is retracted back into the autoinjector body after the injection, the passage may simply be in a forward end of the autoinjector body. In another arrangement, the walls of the passage may comprise a needle shroud element which is relatively moveable to the body portion. 
     Although the invention may be used where the syringe is fixed relative to a body portion, with a needle shroud movable relative to the syringe and the body portion, it is preferred for the syringe to be movable relative to the body portion from a rearward position to a forward position. 
     In one type of configuration, the syringe may include a boot element which covers the needle prior to use and which is withdrawable longitudinally to expose the needle. In this instance the device conveniently includes a removable cap which initially covers at least part of the front end of the device and which is removable longitudinally to withdraw the boot. 
     Preferably the boot has an external diameter (or maximum transverse dimension) that fits with clearance in the rearward end of said passage but which passes the forward end only on deformation of said deflectable portions. 
     Preferably, the cap includes a plurality of fingers which, when the cap is in its initial position, extend rearwardly down the passage to engage the boot. 
     Preferably, when the cap is in its initial position, the fingers on the cap alternate with the projections in the passage angularly about the longitudinal axis of the passage. Preferably they together define a rearward generally cylindrical surface that surrounds with clearance an external surface of the boot element, with the fingers extending further to provide gripping regions to engage the cap. Preferably, the passage includes support surfaces for engaging the outer surfaces of the plurality of fingers on the cap as the cap is withdrawn, thereby to prevent splaying of the fingers on the cap as the cap is withdrawn. 
     According to another aspect of this invention, there is provided an injection device comprising:
         a body portion;   a syringe having a needle at its forward end, and a boot covering the needle;   one or more walls defining an elongate passage relative to which said syringe may pass between a rearward, retracted, position in which a forward tip of the needle is shrouded by said passage and a forward, extended position in which said forward tip projects from the forward end of said passage,       

     a plurality of elongate transverse projections projecting inwardly from the wall of the passage to reduce the effective cross-section of the passage, and 
     a removable cap initially disposed at the front end of the device and having a plurality of elongate fingers which when the cap is in its initial position extend rearwardly down the passage to engage the boot, 
     wherein said fingers are angularly interspersed with said transverse projections. 
     In this way the requirement for the cap fingers to extend down the shrouding passage does not require an enlarged effective bore, as the transverse projections that define the effective bore can be angularly alternated with the cap fingers. 
     Whilst the invention has been described above, it extends to any inventive combination of the features set out above, or in the following description or claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways and, by way of example only, an embodiment thereof will now be described with reference to the figures, in which: 
         FIGS. 1( a ) and ( b )  are a side view of an autoinjector arrangement of this invention, and a detail on the front end respectively; 
         FIG. 2  is a detailed view in section showing the cap and the needle shroud when separate; 
         FIG. 3  is a view similar to  FIG. 2  but with the cap assembled with the needle shroud; 
         FIG. 4( a )  is a section view through the front end of the device as supplied with the cap and boot in their initial positions; 
         FIG. 4( b )  is a view similar to  FIG. 4( a )  but with the cap and boot removed, and the shroud in a retracted position; 
         FIG. 4( c )  is a view similar to  FIG. 4( b )  but showing the syringe in an overshoot position; 
         FIG. 5( a )  is an isometric section view through the front end of the device showing the cap and boot in the condition as supplied; 
         FIG. 5( b )  is a view similar to  FIG. 5( a )  except with the boot removed for clarity; 
         FIG. 5( c )  is a view showing the cap and boot removed, and 
         FIG. 5( d )  is a view with the syringe in an overshoot position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , the embodiment of autoinjector comprises a main body portion  10  containing a drive mechanism (not shown) which, when fired, urges a syringe contained within the housing forwardly so that its needle projects beyond the front end  14  of the housing to penetrate an injection site and thereafter drives a piston down the syringe to expel a dose. A needle shroud  16  is telescopically mounted on the body for movement between the extended position seen in  FIG. 1  and a retracted position in which it is generally flush with the end of the housing (e.g.  FIGS. 4 and 5 ). The needle shroud  16  is biased forwardly and, before the injection, is free to move against the spring bias but after the injection is locked out in the position shown in  FIG. 1  to prevent access to the needle. 
     Referring now to  FIG. 2 , the needle shroud is of generally cylindrical form having two rearwardly divergent arms  18  which cooperate with a further mechanism (not shown) within the main body portion  10  to lock the shroud  16  in its extended position on completion of an injection. The shroud in this embodiment is formed of a one piece plastic moulding. On the inner surface of the cylindrical portion there is defined an internal collar region  20  of slightly reduced diameter. Rearwardly of the collar region is defined an annular slot  22  and four equi-spaced arcuate surfaces  24  acting as a retention and guide respectively for a compression spring (not shown) that urges the shroud forwardly. Forwardly of the collar region four transverse projections  26  extend longitudinally. For the first part of their length the projections  26  are integral with the inner surface  27  of the cylindrical portion but their forward ends  28  are free of the cylindrical surface and are therefore capable of resilient flexing movement. The forward ends  28  are inclined inwardly towards the forward end of the passage as shown. The forward ends are stiffened by a rib  30  such that they flex generally about a hinge region  32 . Between each transverse projection  26  is a longitudinal guide rib  34  which cooperates with the fingers  46  on the cap as to be described below. The forward ends  28  of the transverse projections  26  are therefore designed so that an object of outer diameter less than the internal diameter of the collar region  20  but greater than the diameter defined by the forward ends of the transverse projections  26  can pass down the passage forwardly and emerge from the passage defined by the cylindrical portion on flexing of the forward ends  28 . However, in the other direction, any object with a diameter greater than that defined by the forward ends  28  will contact the forward ends and tend to flex them inwards thereby further reducing the diameter of the passage. 
     Referring now to the cap  38 , in this embodiment this is of elliptical outer cross-section to slide over a corresponding shaped forward end of the main body portion  10  of the autoinector. The cap has a flat front end  40  and a tubular elliptical skirt  42 . Extending rearwardly from a circular aperture  44  in the flat front end  40  are four fingers  46  having barbs  48  at their rear ends. Each of the fingers  46  has an arcuate inner surface which, together with inner surfaces of the main parts of the transverse projections  26  defines a generally cylindrical space, when the cap is assembled in the position of  FIG. 3 . The outer surfaces of the fingers  46  slide over respective guide ribs  34  on the inner surface of the shroud to constrain the fingers  46  against splaying. Furthermore, the inner surface of the collar  20 , being of slightly reduced diameter, further constricts the fingers  46  to urge them more tightly against the boot during the initial phases of boot removal. 
     Referring now to  FIGS. 4( a ) to ( c ) and 5( a ) to ( d ) , in  FIGS. 4( a ) and 5( a )  the front end of the autoinjector is shown in the condition as supplied. Thus the needle  50  of the syringe is covered by a boot  52  including an insert  54  of soft rubber material which seals around the spigot  55  at the front end of the barrel of the syringe to keep the needle sterile. In this condition the barbs  48  on the fingers  46  of the cap  38  engage behind a rearwardly facing shoulder on the rear end of the boot  52  and are constrained against radially outward movement by the constriction provided by the collar region  20  as aforesaid. 
     In order to prepare for an injection, the cap  38  is slid forwardly off the front end of the housing  10  and in doing so the boot  52  is pulled off the syringe needle  50 . 
     Removing the cap also allows the needle shroud  16  to move forwardly under the influence of the compression spring. However the shroud can retract into the housing against the spring when the device is pressed against an injection site, as shown in  FIG. 4( b )  and  FIG. 5( c )  ready for injection. However it is important also to ensure, for safety, that it is not possible for a child to push their finger into the needle shroud and contact the needle. The front ends  28  of the transverse projections  26  are therefore designed so that they can expand a little to allow the boot  52  to be passed forwardly down the passage and removed but then return to a smaller diameter in which they define a smaller bore and which tends to further close if an attempt to made to pass a fingertip into the bore. 
     In addition, as shown in  FIG. 4( c )  and  FIG. 5( d )  the forward ends  28  also perform an important safety function in the unlikely event that the syringe over-extends during the penetration phase. This may for example occur if the flanges on the rear end of the syringe barrel break off. Should this happen, the syringe movement will be slowed and arrested by the inwardly directed forward ends  28  of the transverse projections thus retaining the syringe  12  in the device. 
     If required, the resilient flexing movement of the free ends  28  may be reinforced by means of a circlip or the like of e.g. metal spring material to mitigate again possible plastic creep if the device is to be stored for long periods.