Abstract:
A medical injector is provided herein which includes a body; a slidable button at least partially disposed in the body; a displaceable plunger disposed in the body; a spring disposed to advance the plunger; and, a releasable retainer for retaining the plunger in a first state against force of the spring. Upon a predetermined extent of sliding movement of the button, the button engages the releasable retainer so as to cause the releasable retainer to release the plunger thus allowing the spring to advance the plunger. Advantageously, the subject invention provides a medical injector having an automated plunger drive which is triggered upon button activation, thereby minimizing premature or failed activations.

Description:
FIELD OF THE INVENTION 
     This invention relates to medical injectors, and, more particularly, to medical injectors having plunger drive mechanisms. 
     BACKGROUND OF THE INVENTION 
     Medical injectors are well known in the prior art, including injectors which have internal drive mechanisms for plunger advancement. Plunger advancement may be utilized to conduct automated reconstitution of a two-or more part medicament and/or to cause automated injection. More specifically, the automation of plunger advancement may be utilized to cause combination of a multiple part (e.g., wet/dry) medicament. In addition, or alternatively, the automated advancement of the plunger may cause a needle to be advanced for injection and/or medicament to be driven through the needle during injection. Such automated action requires a trigger mechanism. Concerns exist over premature or failed trigger activation. 
     SUMMARY OF THE INVENTION 
     A medical injector is provided herein which includes a body; a slidable button at least partially disposed in the body; a displaceable plunger disposed in the body; a spring disposed to advance the plunger; and, a releasable retainer for retaining the plunger in a first state against force of the spring, Upon a predetermined extent of sliding movement of the button, the button engages the releasable retainer so as to cause the releasable retainer to release the plunger thus allowing the spring to advance the plunger. Advantageously, the subject invention provides a medical injector having an automated plunger drive which is triggered upon button activation, thereby minimizing premature or failed activations. 
     These and other features of the subject invention will be better understood through a study of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a medical injector formed in accordance with the subject invention; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line  3 - 3  of  FIG. 1 ; 
         FIG. 3A  is an enlarged section taken from  FIG. 3 ; 
         FIG. 4  is an exploded view of a medical injector formed in accordance with the subject invention; 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 1 ; 
         FIG. 6  shows an interior sleeve useable with the subject invention; 
         FIG. 7  is a perspective view of a dose ring useable with the subject invention; and, 
         FIG. 8  is a schematic showing an arrangement for restricting radial motion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the figures, a medical injector is shown and generally designated with the reference numeral  10 . The medical injector  10  may he of various types, but preferably is of the pen injector type. The medical injector  10  may be used to administer various injectable liquids, particularly medicaments. 
     With reference to the figures, the medical injector  10  includes a body  12  and an axially-displaceable plunger  14  disposed therein. The plunger  14  may be formed as a single piece or modular components. The modular components may be fixed to one another or located adjacently, but not connected, so as to move together. A spring  16  is also provided configured and positioned to advance the plunger  14  a predetermined distance. Preferably, the spring  16  is a compression or coil spring, but other biasing elements may likewise he utilized. The spring  16  is preferably disposed between the plunger  14  and a portion of the body  12 , such as cross-piece  18 . 
     It is preferred that the plunger  14  be advanced in a distal direction. As used herein, distal refers to a direction towards a patient during use, while proximal refers to a direction away from a patient during use. 
     A releasable retainer  20  is provided configured and positioned to releasably retain the plunger  14  in an initial first state against the force of the spring  16 . The releasable retainer  20  may include one or more deflectable latch tabs  22  preferably formed to extend outwardly from the plunger  14 . Correspondingly, one or more ledges  24  are defined in the body  12 . 
     The latch tabs  22  are inherently biased outwardly with the ledges  24  being positioned and configured to interferingly engage free ends  26  of the latch tabs  22  under force of movement of the spring  16 . With this arrangement, distal advancement of the plunger  14  is limited due to interengagement between the latch tabs  22  and the ledge  24 . The plunger  14 , can, thus, be retained in an initial, first state before use. 
     A slidable button  28  is disposed in the body  12  to be movable relative thereto. The button  28  has a proximal end  30  which is accessible by a user. At least one arm  32 , preferably two, extends distally from the proximal end  30  through corresponding openings  35  formed in the cross-piece  18 , One or more outwardly biased tangs  37  may extend from the arms  32  configured to engage against the cross-piece  18  and resist proximal movement of the button  28 . 
     The releasable retainer  20  is configured such that, the button  28  engages the releasable retainer  20  so as to cause the releasable retainer  20  to release the plunger  14  thereby allowing the spring  16  to advance the plunger  14 . In particular, with sufficient distal advancement of the button  28 , the arms  32  are shaped to telescope over a portion of the latch tabs  22  and, with sufficient distal advancement of the button  22 , the arms  32  cause the latch tabs  22  to be inwardly deflected from the ledges  24 , as shown in dashed lines in  FIG. 3A . The arms  32  define a smaller diameter than the tabs  22  so that with sufficient distal displacement the arms  32  force the tabs  22  inwardly, The plunger  14  is then free to move distally. 
     The ledges  24  may be formed on the body  12 . Alternatively, the ledges  24  may be formed on a component within the body  12 , such as the interior sleeve described below. In addition, the location of the tabs  22  and the ledges  24  may be reversed so that the tabs  22  are located in the body  12  (on the body  12  itself or on a component therewithin) and that the ledges  24  are formed on the plunger  4 . Various cooperating shapes of the elements may be utilized. 
     The medical injector  10  includes a reservoir  34  disposed in the body  12  formed to accommodate medicament or other substance  36  for injection into a patient. As shown in  FIG. 4 , the reservoir  34  may be a single chamber disposed in a barrel  38  sealed at a proximal end by a septum  40  and sealed at a distal end by a stopper  42  which is formed to he slidable through the barrel  38  for urging the substance  36  therefrom, as known in the art. The medical injector  10  also includes a needle mounting surface  44  having features  46  formed thereon for mounting a needle  48  thereto. The needle  48  may include a hub  50  having mounting features  52  provided thereon for cooperative engagement with the features  46  in mounting the needle  48  to the needle mounting surface  44 . The features  46  and the mounting features  64  may be of any known cooperating elements which permit a mechanical connection therebetween, such as threads or bayonet lock, and/or a frictional interengagement, such as a Luer mounting. The needle mounting surface  44  may be formed on the body  12  or a component thereof such as an adapter mounted to the barrel  38 . 
     The needle  48  also includes a needle cannula  51  having a distal end  56 , formed for insertion into a patient, and a proximal end  58 . 
     The reservoir  34  may be configured to accommodate multiple components which are mixable for reconstitution. For example, as shown in  FIG. 4 , the reservoir  34  may accommodate first and second mixable components  60 ,  62 . The stopper  42  may be associated with the reservoir  34  such that distal advancement of the stopper  42  over a predetermined distance shall cause mixing of the first and second mixable components  60 ,  62 . Any known arrangement for allowing such mixing may be utilized. By way of non-limiting example, the first and second mixable components  60 ,  62  may be separated by a secondary stopper  64 . The secondary stopper  64  divides the reservoir  34  into first and second chambers  66 ,  68 , respectively, accommodating the first and second mixable components  60 ,  62 . The septum  40  seals off the distal end of the first chamber  66 , while the stopper  42  is positioned to seal off the proximal end of the second chamber  68 . Preferably, if a dry component is used as one of the mixable components, the dry mixable component is located in the first chamber  66 . 
     One or more by-pass channels  70  are formed in the wall of the reservoir  34 . In an initial state, as shown in  FIG. 4 , the secondary stopper  64  is located at least partially proximally of the by-pass channels  70  so as to define a seal between the first and second chambers  66 ,  68  and to define a seal between the second chamber  68  and the by-pass channels  70 . With distal advancement of the stopper  42 , and with the second mixable component being wet and generally incompressible, force of movement of the stopper  42  is transmitted to the secondary stopper  64  through the second mixable component  62 . With sufficient distal movement of the secondary stopper  64 , the second chamber  68  comes into communication with the by-pass channels  70 , thus allowing the second mixable component  62  to be urged into the first chamber  66  with further distal movement of the stopper  42 . With sufficient distal advancement of the stopper  42 , the second chamber  68  is collapsed with none or substantially none of the second mixable component  62  remaining therein. In addition, the secondary stopper  64  is located so as to define a seal between the first chamber  66  and the by-pass channels  70 . The first and second mixable components  60 ,  62  are mixed within the first chamber  66 , such as through agitation of the medical injector  10 , so as to produce the injectable substance  36 , ready for injection. 
     The barrel  38  of the reservoir  34  may be the barrel of a separate drug cartridge, as shown in the figures, or a portion of the medical injector  10 , particularly the body  12 . 
     As will be recognized by those skilled in the art, other arrangements for permitting reconstitution may be utilized. In addition, more than two-part systems, such as three-part and so forth, systems may be utilized. Active medical ingredients may be included in one or both of the first and second mixable components  60 ,  62 . The first mixable component  60  may be dry (e.g., a powder or granular substance and/or a liquid (e.g., flowable (slurry or liquid)). As mentioned above, the second mixable component  62  is preferably only a wet flowable component, such as a liquid or slurry. 
     Distal advancement of the plunger  14  under force of the spring  16  may be used to achieve one or more objectives. The plunger  14  is configured to act against the stopper  42  and cause displacement thereof. With the reservoir  34  being configured for reconstitution, autoreconstitution of the contents of the reservoir  34  may be achieved. In addition, or alternatively, the medical injector  10  may be configured to be an autoinjector, where the needle  48  is initially housed within the body  12  and forced thereout of under force of the spring  16  so as to pierce a patient&#39;s skin, e.g., with forward movement of the reservoir  34 , as known in the art. In addition, or alternatively, distal advancement of the plunger  14  may cause administration of the contents of the reservoir  34  through the injected needle. 
     Depending on the desired effect, the medical injector  10  may be configured to have the plunger  14  be driven a predetermined distance. A physical stop, such as interengagement between a stop  70  formed on the plunger  14  (which can be defined by one of more of the latch tabs  22  or the tabs  81 ) and a proximal end  74  of the reservoir  34  (e.g., proximal end of the barrel  38 ), may be employed to limit distal advancement of the plunger  14 , Under certain circumstances, the plunger  14  may be distally advanced without the needle  48  being mounted to the medical injector  10 . Thus, the reservoir  34  is not vented during such action. With the needle  48  being subsequently mounted to the reservoir  34 , any residual gases trapped in the reservoir  34  are purged through the needle  48 . It may be preferred to not provide a physical stop to the distal advancement of the plunger  14 . In this manner, the contents of the reservoir  34  may be maximally compressed under force of the spring  16 . With subsequent mounting of the needle  48  onto the medical injector  10 , the reservoir  34  is vented thus permitting further distal advancement of the plunger  14 . This secondary distal advancement may assist in priming the needle  48  for use. 
     The medical injector  10  may be a fixed dose injector configured to administer single or multiple fixed doses. In addition, the medical injector  10  may be configured to permit dose setting for either a single or multiple doses. In a preferred embodiment, the medical injector  10  is a single, variable-dose autoreconstitution injector. 
     As will be appreciated by those skilled in the art, various configurations to permit dose setting may be utilized. It is preferred that the body  12  be formed of first and second body portions  76 ,  78  which are rotatably coupled. In this manner, relative rotation between the first and second body portions  76 ,  78  permits dose selection for the medical injector  10 . Preferably, to obtain rotatability, as shown in  FIG. 2 , a track  80  is formed in one of the first and second body portions  76 ,  78 , with one or more detents  82 , formed opposite the track  80 , being seated in the track  80  so as to lock the first and second body portions  76 ,  78  together once assembled. The detents  82  may be formed slidable along the track  80  so as to permit the first and second body portions  76 ,  78  to rotate relative to one another. One or more stops  84  may be located along the track  80  to limit the extent of relative rotation. 
     In a preferred arrangement, with reference to  FIGS. 2-4 , the second body portion  78  may include an interior sleeve  86  on which the detents  82  are formed. It is preferred the interior sleeve  86  be non-rotatably coupled to the first body portion  76 . The stops  84  may be provided on the first body portion  76  to prevent rotation. Li addition, it is preferred that the interior sleeve  86  be coupled to the second body portion  78  in any known manner so as to permit rotation of the second body portion  78  thereabout such as through mating snap fingers  88  coupled adjacent the cross-piece  18 , particularly on the proximal side thereof. With the interior sleeve  86  being non-rotatably coupled to the first body portion  76 , the interior sleeve  86  is held fixed with the second body portion  78  being rotatable thereabout. 
     Preferably, for dose selection, the plunger  14  rotates with the second body portion  78 . One or more tabs  81  may extend from the plunger  14  so as to be received in corresponding slots  83  formed in the second body portion  78 , as shown in  FIG. 5 . By-pass slots  85  may be formed in the interior sleeve  86  which allow the tabs  81  to pass therethrough. The by-pass slots  85  may extend axially along the interior sleeve  86  so as to provide a straight-line path for distal advancement of the plunger  14 . 
     For dose selection, and by way of non-limiting example, a dose ring  90  may he provided with a plurality of axially and radially spaced-apart abutment surfaces  92 . 
     The abutment surfaces  92  are axially alignable with an engagement surface  94  formed on the plunger  14  such that with sufficient distal displacement of the plunger  14  at least one of the abutment surfaces  92  will be caused to be engaged by the engagement surface  94  thus limiting the stroke of the plunger  14 . The engagement surface  94  may be defined on one or more of the tabs  81 . With this arrangement, a controlled amount of distal displacement of the plunger  14  may be transmitted to the stopper  42 . Stem  91  of the plunger  14  passes through opening  93  of the dose ring  90  to obtain proper alignment of the engagement surface  94  with the corresponding abutment surface  92  and so that the stem  91  may engage the stopper  42 . Moreover, stroke length corresponding to the movement of the plunger  14  may be adjusted depending on the abutment surface  92  which is in engagement with the engagement surface  94 . The greater the initial distance of the abutment surfaces  92  from the engagement surface  94 , the corresponding greater dose that will be caused to be administered. Regardless of the selected dose amount, it is preferred that the plunger  14  have a fixed length of stroke for distal displacement during administration of an injection. The further abutment surfaces  92  provide greater distal movement of the plunger  14 . The extent of movement of the plunger  14  dictates the extent of movement of the stopper  42  and, thus, dictates the amount of the injectable solution  36  to be driven from the reservoir  34  in an injected dose. The dose ring  90  is preferably stationary. A spring arm  120  may extend from the dose ring  90  to resiliently press against the plunger  14  and provide stability thereto. 
     The dose is selected by rotating the second body portion  78  which is fixed to the plunger  14  so as to rotate therewith. To prevent the second body portion  78  from setting a dose prior to proper preparation of the medical injector  10 , such as prior to mixing of the mixable components  60 ,  62 , rotation of the plunger  14  may be limited by interengagement of the tabs  81  with the by-pass slots  85 . As shown in  FIG. 6 , open space  71  may be defined at he distal terminus of the by-pass slots  85  which extends radially to permit rotation of the tabs  81  thereinto. The open space  71  may be defined by an enlarged diameter portion of the interior sleeve  86  which is of limited depth in the wall of the interior sleeve  86  or extends completely therethrough. In this manner, doses can be adjusted by rotating the plunger  14  to axially locate the engagement surface  94  with a desired of the abutment surfaces  92 . The by-pass slots  85  may be formed with one or more catches  73  which initially catch the tabs  81  upon distally advancing the predetermined distance and prior to dose setting. By permitting radial adjustment at the terminus of the by-pass slots  85 , dose setting may be restricted to post-advancement of the plunger  14 . 
     It is preferred that the second body portion  78  be releasably retained in positions corresponding to the various dose settings. In this manner, it is preferred that once a dose has been set, there is no inadvertent rotation of the second body portion  78 , thus avoiding that an improper of the abutment surfaces  92  engage the engagement surface  94 . Such an arrangement is disclosed in U.S. Pat. No. 6,793,646. As shown in U.S. Pat. No. 6,793,646, with reference to  FIG. 8 , one or more tabs  110  may be formed on the interior sleeve  86  which are selectively engageable with one or more ratchet teeth  112  formed on the second body portion  78 . The ratchet teeth  112  may be circumferentially spaced apart and positioned to represent dose settings corresponding to the abutment surfaces  92 . The tabs  110  nest in between the ratchet teeth  112  at given radial positions of the plunger  14  corresponding to different dose sizes. With turning of the second body portion  14 , the tabs  110  are caused to by-pass the ratchet teeth  112 . The ratchet teeth  112  maintain the radial position of the second body portion  78 . 
     In addition, it is preferred that the plunger  14  be limited in axial movement so as to permit a fixed stroke length of distal advancement for dose administration. The stroke of an injection is defined by the extent of distal movement of the plunger  14 . The plunger  14  may be advanced in any known manner for injection, including under force of movement of the spring  16 . 
     Indicia  116  may be provided to represent doses. The indicia  116  may include numeral representations and a pointer or other indicator. The indicia  116  may be on both the first and second body portions  76 ,  78  to provide dose indications during relative rotation therebetween in dose setting.