Abstract:
One form of the invention provides a needle-free injection system including the following components: a nozzle portion having a glass wall defining a drug storage space, and an injection wall defining a drug injection space, the injection wall being aligned with the glass wall and defining a plurality of drug bypass conduits disposed adjacent a forward end of the drug injection space; an injection orifice defined at the forward end of the injection space; a drug plunger defining a rearward end of the storage space; a portion of dried drug initially disposed between the storage space and the injection space, and being displaceable into the injection space adjacent the bypass conduits; and a pierceable gas cartridge for providing injection power to the drug plunger.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This is a continuation of the following applications: U.S. Ser. No. 09/799,787 filed Mar. 5, 2001 for DISPOSABLE NEEDLE-FREE INJECTION APPARATUS AND METHOD and International Application No. PCT/US02/07299, filed Mar. 5, 2002 for DISPOSABLE NEEDLE-FREE INJECTION APPARATUS AND METHOD. The subject matter of each application is incorporated herein by this reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to a single-use disposable needle-free (or needleless) jet injection device. Specifically, this invention relates to such a jet injection device that comprises a hand-held injector having a pre-filled drug cartridge sealingly carrying injectable drug, a sealed cylinder of pressurized gas, a piercing mechanism for penetrating the gas cylinder, and a trigger device for releasing the discharge mechanism. The device is smaller and has fewer parts than prior disposable systems, and can be easily assembled and filled using automated equipment.  
         RELATED TECHNOLOGY  
         [0003]    Needle-free or needleless hypodermic jet injection devices have been in commercial use for over 40 years. A number of these devices have used pressurized gas to power a hypodermic jet injection. The related technology includes a number of teachings for gas-powered injection devices, including: U.S. Pat. No. 4,596,556, issued to J. Thomas Morrow, et al.; U.S. Pat. No. 4,913,699, issued to James S. Parsons, and U.S. Pat. No. 5,730,723, issued to Thomas P. Castellano, et al. WIPO publication WO 97/37705 also discloses a gas powered disposable needle-free hypodermic jet injector.  
           [0004]    The Morrow, et al. &#39;556 patent is believed to teach a reusable hypodermic jet injection device in which a housing receives a shell or cartridge having a bore leading to a discharge aperture. Within the bore is received both a plunger sealingly engaging the bore, and a pressurized gas cylinder that rests against the plunger. The injection device includes a ram having a penetrating tip confronting a penetrable wall section and seal of the gas cylinder, and a discharge mechanism for driving the ram through the penetrable wall section of the gas cylinder when a trigger device is released. Discharge of the pressurized gas from the cylinder drives the plunger to effect a jet injection, and also drives the seal of the gas cylinder to effect resetting of the discharge mechanism. The shell with its plunger and spent gas cylinder is discarded after an injection; a new shell, pre-filled with medication and with a new gas cylinder, is used for each injection.  
           [0005]    The Parsons &#39;699 patent is believed to teach a single-use jet injector that is discarded after one use. This injector is believed to have a body with a pair of gas chambers separated by a breakable valve. One of the gas chambers contains a pressurized gas, while the other chamber is sealingly bounded by a piston that drives a plunger. The plunger sealingly bounds a chamber into which a dose of medication is loaded by the user before the injection. This medication dose chamber leads to an injection orifice so that when the valve is broken, the piston and plunger are moved by pressurized gas communicated to the second chamber, and the plunger drives the medication forcefully out of the injection orifice to form an injection jet. After a single use, the device is discarded.  
           [0006]    The Castellano &#39;723 patent, which was issued in 1998 and which does not cite the earlier Parsons &#39;699 patent, is believed to teach substantially the same subject matter as Parsons et al.  
           [0007]    WIPO publication WO 97/37705 published pursuant to a Patent Cooperation Treaty (PCT) application for joint inventors Terence Weston and Pixey Thornlea, is believed to disclose a disposable hypodermic jet injector in which the device is powered by a gas pressure spring of the type common in the tool and die art as a substitute for the conventional metal spring-powered ejector pin. In the Weston device, the ram of the gas pressure spring is held in a contracted position by a trigger mechanism. When the trigger mechanism is released, the gas pressure spring is supposed to expand and drive a piston sealingly received in a bore and leading to a fine-dimension orifice to produce a jet hypodermic injection from liquid held in the bore ahead of the piston.  
           [0008]    The Weston device is thought to have several deficiencies such as difficult and costly manufacturing and sterilization processes because the pressurized gas and a drug dose need to be contained in the same package, and a possible inability to endure long-term storage while still retaining the gas pressure in the gas spring. In other words, the gas pressure spring of the Weston device contains only a small quantity of gas, and depends upon the sealing relationship of the ram of this spring with a cylinder within which the ram is movably and sealingly received in order to retain this gas pressure. Even a small amount of gas leakage over time will be enough to render this injector inoperative.  
           [0009]    It also is known in this art to provide a needle-free injection system having two plungers that are initially spaced adjacent either end of a glass drug storage sleeve, with liquid drug being disposed between the plungers within the sleeve. Such a system also includes a plastic drug storage chamber disposed coaxially with and forwardly of the glass drug storage sleeve. The forward end of the plastic drug chamber terminates in an injection orifice. The plastic drug chamber includes an enlarged portion that permits drug to flow past the forward plunger when that plunger is aligned with the enlarged portion.  
           [0010]    In this earlier system, axial force is exerted on the rear plunger immediately prior to injection. Because liquid drug is disposed in the space between the plungers, the plungers move in unison in a forward direction until the forward plunger is aligned with the enlarged portion. At that point, the continued forward travel of the rearward plunger forces liquid drug around the forward plunger until all of the drug is disposed in the plastic drug chamber forward of both plungers, which are now in abutment. The unit thus is ready for actuation.  
           [0011]    When the unit is actuated the plungers both exert a forward axial force, causing liquid drug to be directed out of the injection orifice and into the patient.  
         SUMMARY OF THE INVENTION  
         [0012]    One form of the invention provides a needle-free injection system including the following components: a nozzle portion having a glass wall defining a drug storage space, and an injection wall defining a drug injection space, the injection wall being coaxial with the glass wall and defining a plurality of drug bypass conduits disposed adjacent a forward end of the drug injection space; a body portion mounted to the nozzle portion such that relative axial movement may be effected between the portions; an injection orifice defined at the forward end of the injection space; a drug plunger defining a rearward end of the storage space; a drug plug initially disposed between the storage space and the injection space, and being displaceable into the injection space adjacent the bypass conduits; and a pierceable gas cartridge for providing injection power to the drug plunger.  
           [0013]    Another form the invention takes is a needle-free injection system including the following components: a nozzle portion defining a forwardly-facing injection orifice; a body portion mounted to the nozzle portion, the portions being displaceable toward each other to prepare the system for actuation; and a safety tab for preventing actuation prior to the time that relative displacement is effected between the nozzle portion and the body portion, the safety tab being frangibly mounted to one of the body portion or the nozzle portion and including a contact part, the safety tab to be contacted and broken when the portions are displaced toward each other.  
           [0014]    Yet another form the invention takes is a method for preparing a needle-free injection unit for injection, comprising the following steps: providing a storage compartment for liquid drug; positioning an injection orifice forwardly of the storage compartment, through which the liquid drug is selectively injected into the patient; providing a pressurized, pierceable gas storage cartridge with a system for conveying pressure to the storage compartment when the cartridge is pierced; positioning a seal between the cartridge and the storage compartment to prevent gas pressure from reaching the storage compartment after the cartridge is pierced, but prior to actuation of the unit, the seal being positioned such that the piercing of the cartridge provides axial pressure on the seal; providing a trigger having a roller positioned such that when axial pressure is provided on the trigger, an outward force is exerted on the trigger; and positioning a trigger actuator outwardly of the trigger to prevent the trigger from moving outwardly until the unit is actuated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is an isometric view of a first embodiment of the present invention, showing the unit ready for shipping to the patient;  
         [0016]    [0016]FIG. 2 is a side elevation sectional view taken along line  2 - 2  of FIG. 1;  
         [0017]    [0017]FIG. 3 is a side elevation sectional view taken along line  3 - 3  of FIG. 1, at 90° from the view of FIG. 2;  
         [0018]    [0018]FIG. 4 is a side elevation sectional view corresponding to FIG. 3 except that the threaded nozzle portion is shown to be about half of the way threaded into the body portion, and the drug plunger and drug plug are shown shifted forwardly, with the drug plug seated in the forward end of the plastic drug chamber;  
         [0019]    [0019]FIG. 5 is a view corresponding to FIG. 4 except that the gas cartridge is shown to be pierced as a result of the nozzle portion being turned entirely into the body portion; the apparatus is ready for injection;  
         [0020]    [0020]FIG. 6A is an end elevation sectional view taken along line  6 A- 6 A of FIG. 5;  
         [0021]    [0021]FIG. 6B is an end elevation sectional view taken along line  6 B- 6 B of FIG. 5;  
         [0022]    [0022]FIG. 6C is an end elevation sectional view taken along line  6 C- 6 C of FIG. 5;  
         [0023]    [0023]FIG. 7 is a view corresponding to FIG. 5 except that liquid drug has now been injected into the patient, and the apparatus is ready for disposal;  
         [0024]    [0024]FIG. 8 is an exploded view of the embodiment of FIGS.  1 - 7 ;  
         [0025]    [0025]FIG. 8A is an enlarged, schematic, fragmentary side elevation sectional view showing the leg and nib construction of the embodiment of FIGS.  1 - 8  that provides a capability of holding the nozzle portion in engagement with the body portion during storage and shipping;  
         [0026]    [0026]FIG. 9 is a schematic, fragmentary plan view of one of the safety tabs included in the embodiment of FIGS.  1 - 8 ;  
         [0027]    [0027]FIG. 10 is a side elevation sectional view taken along line  10 - 10  of FIG. 9;  
         [0028]    [0028]FIG. 11 is a fragmentary, end elevation sectional view taken along line  11 - 11  of FIG. 9;  
         [0029]    [0029]FIG. 12 is a side elevation sectional view of a second embodiment, designed for intradermal injection, showing the unit ready for shipping;  
         [0030]    [0030]FIG. 13 is a fragmentary, exploded view of a third embodiment, showing ball bearings used in place of the trigger elements;  
         [0031]    [0031]FIG. 14 is a fragmentary, side elevation sectional view of a fourth embodiment, showing the use of a smaller O-ring seal to reduce the amount of axial force on the seal;  
         [0032]    [0032]FIG. 15 is a side elevation view of a fifth embodiment, showing only the proximal end of the nozzle portion, the nozzle portion threads including a pair of slots;  
         [0033]    [0033]FIG. 16 is an end elevation sectional view taken along line  16 - 16  of FIG. 15, showing one of the two slots;  
         [0034]    [0034]FIG. 17 is a fragmentary side elevation view of the body portion of the fifth embodiment, showing the clip at the distal end thereof; and  
         [0035]    [0035]FIG. 18 is an end elevation sectional view taken along line  18 - 18  of FIG. 17, showing the inclined face of the body portion clip of the fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0036]    The objects of the invention are best achieved when the invention takes the form of the embodiment depicted in the figures. FIGS.  1 - 11  depict a first embodiment of the apparatus that is designated generally with the numeral  10 . FIG.  1  depicts the three basic components of the preferred embodiment  10 —a nozzle portion  12 , a body portion  14  and a trigger portion  16 . These portions will be individually discussed as this description continues.  
         [0037]    Reference should first be made to FIGS. 2 and 3, which depict apparatus  10  as it is packaged, shipped and received by the customer. The customer in this case may be a clinic, a physician or even a patient. Nozzle portion  12  includes outwardly facing threads  22  that are received in body portion  14 , as will be explained in a moment. Extending between nozzle portion  12  and body portion  14  is an inner sleeve  17  having an enlarged section  19  disposed in the body portion and a reduced section  21  disposed in the nozzle portion. Sleeve  17  is sized to fit tightly into the nozzle portion. It is fit into the body portion in a tight sliding fit to permit the nozzle portion to be rotated into the body portion.  
         [0038]    Body portion  14  includes a body  24  with a pair of nozzle portion engagement clips  25  designed to engage the nozzle portion. As shown best in FIG. 8A, each of the clips has an inwardly extending engagement nib  27 . The engagement nibs  27  engage the proximal-most threads  22  to hold the body and nozzle portion together prior to the point that they are fully threaded into each other.  
         [0039]    More specifically, the embodiment shown in FIG. 8A has nibs  27 , each of which include two faces. The proximal face  27   a  extends at about a 90° angle, while the distal face  27   b  extends at about a 45° angle. When first thread  22  is slid over the two clips  25  on the opposite sides of the body portion, the resiliency of the clips permits the clips to bend outwardly to receive the end of the nozzle portion. During this bending and insertion process, the 90° leading edge of the first thread  22  slides over the distal face  27   b  of nib  27 . Clip  25  snaps back once the first thread has cleared the nib. The 90° nib face  27   a  complements the 90° leading edge of the first thread  22  to prevent the nozzle portion from falling out of or being removed from the body portion.  
         [0040]    The resiliency of the two clips  25  provides resistance to the nozzle portion being pushed over the 45° face  27   b  of nib  27 . Thus, during shipment the nozzle portion will not be sliding in and out of the body portion. Once the patient has received the apparatus  10  and wants to prepare it for actuation, he/she can thread the nozzle portion into the body portion, permitting the 90° face of the next thread  22  to ride over the 45° face  27   b  as clip  25  bends outwardly and snaps back into place once the second thread has cleared the 45° face  27   b  of nib  27 .  
         [0041]    Also included in body  24  is a pair of trigger engagement slots  28  that extend into the end of the body facing trigger portion  16  (see FIG. 1). Trigger engagement slots  28  are disposed 180° across the trigger portion from each other; only one of these slots shows in the figures.  
         [0042]    [0042]FIGS. 1 and 9- 11  depict a generally U-shaped safety tab  30  that is frangibly (or breakably) mounted by three thin webs  33  within one of the trigger engagement slots  28 . Two of the safety tabs  30  may be provided, at the option of the designer, in which case, one safety tab  30  would be positioned within each of the trigger engagement slots  28 . Safety tab  30  includes an inwardly-extending chamfered surface  31  (see FIG. 10) that is designed to be contacted by a corresponding chamfered surface to be described below.  
         [0043]    As shown in FIGS.  2 - 8 , threads  40  are included in the distal end of the inner side of body  24 . These threads  40  complement threads  22  in nozzle portion  12 , so that when the patient is ready to use apparatus  10  to effect injection, nozzle portion  12  may be rotated into body  24 . FIG. 4 shows nozzle portion  12  to be threaded about halfway into body portion  14 . By comparing FIGS. 3 and 4, it can be seen that a drug plunger  66  and a drug plug  62  (to be described below) have shifted to the right. With the components in this position the unit is considered primed because air has been removed from the front part of nozzle portion  12 . FIG. 5 shows nozzle portion  12  to be threaded all of the way into body portion  14 . In this final threading step a piercing pin  100  pierces a gas cartridge  102 , and the apparatus is ready for injection. This operation of apparatus  10  will be explained in more detail below.  
         [0044]    Again as shown best in FIGS. 1 and 2, trigger portion  16  includes a trigger actuation portion  50  that is in the form of two pads, one on each side of trigger portion  16 . Trigger actuation portion  50  also includes a pair of axially extending trigger members  52  that are aligned with and extend slightly into trigger engagement slots  28  at 180° positions across the apparatus. Safety tab  30  is frangibly mounted in each trigger engagement slot  28  by thin webs  33  as mentioned above.  
         [0045]    Referring now to FIG. 8, a pair of trigger actuators  53  are shown to be positioned within trigger members  52 . These trigger actuators cooperate to hold a pair of trigger elements  90  in a radially inward position to prevent actuation of the apparatus until the trigger portion  16  is slid forward toward body portion  14 . This operation will be described in more detail below.  
         [0046]    [0046]FIG. 8 also shows a pair of longitudinally extending ribs  55  that fit into complementing slots (not shown) in trigger portion  16 . These ribs  55  also show in FIG. 6A. Immediately rearward of these ribs are a pair of nibs  57  (see FIGS.  3 - 5 , 7  and  8 ), each of which includes a rearward inclined face so that trigger portion  16  can be slid onto this rearward part of the body.  
         [0047]    As identified in FIGS.  3 - 5 , a pair of corresponding trigger nibs  59  and  61  define a trigger portion slot (not shown) designed to receive body nibs  57  on each side of the trigger portion. The trigger nibs  59  and  61  are positioned on the inner side of a pair of clips  65  that are cut into the rear of trigger actuation portion  50 . One of these clips  65  appears in FIGS. 1 and 8. Clips  65  are on opposite sides of the trigger portion, and provide the resiliency needed so that trigger portion  16  can snap into body portion  14 . The complementing inclination of the nib faces permits the trigger actuation portion to slide forward during actuation, but does not permit the trigger portion to be removed from the body portion. It thus operates in much the same fashion as clip  25  discussed above.  
         [0048]    [0048]FIG. 2 and subsequent figures show the interior, working portions of apparatus  10 . Starting from the right in FIG. 2, an injection orifice  54  provides the means by which liquid drug exits apparatus  10  in a defined, high-pressure stream directed into the patient. A liquid drug chamber is depicted generally at  56 , and includes a plastic drug chamber  58  defined by the inwardly facing wall of nozzle portion  12 , and a drug storage chamber  51  defined by a glass cartridge  60 . Glass cartridge  60  retains the liquid drug during storage and shipment and prior to the point that apparatus  10  is converted to its primed mode with nozzle portion  12  being rotated into body portion  14  as described above.  
         [0049]    Positioned between drug storage chamber  51  and plastic drug chamber  58  is a drug plug  62 . Positioned at the rearward or proximal end of drug storage chamber  51 , within glass cartridge  60 , is a drug plunger  66 . The resilient material of which drug plunger  66  and drug plug  62  are fabricated is sufficiently impermeable that liquid drug absorption is not a problem. The material is also inert so that there is no chemical or biological reaction to the drug. Butyl rubber has both of these features.  
         [0050]    In apparatus  10 , glass cartridge  60  is provided to store the liquid drug. Most conventional plastics are too permeable to allow long-term storage, so liquid drug is stored in glass cartridge  60  in drug storage chamber  51 , and is injected from plastic drug chamber  58 , which is the ideal function of each material.  
         [0051]    Defined in the walls of plastic drug chamber  58 , at the forward end therof, are three drug bypass conduits 64, evenly spaced around the periphery at 120° increments. These are shown in cross-section in FIG. 6C. While three drug bypass conduits  64  are included, any number of conduits can be utilized. However many conduits are included, they should be symmetrically positioned around the periphery of plastic drug chamber  58 .  
         [0052]    As shown best in FIGS. 2 and 3, bypass conduits  64  include axially-extending portions that extend along the length of plastic drug chamber  58 . These portions are shown in section in FIG. 6C. As shown best in FIGS. 2 and 3, bypass conduits  64  also include generally radially-extending portions, which follow the narrowing of the plastic drug chamber. As shown in FIG. 6C, the portions of the inward facing nozzle wall extending between bypass conduits  64  actually support drug plug  62  from the sides and from the front (see also FIGS. 4, 5 and  7 ). The drug bypass conduits  64  are provided to permit liquid drug disposed in plastic drug chamber  58  to flow from the area between drug plunger  66  and drug plug  62 , and around the drug plug, to displace any air in the forward portion of the plastic drug chamber  58 , thus priming the apparatus. During actual injection, liquid drug is driven through bypass conduits  64 , out injection orifice  54  and into the patient.  
         [0053]    Positioned at the proximal end of sleeve  17  is a seal  68  designed to prevent liquid drug from migrating rearwardly along glass cartridge  60  during the priming of apparatus  10  and during injection of drug into the patient. Seal  68  is normally in the form of an O-ring, but other conventional seals may alternatively be used.  
         [0054]    A gas piston  70  is positioned along the longitudinal centerline of apparatus  10  in alignment with drug plunger  66  and drug plug  62 . Gas piston  70  extends rearwardly or to the left in the figures to contact a gas pressure drive rod  72 . Gas piston  70  includes a centrally disposed gas plunger  74  that extends rearwardly into a gas pressure channel  76  that passes through the longitudinal center line of gas pressure drive rod  72 . Each of the gas piston  70  and the gas pressure drive rod  72  include cupped portions  78  and  80 , respectively, which face each other in a complementing concave configuration.  
         [0055]    Gas pressure channel  76  facilitates the passage of gas pressure through the center of the apparatus. A pair of channels  104  extend radially outwardly from gas pressure channel  76  adjacent the rearward end thereof to facilitate the passage of gas pressure from the periphery of the gas pressure drive rod  72  to gas pressure channel  76 .  
         [0056]    As shown best in FIG. 7, gas piston cupped portion  78  acts to seal gas as it is being expelled out of gas pressure channel  76 . The pressurized gas forces the periphery of cupped portion  78  against the inner surface of sleeve  17  to drive gas piston  70  forwardly toward drug plunger  66 . The gas pressure is sealed from being exhausted rearwardly by gas pressure drive rod cupped portion  80  that is also forced outwardly against the inner surface of sleeve  17 .  
         [0057]    Gas pressure drive rod  72  includes a shoulder member  82  that extends radially outwardly almost all of the way to the inner surface of body  24 . Shoulder member  82  includes a rearwardly-facing beveled edge  35 , which cooperates with chamfered edge  31  of safety tab  30 , as will be described in detail below.  
         [0058]    Continuing to move rearwardly or to the left in FIGS.  2 - 5  and  7 , body  24  can be seen to include a rearward annulus  84  that engages a fixed washer seat  86  having a beveled or angled left side  86   a  that in turn holds a trigger ring  88  surrounding gas pressure drive rod  72 . A pair of trigger elements  90  are mounted to trigger ring  88 , also surrounding gas pressure drive rod  72 . As shown best in FIG. 8, a breakaway connection is provided between trigger ring  88  and trigger element  90 , for reasons that will be understood as this description continues. Trigger elements  90  are identical to each other, disposed 180° apart. Each trigger element  90  has left and right beveled or angled sides  90   a  and  90   b , respectively. The right beveled sides  90   b  have a bevel angle that complements that of the left beveled side of fixed washer seat  86   a . That angulation is, in the preferred embodiment, approximately 22 degrees.  
         [0059]    Continuing along gas pressure drive rod  72 , a sliding bushing  92  can be seen. The right hand face  92   a  of sliding bushing  92  is beveled or angled to correspond to the angulation of the rearward beveled faces  90   a  of trigger elements  90 , again, typically 22 degrees. Like trigger ring  88 , sliding bushing  92  fits around gas pressure drive rod  72 . This is not a sealing engagement, however, so a sealing ring  94  is positioned immediately rearwardly or to the left of sliding bushing  92 , also surrounding gas pressure drive rod  72 . Sealing ring  94  is typically in the form of an O-ring, but might alternatively take other forms.  
         [0060]    Continuing rearwardly or to the left of sealing ring  94 , a spacer bushing  96  can be seen surrounding gas pressure drive rod  72  at the rearward or left-most end thereof. Like sliding bushing  92 , spacer bushing  96  surrounds gas pressure drive rod  72 , but does not provide a sealing fit, gas sealing being provided solely at sealing ring  94 .  
         [0061]    This rearward or left-most end of gas pressure drive rod  72  includes an undercut piercing pin receiving seat  98  designed to receive a piercing pin  100 . Piercing pin  100  is positioned immediately adjacent a forward or right-facing end of a gas cartridge  102  so that when leftward pressure is exerted on piercing pin  100 , gas cartridge  102  is pierced, thereby releasing pressurized Nitrogen or other gas from the cartridge to drive the injection process.  
         [0062]    [0062]FIGS. 6A, 6B and  6 C have been included to show the internal components of apparatus  10  in linear cross section. All of the components depicted in these views have already been discussed, except for the four evenly spaced, generally cylindrical slots that appear in FIG. 6B between trigger members  52  and trigger actuator  53 . The slots, which have not been identified with a numeral, are included merely to facilitate automated installation of trigger member  92  into trigger portion  16 . They serve no real function in the operation of apparatus  10 , which shall now be described.  
       Operation of the Embodiment of FIGS.  1 - 11   
       [0063]    As mentioned earlier, FIGS.  1 - 3  depict apparatus  10  in its shipping or storage configuration. When nozzle portion  12  is fully rotated into body portion  14 , apparatus  10  is ready for actuation. The conversion process is depicted about half of the way completed in FIG. 4, and completed, ready for injection, in FIG. 5.  
         [0064]    It can be seen that during this process of rotating nozzle portion  12  into body  24 , gas piston  70  exerts a rightward or distal force on drug plunger  66 . As the relative positions of the nozzle and body portions change from the positions of FIG. 3 to those of FIG. 5, drug plunger  66  and drug plug  62  move from being disposed within glass cartridge  60  in storage chamber  51  to positions in which the drug plunger is disposed within the glass cartridge, but the drug plug is in its forward-most position in plastic drug chamber  58 , aligned with drug bypass conduits  64 . The drug plunger and the drug plug move together until this point because the liquid drug is trapped between them.  
         [0065]    Once drug plug  62  clears glass cartridge  60 , liquid drug can flow around the drug plunger via drug bypass conduits  64  and dribble out injection orifice  54 . This removes any air in the front of the plastic drug chamber  58  and primes apparatus  10  for activation. Prior to actuation, however, gas cartridge  102  must be pierced. This is done by completely threading the nozzle portion  12  into the body portion  14 , as depicted in FIG. 5.  
         [0066]    However, gas is not yet released to the body portion or the nozzle portion because sealing ring  94  prevents gas from passing beyond that point in the apparatus. Specifically, gas pressure is prevented from flowing into radial channels  104  as long as the sealing ring is disposed rearwardly of the radial channels. Radial channels  104  are also blocked by sliding bushing  92 , but because this is not a sealing contact, this does not prevent the passage of gas pressure.  
         [0067]    As rotation of nozzle portion  12  into body portion  14  is completed, beveled or chamfered edge  35  of shoulder  82  contacts chamfered edge  31  of safety tab  30 . The complementing beveled faces force the safety tab away from the apparatus, breaking the connection at thin webs  33 . This disengages the safety tab from the apparatus, permitting it (or “them” if there are two safety tabs) to fall out of trigger engagement slot  28 . This clears a space for trigger member(s)  52  to enter the trigger engagement slot(s)  28 .  
         [0068]    Once rotation of nozzle portion  12  into body portion  14  is complete as depicted in FIG. 5, apparatus  10  is primed and ready for actuation. At this point, gas cartridge  102  has been pierced by piercing pin  100 , although the gas pressure is still contained by sealing ring  94 . Liquid drug is disposed in plastic drug chamber  58  adjacent injection orifice  54 , forward of drug plunger  66  and forward and rearward of drug plug  62 . In fact, some of the drug may have actually dribbled out of the drug orifice, simply to ensure that any remaining air has been completely removed from plastic drug chamber  58 .  
         [0069]    Until the apparatus is actuated, the pair of trigger actuators  53  hold the two trigger elements  90  against gas pressure drive rod  72 . A radially-outward force is being exerted on the trigger elements as a result of the forward thrust on sealing ring  94  and the angulation of the interface between sliding bushing  92  and trigger elements  90  at  92   a  and  90   a  respectively, and between fixed washer  86  and trigger elements  90  at  86   a  and  90   b , respectively. The forward thrust is, of course, provided by the gas pressure being exerted on the sealing ring because of the piercing of the gas cartridge.  
         [0070]    In order to effect injection, trigger actuation portion  50  is slid to the right or in a forward direction. By sliding trigger actuation portion  50 , trigger members  52  are permitted to move into trigger engagement slots  28 . Trigger actuators  53  therefore no longer hold trigger elements  90  radially inwardly, and the gas pressure being exerted on sealing ring  94  and sliding bushing  92  causes the sliding bushing to push to the right so that the complementing angled faces cause the trigger elements to be shifted outwardly to the gap formed by the removal of the trigger actuators, as shown in FIG. 7. The radially-outward force on the trigger elements once the trigger actuators have moved is sufficient to break the connection between trigger ring  88  and trigger elements  90  depicted in FIG. 8. Once trigger elements  90  are moved radially outwardly, sliding bushing  92  continues to slide to the right. Along with the sliding of the sliding bushing, sealing ring  94  moves to the right as well, past radial channels  104 . This permits gas under pressure to be directed along the interface between spacer bushing  96  and gas pressure drive rod  72 , thereby passing into radial channels  104  and gas pressure channel  76 . Gas thus rushes through gas pressure channel  76  and gas pressure drive rod  72  and into the interior of body  24 . This forces gas plunger  74  out of gas pressure channel  76 , exerting gas pressure on gas piston cupped portion  78 . This forces the cupped portion against inner sleeve  17 , sealing the interface between these components and driving gas piston  70  to the right.  
         [0071]    As gas piston  70  is driven to the right, it forces drug plunger  66  forwardly, forcing liquid drug from glass drug storage chamber  51 , through drug bypass channels  64 , and out through injection orifice  54 , into the patient.  
         [0072]    The embodiment of FIGS.  1 - 11  is designed for subcutaneous injection. Therefore it does not include an intradermal spacing feature. Such a feature is included in the embodiment depicted in FIG. 12. This variation will now be described.  
       Intradermal Injection Embodiment of FIG.  12   
       [0073]    [0073]FIG. 12 depicts a second embodiment of the present invention, which is indicated generally at the numeral  110 . This embodiment  110  is virtually identical to apparatus  10  except that nozzle portion  112  includes an intradermal spacing section  118 . Thus, it can be seen that the injection orifice  154  is spaced away from the skin of the patient during injection. This results in the liquid drug being directed into but normally not entirely through the skin of the patient.  
         [0074]    It can be seen in FIG. 12 that, other than dimensional differences and the provision of intradermal spacing section  118 , the nozzle portion  112 , body portion  114  and trigger portion  116  are essentially identical to corresponding portions of apparatus  10 . The size of the injection orifice and the volume of liquid drug are slightly different when comparing apparatus  110  and apparatus  10 , but those parameters are up to the product designer and the physicians involved in effecting the injections.  
       Embodiment of FIG.  13   
       [0075]    [0075]FIG. 13 depicts another embodiment that is identical to apparatus  10  of FIGS.  1 - 11 , except that it includes a pair of ball bearings  290  in place of trigger elements  90  and trigger ring  88 . Given the spherical configuration of balls  290 , they include inclined surfaces (sometimes referred to herein as angled faces) which will cooperate with the complementing inclined surfaces  292   a  of sliding bushing  292  and  286   a  of fixed washer  286  in the same fashion as previously described with respect to apparatus  10 .  
         [0076]    It may be desirable in some applications to include more than two ball bearings; it may also be desirable to include some sort of conventional ball bearing cage (not shown in the figures).  
       Embodiment of FIG.  14   
       [0077]    [0077]FIG. 14 is a fragmentary sectional view showing an embodiment that includes a smaller O-ring seal than seal ring  94  of apparatus  10  of FIGS.  1 - 11 . This smaller seal, identified at  394 , is provided in order to reduce the amount of axial force exerted on the seal ring and the trigger element  390 . This embodiment of FIG. 14 is actually the presently preferred mode of practicing the invention.  
         [0078]    The embodiment of FIG. 14 is identical in most respects to apparatus  10 , except that it includes a spacer bushing  396  that has a pair of steps to accommodate the smaller seal  394 . A second seal  397 , typically in the form of an O-ring, is included in spacer bushing  396  to prevent pressure from leaking past the interface between body portion  316  and the spacer bushing. Sliding bushing  392  is generally L-shaped to complement the configuration of spacer bushing  396  and the fit of seal  394 . A trigger element  390  is shown having angled faces to complement those of sliding bushing  392  and fixed washer  386 , as with the prior embodiments. A trigger ring may also be included to facilitate the assembly of trigger elements  390 , but it has not been depicted for purposes of simplification.  
         [0079]    In operation, after gas cartridge  302  is pierced, forward axial pressure is exerted on seal  394 , but because the seal has a smaller surface than seal ring  94 , the forward force is less than with apparatus  10 . This results in less force on trigger elements  390 , which reduces the outward bias on the trigger elements prior to actuation of the unit. The bias is sufficient, however, to break any connection between a trigger ring (not shown) and the trigger elements. In other respects, the construction and operation of this embodiment is identical to that of apparatus  10 .  
       Embodiment of FIGS.  15 - 18   
       [0080]    FIGS.  15 - 18  depict another embodiment that includes a variation of the system for engaging nozzle portion  412  and body portion  414 . As shown best in FIGS. 15 and 16, a pair of notches  423  and  427  are provided in threads  422  of nozzle portion  412 . As shown in FIG. 16, each notch  423  and  427  includes a 90 degree face  423   a  and an angled face  423   b . Complementing these faces, as shown in FIG. 18, is a 90 degree face  425   a  and an angled face  425   b  in clip  425 . Thus, when nozzle portion  412  is only partially threaded onto body portion  414  for shipping, the natural resiliency of clip  425  enables angled clip face  425   b  to ride over angled slot face  423   b . When threaded beyond that point, 90 degree faces  423   a  and  425   a  are in abutment, preventing the nozzle and body portions from threading off of each other. When the nozzle and body portions are entirely threaded onto each other, such as when the gas cartridge has been pierced and the apparatus is ready for actuation, a corresponding 90 degree face of slot  427  engages 90 degree face  425   a  of clip  425  to prevent the nozzle and body portions from being even partially threaded off each other. This ensures that when the trigger mechanism is actuated, the nozzle and body portions will be fully engaged. It also prevents any disassembly of the unit after the gas cartridge has been pierced. This body and nozzle engagement system of FIGS.  15 - 18  is presently considered the best mode of engaging the nozzle and body portions.  
         [0081]    Other changes and modifications of the present invention can be made without departing from the spirit and scope of the present invention. Such changes and modifications are intended to be covered by the following claims.