Abstract:
A holder with a safety shield for a drug delivery device; the shield obstructing access to a needle of the drug delivery device following use thereof. The safety shield may be actively deployed, in which case the health care worker must perform an action beyond complete depression of the pusher into the body of the drug delivery device to deploy the shield. Alternatively, the safety shield may be deployed passively or automatically, in which case deployment of the shield occurs upon complete depression of the pusher into the body, with no additional action required of the health care worker. The safety shield is spring-loaded and released to its extended position by a mechanical coupling of a series of position members, including levers, formed on the holder and the drug delivery device.

Description:
[0001]     This application claims priority of U.S. Provisional Appl. No. 60/443,826, filed Jan. 30, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an injection device comprising a holder with a safety shield for a drug delivery device and more particularly, to a holder having a deployable safety shield that may be deployed to cover the end of a needle cannula after use to prevent exposure of the user to the contaminated needle and to reduce the risk of injury from accidental needle-stick.  
         [0003]     The risks of accidental needle-stick injury following use of a drug delivery device, such as a hypodermic syringe, are well known. In fact, legislation has been enacted in the United States requiring that certain types of syringes include features intended to reduce or eliminate the possibility of accidental needle-stick. In addition to any Federally mandated requirements for such features, any device for use in connection with a syringe intended to address the risk of needle-stick injury should be simple to use and reliable so as to ensure that the device performs its intended function in every instance.  
         [0004]     Many devices have been developed for shielding needles after use. Some of these devices are complex, and some require considerable manipulation by the user to position the shield about the needle to protect the user. In some cases, such manipulation may require the use of both hands of the user.  
         [0005]     Some prior art devices having deployable shields for shielding needles may lack precise control for deploying the shield. As a result, the shield may deploy when such deployment is not intended. Such unintended deployment may have numerous disadvantages. For example, if the deployment occurs when the needle is inserted into the patient, then this may interfere with the dispensing of the medication contained in the syringe. In some prior art devices, unintended deployment may also occur during shipment of the device (assembled with or without a syringe) rendering the device unusable for an actual injection.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a holder for a drug delivery device such as, for example, a hypodermic syringe assembly. The inventive holder includes a selectively deployable safety shield that prevents access to the needle forward tip following use of the syringe assembly to enhance safety of the user. The present invention is also directed to an injection device comprising a drug delivery device contained within a holder having a selectively deployable safety shield that prevents access to the contaminated needle forward tip after use of the drug delivery device.  
         [0007]     The inventive holder includes a deployable safety shield that extends to cover the forward tip of the needle following injection by the health care worker. In one aspect of the subject invention, the safety shield may be “actively” deployed by performance of an action beyond the normal completion of the injection stroke of the pusher in the syringe body. In a further aspect of the subject invention, the safety shield may be “passively” deployed upon completion of the injection stroke with no additional action required of the health care worker.  
         [0008]     The safety shield of the holder is spring-loaded and movable from a first or retracted position in which the forward tip of the needle is exposed, to a second or extended position in which the forward tip of the needle is contained within the safety shield. The safety shield is biased by a biasing means to move from the first position to the second position. The safety shield may be released from the first position by alignment and mechanical coupling of a plurality of components, including components provided on the holder and syringe. Prior to use of the drug delivery device, those plurality of components are not all in alignment and activation of the safety shield is not possible, i.e., the safety shield cannot be caused to move from the first position to the second position under bias by the spring. Once the complete dose of medicament contained in the medical device is injected into the patient, the plurality of components are brought into alignment and may be mechanically coupled together to effect release of the safety shield from the first position and enable movement of the safety shield from the first position to the second position.  
         [0009]     These and other features of the invention will be more fully understood from the following description of specific embodiments of the invention taken together with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     In the drawings, wherein like reference characters denote similar elements throughout the several views:  
         [0011]      FIG. 1  is a side view of a drug delivery device and holder constructed in accordance with an embodiment of the present invention;  
         [0012]      FIG. 2  is an exploded side view of the drug delivery device and holder of  FIG. 1 ;  
         [0013]      FIG. 3  an exploded perspective view of the holder of  FIG. 1 ;  
         [0014]      FIG. 4  is a cross-sectional side view of the holder and drug delivery device of  FIG. 1  prior to use;  
         [0015]      FIG. 5  is a cross-sectional side view of the holder and drug delivery device of  FIG. 1  after use and prior to deployment of the safety shield;  
         [0016]      FIG. 6  is a cross-sectional side view of the holder and drug delivery device of  FIG. 1  after deployment of the safety shield;  
         [0017]      FIG. 7  is a side view of an alternative embodiment of the holder and drug delivery device of the present invention;  
         [0018]      FIG. 8  is a cross-sectional side view of the holder and drug delivery device of  FIG. 7  prior to use;  
         [0019]      FIG. 9  is a perspective view of the holder and drug delivery device of  FIG. 7  after use and after deployment of the safety shield; and  
         [0020]      FIG. 10  is a schematic of a pusher cap locking mechanism useable with the subject invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The present invention is directed to a holder and to an injection device having the combination of the holder and drug delivery device. The holder includes a housing and a safety shield provided in the housing movable from a first or retracted position, in which a forward tip of a needle cannula of the drug delivery device is exposed, to a second or extended position, in which the forward tip of the needle cannula is contained within the safety shield. The drug delivery device is preferably a syringe comprising a body having proximal and distal ports and a reservoir within which a drug substance may be held. The syringe further comprises a needle cannula provided on the body, the needle cannula having a forward tip, preferably sharpened, and a rearward tip in fluid communication with the reservoir. The syringe further comprises a pusher including a pusher cap having a cap wall, a pusher stem and a stopper at one end of the pusher stem. The stopper is movable in the reservoir in a proximal to distal direction over a length defining an injection stroke. Various components provided on the housing and drug delivery device are selectively alignable when the stopper has been caused to be inserted into the reservoir a predetermined extent, i.e., upon completion of an injection stroke. Alignment of the various components enables the safety shield to be released from its first or retracted position. Release of the safety shield upon alignment of the various components may be effected by the user depressing or activating a release mechanism, or it may occur automatically upon completion of the injection stroke. Once activated, the safety shield is caused to move by a biasing means such as, for example, a coil spring, from the first position to the second or extended position.  
         [0022]     The terms “distal” and “proximal” are used herein as reference designations only to facilitate description of the present invention. As used herein, the term “distal” refers to a location, element or component that is near the patient (i.e., the needle end of the device), and the term “proximal” refers to a location, element or component that is near the user of the injection device (i.e., the pusher cap end of the device).  
         [0023]     Referring next to the drawings, the various embodiments of the present invention will now be discussed in detail. Referring first to FIGS.  1  to  6 , an injection device is depicted and generally identified by reference character  10 . The inventive injection device  10  comprises a holder  200  and a drug delivery device. By way of non-limiting example, the drug delivery device is shown to be a syringe and is designated by the reference numeral  18 . Other drug delivery devices may be used with the subject invention and any syringe design may be used. For illustrative purposes, a particular syringe design is described and depicted herein. The syringe  18 , as shown in  FIGS. 2 and 4 - 6 , includes a longitudinally elongate syringe body  11  having an internal reservoir  12  for containing a drug substance, that term being used herein to refer to any liquid medicament injectable into a patient, including, by way of illustration and not limitation, therapeutic drugs, vaccines, and the like. The syringe body  11  has a distal port  13  through which the drug substance contained in the reservoir may exit therefrom. The syringe body  11  also has a proximal port  14 . A needle cannula  16  is in fluid communication with the reservoir  12  via the distal port  13 . The holder  200  provides shielding of the needle cannula  16  after use of the injection device  10  to reduce the likelihood of accidental needle-stick injury to the user or patients.  
         [0024]     The syringe  18  further has a pusher  250  which includes a cylindrical pusher cap  252  having a longitudinal cavity  254  which is bounded by a cap wall  256 . The pusher  250  further includes a pusher stem  258  connected in coaxial relation to the cap  252  for insertion of the pusher stem through the proximal port  14  into the reservoir  12 . The distal end of the pusher stem  258  is constituted by a plunger or stopper  24 . With the pusher stem  258  acting on the plunger  24 , the proximal to distal advancement of the pusher stem  258  into the reservoir  12  reduces the volume thereof resulting in the exiting of the drug substance through the distal port  13 .  
         [0025]     The needle cannula  16  has rearward and forward tips  33 ,  34 , respectively ( FIG. 4 ). The needle cannula  16  is supported on the syringe body  11  such that the forward tip  34  is distal of the syringe body  11 . The rearward tip  33  of the needle cannula  16  is in fluid communication with the reservoir  12  through the distal port  13  such that drug substance within the reservoir can flow through the needle cannula  16  and exit through the forward tip  34 . The needle cannula  16  may have any length, depending upon the type of injection desired. For example, the inventive injection device  10  may be used to deliver intramuscular, subcutaneous, intradermal, interstitial, or other types of injections. In an alternative embodiment (see, e.g.,  FIGS. 5 and 6 ), a limiter  300  may be provided on the distal end of the syringe body  18  such as that disclosed in U.S. Pat. No. 6,494,865 B1, the entire disclosure of which is hereby incorporated by reference herein. The limiter  300  defines a skin engaging surface  310  having a preferred outer diameter of approximately 5.5 mm. The forward tip  34  of the needle cannula  16  extends beyond the skin engaging surface  310  a distance ranging from 0.5 mm to 3 mm. The combination of the skin engaging surface  310  and limited length of the needle cannula  16  provide a device particularly well-suited for administering an injection into the intradermal space of a patient&#39;s skin. As will be appreciated by those skilled in the art, any skin engaging surface configuration may be used with the subject invention to achieve intradermal injections.  
         [0026]     As best shown in  FIG. 3 , the holder  200  includes a housing  210 , a safety shield  220 , a biasing means  230 , and a retainer ring  240 . The syringe  18  is placeable within the syringe holder  200  and may be prefilled with the drug substance.  
         [0027]     With reference to  FIGS. 3-6 , the housing  210  includes a housing body  260  which is cylindrical and has a longitudinal housing cavity  262 . One or more windows  216  may extend through the wall of the housing body  260  to expose the housing cavity  262 .  
         [0028]     The housing body  260  has an outer surface which is preferably shaped to accommodate the thumb and middle finger of the user&#39;s hand to facilitate gripping of the housing  210 , which may be by a single hand of the user. Such shaping of the outer surface of the housing body  260  may be by one or more depressions  214  which are preferably provided as a pair of diametrically opposed depressions  214  located on opposite sides of the housing body  260  to facilitate gripping of the syringe holder  200  during use (see, e.g., FIGS.  4  to  6 ). The depressions  214  may be textured or otherwise contain a feature that enhances gripping by the user. Alternative shapes of the outer surface of the housing body  260  to facilitate gripping are possible. For example, the intermediate portion  264  of the outer surface between the proximal and distal ends  266 ,  268  of the housing  210  may have a peripheral dimension which is reduced relative to the peripheral dimensions of the proximal and distal ends  266 ,  268  of the housing  210 . Such a reduced peripheral dimension may provide the outer surface of the housing body  260  with the shape of an hourglass or venturi to accommodate the thumb and middle finger of the user&#39;s hand allowing a user&#39;s index finger to act on the pusher  250  as described below.  
         [0029]     Preferably, the housing body  260  includes concentrically aligned inner and outer walls  261 ,  263  at the proximal end  266  thereof. An insertion gap  265 , which is preferably generally annular, is defined between the walls  261 ,  263  and is sized to accommodate the cap wall  256 . An inner wall slot  267  extends through the inner wall  261 , distally from a proximal end  273  of the inner wall  261  and is formed to receive the ring lever described below. At the base of the inner wall slot  267 , a housing edge  270  extends inwardly. A secondary slot  269 , preferably having less depth than the inner wall slot  267 , extends distantly from the housing edge  270  and terminates at a secondary edge  271 . Preferably, the inner wall slot  267  and the secondary slot  269  are longitudinally aligned to form a continuous longitudinal slot.  
         [0030]     The safety shield  220  includes a shield body  222  which is cylindrical and coaxially supported within the housing body  260 . The proximal end of the shield body  222  terminates at a collar portion  224 . The collar portion  224  is cylindrical and has increased inner and outer diameters relative to the adjoining portion of the shield body  222  resulting in an internal edge  225  which is annular and generally defines the distal end of the collar portion  224 .  
         [0031]     The safety shield  220  is longitudinally displaceable relative to the housing  210  between retracted and extended positions, as shown in  FIGS. 5 and 6 , respectively. When in the retracted position, the forward tip  34  of the needle cannula  16  is exposed and the injection device  10  may be used to inject a drug substance into the body of a patient. When in the extended position, the forward tip  34  of the needle cannula  16  is contained within the safety shield  220  and the safety shield  220  is preferably locked in place to prevent inadvertent and unintended contact with the forward tip  34  by a user or the patient. The safety shield  220  has a distal end  223  which is distal of the forward tip  34  when the safety shield  220  is in the extended position. Thus, the safety shield  220  prevents accidental needle-stick injury to the user or patient.  
         [0032]     The safety shield  220  further includes a latch means which may be constituted by a shield latch  226  which is connected to the shield body  222  distally of the collar portion  224  and extends longitudinally relative thereto. The shield latch  226  terminates in a latch tab  228  which is adjacent to the collar portion  224  and extends radially outward. The shield latch  226 , due to its cantilevered connection to the shield body  222 , is able to be deflected radially between ready and released positions. The latch tab  228  is positioned to be within the inner wall slot  267  and engaged against the housing edge  270 , with the shield  220  being in a retracted position. The engagement between the latch tab  228  and housing edge  270  resists longitudinal displacement of the safety shield  220  to the extended position, while the inner wall slot  267  prevents rotation of the safety shield  220  relative to the housing  260 .  
         [0033]     In addition, the safety shield  220  may include a marker or indicia  218 , e.g., a red-colored tag. The indicia is located on the safety shield  220  such that it is not viewable through the window  216  with the safety shield  220  being in a retracted position ( FIG. 4 ), but viewable through the window  216  with the safety shield  220  being in an extended position ( FIG. 6 ). The indicia  218  provides a user with a warning that the injection device  10  has been used.  
         [0034]     A plurality of components provided on the holder  200  and the syringe  18  comprise a release mechanism. The release mechanism may be in one of a ready position and a release position. When in the ready position, one of the components of the release mechanism is not in radial alignment with the other components of the release mechanism. When in the release position, all of the components of the release mechanism are radially aligned with each other, and the safety shield  220  may be released from its retracted position and biased towards its extended position. As discussed further, the release mechanism may automatically release the safety shield  220  from its retracted position at the end of an injection stroke. This embodiment is referred to herein as passive activation. Alternatively, one or more components of the release mechanism may require manipulation by the user to release the safety shield  220  from its retracted position. This embodiment is referred to herein as active activation.  
         [0035]     In the embodiment of  FIGS. 1-6 , an active release mechanism is depicted. Specifically, the retainer ring  240  includes a ring body  242  which is coaxially supported around the syringe body  11  and longitudinally fixed thereto by a plurality of longitudinal ring clips  243 , which may number five, extending proximally from the ring body  242 , as shown in  FIG. 3 . Each of the ring clips  243  has a radially inward extending lip which, together with the ring body  242 , sandwiches an annular proximal flange  20  which extends outwardly from the proximal end of the syringe body  11  (see, e.g.  FIG. 4 ). The retainer ring  240  further includes longitudinal ring latches  245  connected to the ring body  242 , preferably a pair in diametrically opposed relation to one another. The ring latches  245  are configured to engage the housing body  260  and, when so engaged, resist proximal longitudinal translation and rotational movement of the ring body  242  relative to the housing body  260 .  
         [0036]     The ring body  242  has an inner diameter which is larger than the outer diameter of the collar portion  224  of the safety shield  220  enabling the ring body  242  to overlap radially the collar portion  224  of the shield body  222 , as shown in FIGS.  4  to  6 . Preferably, distal edge  244  of the ring body  242  engages the proximal end  273  of the inner wall  261 .  
         [0037]     The retainer ring  240  includes a ring lever  246  which extends from the ring body  242  for radially inward deflection between ready and released positions. Upon assembly, the ring lever  246  is located in the inner wall slot  267  at generally the same longitudinal location as the latch tab  228 . With the latch tab  228  being located in the inner wall slot  267  as indicated above, the ring lever  246  and the latch tab  228  are radially aligned and, as such, sufficient inward deflection of the ring lever  246  results in engagement of the ring lever  246  with the latch tab  228 .  
         [0038]     The biasing means may be constituted by a helical spring  230 . The spring  230  is in coaxial relation to and external of the syringe body  11  between the retainer ring  240  and safety shield  220 . The proximal end of the spring  230  is contained within the retainer ring  240 , the inner diameter of which is larger than the outer diameter of the spring  230 . The distal end of the spring  230  is contained within the collar portion  224  of the shield body  222 , the inner diameter of which is also larger than the outer diameter of the spring  230 .  
         [0039]     In assembling the holder  200 , the retainer ring  240  is secured to the housing body  260  by the ring clips  243 , as described above. In an assembled state, as shown in  FIG. 4 , the spring is compressed resulting in the spring urging the safety shield  220  toward the extended position. This urging is resisted by the engagement between the latch tab  228  and the housing edge  270 .  
         [0040]     The holder  200  includes a means for deflection which, by way of non-limiting illustration in a first embodiment, is constituted by a pushbutton  212  formed in the outer wall  263  of the housing body  260  as shown in FIGS.  1  to  6 . With the holder  200  assembled, the pushbutton  212 , ring lever  246 , and shield latch  224  are radially aligned on the housing body  260 . The pushbutton  212  is positioned radially outward of the ring lever  246 .  
         [0041]     The pushbutton  212  may be selectively deflected radially inward into the insertion gap  265  by a user from ready to released positions. The pushbutton  212 , ring lever  246  and shield latch  224  are sized to provide a gap or radial clearance between the pushbutton  212  and ring lever  246 , and/or the ring lever  246  and shield latch  224 . This radial clearance is sufficient such that, prior to the insertion of a portion of the drug delivery device into the radial clearance, the deflection of the pushbutton  212  to the released position does not result in disengagement of the shield latch  224  from the housing edge  270 . For example, the elements herein are preferably configured so that insertion of the cap wall  256  into the insertion gap  265  prior to the end of an injection stroke, the deflection of the pushbutton  212  to the released position does not result in disengagement of the shield latch  224  from the housing edge  270 . Preferably, the radial clearance is selected such that full deflection of a particular element, e.g., the pushbutton  212 , shall not result in engagement with another of the elements of the release means, e.g., the ring lever  246 . Additionally, it is preferred, although not necessary, a portion of the drug delivery device will not be inserted into the radial clearance until the injection is complete. Thus, the safety shield  220  will not move from the retracted position to the extended position before and until administration of an injection is complete and the stopper  24  has been moved longitudinally through the reservoir  12  so as to cause the entire contents thereof to be expelled through the needle cannula  16 , i.e., at the end of an injection stroke. The injection stroke will generally coincide with the stopper  24  traversing the full length of the reservoir  12 .  
         [0042]     It should be understood by a person skilled in the art from the disclosure provided herein that the precise position of the stopper  24  does not necessarily determine completion of an injection stroke nor the point at which the safety shield  220  may be released from the retracted position and caused to move toward the extended position. Rather, radial alignment of all components of the release means determine the point at which the safety shield  220  may be released from its retracted position.  
         [0043]     When the holder  200  is fully assembled as shown in  FIG. 4  and the reservoir  12  contains fluid for injection into a patient, the inventive injection device  10  is ready for application to the patient. The holder  200  may be separately prepared from the syringe  18 . The syringe  18  is insertable into the housing cavity  262  with the flange  20  being locked onto by the ring clips  243 . Under certain (and appropriate) circumstances, the holder  200  may be disengaged from a used syringe  18  and re-used.  
         [0044]     Initially, the housing body  260  is gripped by placing the thumb and middle finger against the portion of the outer surface of the housing body  260  which is shaped to accommodate the thumb and middle finger. This portion of the outer surface may be the depressions  214  such that the end of the thumb is inserted into one of the depressions  214  and the end of the middle finger is inserted into the other of the depressions  214 . Alternatively, the portion of the outer surface against which the thumb and middle finger is placed may be the intermediate portion  264  of the housing body  260  having the shape of an hourglass or a venturi where the intermediate portion  264  has a reduced peripheral dimension relative to the proximal and distal ends  266 ,  268  of the housing  210 .  
         [0045]     With the housing body  260  being gripped, the housing  210  is oriented relative to the skin of the patient such that the injection device  10  is generally perpendicular to the skin of the patient and the forward tip  34  of the needle cannula  16  is adjacent to the skin of the patient. The holder  200  is then displaced toward the skin in generally perpendicular relation thereto such that the forward tip  34  punctures the skin and enters the patient&#39;s body.  
         [0046]     The index finger of the user&#39;s hand is then moved into contact with the pusher cap  252 , and the pusher cap  252  is depressed to advance the pusher stem  258  into the reservoir  12 . The advancement of the pusher stem  258  into the reservoir  12  results in movement of the stopper  24  in a proximal to distal direction and fluid injection through the needle cannula  16 . The pusher stem  258  is advanced a distance sufficient to cause the stopper  24  to traverse the longitudinal length of the reservoir  12 , this advancement defining the injection stroke. At the end of the injection stroke, the cap wall  256  is inserted into the insertion gap  265  between the pushbutton  212  and ring lever  246 , as shown in  FIG. 5 . Preferably, the cap wall  256  has sufficient longitudinal length to be interposed between the pushbutton  212  and the ring lever  246 . Consequently, the radial clearance between the pushbutton  212  and the ring lever  246  is eliminated. Prior to the injection stroke, it is preferred that the cap wall  256  be located proximally of the ring lever  246 .  
         [0047]     To activate the safety shield  220 , the pushbutton  212  is inwardly deflected resulting in inward deflection of the cap wall  256  of the pusher cap  252  and, in turn, resulting in the deflection of the ring lever  246  to the released position thereof. This causes the deflection of the shield latch  224  to the released position thereof resulting in the latch tab  228  disengaging from the housing edge  270 . This enables the spring  230  to urge the safety shield  220  to the extended position, with the latch tab  228  traveling through the secondary slot  269 , to cover the forward tip  34  of the needle cannula  16  upon completion of an injection, as shown in  FIG. 6 ,. The latch tab  228  engages the secondary edge  271  to prevent further distal movement of the safety shield under force of the spring  230 . Preferably, a locking slot  275  extends radially from the secondary edge  271  formed to entrap the latch tab  228 . In this manner, the safety shield  220  may be locked in the extended position. The secondary slot  269  and/or the locking slot  275  prevents rotation of the safety shield  220  relative to the housing  260  with the safety shield  220  being in the extended position.  
         [0048]     Activation of the safety shield  220  is thus only possible at the end of the injection stroke, when the pusher  250  is fully engaged into the housing body  260 . Depression of the pushbutton  212  prior to an injection or after partial injection of the fluid contents has no effect, i.e., the safety shield  220  can only be released and caused by the spring  230  to move to cover the needle at the end of the injection stroke when the cap wall  256  is fully engaged in the insertion gap  265 . The pushbutton  212 , cap wall  256 , and ring lever  246  establish components of a release mechanism based on the cooperation thereof, when radially aligned, to deflect the shield latch  224  to the released position thereof  
         [0049]     Although not shown, in addition or in the alternative, the push cap  252  may include a wall or other element configured to fill a radial clearance between the ring lever  246  and the latch tab  228 . Also, the shield latch  224  may be configured to be directly deflected by the cap wall  256 , without the intervening ring lever  246 .  
         [0050]     In a second embodiment of the holder  200 , which is depicted in FIGS.  7  to  10 , deployment of the safety shield  220  occurs automatically at the end of the injection stroke and when the cap wall  256  is fully engaged in the housing body  210 . No external pushbutton  212 , or equivalent, is required. Rather, in this second embodiment, the means for inward deflection includes a molded in ramp  248  on a surface of the retainer ring  240 , as shown in  FIG. 8 . This results in activation of the safety shield  210  at the end of the injection stroke without an additional action by the user, e.g., depression of a pushbutton or other activating means.  
         [0051]     With the injection device  10  assembled, the ramp  248 , ring lever  246 , and shield latch  224  have generally the same longitudinal position relative to the housing body  260  enabling the radial alignment therebetween. The ramp  248  protrudes radially outward from the ring lever  246  such that a proximal portion of the ramp  248  has a smaller radial dimension relative to a radial dimension of a distal portion of the ramp  248 .  
         [0052]     Longitudinal insertion of the cap wall  256 , upon completion of the injection stroke, between the housing body  260  and ramp  248  causes the deflection of the ring lever  246  to the released position thereof This, in turn, causes the deflection of the shield latch  224  to the released position thereof resulting in the deployment of the safety shield  220 , as shown in  FIG. 9  and in the same manner described herein for the syringe holder  200  including the pushbutton  212 . Accordingly, the ramp  248  provides for automatic deployment of the safety shield  220  upon completion of an injection stroke and insertion of the cap wall  256  between the housing body  260  and ramp. The cap wall  256 , ramp  248 , and ring lever  246  establish components of the release mechanism based on the cooperation thereof, when radially aligned, to deflect the shield latch  224  to the released position thereof.  
         [0053]     Advantageously, the insertion gap  265  is adjacent to the ramp  248 , and with no pushbutton  212 , the outer wall  263  is formed solidly and continuously about the ramp  248 . Accordingly, no direct external access to the ramp  248  is provided. Also, the insertion gap  265  ensures that no element of the holder  200  is adjacent to the ramp  248 . In this manner, unwanted deflection of the ring lever  246  is avoided which may result in inadvertent activation of the safety shield  220 .  
         [0054]     As an additional aspect of the injection device  10 , and with reference to  FIG. 10 , a detent  301  may be provided on the cap wall  256 , preferably at the bottom edge thereof. A longitudinal protrusion  303  may also extend from the ring lever  246  having a notch  305  into which the detent  301  may be seated to restrain movement of the pusher cap  252 . With sufficient distal force, the detent  301  may be unseated, allowing the push cap  252  to advance distally during an injection stroke. The longitudinal protrusion  303  may be provided with a shaped end or secondary notch  307  into which the detent  301  may be seated upon completion of the injection stroke to restrain movement of the pusher cap  252 . As will be appreciated by those skilled in the art, the detent  301  and notches  305 ,  307  may be formed to prevent proximal movement of the pusher cap  252  relative to the ring lever  246 .  
         [0055]     Further, the syringe  18  may be provided with a removable tip cap  19 , as depicted in  FIGS. 1, 2 ,  7  and  8 , which covers the forward or distal tip  34  of the needle cannula  16  prior to use for safety and sterility and/or after use as an additional safety device.  
         [0056]     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concept described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.