Abstract:
A syringe for dispensing a fluid comprising: a barrel for containing the fluid; a plunger having a plunger head slideably mounted and retractable within the barrel; and locking means. The locking means includes fixing means which, when engaged, permanently prevent retraction of the plunger head relative to the barrel beyond a predetermined distance, thereby limiting the travel of the plunger head.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to syringes. In particular, but not exclusively, the invention relates to syringes having means to limit the dose that may be dispensed by the syringe. 
   Pre-filled syringes of medicine are supplied to hospitals and other medical centres. Syringes are generally available in a number of standard sizes to provide such doses as 1, 3, 5, 10, 20, 30 and 50 ml. An individual patient may require a dose which is not one of these standard volumes. Therefore, a combination of standard doses will be supplied. This adds to the cost of treatment and causes greater discomfort to the patient. Combining standard doses can also cause error in the dosage applied, and lead to a decrease in accuracy of the dosage dispensed. 
   It is known to provide standard syringes which include a clamping device mounted to the plunger to limit the volume of fluid that is dispensed, thereby allowing non-standard dosages. These clamping devices are selectively positionable along the plunger at discrete locations. However, accidental movement of the clamping device can occur. Also, for disposable syringes, it is advantageous to provide a simple method of permanently locking the clamping device at a specific dosage. 
   BRIEF SUMMARY OF THE INVENTION 
   It is advantageous to provide a pre-filled syringe including a locking device which may only be fitted at the time of assembly and filling. Once assembled and filled, it is preferable that the locking device be operated for permanent locking such that the syringe can not be altered by a user of the syringe. 
   According to a first aspect of the present invention there is provided a syringe for dispensing a fluid comprising:
         a barrel for containing the fluid;   a plunger having a plunger head slidably mounted and retractable within the barrel; and   locking means, wherein:   the locking means includes fixing means which, when engaged, permanently prevent retraction of the plunger head relative to the barrel beyond a predetermined distance, thereby limiting the travel of the plunger head.       

   Preferably the locking means comprises a locking member provided at the plunger, and the fixing means comprises means to prevent sliding of at least a portion of the locking member relative to the plunger. 
   In a first embodiment of the present invention, the sliding prevention means comprises one or more teeth provided at the locking member for embedding into the plunger to permanently fix the locking member relative to the plunger. Preferably the fixing means further comprises means to prevent removal of the locking member from the plunger. Preferably the removal prevention means comprises a permanent lock. 
   Preferably the locking member comprises two hinged portions and the permanent lock is provided opposite the hinge. Preferably the permanent lock comprises a resilient tab positioned at one of the hinged portions and a slot positioned at the other of the hinged portions. Preferably the resilient tab includes a number of barbs that interlock with a number of detent members provided at an internal surface of the slot. Closing of the hinged portions causes the resilient tab to locate in the slot to prevent further opening of the hinged portions. Preferably the permanent lock is tamper-proof. 
   Preferably the plunger comprises a plurality of webs extending radially from a central axis of the plunger. Preferably the locking member includes a portion that is complementary in profile to the plunger for mounting the locking member to the plunger. Preferably at least a portion of the plunger is cruciform and each hinged portion of the locking member includes an oversized slot for receiving an arm of the cross. Closing of the hinged portions with each slot receiving an arm of the cross results in enclosure of a section of the plunger by the locking member. 
   Preferably the locking member is provided with dosage indicating means. 
   Preferably at least the locking member is formed from a polymer. 
   In a second embodiment of the present invention, the locking means comprises a longitudinal rail member provided at the plunger, and a locking member slidably mounted to the rail member. Preferably the locking member comprises a locking ring provided around the rail member. 
   Preferably the rail member is formed integrally with the plunger. 
   Preferably the rail member is provided substantially along all of the length of the plunger. Preferably the rail member is integral with the plunger at each longitudinal end, and is spaced apart from the plunger between each end. 
   Preferably the rail member is provided between two adjacent webs of the plunger. Preferably the rail member is adapted to fit into the quadrant defined by two arms of the cruciform plunger and the barrel. 
   Alternatively the rail member comprises a longitudinal insert. Preferably the rail member includes one or more mounting members for mounting the insert to the plunger. Preferably the rail member is connected to one or more mounting members at each longitudinal end, and is spaced apart from the mounting members between each end. 
   Preferably the rail member includes a plurality of corrugations to form graduations along the rail member. Preferably the corrugations are spaced such that each graduation corresponds to a predetermined change in the volume defined by the barrel and plunger head. The predetermined distance is proportional to the predetermined change in volume. Preferably the predetermined change in volume is 1 milliliter or more. 
   Preferably the lateral width of the rail member is greater than the depth of the rail member. Preferably the corrugations are provided only at the lateral sides of the rail member. Preferably an engaging member protrudes from one portion of the internal surface of the locking ring. Preferably the locking ring is adapted to freely slide along the rail member when the locking ring is at a first orientation such that the engaging member does not engage with the corrugations. Preferably the locking ring is further adapted to prevent sliding along the rail member when the locking ring is at a second orientation such that the engaging member engages with the corrugations. Preferably the locking ring includes indenting means such that the locking ring permanently prevents sliding along the rail member when the locking ring is at the second orientation. 
   Preferably the indenting means comprises an internal indent member provided at a guiding surface of the locking ring. Preferably the indenting means comprises an external indent member for engaging with a portion of the rail member. Preferably the external indent member is engageable with a side rail of the rail member. 
   Preferably the locking ring includes an arm extending from the outer circumference of the ring. Preferably the arm provides means for rotating the locking ring when mounted to the rail member. Preferably the arm further provides a stop which contacts the barrel when the plunger head is advanced into the barrel. Therefore, the arm limits the travel of the plunger head. 
   According to a second aspect of the present invention there is provided a locking member for a syringe, the syringe having a barrel for containing a fluid, and a plunger having a plunger head slidably mounted and retractable within the barrel, the locking member being provided at the plunger or barrel and provided with fixing means which, when engaged, permanently prevent retraction of the plunger head relative to the barrel beyond a predetermined distance, thereby limiting the travel of the plunger head. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  shows a longitudinal view of a syringe according to the prior art; 
       FIG. 2  shows a longitudinal view of a syringe according to a first embodiment of the present invention; 
       FIG. 3  shows a plan view of the locking member of the syringe of  FIG. 2  in a fully opened position; 
       FIG. 4  shows a plan view of the locking member of  FIG. 3  in a fully closed position; 
       FIG. 5  shows a plan view of the locking member in a partially open position and the plunger of the syringe of  FIG. 2 ; 
       FIG. 6  shows the locking member in a fully closed position and plunger of  FIG. 5 ; 
       FIG. 7  shows a perspective view of the longitudinal insert of a locking member according to a second embodiment of the present invention; 
       FIG. 8  shows a side view of the insert of  FIG. 7 ; 
       FIG. 9  shows a detailed side view of a portion of the insert of  FIG. 7 ; 
       FIG. 10  shows a sectional plan view of the locking ring of a locking member according to a second embodiment of the present invention; 
       FIG. 11  shows a perspective view of the locking ring of  FIG. 10 ; 
       FIG. 12  shows a perspective view of an alternative locking ring at a first orientation; 
       FIG. 13  shows a perspective view of the alternative locking ring of  FIG. 12  at a second orientation. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , there is shown a syringe  10  according to the prior art. The syringe  10  includes a barrel  20  that contains the fluid to be dispensed from the nozzle  12  of the syringe  10 . Slidably mounted within the barrel  20  is the plunger head  36  of a plunger  30 . The plunger  30  includes a grip  32  located at the far end of the plunger  30  for extracting the plunger  30  out of, and retracting the plunger  30  into, the barrel  20 . The plunger  30  includes a scale  14  for indicating the volume of fluid that is dispensed. The plunger head  36  sealingly engages with the barrel  20  in a known manner. 
     FIG. 1  shows the syringe  10  with the plunger  30  fully extended. The plunger  30  is free to slidably retract into the barrel  20  until the grip  32  makes contact with an end stop  22  provided on the barrel  20 . 
     FIG. 2  shows a syringe  10  according to a first aspect of the present invention. The syringe  10  is similar to that of  FIG. 1  except for the inclusion of locking means in the form of a locking member  40 . Other like features are denoted using like reference numerals. 
   The locking member  40  is mounted on the plunger and, when it is not engaged as explained below, may be positioned at any location along the plunger  30  between the grip  32  and the end stop  22 . As before, a scale  14  is provided on the plunger and dosage indicating means  42  are provided on the locking member  40 . 
   Referring to  FIGS. 3 to 6 , plan views of the locking member  40  are shown. The locking member  40  comprises two semicircular portions  44 ,  46  connected together by a hinge  48 . Diametrically opposite the hinge, when the two semicircular portions  44 ,  46  are brought together, is removal prevention means in the form of a permanent lock  50 . 
   Along the abutting edges  52  of the semicircular portions  44 ,  46  are provided a number of teeth  54 . As shown particularly in  FIG. 6 , these teeth are provided for embedding into the plunger  30  to prevent sliding of the locking member  40  relative to the plunger  30 . 
   Together the teeth  54  and permanent lock  50  provide fixing means to prevent sliding or removal of the locking member  40  relative to the plunger  30 . Therefore, retraction of the plunger head relative to the barrel beyond a predetermined distance is permanently prevented. 
   The permanent lock  50  comprises a resilient tab  58  positioned at one of the hinged portions  44 , and a slot  56  located at the other hinged portion  46 . The tab  58  includes a number of barbs (not shown) along its length. The slot  56  includes a number of detent members (not shown) provided on an internal surface of the slot  56 . As the two hinged portions  44 ,  46  are brought together, the barbs of the resilient tab  58  interlock with the detent member. In normal use, the two hinged portions  44 ,  46  are thus permanently locked together. The permanent lock  50  is therefore tamper-proof, as the user is prevented from removing the resilient tab  58  from the slot  56 . 
   Each hinged portion  44 ,  46  includes a slot  60 . A typical plunger  30  is cruciform and the slots  60  are provided to receive an arm  34  of the cross. The slots  60  are oversized relative to the thickness of the arms of the cross so that the arms  34  may be received when the locking member  40  is pivoting towards a closed position. 
   The hinge  48  and permanent lock  50  are positioned such that, when the locking member is closed, a gap  62  exists between the two hinged portioned  44 ,  46 . Therefore the arms perpendicular to those received in the slots  60  are located in the gap  62 . The gap  62  and slots  60  define a portion of the locking member  40  which is complimentary in profile to the plunger  30 . 
   The components of the syringe  10  are typically made from a polymer. 
     FIGS. 7 to 11  show a second embodiment of the present invention. 
   The locking member comprises a rail member in the form of a longitudinal insert  70  and a locking ring  90  which may be mounted to the insert  70 . However, it is to be appreciated that the rail member may form an integral portion of the plunger  30 . The plunger  30  is typically a moulded polymer and the rail member may be included with the plunger  30  during the moulding process. 
     FIGS. 7 to 9  show the longitudinal insert  70 . The insert  70  is adapted to fit into the quadrant defined by two arms  34  of the cruciform plunger  30  and the barrel  20 . The insert  70  includes two side rails  72 , a top portion  74  and a base portion  76 . The side rail  72 , top portion  74  and base portion  76  act as mounting members for abutting and mounting the insert  70  to the plunger  30 . 
   The insert  70  further includes a central rail  80  for carrying the locking ring  90 . The rail  80  is connected to the top portion  74  and base portion  76  but, as shown in  FIG. 8 , is spaced apart from the side rails  72 . 
   As best shown in  FIG. 9 , the rail  80  includes a number of corrugations  82  which form graduations along the rail  80 . The spacing of the corrugations are such that each graduation corresponds to a predetermined change in volume defined by the barrel  20  and plunger head  36 . The predetermined change in volume is one milliliter. For syringes which provide larger doses, the predetermined change in volume may be greater than one milliliter. Dosage indicating means (not shown) may be provided at the insert  70 . 
   The rail  80  has a greater width (measuring in the direction of arrow A in  FIG. 8 ) than the depth of the rail  80 . The corrugations  82  are provided only at the lateral sides of the rail  80 . 
     FIGS. 10 and 11  show the locking ring  90 . Fixing means is provided at the internal surface  92  of the locking ring  90  for fixing the locking ring  90  relative to the insert  70 , and therefore the plunger  30 . The fixing means comprises an engaging member  94  and a guiding surface  96 . At a first orientation of the locking ring, the guiding surface  96  and engaging member  94  are adjacent the surfaces of the rail member, the distance between which define the depth of the rail  80 . This depth is less than the distance between the guiding surface  96  and engaging member  94  and therefore the locking ring is free to slide along the rail  80 . When the locking ring  90  is rotated towards a second orientation, the guiding surface  96  comes into contact with the lateral sides of the rail  80  due to the greater width of the rail  80 . The available internal distance is gradually decreased by the guiding surface  96  as rotation occurs. The locking ring  90  is permanently fixed at the second orientation as the engaging member fully engages with the corrugations  82  at one lateral side and an edge of the opposing lateral side is forced into an internal indent  98  provided at the guiding surface  96 . 
   For additional permanent fixing at the second orientation, an external indent provided by a resilient tab  99  may be provided at the locking ring  90  and this is shown in  FIGS. 12 and 13 . The tab  99  resiliently deforms and then engages with a side rail  72  as the locking ring  90  is moved from the first to the second orientation. 
   The locking ring  90  includes an arm  100  which extends from the outer circumference  102  of the locking ring  90 . This arm  100  provides means for rotating the locking ring  90  when it is mounted to the rail member  80 . When the locking ring  90  has been permanently fixed relative to the insert  70 , the arm  100  also provides a stop when the plunger head  36  is advanced into the barrel  20 . The arm therefore limits the travel of the plunger head  36 . 
   The locking ring  90  further includes a stop surface  104  which contacts a side rail  72  at the second orientation and prevents further rotating of the locking ring  90 . 
   The rail  80  is connected to a web member  77  of the base portion  76 . The web member  77  is sufficiently thin such that it can pass through a gap  106  provided at the locking ring  90 . This allows fitting of the locking ring  90  to the insert  70 . It should be appreciated that the locking ring  90  can only be fitted at the time of assembly and filling of the syringe as the plunger  30  must be fully extracted to expose the web member  77 . 
   The insert  70  can be fitted to the plunger  30  in a number of known ways, such as using an adhesive. The insert  70  and locking ring  90  are typically made from a polymer. 
   Various modifications and improvements can be made without departing from the scope of the present invention. For example, at least a portion of the locking member may be provided at the barrel.