Abstract:
An Injection device for administering a dose of liquid medicament to patient comprises—a syringe containing the dose of medicament—a hollow injection needle adapted to penetrate skin of the patient, —a stopper translatably disposed within syringe, —a plunger connectable to stopper and translatable in at least a proximal direction to displace stopper in the proximal direction and—a releasable noise component capable of, upon release, generating an audible and/or tactile feedback. The proximal displacement of stopper causes the dose of the medicament to be expelled through the hollow injection needle. The noise component is released when the plunger reaches a position relative to the syringe in which stopper is located in proximity of a proximal end of the syringe. The released noise component impacts on at least one component of the injection device to generate the audible and/or tactile feedback indicating the end of the injection.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to an injection device for administering a dose of a liquid medicament according to the preamble of claim  1 . 
       BACKGROUND OF THE INVENTION 
       [0002]    Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical. 
         [0003]    Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors. 
         [0004]    In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems. 
         [0005]    The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves. 
         [0006]    Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc. 
         [0007]    Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient&#39;s skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Injection forces/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring. 
         [0008]    US 2002/0095120 A1 discloses an automatic injection device which automatically injects a pre-measured quantity of fluid medicine when a tension spring is released. The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston forward inside the ampoule. After the fluid medicine has been injected, torsion stored in the tension spring is released and the injection needle is automatically retracted back to its original storage position. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide an improved injection device. 
         [0010]    The object is achieved by an injection device according to claim  1 . 
         [0011]    Preferred embodiments of the invention are given in the dependent claims. 
         [0012]    In the context of this specification the term proximal refers to the direction pointing towards the patient during an injection while the term distal refers to the opposite direction pointing away from the patient. The term inwards refers to a radial direction pointing towards a longitudinal axis of the auto-injector whereas the term outwards refers to the opposite direction radially pointing away from the longitudinal axis. 
         [0013]    An injection device for administering a dose of a liquid medicament to a patient comprises
       a syringe containing the dose of the medicament   a hollow injection needle adapted to penetrate the skin of the patient,   a stopper translatably disposed within the syringe,   a plunger connected to the stopper and translatable in at least a proximal direction to displace the stopper in the proximal direction and   a releasable noise component capable of, upon release, generating an audible and/or tactile feedback to a user. The proximal displacement of the stopper causes the dose of the medicament to be expelled through the hollow injection needle. The noise component is released when the plunger connected to the stopper reaches a position relative to the syringe in which the stopper is located in proximity of a proximal end of the syringe. The released noise component impacts on at least one component of the injection device to generate the audible and/or tactile feedback indicating the end of the injection.       
 
         [0019]    Injections need to be frequently performed by healthcare professionals or patients with chronical illnesses like diabetes. Often, it is hard to properly estimate the time required to fully expel the dose of the medicament contained in the syringe of the injection device as this depends, amongst others, on the specific layout of the injection device and on the viscosity of the medicament. Furthermore, nowadays injection devices often obstruct a direct view of the syringe contained therein to alleviate a possible patient&#39;s fear of needles. On the downside, this also makes it impossible to visually verify the location of the stopper within the syringe barrel. The injection device according to the invention generates an audible and/or tactile feedback to the user just before the medicament is fully expelled and the stopper bottoms out in the syringe. This makes it easier for the user to get used to an unfamiliar injection device or ensures that the injection is properly carried out and the dose of the medicament is completely disposed beneath the skin of the patient even when medicaments of different viscosities are injected. In particular, the audible and/or tactile feedback helps to avoid an underdosage or a waste of the medicament. 
         [0020]    The noise component interacts with at least part of a chassis, a case, a trigger button, a carrier, the plunger and/or a sleeve trigger of the injection device to generate the audible and/or tactile feedback. The audible and/or tactile feedback is generated by incorporating functional elements of the injection device that primarily provide, amongst others, a housing, a release element for an injection mechanism, a insertion mechanism for the injection needle or a retraction mechanism for providing needle safety after the injection is completed. 
         [0021]    According to one possible embodiment of the invention, the injection device is arranged as an auto-injector that is operated by a number of key mechanical operations:
       The case is advanced relative to the chassis compressing a control spring giving the user the impression of depressing a skin interlock sleeve. All other components remain in the same place during case advance resulting in the trigger button appearing from the distal end of the case.   The user pushes the trigger button which can now be operated. Button depression directly moves the carrier and hence the drive sub-assembly in the proximal direction a set distance until the control spring takes over via a first collar and inserts the needle into the injection site.   The trigger button stops on the distal end of the case as the carrier continues translating in the proximal direction. The relative motion of the carrier relative to the trigger button is used to release the drive spring just before full insertion depth is reached, e.g. by pulling a peg on the trigger button out of the carrier thus allowing the plunger to move. The drive spring drives the plunger down the syringe barrel expelling the medicament.   A noise mechanism is released when the plunger is near the end of travel shortly before the stopper bottoms out in the syringe, indicating the end of injection to the user.   The needle remains fully inserted until the user moves the case back a set distance at which point the second collar decouples from the case and couples to the carrier while the first collar decouples from the carrier and couples to the chassis thus allowing the control spring to retract the carrier and hence the needle.       
 
         [0027]    According to another possible embodiment, at least one of the components of the injection device involved in generating the tactile and/or audible feedback has a physical shape or design suitable for amplifying and/or transmitting a sound. In particular, the component may be arranged as the carrier having a tubular shape or as a drum-like trigger button to amplify the sound. The noise component may directly impact on the component to produce the sound or, alternatively, the component may be operatively connected to a second component having a shape suitable for amplifying the sound. 
         [0028]    Advantageously, the component adapted to provide a tactile feedback is part of an exterior component of the injection device that is in particular gripped and actuated by the user during an injection like, for example, the trigger sleeve, the case or the trigger button. The exterior component is in contact with a body part of the user performing the injection to facilitate recognition of the tactile feedback. 
         [0029]    According to yet another possible embodiment of the invention, the plunger is driven proximally by the action of a relaxing drive spring to translate the stopper in the proximal direction and to dispose the dose of the medicament beneath the skin of the patient. The injection device may be designed as an auto-injector that automatically expels the dose of the medicament upon actuation of the trigger sleeve or the trigger button. Alternatively, the injection device may be designed as a manual injection device, wherein the plunger has to be manually pushed to administer the dose of the medicament to the patient. 
         [0030]    According to yet another possible embodiment of the invention, the noise component is biased by a noise spring and, upon release, accelerated by the noise spring and driven towards the at least one component of the injection device to generate the audible and/or tactile feedback to the user. The noise spring ensures that the generated feedback is sufficiently strong to be easily recognised by the user. 
         [0031]    According to yet another embodiment of the invention, the syringe is translatably arranged with respect to the case of the injection device. A noise release mechanism couples the noise component to a translatory movement of the syringe until release of the noise component. This in particular allows providing injection devices that are always needle safe, i.e. the needle is covered before and after the injection, with an audible and/or tactile feedback indicating the end of the injection. During the needle insertion phase of the injection, the syringe travels proximally to expose and insert the injection needle. During this phase, the noise component is coupled to the movement of the syringe and travels with the syringe in the proximal direction. Upon completion of the injection, the noise component is released to generate the audible and/or tactile feedback. 
         [0032]    In particular, the syringe may be mounted to the carrier that is translatably arranged with respect to the case of the injection device. The noise release mechanism is arranged between the carrier and the noise component to couple the noise component to the translatory movement of the syringe. 
         [0033]    According to yet another possible embodiment, the noise spring biasing the noise component is grounded to the case and compressed and charged by the proximal movement of the syringe with respect to the case. This allows the noise spring to be arranged and stored within the injection device in an unstressed state. The noise spring is charged when the injection device is used. This helps to avoid material fatigue and ensures that the injection device works reliably even after long periods of storage. 
         [0034]    In particular, the noise release mechanism may comprise a second resilient arm that is deflectable in a radial outward direction to release the noise component. The plunger comprises a distal plunger sleeve that abuts against the second resilient arm in the radial outward direction to prevent release of the noise component. The distal plunger sleeve moves with the plunger that translates the stopper to expel the dose of the medicament through the hollow injection needle. The distal plunger sleeve prevents the deflection of the second resilient arm until the stopper almost bottoms out within the syringe and is located in proximity of the proximal end of the syringe. 
         [0035]    According to the same embodiment, the noise component comprises an elongate portion with an outward eleventh ramp that is engaged by ramped inward boss of the second resilient arm to couple the noise component to the syringe carrier. The outward deflection of the second resilient arm causes disengagement of the outward eleventh ramp from the inward boss releasing the noise component to generate the audible and/or tactile feedback to the user. 
         [0036]    The injection device or auto-injector may preferably be used for subcutaneous or intra-muscular injection, particularly for delivering one of an analgetic, an anticoagulant, insulin, an insulin derivate, heparin, Lovenox, a vaccine, a growth hormone, a peptide hormone, a proteine, antibodies and complex carbohydrates. 
         [0037]    The term “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound, 
         [0000]    wherein in one embodiment the pharmaceutically active compound has a molecular weight up to 1500 Da and/or is a peptide, a proteine, a polysaccharide, a vaccine, a DNA, a RNA, a antibody, an enzyme, an antibody, a hormone or an oligonucleotide, or a mixture of the above-mentioned pharmaceutically active compound,
 
wherein in a further embodiment the pharmaceutically active compound is useful for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy, thromboembolism disorders such as deep vein or pulmonary thromboembolism, acute coronary syndrome (ACS), angina, myocardial infarction, cancer, macular degeneration, inflammation, hay fever, atherosclerosis and/or rheumatoid arthritis,
 
wherein in a further embodiment the pharmaceutically active compound comprises at least one peptide for the treatment and/or prophylaxis of diabetes mellitus or complications associated with diabetes mellitus such as diabetic retinopathy,
 
wherein in a further embodiment the pharmaceutically active compound comprises at least one human insulin or a human insulin analogue or derivative, glucagon-like peptide (GLP-1) or an analogue or derivative thereof, or exedin-3 or exedin-4 or an analogue or derivative of exedin-3 or exedin-4.
 
         [0038]    Insulin analogues are for example Gly(A21), Arg(B31), Arg(B32) human insulin; Lys(B3), Glu(B29) human insulin; Lys(B28), Pro(B29) human insulin; Asp(B28) human insulin; human insulin, wherein proline in position B28 is replaced by Asp, Lys, Leu, Val or Ala and wherein in position B29 Lys may be replaced by Pro; Ala(B26) human insulin; Des(B28-B30) human insulin; Des(B27) human insulin and Des(B30) human insulin. 
         [0039]    Insulin derivates are for example B29-N-myristoyl-des(B30) human insulin; B29-N-palmitoyl-des(B30) human insulin; B29-N-myristoyl human insulin; B29-N-palmitoyl human insulin; B28-N-myristoyl LysB28ProB29 human insulin; B28-N-palmitoyl-LysB28ProB29 human insulin; B30-N-myristoyl-ThrB29LysB30 human insulin; B30-N-palmitoyl-ThrB29LysB30 human insulin; B29-N—(N-palmitoyl-Y-glutamyl)-des(B30) human insulin; B29-N—(N-lithocholyl-Y-glutamyl)-des(B30) human insulin; B29-N-(ω-carboxyheptadecanoyl)-des(B30) human insulin and B29-N-(ω-carboxyheptadecanoyl) human insulin. 
         [0040]    Exendin-4 for example means Exendin-4(1-39), a peptide of the sequence H-His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2. 
         [0041]    Exendin-4 derivatives are for example selected from the following list of compounds: 
       H-(Lys)4-des Pro36, des Pro37 Exendin-4(1-39)-NH2, 
     H-(Lys)5-des Pro36, des Pro37 Exendin-4(1-39)-NH2, 
     des Pro36 [Asp28] Exendin-4(1-39), 
     des Pro36 [IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14, Asp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39), 
     des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39); or 
     des Pro36 [Asp28] Exendin-4(1-39), 
     des Pro36 [IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14, Asp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14, IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39), 
     des Pro36 [Trp(O2)25, IsoAsp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14 Trp(O2)25, Asp28] Exendin-4(1-39), 
     des Pro36 [Met(O)14 Trp(O2)25, IsoAsp28] Exendin-4(1-39), 
       [0042]    wherein the group -Lys6-NH2 may be bound to the C-terminus of the Exendin-4 derivative;
 
or an Exendin-4 derivative of the sequence
 
       H-(Lys)6-des Pro36 [Asp28] Exendin-4(1-39)-Lys6-NH2, 
     des Asp28 Pro36, Pro37, Pro38Exendin-4(1-39)-NH2, 
     H-(Lys)6-des Pro36, Pro38 [Asp28] Exendin-4(1-39)-NH2, 
     H-Asn-(Glu)5des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-NH2, 
     des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36 [Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2, 
     H-des Asp28 Pro36, Pro37, Pro38 [Trp(O2)25] Exendin-4(1-39)-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-NH2, 
     des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36 [Met(O)14, Asp28] Exendin-4(1-39)-Lys6-NH2, 
     des Met(O)14 Asp28 Pro36, Pro37, Pro38 Exendin-4(1-39)-NH2, 
     H-(Lys)6-desPro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2, 
     des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-Asn-(Glu)5 des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-Lys6-des Pro36 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-Lys6-NH2, 
     H-des Asp28 Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25] Exendin-4(1-39)-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Asp28] Exendin-4(1-39)-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-NH2, 
     des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
     H-(Lys)6-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(S1-39)-(Lys)6-NH2, 
     H-Asn-(Glu)5-des Pro36, Pro37, Pro38 [Met(O)14, Trp(O2)25, Asp28] Exendin-4(1-39)-(Lys)6-NH2, 
       [0043]    or a pharmaceutically acceptable salt or solvate of any one of the afore-mentioned Exedin-4 derivative. 
         [0044]    Hormones are for example hypophysis hormones or hypothalamus hormones or regulatory active peptides and their antagonists as listed in Rote Liste, ed. 2008, Chapter 50, such as Gonadotropine (Follitropin, Lutropin, Choriongonadotropin, Menotropin), Somatropine (Somatropin), Desmopressin, Terlipressin, Gonadorelin, Triptorelin, Leuprorelin, Buserelin, Nafarelin, Goserelin. 
         [0045]    A polysaccharide is for example a glucosaminoglycane, a hyaluronic acid, a heparin, a low molecular weight heparin or an ultra low molecular weight heparin or a derivative thereof, or a sulphated, e.g. a poly-sulphated form of the above-mentioned polysaccharides, and/or a pharmaceutically acceptable salt thereof. An example of a pharmaceutically acceptable salt of a poly-sulphated low molecular weight heparin is enoxaparin sodium. 
         [0046]    Pharmaceutically acceptable salts are for example acid addition salts and basic salts. Acid addition salts are e.g. HCl or HBr salts. Basic salts are e.g. salts having a cation selected from alkali or alkaline, e.g. Na+, or K+, or Ca2+, or an ammonium ion N+(R1)(R2)(R3)(R4), wherein R1 to R4 independently of each other mean: hydrogen, an optionally substituted C1-C6-alkyl group, an optionally substituted C2-C6-alkenyl group, an optionally substituted C6-C10-aryl group, or an optionally substituted C6-C10-heteroaryl group. Further examples of pharmaceutically acceptable salts are described in “Remington&#39;s Pharmaceutical Sciences” 17. ed. Alfonso R. Gennaro (Ed.), Mark Publishing Company, Easton, Pa., U.S.A., 1985 and in Encyclopedia of Pharmaceutical Technology. 
         [0047]    Pharmaceutically acceptable solvates are for example hydrates. 
         [0048]    The drive spring and control spring may be compression springs. However, they may likewise be any kind of stored energy means such as torsion springs, gas springs etc. 
         [0049]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0051]      FIGS. 1A-B  shows two longitudinal sections of an auto-injector in different section planes in a state prior to use, 
           [0052]      FIGS. 2A-B  shows two longitudinal sections of the auto-injector after removal of a cap and a protective needle sheath, 
           [0053]      FIGS. 3A-B  shows two longitudinal sections of the auto-injector with a proximal end pressed against an injection site, 
           [0054]      FIGS. 4A-B  shows two longitudinal sections of the auto-injector with a trigger button depressed, 
           [0055]      FIGS. 5A-B  shows two longitudinal sections of the auto-injector during needle insertion into the injection site, 
           [0056]      FIGS. 6A-B  shows two longitudinal sections of the auto-injector with the needle fully inserted, 
           [0057]      FIGS. 7A-B  shows two longitudinal sections of the auto-injector during injection near the end of dose, 
           [0058]      FIGS. 8A-B  shows two longitudinal sections of the auto-injector at the end of dose, 
           [0059]      FIGS. 9A-B  shows two longitudinal sections of the auto-injector removed from the injection site, 
           [0060]      FIGS. 10A-B  shows two longitudinal sections of the auto-injector with the needle retracted into a needle safe position, 
           [0061]      FIGS. 11A-D  shows schematic views of a detent mechanism for controlling movement of a carrier relative to a chassis of the auto-injector in four different states, 
           [0062]      FIGS. 12A-F  shows schematic views of a needle insertion control mechanism for controlling movement of a first collar in six different states, 
           [0063]      FIGS. 13A-C  shows schematic views of a syringe retraction control mechanism in three different states 
           [0064]      FIGS. 14A-C  shows schematic views of a noise release mechanism for audibly indicating the end of injection in three different states, 
           [0065]      FIGS. 15A-C  shows schematic views of a plunger release mechanism in three different states, 
           [0066]      FIGS. 16A-C  shows schematic views of a button release mechanism in three different states, 
           [0067]      FIG. 17  is an isometric view of an alternative embodiment of the plunger release mechanism, 
           [0068]      FIG. 18  is a longitudinal section of an alternative embodiment of the button release mechanism, 
           [0069]      FIGS. 19A-B  shows longitudinal sections of an alternative embodiment of the detent mechanism, 
           [0070]      FIG. 20  is a longitudinal section of a third embodiment of the detent mechanism, 
           [0071]      FIG. 21  is a longitudinal section of an alternative embodiment of the noise release mechanism, 
           [0072]      FIGS. 22A-B  shows longitudinal sections of an alternative embodiment of the needle insertion control mechanism, also arranged to perform the function of the detent mechanism on needle retraction and needle insertion, 
           [0073]      FIG. 23  is an isometric view of the needle insertion control mechanism of  FIG. 22 , 
           [0074]      FIGS. 24A-B  shows longitudinal sections of a third embodiment of the needle insertion control mechanism, also arranged to perform the functions of the detent mechanism, 
           [0075]      FIG. 25  is an isometric view of the needle insertion control mechanism of  FIG. 24 , 
           [0076]      FIGS. 26A-B  shows longitudinal sections of a third embodiment of the noise release mechanism, and 
           [0077]      FIGS. 27A-B  is another embodiment of the auto-injector having a wrap-over sleeve trigger instead of a trigger button. 
       
    
    
       [0078]    Corresponding parts are marked with the same reference symbols in all figures. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0079]    A ramped engagement in the terminology of this specification is an engagement between two components with at least one of them having a ramp for engaging the other component in such a manner that one of the components is flexed aside when the components are axially pushed against each other provided this component is not prevented from flexing aside. 
         [0080]      FIGS. 1 a  and 1 b    show two longitudinal sections of an auto-injector  1  in different section planes, the different section planes approximately 90° rotated to each other, wherein the auto-injector  1  is in an initial state prior to starting an injection. The auto-injector  1  comprises a chassis  2 . In the following the chassis  2  is generally considered as being fixed in position so motion of other components is described relative to the chassis  2 . A syringe  3 , e.g. a Hypak syringe, with a hollow injection needle  4  is arranged in a proximal part of the auto-injector  1 . When the auto-injector  1  or the syringe  3  is assembled a protective needle sheath  5  is attached to the needle  4 . A stopper  6  is arranged for sealing the syringe  3  distally and for displacing a liquid medicament M through the hollow needle  4 . The syringe  3  is held in a tubular carrier  7  and supported at its proximal end therein. The carrier  7  is slidably arranged in the chassis  2 . 
         [0081]    A drive spring  8  in the shape of a compression spring is arranged in a distal part of the carrier  7 . A plunger  9  serves for forwarding the force of the drive spring  8  to the stopper  6 . 
         [0082]    The drive spring  8  is loaded between a distal carrier end face  10  of the carrier  7  and a thrust face  11  arranged distally on the plunger  9 . 
         [0083]    The carrier  7  is a key element housing the syringe  3 , the drive spring  8  and the plunger  9 , which are the components required to eject the medicament M from the syringe  3 . These components can therefore be referred to as a drive sub-assembly. 
         [0084]    The chassis  2  and the carrier  7  are arranged within a tubular case  12 . A trigger button  13  is arranged at a distal end of the case  12 . In a plunger release mechanism  27  a peg  14  protrudes from a distal end face of the trigger button  13  in the proximal direction P between two resilient arms  15  originating from the distal carrier end face  10  thus preventing them from flexing towards each other in an initial state A illustrated in  FIG. 15A . In  FIG. 15A  only one of the resilient arms  15  is shown to illustrate the principle. Outwardly the resilient arms  15  are caught in respective first recesses  16  in a distal plunger sleeve  17  attached distally to the thrust face  11  and arranged inside the drive spring  8 . The engagement of the resilient arms  15  in the first recesses  16  prevents axial translation of the plunger  9  relative to the carrier  7 . The resilient arms  15  are ramped in a manner to flex them inwards on relative motion between the plunger  9  and the carrier  7  under load of the drive spring  8 , which is prevented by the peg  14  in the initial state A. 
         [0085]    The carrier  7  is locked to the chassis  2  for preventing relative translation by a detent mechanism  18  illustrated in more detail in  FIGS. 11A to 11D . 
         [0086]    The trigger button  13  is initially engaged to the case  12  by a button release mechanism  26  and cannot be depressed. The button release mechanism  26  is illustrated in detail in  FIGS. 16A to 16C . Referring now to  FIG. 16A  the button release mechanism  26  comprises a resilient proximal beam  13 . 1  on the trigger button  13 , the proximal beam  13 . 1  having an outward first ramp  13 . 2  and an inward second ramp  13 . 3 . In an initial state A illustrated in  FIG. 16A  the outward first ramp  13 . 2  is engaged in a ramped first case detent  12 . 1  preventing the trigger button  13  from moving out of the distal end D. The trigger button  13  proximally abuts both the case  12  and the carrier  7  hence being prevented from being depressed in the proximal direction P. 
         [0087]    Referring again to  FIGS. 1A and 1B  a control spring  19  in the shape of another compression spring is arranged around the carrier  7  and acts between a proximal first collar  20  and a distal second collar  21 . The control spring  19  is used to move the carrier  7  and hence the drive sub-assembly in the proximal direction P for needle insertion or in the distal direction D for needle retraction. 
         [0088]    In the state as delivered as shown in  FIGS. 1 a  and 1 b    a cap  22  is attached to the proximal end of the case  12  and the protective needle sheath  5  is still in place over the needle  4  and the needle hub. An inner sleeve  22 . 1  of the cap  22  is arranged inside the chassis  2  and over the protective needle sheath  5 . In the inner sleeve  22 . 1  a barb  23  is attached. The barb  23  is engaged to the protective needle sheath  5  for joint axial translation. 
         [0089]    A sequence of operation of the auto-injector  1  is as follows: 
         [0090]    A user pulls the cap  22  from the proximal end of the case  12 . The barb  23  joins the protective needle sheath  5  to the cap  22 . Hence, the protective needle sheath  5  is also removed on removal of the cap  22 .  FIGS. 2 a  and 2 b    show the auto-injector  1  with the cap  22  and needle sheath  5  removed. The carrier  7  and syringe  3  are prevented from moving in the proximal direction P by the detent mechanism  18  being in a state A as in  FIG. 11A . Referring now to  FIG. 11A , the detent mechanism  18  comprises a resilient beam  2 . 1  on the chassis  2  with an inwardly protruding first beam head  2 . 2 . The first beam head  2 . 2  has a proximal third ramp  2 . 3 . The detent mechanism  18  further comprises a rhomboid ramp member  7 . 1  on the carrier  7  having a proximal fourth ramp  7 . 2  and a distal fifth ramp  7 . 3 . In state A a rounded off distal side of the first beam head  2 . 2  abuts the ramp member  7 . 1  in the distal direction D resisting movement of the carrier  7  in the proximal direction P relative to the chassis  2 . A rib on the case  12  is provided for preventing outward deflection of the resilient beam  2 . 1  thereby also preventing motion of the carrier  7  relative to the chassis  2 . 
         [0091]    Referring again to  FIGS. 2A and 2B  the user grabs the case  12  and places the chassis  2  protruding from the case  12  at the proximal end P against an injection site, e.g. a patient&#39;s skin. As the auto-injector  1  is pressed against the injection site the case  12  translates in the proximal direction P relative to the chassis  2  into an advanced position as illustrated in  FIGS. 3A and 3B . The second collar  21  is locked to the case  12  and is moved with the case  12  relative to the chassis  2  and relative to nearly all other components of the auto-injector  1  thus slightly compressing the control spring  19  against the first collar  20  which is prevented from moving in the proximal direction P by the chassis  2  due to a needle insertion control mechanism  24  being in a state A illustrated in detail in  FIG. 12A . Referring now to  FIG. 12A , a resilient member in the shape of an arrowhead  20 . 1  is proximally arranged on the first collar  20 . The first collar  20  with the arrowhead  20 . 1  is being forced in the proximal direction P under load of the compressed control spring  19 . An outward sixth ramp  20 . 2  on the arrowhead  20 . 1  interacts with a second distal seventh ramp  2 . 4  on the chassis  2  ramping the arrowhead  20 . 1  in an inward direction I which is prevented by the arrowhead  20 . 1  inwardly abutting the carrier  7 . Hence, the first collar  20  cannot translate in the proximal direction P. 
         [0092]    Referring again to  FIGS. 3A and 3B  the second collar  21  is locked to the case due to a syringe retraction control mechanism  25  being in a state A illustrated in detail in  FIG. 13A . Referring now to  FIG. 13A , the syringe retraction control mechanism  25  comprises a resilient proximal beam  21 . 1  on the second collar  21 , the proximal beam  21 . 1  having a second beam head  21 . 2  having an inward boss  21 . 3  and a distal outward eighth ramp  21 . 4 . The distal outward eighth ramp  21 . 4  is engaged in a ramped second case detent  12 . 2  in a manner ramping the second beam head  21 . 1  in the inward direction I with the second collar  21  under load of the control spring  19  in the distal direction D which is prevented by the inward boss  21 . 3  inwardly abutting the carrier  7 . 
         [0093]    Referring again to  FIGS. 3A and 3B , if the user was to move the case  12  away from the injection site, the control spring  19  expands returning the auto-injector  1  to the initial condition after removal of the cap  22  as illustrated in  FIGS. 2A and 2B . 
         [0094]    In the state as in  FIGS. 3A and 3B  the carrier  7  continues to be prevented from moving in the proximal direction P by the detent mechanism  18 , however with the case  12  in its advanced position the detent mechanism  18  is unlocked as the rib on the case  12  has also moved and no longer prevents outward deflection of the resilient beam  2 . 1 . Movement of the case  12  relative to the carrier  7 , which is locked to the chassis  2  by the detent mechanism  18 , causes the button release mechanism  26  to switch to a state B illustrated in  FIG. 16B . The trigger button  13  cannot translate with the case  12  in the proximal direction P as it is abutted against the carrier  7 . The ramp on the first case detent  12 . 1  interacts with the outward first ramp  13 . 2  on the proximal beam  13 . 1  on the trigger button  13  deflecting the proximal beam  13 . 1  in the inward direction I thus engaging the inward second ramp  13 . 3  on the proximal beam  13 . 1  in a ramped carrier detent  7 . 4  arranged in the carrier  7 . As the case  12  is translated further in the proximal direction P it supports the proximal beam  13 . 1  outwardly thus locking the trigger button  13  to the carrier  7 . The trigger button  13  now protrudes from the distal end D of the chassis  12  and is ready to be pressed. 
         [0095]    In the state as in  FIGS. 3A and 3B  the user depresses the trigger button  13  in the proximal direction P. As the trigger button  13  abuts against the carrier  7  the carrier  7  is pushing in the proximal direction P against the chassis  2 , the carrier  7  and the chassis  2  interacting in the detent mechanism  18 . The force exerted by the user pressing the trigger button  13  is resolved through the chassis  2  onto the injection site, not between the trigger button  13  and the case  12 . The detent mechanism  18  provides a resistive force when the user pushes the trigger button  13 . Once the user applies a force which exceeds a pre-determined value the detent mechanism  18  releases, initiating the injection cycle. Referring now to  FIG. 11B  showing the detent mechanism  18  in a state B, the resilient beam  2 . 1  on the chassis  2  begins to bow under load from the rhomboid ramp member  7 . 1  on the carrier  7 , storing elastic energy. Despite the proximal fourth ramp  7 . 2  on the ramp member  7 . 1  friction between the contacting faces of the first beam head  2 . 2  and the proximal fourth ramp  7 . 2  prevents movement of the first beam head  2 . 2  in the outward direction O until the straightening force in the resiliently deformed beam  2 . 1  is sufficiently large to overcome it. At this point the resilient beam  2 . 1  is deflected in the outward direction O moving out of the way of the carrier  7  thus allowing the carrier  7  to translate in the proximal direction P. When the carrier  7  travels sufficiently far in the proximal direction P the rhomboid ramp member  7 . 1  on the carrier  7  passes under the first beam head  2 . 2  thus allowing it to relax and move back in the inward direction I distally behind the rhomboid ramp member  7 . 1  in a state C illustrated in  FIG. 11C  at the same time constraining translation of the carrier  7  in the distal direction D relative to the chassis  2 . 
         [0096]    Once the carrier  7  slides far enough in the proximal direction P relative to the first collar  20  the needle insertion control mechanism  24  is switched to a state B as illustrated in  FIG. 12B . In  FIG. 12B  the carrier  7  has been translated in the proximal direction P in such a manner that the arrowhead  20 . 1  on the first collar  20  is no longer inwardly supported. This may be achieved by a second recess  7 . 5  in the carrier  7 . The arrowhead  20 . 1  is now deflected in the inward direction I into the second recess  7 . 5  under load of the control spring  19  arriving at a state C as illustrated in  FIG. 12C . The first collar  20  is now decoupled from the chassis  2 . Instead, the arrowhead  20 . 1  couples the first collar  20  to the carrier  7  by an inward ninth ramp  20 . 3  engaging a distal tenth ramp  7 . 6  on the carrier  7  at the proximal end of the second recess  7 . 5 . Hence, the control spring  19  continues moving the carrier  7  in the proximal direction P from this point. Whilst the user advances the needle  4  by a proportion of its travel, the control spring  19  takes over insertion before the needle  4  protrudes from the proximal end P. Therefore the user experience is that of pressing a button, rather than manually inserting a needle. 
         [0097]    The detent mechanism  18  relies on the user applying a force rather than a displacement. Once the force applied exceeds the force required to switch the detent the user will push the trigger button  13  fully, ensuring that the first collar  20  will always switch. If the user fails to pass the detent, the trigger button  13  returns to its unused state ready for use as illustrated in  FIGS. 3A and 3B . This feature avoids the auto-injector  1  arriving in an undefined state. 
         [0098]      FIGS. 4A and 4B  show the auto-injector  1  with the trigger button  13  depressed sufficiently for the control spring  19  to couple on to the carrier  7  and continue moving the carrier  7  forwards, but not yet abutting the case  12 . 
         [0099]    The carrier  7  coupled to the first collar  20  is translated in the proximal direction P driven by the control spring  19 . As the syringe  3  is arranged for joint axial translation with the carrier  3  the syringe  3  and needle  4  are also translated resulting in the needle  4  protruding from the proximal end P and being inserted into the injection site. The trigger button  13  returns to its initial position relative to the case  12  and latches back to the case  12  from the carrier  7  as in state A in  FIG. 16  A. The carrier  7  translates further in the proximal direction P preventing inward deflection of the proximal beam  13 . 1  so the outward first ramp  13 . 2  cannot disengage from the first case detent  12 . 1 . 
         [0100]    Immediately prior to the needle  4  reaching full insertion depth as illustrated in  FIGS. 5A and 5B  the peg  14  on the trigger button  13  is completely pulled out from between the resilient arms  15  on the carrier  7 . Hence, the plunger release mechanism  27  arrives in a state B shown in  FIG. 15B  with the resilient arms  15  no longer inwardly supported by the peg  14 . Due to the ramped engagement of the resilient arms  15  in the first recess  16  they are deflected in the inward direction I under load of the drive spring  8  arriving in a state B illustrated in  FIG. 15C . Hence, the plunger  9  is released from the carrier  7  and driven in the proximal direction P by the drive spring  8 , ready to inject the medicament M. The force to pull the peg  14  out from between the resilient arms  15  is provided by the control spring  19  while the force required to deflect the resilient arms  15  out of engagement to the plunger  9  is provided by the drive spring  8 . 
         [0101]    While the plunger  9  moves and closes a gap to the stopper  6  the movement of the carrier  7  in the proximal direction P is completed by the control spring  19  pushing the first collar  20 . As the carrier  7  moves with respect to the chassis  2  during needle insertion the needle insertion mechanism  24  arrives in a state D illustrated in  FIG. 12D . The arrowhead  20 . 1  has moved with the carrier  7  and is still kept inwardly deflected by the chassis  2  thus preventing the first collar  20  from disengaging the carrier  7 . The arrowhead  20 . 1  must be able to deflect in the outward direction O to allow retraction which will be discussed below. In order to allow outward deflection the arrowhead  20 . 1  travels proximally beyond the part of the chassis  2  shown in  FIGS. 12A to 12F  next to an aperture  2 . 5  in the chassis  2 . However, as long as the case  12  is being kept pressed against the injection site and not allowed to return in the distal direction D beyond a predefined distance under load of the control spring  19  the arrowhead  20 . 1  will be kept from deflecting in the outward direction O by a first rib  12 . 3  on the case  12  (not illustrated in  FIG. 12A  to F, see  FIGS. 5A to 8A ) during about the second half of its motion for needle insertion. 
         [0102]    The needle  4  is now fully inserted into the injection site as illustrated in  FIGS. 6A and 6B . The time between the trigger button  13  pressed and the needle  4  being fully inserted is very short, however several mechanical operations take place in this time. The needle insertion depth is defined by the carrier  7  relative to the chassis  2  not relative to the case  12 , so if the user flinches or fails to hold the auto-injector  1  hard against the skin, only the case  12  will move in the distal direction D while the injection depth remains constant. 
         [0103]    As soon as the plunger  9  has closed the gap to the stopper  6  under force of the drive spring  8  the stopper  6  is pushed in the proximal direction P within the syringe  3  displacing the medicament M through the needle  4  into the injection site. 
         [0104]    Immediately prior to the end of injection with the stopper  6  having almost bottomed out in the syringe  3  as illustrated in  FIGS. 7A and 7B  a noise component  28  is released. The stack up of tolerances, most notably due to the syringe  3  requires that the noise must always be released prior to the end of injection. Otherwise, with certain combinations of parts, the noise would not always release. The noise component  28  comprises an elongate portion  28 . 1  arranged within the distal plunger sleeve  17  and a distal end plate  28 . 2  arranged between the carrier end face  10  and an end face of the trigger button  13 . Two second resilient arms  30  originate from the distal carrier end face  10  and extend in the proximal direction P. A noise spring  29  is arranged to bias the noise component  28  in the distal direction D relative to the carrier  7  by proximally bearing against a rib on the second resilient arms  30  and distally against the noise component  28  (not illustrated). 
         [0105]    Note: the noise component  28  is not illustrated in  FIGS. 16A , B and C for clarity since it does not affect the function of the button release mechanism  26 . A noise release mechanism  31  for releasing the noise component  28  is schematically illustrated in  FIGS. 14A, 14B and 14C . Referring now to  FIG. 14A , the noise release mechanism  31  comprises the second resilient arms  30 . A ramped inward boss  30 . 1  is arranged on each second resilient arm  30  which is engaged to a respective outward eleventh ramp  28 . 3  on the elongate portion  28 . 1  of the noise component  28  in such a manner that the second resilient arm  30  is deflected in the outward direction O under load of the noise spring  29 . In an initial state A of the noise release mechanism  31  the second resilient arms  30  are prevented from being outwardly deflected by outward support of the distal plunger sleeve  17  thus preventing translation of the noise component  28  relative to the carrier  7 . The noise release mechanism  31  remains in state A until immediately prior to the end of injection with the stopper  6  having almost bottomed out in the syringe  3  as illustrated in  FIGS. 7A and 7B . At this point the plunger  9  has been translated in the proximal direction P relative to the carrier  7  to such an extent that the second resilient arms  30  are no longer supported by the distal plunger sleeve  17 . The noise release mechanism  31  has thus arrived in a state B illustrated in  FIG. 14B . Due to the ramped engagement between the ramped inward boss  30 . 1  and the outward eleventh ramp  28 . 3  the second resilient arm  30  is outwardly deflected under load of the noise spring  29  thus disengaging the noise component  28  from the carrier  7  and allowing the noise component  28  to move in the distal direction D driven by the noise spring  29  in a state C illustrated in  FIG. 14C . Hence, the noise component  28  is accelerated in the distal direction D and the distal end plate  28 . 2  impacts on the inside of the trigger button  13  producing audible and tactile feedback to the user that the injection is about finished. 
         [0106]      FIGS. 8A and 8B  show the auto-injector  1  with the stopper  6  having entirely bottomed out in the syringe  3 . 
         [0107]    As mentioned above the user is able to let the case  12  move by a few millimetres in the distal direction D under the force of the control spring  19  without affecting the position of the needle  4  as long as that motion is below a predefined distance. If the user wishes to end the injection, at any time, they must allow the case  12  to move in the distal direction D beyond that distance.  FIGS. 9A and 9B  show the auto-injector  1  lifted from the injection site with the case  12  moved all the way in the distal direction D so that the chassis  2  protrudes from the proximal end of the case  12 . As the case  12  is moved the first collar  20  releases the carrier  7  and then the second collar  21  releases from the case  12  and pulls the carrier  7  in the distal direction D. The sequencing of this switching is critical as retraction will fail if both collars  20 ,  21  are attached to the carrier  7  at the same time. This is overcome by separating the switching of the collars  20 ,  21  by a significant displacement of the case  12 . 
         [0108]    The switching of the first collar  20  is illustrated in  FIGS. 12E  and F. In  FIG. 12E  the case  12  has been allowed to move in the distal direction D under load of the control spring  19  during removal of the auto-injector  1  from the injection site. The first rib  12 . 3  (not illustrated, see  FIG. 9A ) is removed from outwardly behind the arrowhead  20 . 1 . The first collar  20  is still being pushed in the proximal direction P by the control spring  19 . Due to the engagement of the inward ninth ramp  20 . 3  on the arrowhead  20 . 1  with the distal tenth ramp  7 . 6  on the carrier  7  the arrowhead  20 . 1  is deflected in the outward direction O into the aperture  2 . 5  of the chassis  2  (illustrated in  FIGS. 12A to 12F ), the needle insertion control mechanism  24  arriving in a state E as illustrated in  FIG. 12E , decoupling the first collar  20  from the carrier  7  and latching it to the chassis  2 . 
         [0109]    As the case  12  is moving further in the distal direction D on removal from the injection site the syringe retraction control mechanism  25  switches from its state A (cf.  FIG. 13A ) into a state B illustrated in  FIG. 13B . The case  12  and the second collar  21  locked to the case  12  move together in the distal direction D while the carrier  7  is held in place by the detent mechanism  18  in its state C as described above (cf.  FIG. 11C ). Due to this motion the inward boss  21 . 3  on the second beam head  21 . 2  of the proximal beam  21 . 1  on the second collar  21  no longer inwardly abuts the carrier  7 . Instead the inward boss  21 . 3  is deflected in the inward direction I into a third recess  7 . 7  in the carrier  7  due to the ramped engagement of the second beam head  21 . 1  to the ramped second case detent  12 . 2  under load of the control spring  19 . The syringe retraction control mechanism  25  thus arrives in a state C as illustrated in  FIG. 13C  with the second collar  21  decoupled from the case  12  and coupled to the carrier  7 . The detent mechanism  18  applies a small retarding force to the movement of the carrier  7  before the syringe retraction control mechanism  25  switches to state C as there is a small sliding force, applied by the second collar  21 , pulling the carrier  7  in the distal direction D on translation of the case  12  in the distal direction D when the needle insertion control mechanism  24  has already been switched into state E. If the carrier  7  moves too far in the distal direction D before the second collar  21  switches, the case  12  runs out of travel before the inward boss  21 . 3  can deflect into the third recess  7 . 7  preventing retraction. 
         [0110]    Starting from the position C of the detent mechanism  18  (cf.  FIG. 11C ) the carrier  7  and hence the rhomboid ramp member  7 . 1  are translated in the distal direction D under load of the control spring  19 . Hence, the distal fifth ramp  7 . 3  of the rhomboid ramp member  7 . 1  engages the proximal third ramp  2 . 3  on the first beam head  2 . 2  of the resilient beam  2 . 1  in a manner deflecting the resilient beam  2 . 1  in the inward direction I. This applies the small retarding force to the movement of the carrier  7  required for ensuring the switching of the second collar  21  to the carrier  7 . The resilient beam  2 . 1  and the rhomboid ramp member  7 . 1  are offset sideways to allow the resilient beam  2 . 1  to pass without contacting the rhomboid ramp member  7 . 1  as soon as the first beam head  2 . 2  is entirely inwardly from the ramp member  7 . 1  in a state D illustrated in  FIG. 11D . 
         [0111]    The control spring  19  is grounded at its proximal end in the case by the first collar  20  being abutted against the chassis  2 . The distal end of the control spring  19  moves the second collar  21  in the distal direction D taking with it the carrier  7  and hence the syringe  3  with the needle  4  overcoming the detent mechanism  18  as illustrated in  FIG. 11D . Note that the needle  4  is retracted out of the skin by the auto-injector  1  as soon as the user allows the case  12  to translate sufficiently far as opposed to auto-injectors with needle shields which require the user to remove the auto-injector from the injection site thereby themselves pulling the needle out of the skin for allowing the needle shield to advance. 
         [0112]    As the movement allowed of the noise component  28  is limited relative to the carrier  7  it is no longer in contact with the trigger button  13  which has moved in the distal direction D with the case  12  on removal from the injection site. When the retraction begins the noise spring  29  does not provide any retarding force. Once the noise component  28  hits the trigger button  13  again on retraction of the carrier  7  the noise spring  29  must be recompressed, reducing the force driving the final part of retraction. In order to ensure a reliable retraction despite this reducing force the control spring  19  must be appropriately dimensioned. 
         [0113]    The retraction ends when the distal collar  21  meets a first back stop  12 . 4  on the case  12  as in  FIGS. 10A and 10B . The arrowhead  20 . 1  on the first collar  20  is inwardly supported by the carrier  7  in a state F illustrated in  FIG. 12F  and thus prevented from deflecting in the inward direction I. The outward sixth ramp  20 . 2  of the arrowhead  20 . 1  is engaged behind the first rib  12 . 3  on the case  12  preventing the case  12  from being pushed in the proximal direction P again. A clearance may be provided between the arrowhead  20 . 1  and the first rib  12 . 3  to allow for tolerances. 
         [0114]    The detent mechanism  18  returns to state A as in  FIG. 11A  locking the carrier  7  in position relative to the chassis  2  as it did initially, however it cannot be unlocked now as the case  12  cannot move relative to the chassis  2 . 
         [0115]    A tab  20 . 4  on the first collar  20  is now visible through an indicator window  32  in the case  12 —indicating the auto-injector  1  has been used. 
         [0116]      FIG. 17  is an isometric view of an alternative embodiment of the plunger release mechanism  27 . The plunger release mechanism  27  prevents movement of the plunger  9  in the proximal direction P relative to the carrier  7  until the carrier  7  is moved in the proximal direction P for needle insertion. As opposed to the plunger release mechanism  27  of  FIG. 15 , where relative movement of the carrier  7  and trigger button  13  are used to trigger the release of the plunger  9 , the alternative embodiment of  FIG. 17  releases the plunger  9  by movement of the carrier  7  relative to the second collar  21 .  FIG. 17  illustrates the plunger release mechanism  27  prior to plunger release. The second collar  21  is shown transparent to improve clarity. The plunger  9  is being pushed in the proximal direction P by the drive spring  8 . In order for the plunger  9  to advance, it must rotate around a twelfth ramp  7 . 8  on the carrier  7 . A ramp member  9 . 1  on the plunger  9  is arranged to engage this twelfth ramp  7 . 8 . Rotation of the ramp member  9 . 1  is blocked by an inward longitudinal rib  21 . 5  on the second collar  21  splined in a longitudinal aperture  7 . 9  in the carrier  7 . The case  12  and the second collar  21  remain in the same position, i.e. coupled to each other for joint axial translation. On depression of the trigger button  13  the carrier  13  and the plunger  9  being part of the drive sub-assembly are moved in the proximal direction P, first by the user pressing the trigger button  13  and then by the control spring  19  taking over via the first collar  20  as described above. Once the carrier  7  moves sufficiently far in the proximal direction P relative to the second collar  21  the ramp member  9 . 1  on the collar  9  comes clear of the longitudinal rib  21 . 5  on the second collar  21  and can rotate past the proximal end of the longitudinal rib  21 . 5  due to its ramped engagement to the twelfth ramp  7 . 8  under load of the drive spring  8 . Hence, the drive spring  8  advances the plunger  9  in the proximal direction P for injecting the medicament M. 
         [0117]      FIG. 18  is a longitudinal section of an alternative embodiment of the button release mechanism  26 . Other than the button release mechanism  26  of  FIG. 16  which gives the appearance of a revealing trigger button  13  on skin contact by switching the ground of the trigger button  13  between the carrier  7  and the case  12 , the button release mechanism  26  of  FIG. 18  starts with the trigger button  13  locked but protruding from the distal end of the case  12 . Once the carrier  7  has moved in the distal direction Don skin contact of the chassis  2 , it is possible to depress the trigger button  13  and activate the auto-injector  1 . This ensures a sequenced operation. 
         [0118]    In the embodiment of  FIG. 18  the trigger button  13  has two proximal beams  13 . 1 , each of them having a ramped outward boss  13 . 4 . In the initial state shown in  FIG. 18  the ramped outward bosses  13 . 4  are engaged in respective fourth recesses  12 . 5  in the case  12 . Disengaging the ramped outward bosses  13 . 4  from the fourth recesses  12 . 5  is prevented by the carrier  7  inwardly supporting the proximal beams  13 . 1  in a manner to keep the proximal beams  13 . 1  from deflecting inwardly. Inward protrusions  13 . 5  on the proximal beams  13 . 1  abut against a second rib  7 . 10  on the carrier  7  in a manner preventing the carrier  7  from moving further in the proximal direction P in the initial state. Once the carrier  7  has moved in the distal direction D on skin contact of the chassis  2  a first window  7 . 11  in the carrier  7  is moved behind the inward protrusion  13 . 5  so as to allow the proximal beams  13 . 1  to be inwardly deflected due to their ramped engagement in the fourth recesses  12 . 5  on depression of the trigger button  13 . The proximal beams  13 . 1  are now outwardly supported by the case  12  and remain engaged to the carrier  7  even on retraction of the needle  4 . The trigger button  13  does therefore not return to its initial position, indicating that the auto-injector  1  has been used. 
         [0119]      FIGS. 19A and 19B  show two longitudinal sections of an alternative embodiment of the detent mechanism  18 . The detent mechanism  18  of  FIGS. 11A to 11D , which may be referred to as a “race track” mechanism because of the first beam head  2 . 2  travelling around the rhomboid ramp member  7 . 1  has multiple functions which control the movement of the carrier  7  relative to the chassis  2 . The alternative detent mechanism  18  of  FIGS. 19A and 19B  uses three clips  7 . 12 ,  7 . 13 ,  2 . 6  to produce the same effect. 
         [0120]    The first clip  7 . 12  is arranged as an outwardly biased resilient beam on the carrier  7  extending from the carrier  7  in the proximal direction P. the first clip  7 . 12  is arranged to prevent the carrier  7  from being moved in the proximal direction P prior to the chassis  2  being depressed or rather the case  12  being translated on skin contact. The first clip  7 . 12  is composed of two sections side by side. A first section  7 . 14  prevents movement of the carrier  7  in the proximal direction P by abutting the chassis  2  in a recess. A second section  7 . 15  is arranged as an outwardly protruding clip head arranged to be ramped inwards by a ramp feature  12 . 6  on the chassis  12  for releasing the first clip  7 . 12  thereby unlocking the carrier  7  from the chassis  2  when the case  12  is being translated in the proximal direction P on skin contact. A longitudinal slot  2 . 7  in the chassis  2  is arranged for allowing the second section  7 . 15  to slide in the proximal direction P once the lock has been released. A slight friction force between the first clip  7 . 12  and the chassis  2  provides the retarding force required to ensure retraction. 
         [0121]    The second clip  7 . 13  is arranged as a resilient beam on the carrier  7  extending in the distal direction D having an outwardly protruding third beam head  7 . 16  with a proximal ramp. The third beam head  7 . 16  serves as a back stop against a third rib  2 . 9  on the chassis  2  for preventing the carrier  7  moving in the distal direction D from its initial position. The carrier  7  and chassis  2  are assembled with the second clip  7 . 13  in this position prior to inserting the syringe  3  into the carrier  7  which is facilitated by the proximal ramp on the third beam head  7 . 16 . The syringe  3  locks the clip in place by preventing inward deflection thus creating a fixed stop. 
         [0122]    The third clip  2 . 6  is a resilient beam on the chassis  2  extending in the distal direction D. A ramped fourth beam head  2 . 8  on the third clip  2 . 6  is arranged to inwardly engage in a fifth recess  7 . 17  in the carrier  7 . Once the first clip  7 . 12  is unlocked, the user can load the third clip  2 . 6  by pressing the carrier  7  in the proximal direction P on depression of the trigger button  13 . The third clip  2 . 6  is loaded in compression, i.e. it will bend outwards and release suddenly due to its ramped engagement to the carrier  7  providing the detent functionality similar to that illustrated in  FIG. 11B . 
         [0123]      FIG. 20  is a longitudinal section of a third embodiment of the detent mechanism  18  which is a variation on the embodiment of  FIGS. 19A and 19B . In this embodiment the detent function of the third clip  2 . 6  has been added into the first clip  7 . 12 . The lock between the case  12  and the carrier  7  is released in the same way, but the detent is provided by deflecting the first clip  7 . 12  inwards a second level which is achieved by the chassis  2  not having a slot  2 . 7  for the second section  7 . 15 . Instead the second section  7 . 15 , once ramped inwards by the ramp feature  12 . 6  on the case  12  has to be further ramped inwards inside the chassis  2  on axial load between the chassis  2  and the carrier  7 , suddenly releasing their engagement. 
         [0124]      FIG. 21  is a longitudinal section of an alternative embodiment of the noise release mechanism  31 . As opposed to the noise release mechanism  31  of  FIG. 14  where the noise spring  29  acts between the carrier  7  and the noise component  28 , in the embodiment illustrated in  FIG. 21  the noise spring  29  acts between the case  12  and the noise component  28 . During needle insertion the noise spring  29  is compressed as the noise component  28  moves with the carrier  7  relative to the case  12 . When the noise component  28  is released by the plunger  9  shortly before the end of dose, the noise component  28  moves in the distal direction D and impacts the trigger button  13 . Other than in  FIG. 14  the noise spring  29  is not being recompressed during needle retraction since it is grounded in the case  12  not in the carrier  7 . 
         [0125]      FIGS. 22A and 22B  show longitudinal sections of an alternative embodiment of the needle insertion control mechanism  24  which is also arranged to perform the detent function of the detent mechanism  18  on needle retraction and needle insertion.  FIG. 23  shows a corresponding isometric view. A fourth clip  20 . 5  on the first collar  20  is arranged as a resilient beam with a beam head having an inward proximal thirteenth ramp  20 . 6  for engaging a fourth rib  7 . 18  on the carrier  7  and outwardly supported by the case  12  so as to keep the first collar  20  engaged to the carrier  7  prior to use, during needle insertion and during injection. When the user lifts the case  12  away from the injection site at the end of injection, a sixth recess  12 . 7  in the case  12  is moved outwardly behind the fourth clip  20 . 5  allowing the fourth clip  20 . 5  to release when the carrier  7  is pulled in the distal direction D by the second collar  21 . Since the fourth clip  20 . 5  has to be ramped outwards a small force is required to release the fourth clip  20 . 5 , providing the retraction detent. 
         [0126]    A fifth clip  2 . 10  on the chassis  2  abuts a block  20 . 7  on the first collar  20  prior to use preventing the first collar  20  and hence the carrier  7  engaged to the first collar  20  from moving in the proximal direction P. In order to release, the fifth clip  2 . 10  must be deflected outwards and over the block  20 . 7 . Outward deflection of the fifth clip  2 . 10  is initially prevented by the case  12 . Once the case  12  has moved on skin contact a second window  12 . 8  in the case  12  appears outwardly from the fifth clip  2 . 10  allowing outward deflection. The fifth clip  2 . 10  is then deflected by a fourteenth ramp  7 . 19  on the carrier  7  when the carrier  7  is pushed in the proximal direction P on button depression as the fourth clip  20 . 5  does allow translation of the carrier  7  in the proximal direction P relative to the first collar  20  but not the other way round. The detent for needle insertion is provided by having to deflect the fifth clip  2 . 10  when it is loaded by the control spring  19 . 
         [0127]      FIGS. 24A and 24B  show longitudinal sections of a third embodiment of the needle insertion control mechanism  24 , also arranged to perform the functions of the detent mechanism  18 .  FIG. 25  is an isometric view of the needle insertion control mechanism  24  of  FIG. 24 . The embodiment is similar to that illustrated in  FIGS. 22A, 22B and 23 . The difference is that the fifth clip  2 . 10  is arranged on the first collar  20  and the block  20 . 7  is arranged on the chassis  2 , i.e. their position has been switched, so there are two clips  2 . 10  and  20 . 5  on the first collar  20 . 
         [0128]    The fourth clip  20 . 5  is identical to that in  FIG. 22B . It keeps the first collar  20  connected to the carrier  7  until the needle retraction is triggered, ensuring full injection depth is reached and maintained until the retraction cycle is initiated by removing the auto-injector  1  from the skin. 
         [0129]    The fifth clip  2 . 10  provides the detent for needle insertion and releases the first collar  20  from the chassis  2 , initiating needle insertion. The fifth clip  2 . 10  prevents the first collar  20  and hence the carrier  7  engaged to the first collar  20  from moving in the proximal direction P prior to use by abutting the block  20 . 7  on the chassis  2 . In order to release, the fifth clip  2 . 10  must be deflected outwards and over the block  20 . 7 . Outward deflection of the fifth clip  2 . 10  is initially prevented by the case  12 . Once the case  12  has moved on skin contact the second window  12 . 8  in the case  12  appears outwardly from the fifth clip  2 . 10  allowing outward deflection. The fifth clip  2 . 10  is then deflected by the fourteenth ramp  7 . 19  on the carrier  7  when the carrier  7  is pushed in the proximal direction P on button depression as the fourth clip  20 . 5  does allow translation of the carrier  7  in the proximal direction P relative to the first collar  20  but not the other way round. The detent for needle insertion is provided by having to deflect the fifth clip  2 . 10  when it is loaded by the control spring  19 . 
         [0130]      FIGS. 26A and 26B  show a longitudinal section of a third embodiment of the noise release mechanism  31 . This embodiment works without the need for a dedicated noise spring. The plunger  9  comprises a proximally ramped rib  9 . 2  arranged to splay two seventh clips  7 . 21  on the carrier  7  immediately prior to the end of dose. When the proximally ramped rib  9 . 2  has travelled past the seventh clips  7 . 21  they snap back and impact the plunger  9  generating a sound. The tubular shape of the carrier  7  helps to transmit the sound.  FIG. 26A  shows the noise release mechanism  31  before release.  FIG. 26B  shows the noise release mechanism  31  after release. Proximal faces of the seventh clips  7 . 21  on the carrier  7  are axially offset to facilitate assembly by lifting the seventh clips  7 . 21  over the distal side of the proximally ramped rib  9 . 2  one by one. 
         [0131]      FIGS. 27A and 27B  show longitudinal sections of another embodiment of the auto-injector  1  in different section planes, the different section planes approximately 90° rotated to each other, wherein the auto-injector  1  is in an initial state prior to starting an injection. The auto-injector  1  is essentially identical to the one described in  FIGS. 1 to 16 . However, other than the auto-injector of  FIGS. 1 to 16  the auto-injector  1  of this embodiment has a wrap-over sleeve trigger instead of a trigger button. 
         [0132]    The wrap-over sleeve trigger  12  is the same component as the case  12  which has a closed distal end face  12 . 10  other than the one in  FIGS. 1 to 16 . An internal trigger button  13  is arranged at the distal end inside the sleeve trigger  12 . Other than in  FIGS. 1 to 16  the trigger button  13  is not visible nor does it protrude from the case  12  in any state. In the initial state a clearance  33  is provided between the distal end face  12 . 10  of the sleeve trigger  12  and the internal trigger button  13  allowing for some travel of the sleeve trigger  12  without interfering with the trigger button  13 . 
         [0133]    As the auto-injector  1  does not differ from the auto-injector of  FIGS. 1 to 16  in other respects it is essentially operated in the same way with the following exceptions: 
         [0134]    As the chassis  2  is placed against the injection site the sleeve trigger  12  translates in the proximal direction P relative to the chassis  2  into the advanced position in a first phase of sleeve travel removing the clearance  33  between the distal end face  12 . 10  of the sleeve trigger  12  and the internal trigger button  13 . As in the embodiment of  FIGS. 1 to 16  this motion unlocks the detent mechanism  18  and the trigger button  13 . As the user continues to depress the sleeve trigger  12  in a second phase of sleeve travel thereby further advancing it in the proximal direction P the distal end face  12 . 10  hits the internal trigger button  13  thereby depressing it until the first collar  20  is released from the chassis  2  and the control spring force is coupled on to the carrier  7 . The carrier  7  then advances until the internal trigger button  13  stops on another rib in the case  12  and the plunger release mechanism  27  is released (note the peg  14  is shorter in this embodiment. 
         [0135]    From a user perspective, the detent mechanism  18  is arranged to provide a resistive force when the user reaches the second phase of sleeve travel. Internally, there is no difference to the embodiment of  FIGS. 1 to 16  at this point. 
         [0136]    Needle insertion is triggered by the user fully advancing the sleeve trigger  12  in the second face of sleeve travel thereby fully depressing the internal trigger button  13  and overcoming the detent mechanism as in the embodiment of  FIGS. 1 to 16 . 
         [0137]    As the control spring  19  takes over on button depression fully advancing the carrier  7  for needle insertion the internal trigger button  13  bottoms out on an internal fifth rib  12 . 11  in the sleeve trigger  12  and the internal trigger button  13  switches back to being locked to the sleeve trigger  12  as in  FIG. 16C . 
         [0138]    The embodiment of  FIGS. 27A and 27B  may also be combined with the alternative features illustrated in  FIGS. 17 to 26 . 
         [0139]    It goes without saying that in all ramped engagements between two components described in the above embodiments there may be just one ramp on one or the other component or there may be ramps on both components without significantly influencing the effect of the ramped engagement. 
       LIST OF REFERENCES 
       [0000]    
       
           1  auto-injector 
           2  chassis 
           2 . 1  resilient beam 
           2 . 2  first beam head 
           2 . 3  proximal third ramp 
           2 . 4  distal seventh ramp 
           2 . 5  aperture 
           2 . 6  third clip 
           2 . 7  slot 
           2 . 8  fourth beam head 
           2 . 9  third rib 
           2 . 10  fifth clip 
           2 . 11  sixth clip 
           3  syringe 
           4  hollow injection needle 
           5  protective needle sheath 
           6  stopper 
           7  carrier 
           7 . 1  ramp member 
           7 . 2  proximal fourth ramp 
           7 . 3  distal fifth ramp 
           7 . 4  carrier detent 
           7 . 5  second recess 
           7 . 6  distal tenth ramp 
           7 . 7  third recess 
           7 . 8  twelfth ramp 
           7 . 9  longitudinal aperture 
           7 . 10  second rib 
           7 . 11  first window 
           7 . 12  first clip 
           7 . 13  second clip 
           7 . 14  first section 
           7 . 15  second section 
           7 . 16  third beam head 
           7 . 17  fifth recess 
           7 . 18  fourth rib 
           7 . 19  fourteenth ramp 
           7 . 20  fifteenth ramp 
           7 . 21  seventh clips 
           8  drive spring 
           9  plunger 
           9 . 1  ramp member 
           9 . 2  proximally ramped rib 
           10  carrier end face 
           11  thrust face 
           12  case 
           12 . 1  first case detent 
           12 . 2  second case detent 
           12 . 3  first rib 
           12 . 4  first back stop 
           12 . 5  fourth recess 
           12 . 6  ramp feature 
           12 . 7  sixth recess 
           12 . 8  second window 
           12 . 9  third window 
           12 . 10  distal end face 
           12 . 11  fifth rib 
           13  trigger button 
           13 . 1  proximal beam 
           13 . 2  outward first ramp 
           13 . 3  inward second ramp 
           13 . 4  ramped outward boss 
           13 . 5  inward protrusion 
           13 . 6  second back stop 
           14  peg 
           15  resilient arm 
           16  first recess 
           17  distal plunger sleeve 
           18  detent mechanism 
           19  control spring 
           20  first collar 
           20 . 1  arrowhead 
           20 . 2  outward sixth ramp 
           20 . 3  inward ninth ramp 
           20 . 4  tab 
           20 . 5  fourth clip 
           20 . 6  inward proximal thirteenth ramp 
           20 . 7  block 
           20 . 8  fifth clip 
           21  second collar 
           21 . 1  proximal beam 
           21 . 2  second beam head 
           21 . 3  inward boss 
           21 . 4  distal outward eighth ramp 
           21 . 5  longitudinal rib 
           22  cap 
           22 . 1  inner sleeve 
           23  barb 
           24  needle insertion control mechanism 
           25  syringe retraction control mechanism 
           26  button release mechanism 
           27  plunger release mechanism 
           28  noise component 
           28 . 1  elongate portion 
           28 . 2  distal end plate 
           28 . 3  outward eleventh ramp 
           29  noise spring 
           30  second resilient arm 
           30 . 1  ramped inward boss 
           31  noise release mechanism 
           32  indicator window 
           33  clearance 
         D distal end, distal direction 
         I inward direction 
         M medicament 
         O outward direction 
         P proximal end, proximal direction