Abstract:
An injection device operable to deliver a dose of medicament from a syringe or cartridge includes a temperature-sensitive arrangement for inhibiting operation thereof under predetermined temperature conditions. This may include a thermally responsive element that adopts a position in which operation of the device is inhibited when a temperature level is passed.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to injection devices and in particular but not exclusively to autoinjectors in which all or part of the injection cycle is automated. The invention also relates to syringes and other hand-operated injection devices. 
     It is generally desirable that an autoinjector performs consistently over a wide temperature range. Although this is achievable in some cases, in others, particularly where the fluid or material properties of the substance or substances to be injected vary significantly with temperature, it may not be possible to provide an autoinjector device that performs consistently at very low or very high temperatures or outside a given temperature range. For example the viscosity of a medicament may vary quite significantly with temperature. 
     Accordingly we have designed an injection device in which the user is alerted if the temperature of the autoinjector is not consistent with the operating range of temperatures. This alert may be active, by inhibiting operation of the device, or passive, by providing a visual indicator, or a combination of both. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, in one aspect this invention provides an injector device operable to deliver a dose of medicament from a syringe or cartridge and including a temperature-sensitive arrangement for inhibiting operation thereof under predetermined temperature conditions. 
     In this way the user may be prevented from using the device under adverse temperature conditions. 
     Operation may be inhibited for example, when a detected temperature is below a predetermined threshold temperature, or 
     when a detected temperature is above a predetermined threshold temperature, or 
     when a detected temperature is outside a predetermined range. 
     Conveniently the autoinjector includes a drive mechanism releasable to express a dose from a syringe or cartridge contained within a housing, and which may additionally be operable to move said syringe or cartridge relative to said housing to cause a needle at a forward end of said syringe or cartridge to project from said housing to penetrate an injection site in use, prior to expressing said dose. In this case, said drive mechanism may include a plunger releasable from a cocked position to move forwardly under the influence of a drive spring, and said temperature-sensitive arrangement may inhibit release of said drive mechanism. Release may be inhibited by blocking movement of a firing element, or by preventing unlatching of a latch arrangement retaining the plunger in its cocked position. 
     Typically existing autoinjectors require two or more operations to be performed to fire the device. For example, a firing trigger may only be movable to a fired position if a safety sleeve has been shifted relative to the device when the device is pressed against an injection site, or after release of a safety catch. In embodiments of this invention the thermally responsive member may directly inhibit movement of the firing trigger, or it may inhibit movement of a safety catch or the like which must be moved to allow the firing trigger to become live. 
     Advantageously said temperature-sensitive arrangement includes a thermally responsive member which, upon passing a predetermined temperature adopts a position in which it inhibits operation of said autoinjector. This may be an upper or lower limit temperature. 
     The position of the thermally responsive member may vary continuously with temperature, or the thermally responsive member may undergo a discrete movement at a predetermined temperature. 
     Conveniently two thermally responsive members are provided, one being designed to inhibit operation of the device below a first predetermined temperature and the other being designed to inhibit operation of the device above a second predetermined temperature. 
     The or each thermally responsive member may be any suitable member that changes shape with temperature, such as is a bi-morph or bi-metallic strip, or a shape memory alloy element. 
     In another embodiment said temperature-sensitive arrangement may include an electrically driven inhibiting element responsive to the output of a heat sensor to inhibit operation of said autoinjector. 
     In addition to actively inhibiting operation, the autoinjector may include an externally visible heat-sensitive indicator operable to provide a visual indication under predetermined temperature conditions. For example said heat-sensitive indicator may undergo a change in colour under predetermined temperature conditions. Alternatively, said heat-sensitive indicator may comprise a coating of thermochromic material adapted to reveal or conceal a symbol or indicia relating to the operational state of the autoinjector under predetermined temperature conditions. 
     In another aspect, this invention provides an injector device including an externally visible heat-sensitive indicator operable to provide a visual indication of the operational state of the device, under predetermined temperature conditions. 
     Whilst the invention has been described above it extends to any inventive combination of the features set out above or in the following description, claims or drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways, and, an embodiment thereof will now be described by way of example only, reference being made to the accompanying drawings in which: 
         FIG. 1  is a horizontal section view through an embodiment of autoinjector in accordance with this invention; 
         FIG. 2  is a detailed view on a portion of the barrel thereof; 
         FIG. 3  is a detailed on the rear end showing forward movement of the trigger button inhibited by a heat sensitive element, and 
         FIG. 4  is a similar view but showing the heat sensitive element shifted to allow forward movement of the trigger button. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The autoinjector shown in the drawing comprises a two part housing comprising forward and rearward generally cylindrical housing parts  10 ′, 10 ″ connected by a screw coupling. A syringe  12  having a piston  14  and a needle  16  is mounted in the forward housing part  10 ′ for movement against the bias of a spring  18  between the retracted position shown in  FIG. 1  in which the needle is inside the forward housing  10 ′, and an extended position in which the needle  16  projects therefrom. 
     The rear housing part  10 ″ contains an elongate plunger  20  having a forward end which fits inside the barrel of the syringe  12  and a rear end having a split arrowhead formation  22  that engages behind a fixed shoulder  24  in the rear end of the rear housing part  10 ″. The plunger  20  is biased forwardly by a main drive spring  26 . A firing button  28  is retained on the rear end of the housing  10 ′, 10 ″ by means of a collar  30 . The firing button  28  has an inner shell  32  that, when the button  28  is pushed forwardly, squeezes together the split arrowhead  22  so that it is released from the shoulder  24  allowing the plunger to move forwardly under the influence of the main drive spring  26 . A safety interlock may be provided which requires relative rotation of one or more of the trigger button  28 , the collar  30  and the rear housing part  10 ″. 
     On firing the device, the plunger  20  moves forwardly to contact the piston  14  and initially to move the syringe forward in the housing until it reaches it forwardmost position, with the needle  16  extending forwardly from the device to penetrate the injection site. Thereafter continued expansion of the spring moves the piston  14  down the syringe to deliver a dose. 
     The autoinjector device is specially designed to include a temperature sensitive arrangement for inhibiting operation of the device if the temperature is less than a predetermined threshold. The temperature sensitive arrangement includes two diametrically opposed bimetallic strips  34  that are anchored at their forward ends to the inner wall of the rear housing part  10 ″ in cantilever fashion so that they can flex inwardly as the temperature increases. In the low temperature position ( FIG. 3 ) the bimetallic strips  34  bear against the inner wall of the housing part  10 ′, 10 ″ and align with a forward flange  36  of the plunger button  38  so that the button is prevented from forward movement and so the device cannot be fired. However, when the temperature experienced by the bimetallic strips increases to a level above a predetermined temperature threshold, the bimetallic strips  34  flex inwardly to the position shown in  FIG. 4  where they no longer obstruct the forward flange  36  and so the trigger button  38  can be depressed to fire the device. 
     The bimetallic strips are just one way of achieving this function. Other “smart metals” or temperature sensitive shape memory alloys may instead be used which likewise undergo a change of shape at or beyond a predetermined temperature. Furthermore, a further set of temperature sensitive strips may be provided which alter shape to block forward movement of the firing button  28  when their temperature exceeds a particular threshold temperature but otherwise permit forward movement of the button. These may be spaced at 90° to the pair of lower limit strips. In this manner operation of the device is inhibited when it is outside a predetermined range of temperatures. 
     Referring again to  FIG. 1 , the forward housing part  10 ′ includes a thermally sensitive indicator region  38  which changes state when a particular operating temperature limit is passed. In a particular embodiment, the thermally sensitive region comprises a coating of thermochromic material. The coating may for example be selected so that it undergoes a colour change at a relevant threshold temperature. Alternatively, the coating may change state from clear to opaque or vice versa at a particular temperature change, thereby revealing or concealing a suitable symbol  40  or the like. Again, the indication may change from clear to opaque or vice versa when the temperature moves outside a particular range. The selection and design of suitable such thermochromic materials will be well known to those skilled in the art. 
     Although heat sensitive elements that change position and/or shape continuously with temperature or at discrete transition temperatures are preferred, in yet another embodiment, not illustrated, a temperature sensor may be provided in or on the housing, and an electrically operated latch or the like may be moved to permit/prevent firing of the device dependant on the temperature detected by the sensor.