Abstract:
A syringe configured with a limited maximum usable capacity. The syringe of the invention desirably has a retractable needle to prevent reuse. In the preferred embodiment, a dose-limiting structure includes a stop-ring member on the head of the plunger that abuts a constriction in the housing when the plunger is moved away from the needle to prevent the further rearward movement of the plunger. Preferably, the syringe of the invention is configured such that a user is tactilely signaled when the plunger has reached a position corresponding to a nominal fixed-dose. If the user attempts to force the stop-ring member beyond the constriction, the plunger seal is stripped off or removed from the plunger head and the syringe rendered inoperable. The features of the invention can also be applied to a nonretracting syringe.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a medical device and more particularly to a fixed-dose syringe that is designed to limit the amount of fluid drawn into the syringe to a predetermined maximum quantity.  
         [0003]     2. Description of Related Art  
         [0004]     Diseases, such as HIV and hepatitis, continue to spread in less developed countries at an alarming rate. A major cause of this proliferation is the reuse of syringes in mass immunization programs. Mass immunization programs, which are set up in third world countries for the purpose of preventing the transmission of infectious diseases, have vaccinators who routinely use the same needle for consecutive vaccines in order to save time and money. For example, while the standard dosage of vaccines is 0.5 ml per person, during these mass immunization programs it is often the case that a 3 cc syringe is filled with 3 ml of vaccine and used to deliver 0.5 ml of vaccine to six people.  
         [0005]     The gravity of the threat posed by AIDS and hepatitis, and the fact that the spread of the dreaded diseases is through reuse of needles by mass immunization programs, has grabbed the attention of many. As a result, the syringe art has disclosed several autodisabling syringes (syringes designed for one-time use) that are rendered inoperable after injection of a predetermined maximum dose, reducing the risk of the transmission of blood-borne pathogens. Such devices include, for example, U.S. Pat. Nos. 4,946,441; 4,961,728; 4,973,310; 5,000,737; 5,562,623; and 6,283,941. Many of the prior art devices, however, contain numerous complicated parts that substantially increase manufacturing costs. Further, the prior art has not produced a fixed-dose syringe for mass production and assembly which is simple, reliable, cost effective, and easy to use, enabling an injection to be performed with quickness, ease, precision and uniformity.  
         [0006]     A fixed-dose syringe is therefore needed that can be manufactured economically and reliably at high speed, that will fully protect the user and others from accidental needle sticks and exposure to blood-borne pathogens, and that is easier, faster and more accurate to use during mass immunization programs because of a limited maximum usable capacity. These and other advantages are provided by the invention disclosed below.  
       SUMMARY OF THE INVENTION  
       [0007]     A fixed-dose syringe is disclosed herein that provides significant advantages over the prior art. If used properly, the syringe of the present invention is rendered unusable following completion of an injection by the use of a retractable needle. This feature of the syringe serves to discourage the reuse of needles, especially in mass immunization programs, and lessens the likelihood of disease transmission in such programs. Further, the syringe is designed to limit the amount of fluid drawn. The invention includes a dose-limiting structure that renders the syringe easier, faster and more accurate to use, especially during mass immunization programs. It should be understood, however, that the dose-limiting advantages of the invention could also be applied to a nonretracting syringe.  
         [0008]     The fixed-dose syringe of the invention comprises an elongated hollow syringe housing preferably having a retraction mechanism mounted in the front end of the housing. The retraction mechanism desirably comprises a needle holder, separable retaining member and spring. A retractable needle biased for retraction in a rearward axial direction is fixed in the needle holder. Disposed in the hollow housing is a plunger comprising a plunger seal in sliding sealed contact with the interior wall of the housing. The plunger also comprises an end cap for applying thumb force and a retraction cavity that receives the retracted needle when the retraction mechanism is actuated by forward movement of the plunger after fluid has been discharged during an injection.  
         [0009]     In a preferred embodiment of the invention, the dose-limiting structure includes an inwardly directed projection on the inside wall of the housing that is positioned behind a specific point corresponding to a maximum intended dose. The dose-limiting structure also includes a stop-ring member that is disposed on the plunger rearwardly of and adjacent to the plunger seal. During aspiration, the approximate nominal fixed dose is drawn when the stop-ring member contacts the inwardly directed projection, limiting further withdrawal of the plunger. Under normal pressure, the plunger head cannot move beyond the projection. If, however, the user attempts to force the plunger head rearwardly beyond the projection, the stop-ring member will not move beyond the projection without stripping or removing the plunger seal off the plunger, preventing the aspiration of additional fluid and preventing the reuse of the syringe even if the needle is not retracted.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The apparatus of the invention is further described and explained in relation to the following figures of the drawings wherein:  
         [0011]      FIG. 1  is an elevation view of the exterior of the syringe in the pre-use position;  
         [0012]      FIG. 2  is a longitudinal cross-sectional view taken along line  2 - 2  of  FIG. 1 ;  
         [0013]      FIG. 3  is an enlarged longitudinal cross-sectional view taken along line  3 - 3  of  FIG. 1  showing the plunger withdrawn to a position corresponding to a nominal fixed-dose;  
         [0014]      FIG. 4  is a longitudinal cross-sectional view, partially broken away, taken from  FIG. 3  and showing the plunger head withdrawn rearwardly to a point where the plunger seal is removed from the plunger and the stop-ring member is still disposed on the plunger; and  
         [0015]      FIG. 5  is a detail view taken from  FIG. 3  showing the plunger with the stop-ring member disposed adjacent to and rearward of the plunger seal, and contacting the dose-limiting projection inside the housing wall. 
     
    
       [0016]     Like reference numerals are used to describe like parts in all figures of the drawings.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The structure and operation of the basic syringe and retraction mechanism as used in the present invention are disclosed, for example, in U.S. Pat. Nos. 5,385,551; 5,578,011; 5,632,733; 6,015,438; and 6,090,077, which are herein incorporated by reference. The present invention further modifies the syringe, as disclosed in those patents, to control the amount of fluid drawn into the syringe. Although the drawings depict a 1 cc syringe modified to administer a maximum dosage of 0.5 ml/cc, it should be understood that the invention is not limited to a particular dosage or size of syringe. For example, the dosage can be restricted to 1.0 ml/cc using a 3 cc syringe.  
         [0018]     Referring to  FIGS. 1 and 2 , fixed-dose syringe  10  preferably comprises tubular housing  12 , retraction mechanism  14  and plunger  16 . Housing  12  comprises a front end portion  18  and an open back end portion  20  with a longitudinally extending wall  22  therebetween. Housing  12  is preferably molded from a substantially transparent polymeric resin such as polypropylene and may be marked with the customary volume graduations on its exterior or may only include the graduation marking for the preferred predetermined dose, which is shown in  FIG. 1  as “0.5 cc/ml.” 
         [0019]     As best seen in  FIG. 5 , preferably wall  22  has an inwardly directed projection  24  with chamfered sides  26 ,  28  and flat  30  inside syringe housing  12 . Projection  24  desirably reduces the inside diameter of housing  12  by approximately 0.007 inch on each side and is an annular constriction. Those of skill in the art upon reading this disclosure will appreciate that the constriction can also be configured in other ways. For example, the constriction can be configured as circumferentially spaced projections. Projection  24  is desirably formed as an integral part of wall  22  during the molding process, but projection  24  can be formed in or inserted into housing  12  in other ways known to those of skill in the art upon reading this disclosure. Projection  24  is spaced a set distance from front end portion  18  of housing  12  so that a user can draw a predetermined maximum intended dose.  
         [0020]     The preferred chamfer angle of side  26  is between about 15 degrees and about 45 degrees, and is more preferably about 30 degrees. The chamfer angle of side  28  is preferably between about 5 degrees to about 10 degrees, and more preferably about 10 degrees. The significance of these angles is discussed below in relation to the operation of the device.  
         [0021]     As shown in  FIGS. 2 and 3 , retraction mechanism  14  is mounted within front end portion  18  of housing  12  and preferably comprises an elongated needle holder  32 , separable retaining member  34 , spring  36  and needle  38 . Needle  38 , which is preferably fixed in needle holder  32  by means of an adhesive  40 , is extended in the unretracted position through front end portion  18  and covered with a removable protective cap  42 . Separable retaining member  34  is preferably a ring-like structure separably and frictionally engaged with needle holder  32  to hold needle  38  against the retraction force applied by compressed spring  36 .  
         [0022]     Referring to  FIGS. 2, 3  and  4 , plunger  16  preferably comprises substantially cylindrical sidewall  46  with a lower end portion  48  and an upper end portion  50 . Lower end portion  48  of plunger  16  comprises a head  52  with a reduced diameter portion  54  flanked by raised annular shoulders  56 ,  58 . An elastomeric plunger seal  60  and a stop-ring member  62  are mounted on the reduced diameter portion  54  in between first and second shoulders  56 ,  58 . Seal  60  is compressed between first shoulder  56  and stop-ring member  62 , is in slidable sealed contact with the interior wall  64  of housing  12 , and has channel  66  along outer wall  68 . Stop-ring member  62  is compressed between plunger seal  60  and second shoulder  58 , and can be configured as a circular part, split circular part, or any other similar configuration. In the preferred embodiment, stop-ring member  62  is made of a suitable medical grade polymeric material that is less compressible than plunger seal  60 . One such preferred polymeric material is an acetal resin marketed under the trademark DELRIN by DuPont. Stop-ring member  62  could also be made of a suitable medical grade metal, such as stainless steel, in which case stop-ring member  62  can be made as a split ring if needed so that it can be installed over annular shoulder  56  during assembly of syringe  10 . Stop-ring member  62  could also be made of a ceramic material.  
         [0023]     The inner diameter of stop-ring member  62  is preferably sized to receive plunger head  52  therethrough with a slight gap sufficient to allow stop-ring member  62  to move freely on plunger head  52  when plunger seal  60  is not mounted on reduced diameter portion  54  of plunger head  52 . The inner diameter of stop-ring member  62 , however, is not large enough for stop-ring member  62  to move beyond first and second shoulders  56 ,  58  without sufficient deformation. The outside diameter of stop-ring member  62  is preferably sized to allow stop-ring member  62  to slide inside housing  12  in fluid chamber  44  when plunger  16  is installed in syringe  10  with plunger seal  60 , but is large enough to restrict the movement of ring  62  past projection  24  during aspiration, as described below.  
         [0024]     Plunger head  52  also has a tip portion  70  forming an opening into retraction cavity  72 . Removable plug member  74  is preferably held in the opening of retraction cavity  72  by frictional engagement and cooperates with head  52  to seal the opening of retraction cavity  72 . Removable plug member  74  also has a front portion  76  extending beyond tip  70 . Retraction cavity  72  at least partially retains retracted needle  36 , needle holder  32 , plug member  74  and spring  36  upon retraction.  
         [0025]     Upper end portion  50  of plunger  16  comprises an end cap  78  for depression of the plunger by the thumb. End cap  78  comprises a circular end wall with an opening  80  for closure  82 . Closure  82  has a head  84  that is connected to a longitudinally extending annular skirt  86 . Head  84  of closure  82  snuggly fits into opening  80  and effectively seals opening  80  so that fluid particles cannot escape. Annular skirt  86  frictionally engages the interior wall of plunger  16 . A vent (not shown) can be disposed in end cap  78  for the venting of retraction cavity  72 ; however, the vent can also be located within the wall of plunger  16 .  
         [0026]     Back end portion  20  of housing  12  comprises laterally extending wings  88  and collar  90 . Laterally extending wings  88  operate in conjunction with end cap  78  to allow one handed operation of the syringe. Collar  90  extends behind laterally extending wings  88  and comprises opening  92 , which closely receives the outer periphery of end cap  78  when plunger  16  is depressed to the retracted position. After retraction has occurred, plunger  16  can no longer be grasped because end cap  78  is neatly tucked into opening  92 .  
         [0027]     Turning now to the operation of syringe  10 ,  FIGS. 1 and 2  show the syringe in the ready-to-fill position. To draw fluid into fluid chamber  44 , needle  38  is inserted into a liquid container, such as a vial, and head  52  of plunger  16  is pulled toward open back end portion  20  of housing  12  until stop-ring member  62  contacts inwardly directed projection  24 . The user will feel contact between stop-ring member  62  and inwardly directed projection  24 . At this point, a preferred limited maximum usable capacity of the syringe has been met.  FIG. 3  depicts the plunger approaching the position corresponding to the nominal capacity of syringe  10 . As used herein, “nominal capacity” shall mean the intended fixed dosage set by the manufacturer. As used herein, the term “limited maximum usable capacity” of a syringe shall mean the capacity sufficient to aspirate the intended nominal capacity. For example, as one skilled in the art will appreciate, when stop-ring member  62  contacts projection  24 , preferably about 10 percent to about 20 percent of fluid in excess of the intended fixed-dose is drawn into syringe  10  so that the user can remove air bubbles or account for ullage if necessary.  
         [0028]     Referring to  FIGS. 2 and 3 , after obtaining the predetermined nominal maximum dosage, needle  38  is then inserted into a patient (not shown) and plunger  16  is depressed toward front end portion  18  to the end-of-injection position. Upon reaching the end-of-injection position (where some fluid may still be emitting from the needle), plunger  16  is forced further down into housing  12 . When this occurs, plunger tip  70  contacts and moves separable retaining member  34 , reducing the frictional engagement between needle holder  32  and separable retaining member  34 . Further depression of plunger  16  also removes plug member  74  from the opening of retraction cavity  72 . When the frictional engagement between needle holder  32  and separable retaining member  34  is less than the retraction force of spring  36 , spring  36  rapidly expands, causing needle holder  32  to propel upwardly into the opened retraction cavity  72 , simultaneously withdrawing needle  38  at least to a position where needle  38  is withdrawn into housing  12 , and neatly tucking end cap  78  into open back end portion  20  of housing  12  to prevent reuse.  
         [0029]     Before needle  38  is inserted into the patient, if the user attempts to move plunger  16  in the rearward direction (marked  57  in  FIG. 4 ) and past the position corresponding to the intended maximum dosage, the user meets resistance. The abutment of stop-ring member  62  with projection  24  causes this resistance. In order to move plunger  16  beyond the position associated with the intended maximum dosage, the user will preferably have to exert about 20 pounds of force on plunger  16 . This amount of resistance is generated as a result of the preferred dimensions of stop-ring member  62  and projection  24 , and the materials used for each. For example, although the chamfer angle for side  28  is smaller so that stop-ring member  62  can move easily over projection  24  when loading plunger  16  during assembly, the larger chamfer angle of side  26  contributes to the amount of force required to move stop-ring member  62  beyond projection  24 . In addition, stop-ring member  62  should be fairly thin but rigid enough that plunger seal  60  is stripped off plunger head  52  if the user pulls plunger  16  beyond the position corresponding to the nominal fixed-dosage. If stop-ring member  62  is too thick or if stop-ring member  62  deforms too easily, when a user attempts to pull plunger  16  beyond the position corresponding to the nominal fixed-dosage, too much pressure may be placed on plunger seal  60  or plunger seal  60  may not resist movement over projection  24 , respectively.  
         [0030]     As evidenced in  FIG. 4 , the further withdrawal of plunger head  52  beyond projection  24  will not draw more fluid into syringe  10  because stop-ring member  62  will not move beyond projection  24  without stripping off or removing plunger seal  60  from plunger head  52 . Without plunger seal  60 , plunger  16  will no longer create suction to draw additional fluid into syringe  10  and the syringe will no longer operate, as plunger seal  60  cannot again be properly mounted on plunger head  52  to create suction. Therefore, removing plunger seal  60  from plunger  16  prevents reuse of syringe  10  even if needle  38  is not retracted after use.  
         [0031]     Upon removal from plunger  16 , plunger seal  60  preferably remains in housing  12  between inwardly directed projection  24  and front end portion  18 . With plunger seal  60  off plunger head  52 , stop-ring member  62  preferably remains on and is free to float about plunger head  52 .  
         [0032]     One skilled in the art will appreciate based on this disclosure that projection  24  could extend further into the housing such that the contact between plunger seal  60  and projection  24  alerts the user that the maximum intended movement of plunger  60  has been reached and if the user attempts to move plunger  16  further rearwardly, plunger seal  60  will be stripped off or removed from plunger  16  without the aid of ring  62 .  
         [0033]     Other alternations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading the present disclosure, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventors are legally entitled.