Abstract:
A medication dispensing apparatus with a spring-driven locking feature includes a drive member movable in a distal direction within a housing, and a fluid container with a piston that is advanceable by the drive member ( 60 ) when such drive member is moved distally by a driving means. The apparatus includes a latching element ( 180 ) having a skid ( 190 ) that is slidable along a surface of the drive member as the drive member passes distally during advancement. The drive member is arranged with the skid so as to maintain a latching lip of the latching element against a spring force in a first position free of the driving means during dose preparing and injecting prior to a final dose administration. The skid-engaging surface shifts distally of the skid such that the skid passes beyond a proximal end of that surface upon administration of a final dose, whereby the latching lip is urged by the spring force from the first position to a second position to physically lock the driving means to prevent further dose preparing and injecting.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention pertains to medication dispensing devices, and, in particular, to a portable medication dispensing device such as an injector pen.  
         [0002]     Patients suffering from a number of different diseases frequently must inject themselves with medication. To allow a person to conveniently and accurately self-administer medicine, a variety of devices broadly known as injector pens or injection pens have been developed. Generally, these pens are equipped with a cartridge including a piston and containing a multi-dose quantity of liquid medication. A drive member, extending from within a base of the injector pen and operably connected with typically more rearward mechanisms of the pen that control drive member motion, is movable forward to advance the piston in the cartridge in such a manner to dispense the contained medication from an outlet at the opposite cartridge end, typically through a needle that penetrates a stopper at that opposite end. In disposable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the entire pen is discarded by a user, who then begins using a new replacement pen. In reusable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the pen is disassembled to allow replacement of the spent cartridge with a fresh cartridge, and then the pen is reassembled for its subsequent use.  
         [0003]     Some injector pens allow a dose to be set that is larger than the amount of useable medicine remaining in the pen. While some users may find such settability undesirable, providing an insufficient remaining dose indicator may not be practical in all cases, such as due to it complicating the pen design. Still further, a shortcoming with some injector pens is that the design platform on which they are based may not allow a manufacturer sufficient options as to the mechanical advantage to provide, such as a mechanical advantage that can be very small in order to readily inject a large volume dose, or which mechanical advantage can be quite large so as to deliver a small volume dose with a suitable plunger travel.  
         [0004]     Thus, it would be desirable to provide an apparatus that can overcome one or more of these and other shortcomings of the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In one form thereof, the present invention provides a medication dispensing apparatus including a housing, a drive member within the housing and movable in a distal direction, a fluid container defining a medicine-filled reservoir with a movable piston at one end and an outlet at the other end, the piston being engageable by the drive member to be advanced toward the outlet a distance equal to a distal movement of the drive member when the drive member is moved distally, a means for driving the drive member distally, and a latching element including a latching lip and a skid. The drive member includes an axially extending, skid-engaging surface along which the skid is slidable as the drive member passes distally during advancement. The skid-engaging surface has an axial length and a proximal end, and the drive member along the axial length is structured and arranged with the skid so as to maintain the latching lip against a spring force in a first position free of the driving means during dose preparing and injecting prior to a final dose administration. The skid-engaging surface shifts distally of the skid such that the skid passes beyond the proximal end upon administration of a final dose, whereby the latching lip is urged by the spring force from the first position to a second position to physically lock the driving means to prevent further dose preparing and injecting.  
         [0006]     One advantage of the present invention is that a medication dispensing apparatus can be provided with an uncomplicated and robust mechanism for automatically locking the apparatus to prevent further use after a final dose of the apparatus has been administered.  
         [0007]     Yet another advantage of the present invention is that a medication dispensing apparatus can be provided which is readily adaptable by the manufacturer to furnish a mechanical advantage during dose administration selected from a wide range of such advantages, such as a small advantage of about two for a large volume dose, up to a large advantage of about sixteen for a small volume dose.  
         [0008]     Another advantage of the present invention is that a medication dispensing apparatus can be provided which is internally configured to utilize space efficiently to allow for a compact design that contributes to a small and symmetrical design-of the apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above-mentioned and other advantages and objects of this invention, and the manner of attaining them, will become more apparent, and the invention itself will be better understood by reference to the following description of embodiments of the invention taking in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a side view of a first embodiment of a medication dispensing apparatus of the present invention, which apparatus is arranged in a ready or ready-to-be-cocked state;.  
         [0011]      FIG. 2  is a longitudinal cross-sectional view of the medication dispensing apparatus of  FIG. 1 ;  
         [0012]      FIG. 3  is a longitudinal cross-sectional view, taken along line  3 - 3  of  FIG. 1 , of the medication dispensing apparatus of  FIG. 1 ;  
         [0013]      FIG. 4  is an exploded, top perspective view of the medication dispensing apparatus of  FIG. 1 , wherein an apparatus cap is also shown;  
         [0014]      FIG. 5  is a bottom perspective view of the medication dispensing apparatus of  FIG. 4 ;  
         [0015]      FIG. 6  is a bottom perspective view of the medication dispensing apparatus of  FIG. 1 , and with a bottom portion of its housing removed to better show internal components of the apparatus;  
         [0016]      FIG. 7  is a bottom perspective view of the medication dispensing apparatus of  FIG. 1 , with portions of its housing and larger pinion removed to better show internal components of the apparatus;  
         [0017]      FIG. 8  is a bottom perspective view of the medication dispensing apparatus of  FIG. 1  after being manipulated from its ready state to a cocked or ready-to-inject state, with portions of its housing and larger pinion removed to better show internal components of the apparatus;  
         [0018]      FIG. 9  is a top perspective view of the medication dispensing apparatus of  FIG. 1 , with a top portion of its housing removed to better show internal components of the apparatus;  
         [0019]      FIG. 10  is a top perspective view of the medication dispensing apparatus of  FIG. 1  after being manipulated from its ready state to a ready-to-inject state, with a portion of its housing removed to better show internal components of the apparatus;  
         [0020]      FIG. 11  is a top perspective view of a portion of the apparatus of  FIG. 1  after being manipulated from its ready state to a ready-to-inject state, with portions of its housing and pinion-engaging piece removed to better show internal components of the apparatus;  
         [0021]      FIG. 12  is a perspective view of a housing half showing a guide of a partial-cocking-preventing mechanism; and  
         [0022]      FIG. 13  is an exploded, top perspective view of another embodiment of a medication dispensing apparatus of the present invention, wherein the apparatus cap is also shown. 
     
    
       [0023]     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale, and certain features may be exaggerated or omitted in some of the drawings in order to better illustrate and explain the present invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring now to  FIGS. 1-12 , there is shown a first embodiment of a medication dispensing apparatus of the present invention. Any directional references in this detailed description with respect to  FIG. 1  or any of the other Figures, such as front, side or back, or up or down, or top or bottom, are intended for convenience of description, and by itself does not limit the present invention or any of its components to any particular positional or spatial orientation.  
         [0025]     The apparatus, generally designated  20 , is an injector pen of a design that builds upon the teachings of U.S. Provisional Patent Application 60/557,545, which also was filed with the United States Receiving Office of the World Intellectual Property Organization and assigned application number ______ on even date with the international filing of this application, the entire contents of which are hereby incorporated by reference. Medication injector pen  20  is a disposable pen that is repeatedly operable by a user to deliver a fixed dose that is established by the pen manufacturer.  
         [0026]     The distal portion  22  of injector pen  20  includes a plastic tubular retainer  24  that holds a cartridge  28  therein. Cartridge  28  is of conventional design, including a medicine-filled reservoir  30  sealed at one end by a slidable piston  32  and sealed at the other end by an injection needle-pierceable septum  33 . Retainer  24  is made of a clear plastic material to allow a user to see the contents of reservoir  30 . Threading  26  on the stepped-down distal end of retainer  24  allow a releaseably mounting of, for example, a conventional injection needle assembly shown at  25 . Pen  20  is shown in  FIGS. 4 and 5  as having a protective cap  29  that removably mounts to the cartridge retainer  24  for protection thereof, which cap has a distal end design at  31  to prevent the capped pen from rolling.  
         [0027]     The proximal portion  34  of injector pen  20  includes a protective external housing  35  that is somewhat elliptical in transverse cross-section. To facilitate assembly of the apparatus, housing  35  is formed from multiple, interconnected injection molded plastic pieces. Housing  35  is shown having longitudinal halves  36  and  38  that are is complementarily designed to mate and be fixedly secured together during manufacture, such as via ultrasonic welding.  
         [0028]     The interior surfaces  37  and  39  of housing halves  36  and  38 , respectively, are shown formed with a variety of ribs and bulkheads that serve to maintain the alignment and guide the motion of the apparatus components disposed within housing  35 . Housing halves  36  and  38  respectively include distally projecting, curved flanges  40  and  42 . During apparatus manufacture, to mount the fluid container to the assembled housing, flanges  40  and  42  are first inserted within the proximal end of retainer  24  radially outward of the cartridge body, and then fixedly secured to the retainer, such as via adhesives or ultrasonic welding. When retainer  24  and housing  35  are so secured, cartridge  28  is axially sandwiched between the interior surface of retainer  24  and an internal bulkhead  44  of the housing to prevent axial movement of the cartridge during use.  
         [0029]     Pen proximal portion  34  includes an axially advanceable drive member generally designated  50 , a gear set generally designated  52 , and a plunger member generally designated  54 .  
         [0030]     Drive member  50  includes a cartridge-engaging piece  60  and a pinion-engaging piece  62 , each injection molded in a single piece from plastic. Cartridge-engaging piece  60  has a square rod-shaped body  64  that extends in the axial direction to a proximal end  65 , and a load distributing, disc-shaped portion  66  formed at the distal end of body  64 . Four angularly spaced, contoured gussets  68  span body  64  and disc  66 .  
         [0031]     Drive member pieces  60  and  62  are constrained by the interior surfaces of housing halves  36  and  38  to be axially translatable and rotatably fixed within the housing. Cartridge-engaging piece  60  is movable in the distal direction and prevented from proximal movement relative to the housing halves, while pinion-engaging piece  62  is clutchably connected to cartridge-engaging piece  60  to be moveable relative thereto in a proximal direction but not the distal direction. These one-way axial motions are achieved with ratchets in apparatus  20 . In particular, body  64  of cartridge-engaging piece  60  includes a row of one-way ramping ratchet teeth  70  on two opposite sides of its four sides, which teeth continue uninterrupted along a portion of the axial length of the body. Ratchet teeth  70  are engaged by a pair of diametrically opposed, resilient tabs or pawls  72  integrally formed with housing half  38 . Pawls  72  slide along and over teeth  70  when drive member piece  60  is advanced distally during use, but abut the transverse, proximal face of teeth  70  to prevent piece  60  from backing up in the proximal direction.  
         [0032]     Proximally of pawls  72 , a pair of diametrically opposed resilient pawls  75  of pinion-engaging piece  62  also engage the same rows of ratchet teeth  70  on opposite sides of body  64 . Pawls  75  slide along and over one or more teeth  70  when pinion-engaging piece  62  is moved proximally during pen cocking, but abut teeth  70  during the distal advancement of pinion-engaging piece  62  during injection, which abutting results in pinion-engaging piece  62  shifting distally the cartridge-engaging piece  60 . The pitch or distance between the transverse face of each adjacent tooth  70  preferably is the distance piston  32  needs to be advanced to deliver the pen&#39;s fixed dose.  
         [0033]     In addition to its pawls  75 , pinion-engaging piece  62  includes a plate-shaped body  77 . A longitudinally extending rack  80  projects from one side of body  77 . A pair of parallel, longitudinally extending ribs  82  project from the opposite side of body  77  and slidable receive rod-shaped body  64  therebetween. Another set of parallel rib portions  83  are shaped to slide along a ridge  45  formed on the interior surface  39  of housing half  38 .  
         [0034]     A fixed or axially stationary rack  84  is included within pen proximal portion  24 . Rack  84  is shown intergrally formed with housing half  38 .  
         [0035]     Plunger member  54  allows a user to control the internal gear set of the apparatus to prepare pen  20  for injection, as well as to perform the injection. Plunger member  54  is formed of a multi-piece construction, including an input element  90 , a button  92 , and a force limiting biasing member  94 .  
         [0036]     Button  92  is molded from plastic and externally sized and shaped to be rotatably fixed while slideable within housing  35 . An internal hollow  93  of button  92  accommodates a biasing member  94  axially extending therethrough, and a series of longitudinally extending, internal ribs  95  of button  92  maintain the alignment of biasing member  94 . The proximal end of button  92  is covered with a softer material shown at  97 , which is formed via an overmolding process. A manually pullable grip portion  96  of button  92  is covered with the soft touch material and extends proximally of the housing  35 . Flanges  98  laterally extend from the distal end of button  92  and, during pen cocking, abut inward lips  100  formed in housing halves  36 ,  38  to limit withdrawal of the plunger member from the housing. An indicating band  102  on button  92  is visible to a user when the button has been properly withdrawn to prepare pen  20  for medication delivery. Button  92  also includes a pair of diametrically opposed latches  101  at the distal ends of slot-defined fingers  103 . Latches  101  inwardly project within hollow  93 , and due to the resiliency of the fingers  103 , snap-fit during manufacturing assembly over transversely extending shoulders  105  of the input element  90  to prevent axial, proximal withdrawal of the button  92  from the input element during operation.  
         [0037]     Plunger element  90  is made of injection molded plastic and is designed in conjunction with the housing to be rotatably fixed while slideable within housing  35 . Plunger element  90  includes a cruciform-shaped protuberance  107  that proximally projects from a plate portion  108 . Plate portion  108  is keyed to be rotatably fixed within the button, and includes the latchable shoulders  105 . Protuberance  107  fits within the distal end of the force limiting biasing member  94  provided as a metal, helically coiled compression spring. The proximal end of biasing member  94  fits around a cruciform-shaped protuberance  109  formed on button  92  within hollow  93 . Spring  94  is captured in a pre-stressed state between the latched plate portion  108  and the interior end of button  92 , which pre-stressing is at least as large as forces the manufacturer expects users to apply on the plunger button during normal plunging to achieve proper pen operation. In one embodiment, in which a mechanical advantage of nominally ten to one is provided by the apparatus, the pre-stressing is in an amount of one pound. Thus, during normal plunging, spring  94  does not further compress and the button  92  and input element  90  shift as a unit and without relative axial motion. Coil spring  94  is also designed with sufficient spacing in its coiling, and with proper elastic properties, such that the spring, by compression, can accommodate movement of button  92  from the cocked position to the ready-to-be-cocked position without movement of plunger element  90 , whereby spring  94  can absorb plunging forces that could damage the internal components.  
         [0038]     Plunger element  90  also includes a bar portion  110  and a block portion  114  which both project distally from plate portion  108 . Near its distal end, bar portion  110  includes a laterally extending portion that serves as a U-shaped bearing or yoke  116 . Yoke  116  extends and opens away from the pen axis. At its distal end, bar portion  110  terminates in an upstanding lip  117  with a ramped face  118 . Lip  117  serves as a catch or hook of the apparatus locking mechanism. Yoke  116  receives the pin  120  of the gear set, which pin defines an axis about which the gear set partially revolves or pivots during use. Block portion  114  serves as a base to which a flexure or follower piece  122  of a partial-cocking-preventing mechanism is insert molded during manufacture.  
         [0039]     Follower piece  122  is made in one piece of a metal stamping and includes an apertured mounting plate  124  that is secured to block  114  during insert molding. A pair of resilient arms  126  longitudinally extend in parallel from mounting plate  124 . Arms  126  serve as leaf springs and are spanned at their distal ends by web  128 . A pawl  129  projects from web  128  toward housing half  36 . Follower  122  directly engages a guide  135  of the partial-cocking-preventing mechanism. Follower arms  126  are closely backed by ribs  82  to better ensure that pawl  129  is not twisted out of a proper engagement with the guide during use.  
         [0040]     Referring also now to  FIG. 12 , guide  135  is integrally formed with the interior surface  37  of housing half  36  and includes a bar portion  138  having an angled, distal end  140  and an angled, proximal end  142 . One longitudinally extending face of bar portion  138  provides a flat travel surface  146 , and the opposite face of the bar portion  138  includes a travel surface  148  equipped with a plurality of ratchet teeth  150 . Teeth  150  are engageable by pawl  129  to prevent distal movement of the plunger after only a partial withdrawal of the plunger in preparation for injection. Teeth  150  can be customized during manufacture to produce the desired number and volume of clicks during movement of the pawl over the row of teeth during use. For example, the provision of a large number of teeth, each having a relatively short height over which the pawl must be cammed outward, may result in clicks that are less distinct and similar in sound to a continuous, low volume buzz. Still further, instead of triangular teeth, the teeth may be lobe-shaped, with the indentation between lobes being where pawl  129  engages to prevent distal motion. Guide  135  further includes first and second abutment shoulders  152  and  154  molded into the housing.  
         [0041]     The partial-cocking-preventing mechanism in the shown embodiment provides an initial reluctance to pen cocking due to the sliding of pawl  129  over distal end  140 , a tactile and audible notice of plunger movement, along with a prevention of plunger return prior to a complete dose preparation, due to the movement of pawl  129  over the row of teeth  150 , an audible notice of complete dose preparation by the striking of abutment shoulder  152  by a distal end portion  130  of one resilient arm  126 , an initial reluctance to injection due to the sliding of pawl  129  over proximal end  142 , and an audible notice of injection completion by the striking of shoulder  154  by a distal end portion  131  of the other resilient arm  126 .  
         [0042]     The gear set utilized in the injection pen is configured to convert plunger member motion of a first distance into drive member motion of a second distance less than the first distance. The gear set shown at  52  is made from a lightweight material such as plastic, and utilizes first and second sized pinions.  
         [0043]     The first or larger sized pinion  160  includes an arcuate section of external gear teeth  162  that mesh with rack  84 . An arcuate section of gear teeth is all that is required due to the small angle of revolution of the pinion necessary for use of the shown pen, which small angle or partial roll is possible due to the nominally ten to one mechanical advantage provided by the shown gear ratio.  
         [0044]     The smaller sized pinion  166  has the same axis of rotation as pinion  160  and includes only an arcuate section of external gear teeth  168 . Gear teeth  168  have a pitch diameter that is less than the pitch diameter of gear teeth  162 . In the shown embodiment, such diameter is about 90% of the diameter of gear teeth  168 , which ratio provides the nominally ten to one mechanical advantage. Smaller ratios may be employed, such as down to 50%, which realizes a two to one mechanical advantage, and larger ratios may alternatively be employed, such as realizing a ratio for a sixteen to one mechanical advantage. Gear teeth  168  meshably engage drive member rack  80 , which rack is parallel to and disposed on the same side of the pinion axis as rack  84 .  
         [0045]     Although pinion  160  and pinion  166  are shown integrally formed, these components can be separately formed and assembled together so as to be contrastable. Pinions  160  and  166  share a common axis of rotation. A pin or axle  120  is located at such axis and is shown integrally formed with the pinions. Pin  120  is sized and shaped to fit into, and pivot or partially rotate within, the opening of yoke  116  during use.  
         [0046]     During pen use, gear set  52  is shifted proximally and then distally in the following manner. The gear set is shifted axially with the plunger element  90  to which it is pinned as such plunger element is pulled out and subsequently plunged in. As gear set  52  moves proximally, the gear set rotates due to pinion  160  being in rolling engagement with fixed rack  84 . As gear set  52  rotates, pinion  166  rolls along drive member rack  80 , but also effectively pulls for a short distance the pinion-engaging piece  62  proximally relative to the cartridge-engaging piece  60  held by the pawls  72 . During plunger element plunging, pinion  160  rolls backs along rack  84 , and pinion  166  rolls along rack  80  while effectively pushing pinion-engaging piece  62  to advance cartridge-engaging piece  60  distally.  
         [0047]     Injection apparatus  20  includes a locking mechanism that prevents use of the apparatus after a final intended dose has been administered thereby. The locking mechanism automatically operates during the injection of such final dose to prevent the plunger from being withdrawn thereafter.  
         [0048]     The locking mechanism includes a generally C-shaped latching element, generally designated  180 . Latching element  180  is formed in a single piece, such as a metal stamping, and includes a spring plate  182 , a pair of installation flanges  184 , and a latch lip  186 . Flanges  184  depend from the distal edge of spring plate  182  and include lower ends  187 . During pen manufacture, ends  187  press fit into complementary slots formed by wall  188  and barbed ribs  189  of the housing half  38  to assemble latching element  180  to the housing to be axially fixed relative thereto.  
         [0049]     Centrally located along the width of the plate  182  is a depending skid  190 . Skid  190  has a lower surface  192  that is blade-shaped and longitudinally extends. Blade  192  directly contacts and slides along an axially extending, smooth surface  71  of cartridge-engaging piece  60 . Skid  190  is formed by cutting and bending downward a portion of plate  182  during manufacture. An additional cut-out  194  opposite the opening formed by the bending downward of skid  190  results in a better symmetry of the plate portion  182  to aid in providing a more uniform springing effect during latching. Latch lip  186  depends from the proximal edge of spring plate  182  in the same direction as skid  190  depends, and is proximally spaced slightly from skid  190 . Skid  190  is selected to be of such a height that its engagement with bar surface  71  results in spring plate  182  being deflected upward and away from its neutral position, whereby lip  186  is laterally spaced from the plunger member  54  extending thereunder, and in particular is spaced laterally from the hook  117  of bar portion  110 . During initial use, blade  192  slides along the untoothed portion of the drive member at surface  71 , with latch lip  186  being spaced from the plunger against the resiliency or spring-force provided by spring plate  182 . When cartridge-engaging piece  60  is driven distally to complete its final injection, blade  192  slides off the proximal end  65  of smooth surface  71 , allowing the resiliency of spring plate  182  to snap latch lip  186  downward. As latch lip  186  moves down, in the event that the plunger member  54  has already been fully shifted distally, the latch lip  186  fits proximally of the hook  117  of bar portion  110 . In the event the shifting plunger has yet to have been shifted distally fully during the final dose administration, as the plunger motion continues the ramped face  118  engages latch lip  186  to temporarily cam latch lip  186  upward, and when the plunger is moved sufficiently distally, latch lip  186  then snaps down over hook  117 . This latching of latch lip  186  with hook  117  prevents any further proximal motion of bar portion  110 , and thereby of the entire plunger member  54 . Although shown directly engaging input element  90 , the latching element may engage other portions of the drive mechanism within the scope of the invention.  
         [0050]     Referring now to  FIG. 13 , there is shown an exploded, perspective view of another embodiment of a medication dispensing apparatus of the present invention. The apparatus, generally designated  220 , is substantially similar to apparatus  20 , with some differences being identified below.  
         [0051]     In particular, the locking mechanism preventing use after an administration of a final intended dose includes a generally L-shaped latching element, generally designated  225 , formed in a single piece, such as a metal stamping. The spring plate  227  of latching element  225  includes a centered aperture  230  that defines webs  232  and  234 . Depending from spring plate  227  along the proximal edge of aperture  230  is a transversely extending skid  236  having an upwardly curved lower end  238 .  
         [0052]     Generally elliptical slots  242  formed through the spring plate form a pair of rims  240  that each include a portion that upwardly projects beyond the top of the spring plate. Rims  240  project from the spring plate in a direction opposite to the direction skid  236  projects. Rims  240  are proximally spaced from skid  236 . The shown rims  240  serve as a pair of latching lips each providing a hook-contacting surface that is larger than that formed merely by the small thickness of the shown spring plate, thereby better distributing loading.  
         [0053]     The proximal edge of spring plate  227  is upturned at  244  to promote the spring plate being cammed over the locking mechanism hooks as may be necessary. Skid  236  still is of a height that its engagement with the bar surface  71  results in spring plate  227  being directed upward and away from its neutral position, whereby rims  240  are spaced from the apparatus plunger disposed thereunder, and in particular from the bar portion hooks.  
         [0054]     In conjunction with this modified latching element, the plunger element  260  includes a pair of spaced, parallel bar portions  262 ,  264  that project distally from a plate portion  266 . Each of bar portions  262 ,  264  includes a lip  266 , with a ramped face  267 , to serve as a rim-engaging hook of the locking mechanism when inserted through the spring plate openings  240 . Only one of the bar portions, namely bar  262 , is provided with the yoke for mounting the gear set  270 .  
         [0055]     The plunger button of the embodiment of  FIG. 13  is formed of two pieces, namely  274  and  276 , which are fixedly secured together during manufacturing assembly. Piece  274  is a different color than piece  276 , and the pieces  274  and  276  are sized such that the proximal end region of piece  274  serves as a colored indicating band that is visible to a user when the plunger button is fully withdrawn to prepare the pen for delivery.  
         [0056]     The embodiment of  FIG. 13  has a mechanical advantage of just over seven, as a ratio of the gear pitch diameters of gear set  270  is  86 %.  
         [0057]     The cartridge engaging piece  280  may be designed with ratchet teeth that are adapted for an initial shipping/storage of a ready-to-be-cocked apparatus in which, while pawls  282  are each similarly situated at the start of their respective ratchet tooth (i.e. proximate the transverse face of the distally adjacent tooth), both anti-back-up pawls  284  are similarly partially cammed outward by their engagement with a middle length portion of different ratchet teeth. These different ratchet teeth so initially engaged by pawls  284  have a shallower slope and therefore lesser height, as measured from the longitudinal axis of the apparatus, than the other teeth in the row, thereby reducing the stress on pawls  284  prior to the first use of the apparatus by the user. In order to possibly account for a single test cycle by the manufacturer during assembly, two adjacent lesser height teeth in each row for engagement with pawls  284  may be provided.  
         [0058]     While this invention has been shown and described as having preferred designs, the present invention may be modified within the spirit and scope of this disclosure. For example, other forms of drive systems, including but not limited to drive systems providing mechanical advantage using rack and pinion designs, possibly such as disclosed in the materials herein incorporated by reference, may be utilized. For example, a gear set may have pinned to its axle an output member which engages the cartridge piston. Such gear set may have one arc of gear teeth that engage a housing rack, and another arc of gear teeth that engage a plunger rack, which racks are positioned on opposite sides of the gear set&#39;s axle. Such arcs of gear teeth may have a common pitch diameter, or the housing rack-engaging gear teeth may have a pitch diameter which is smaller or larger than the plunger rack-engaging gear teeth. Still further, in another version the gear set may be pinned to the housing. A plunger rack of the system may engage gear teeth of the gear set having a larger pitch diameter, and a rack of the output member which engages the cartridge piston may engage teeth of the gear set having a smaller pitch diameter. Still further, for an unpinned or rolling gear set, a plunger rack may engage gear teeth with a first pitch diameter, a rack of an output member which engages the cartridge piston may engage gear teeth with a smaller pitch diameter, and a housing rack, which is positioned on the opposite side of the gear set&#39;s center from the plunger and output racks, may engage gear teeth with a pitch diameter that is the same or smaller than that of teeth engaging the plunger rack. Still further, in a rolling gear set design related to the materials herein incorporated by reference, the plunger rack may engage teeth with a smaller pitch diameter than the pitch diameter of gear teeth/engaging the housing rack. This application is therefore intended to cover any variations, uses or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.