Patent Publication Number: US-2019184104-A1

Title: Housing for an Injection Device

Description:
The present invention relates in one aspect to a housing of an injection device, such like a pen-type injector which is operable for setting and dispensing of a dose of a medicament. In particular, the invention relates to an interconnection of two housing components of an injection device 
     BACKGROUND AND PRIOR ART 
     Injection devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe. 
     Injection devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient&#39;s suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable injection devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous. 
     Typically, such devices comprise a housing including a particular cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. Such devices further comprise a drive mechanism, usually having a displaceable piston rod which is configured to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal direction or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is in fluid communication with an interior of the cartridge and which is configured to be coupled to a distal end section of the housing of the injection device. 
     The medicament to be dispensed by the injection device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable injection devices an empty cartridge is replaceable by a new one. In contrast to that, injection devices of disposable type are to be discarded when the medicament in the cartridge has been dispensed or used-up. 
     Document WO 2008/003560 A1 describes for instance a pre-filled injection device having a container and a dose setting mechanism encapsulated inside a housing. The housing is made from two parts which are locked together by a bayonet coupling. In addition to the bayonet coupling, the two parts are also provided with irreversible locking means locking the two parts permanently together. 
     During a final assembly process of such handheld injection devices a cartridge containing the injectable medicament is positioned and assembled inside a distal housing component forming the cartridge holder. A drive mechanism including at least a piston rod to operably engage with the piston of the cartridge is assembled inside a proximal housing component that forms or constitutes a body. The cartridge holder with the cartridge assembled therein forms a cartridge holder preassembly whereas the body with the drive mechanism assembled therein forms or constitutes a body preassembly. 
     During a final step of assembly the cartridge holder preassembly and the body preassembly are assembled together. For this a proximal end of the cartridge holder is fixed to a distal end of the body. Typically, cartridge holder and body comprise an insert section and a correspondingly-shaped receptacle so that the proximal end of the cartridge holder and the distal end of the body are assembled in a nested or interleaved way. In a mutually overlapping section there are typically provided positively engaging locking means, such like radially outwardly or radially inwardly extending mutually corresponding snap features. For instance, an insert section of the cartridge holder may be provided with at least one or several through holes in a sidewall section that are configured to receive and to engage with at least one radially inwardly protruding latch element provided on an inside facing portion of a sidewall of the receptacle of the body, in which the insert section of the cartridge holder is located. 
     Such a clip connection based on snap features and holes may be disadvantageous for a barrel of the cartridge made from a vitreous material. The cartridge firmly attached or assembled inside the cartridge holder may experience a non-neglectable radially inwardly directed compression as the snap features of the receptacle of the body compress a portion of the cartridge holder radially inwardly before they snap into correspondingly-shaped holes in the insert section of the cartridge holder. In order to establish such clip connections the sidewall of interleaved housing sections of cartridge holder and body are temporally subject to a radial deformation. Even though such radial deformations of the cartridge holder are rather marginal they may cause significant stress to the glass cartridge assembled therein. 
     It is therefore an object of the present invention to improve the mechanical connection between housing components of a handheld injection device, such as an injection pen, that provides a reliable and stable fixing of the housing components without exerting significant stress to the glass cartridge during assembly. A mechanical stress level applied to the cartridge should be at least drastically reduced compared to prior art solutions. It is a further aim to provide a non-detachable or irreversible connection of two housing components of an injection device, which is robust and long-lasting and which is configured to withstand external mechanical forces. 
     SUMMARY 
     In one aspect a housing for an injection device, in particular for a pen-type injection device is provided. The housing comprises a body to accommodate a drive mechanism to operably engage with a piston of a cartridge. The cartridge is typically filled with a liquid injectable medicament. The housing further comprises a cartridge holder to accommodate the cartridge. The cartridge holder typically has a cartridge receiving space that is completely captured or taken by the cartridge when assembled inside the cartridge holder. In a final assembly configuration the cartridge receiving space coincides with the outer circumference and with the outer geometry of the cartridge assembled therein. 
     The cartridge holder and the body are of elongated shape and extend along an axial direction. The cartridge holder and the body may be of substantially tubular or cylindrical shape. The axial direction may thus coincide with the longitudinal axis of the tubular or cylindrically-shaped cartridge holder or with the co-aligned body. The cartridge holder further has an insert section at a proximal end and the body has a receptacle at a distal end to receive the insert section of the cartridge holder. In a final assembly configuration the body and the cartridge holder are aligned substantially parallel with their longitudinal axes and the insert section of the cartridge holder is located and fitted inside the receptacle of the body. Hence, the outer diameter of the insert section matches with the inner diameter of the receptacle. In this way cartridge holder and body are assembled in a nested or interleaved way in which the receptacle and the insert section of body and cartridge holder mutually overlap in a radial direction. 
     The body comprises a first latch element on an inside of a sidewall of the receptacle and the cartridge holder comprises a first through recess in a sidewall of the insert section. The through recess is configured to receive the first latch element when cartridge holder and body arrive in a final assembly configuration. The through recess comprises a narrowed neck receiving portion extending axially into a widened latch receiving portion. A first width of the neck receiving portion is smaller than a second width of the latch receiving portion. As seen in an axial direction and as the neck receiving portion extends axially into the latch receiving portion, the width of the through recess widens, typically in transverse or tangential direction when assuming a substantially cylindrically-shaped body or cartridge holder. 
     The first latch element and the first through recess are configured to form a clip connection or a snap fit connection of cartridge holder and body. The first latch element and the first through recess are configured to provide a positive interlock of cartridge holder and body. Typically but not necessarily the first latch element and the first through recess are configured to establish and to provide a non-releasable engagement of cartridge holder and body. Once assembled cartridge holder and body cannot be detached or released without substantially destroying at least one of the cartridge holder and the body. The positive engagement of the cartridge holder and the body as provided by the at least first latch element and the at least one through recess is of permanent type or of non-releasable type. 
     The neck receiving portion and the latch receiving portion of the first through recess form a kind of an indentation or undercutting as the first latch element is introduced in axial direction into said first through recess. The indentation or the undercutting are located in the sidewall of the cartridge holder and extend in a tangential or circumferential direction. 
     Typically, the first latch element extends inwardly from the inside of the sidewall of the receptacle. The radial or inwardly directed extension of the first latch element substantially matches with the thickness of the sidewall of the insert section of the cartridge holder. Hence, in a final assembly configuration the first through recess of the cartridge holder may be completely occupied by the first latch element. The outer or circumferential geometry of the first latch element matches with an inner geometry of the first through recess. Since the first width of the neck receiving portion is smaller than the second width of the latch receiving portion and since the first through recess is configured to receive the first latch element the sidewall of the insert section of the cartridge holder may be predominantly subject to a temporary and flexible deformation in tangential or lateral direction with regard to the tubular elongation of the cartridge holder. 
     For establishing of a positive interlock of cartridge holder and body inevitable radial deformations or inwardly directed deformations of the cartridge holder can be remarkably reduced compared to solutions as they are known in the prior art. In effect, mechanical load applied to the cartridge during assembly and during a mutual fixing of cartridge holder and body can be further reduced. A danger or likelihood of damaging the cartridge during a final assembly process of the housing or of the injection device can be reduced. At the same time a durable, reliable and non-releasable interconnection of body and cartridge holder can be provided. 
     According to an embodiment the first through recess adjoins the proximal end of the cartridge holder. The through recess is further open towards the proximal end of the cartridge holder. In other words, the first through recess is a kind of a slit extending from a proximal end of the cartridge holder, hence from a proximal end of the cartridge holder&#39;s insert section towards the distal direction. Since the first through recess adjoins the proximal end a sidewall section of the insert section adjoining the first through recess becomes flexible in a tangential direction. This enables generation of a positive interconnection of the first latch element and the first through recess only by way of a flexible deformation of the insert section of the cartridge holder in tangential direction. In this way a degree of radially inwardly directed load acting on a cartridge located inside the cartridge holder can be further reduced or even entirely eliminated. 
     According to another embodiment the neck receiving portion of the first through recess adjoins the proximal end of the insert section. The neck receiving portion is further located axially between the latch receiving portion and the proximal end of the insert section. The neck receiving portion with a rather limited first width may form a rather constricted opening or a kind of a bottleneck through which the first latch element is to be urged in distal direction in order to arrive in the latch receiving portion. Typically, in a transition area between the neck receiving portion and the latch receiving portion the first through recess comprises at least one abutment face facing in distal direction so as to engage with a correspondingly-shaped abutment face of the first latch element facing in proximal direction. Said abutment faces of the first latch element and the first through recess may axially engage as the insert section of the cartridge holder has been fully received inside the receptacle of the body thus forming at least a portion of an axial interlock of cartridge holder and body. 
     In another embodiment the first latch element comprises a narrowed neck portion extending axially into a widened latch portion. The neck portion of the first latch element corresponds and substantially coincides with the neck receiving portion of the first through recess. Also the latch portion of the first latch element corresponds to or coincides with the latch receiving portion of the first through recess. In this way and as a final assembly configuration of cartridge holder and body has been reached the first latch element may entirely occupy the first through recess. 
     In a further embodiment the latch portion comprises a maximal width that is larger than the first width of the neck receiving portion of the first through recess. The first width, the second width as well as the maximal and a minimal width of the first through recess and of the latch portion is measured in tangential, circumferential or lateral direction, i.e. perpendicular to the axial or longitudinal direction of the body or cartridge holder but along the extension of the sidewalls of cartridge holder and body, respectively. 
     Since the maximal width of the latch portion is larger than the first width of the neck receiving portion and since the latch portion and the latch receiving portion as well as the neck receiving portion are located at a common radial distance from a center axis of the cartridge holder or body and since the outer circumference or the outer diameter of the insert section substantially matches with the inner circumference or inner diameter of the receptacle of the body a positive engagement of the first latch element with the first through recess is attainable only by way of a sliding and translational movement of the insert section into the receptacle in proximal direction. 
     Due to the above mentioned geometries of maximal width and first width of latch portion and neck receiving portion at least one of the first latch elements and the sidewall of the cartridge holder will be subject to a temporary elastic deformation during the assembly process. As the first latch element is urged axially into the first through recess the narrowed neck portion of the first through recess will be subject to a widening in tangential direction, hence perpendicular to the axial or longitudinal direction but not in radial direction. It is particularly the cartridge holder in the region of its first through recess that is subject to a tangential elastic deformation during the assembly process of cartridge holder and body. In this way the degree of an elastic deformation in radial direction can be substantially reduced or entirely eliminated, thereby reducing the mechanical load that may be otherwise applied to the vitreous barrel of the cartridge. 
     According to another embodiment the latch portion of the first latch element is wedge-shaped in tangential direction with an increasing width in proximal direction. Hence, a distal end of the first latch element facing towards the cartridge holder has a smaller width than a proximal end of the first latch element. By means of a wedge-shaped geometry the first latch element is operable to continuously and smoothly widen the narrowed neck receiving portion of the first through recess during the process of assembly. Once a final assembly configuration has been reached the wedge-shaped first latch element entirely occupies the correspondingly-shaped latch receiving portion of the first through recess. The narrowed neck portion of the first latch element may entirely occupy the correspondingly-shaped neck receiving portion of the first through recess. In this way and once the latch element completely occupies the first through recess the mutually corresponding geometric structures of the latch element and the first through recess effectively inhibit any rotational motion of the cartridge holder relative to the body. 
     Typically, the first latch element is symmetric with regard to the axial longitudinal direction. It comprises a wedge-shaped geometry towards both lateral or tangential faces. In this way, the effect of tangentially widening the narrowed neck receiving portion of the first through recess can be improved. 
     According to another embodiment the latch portion comprises a minimal width at a distal end and further comprises the maximal width at a proximal end. The minimal width of the latch portion is typically smaller than the first width of the neck receiving portion of the first through recess. In this way at least the distal end of the latch portion is insertable into the neck receiving portion of the first through recess without any deformation of the cartridge holder or body. The distal end of the latch portion is insertable in distal direction into the neck receiving portion which is open towards the proximal direction. During the assembly process and during the further movement of the latch element into the first through recess and into the neck receiving portion the wedge-shaped side faces of the first latch element will get in abutment with oppositely located sidewall sections of the cartridge holder that confine the neck receiving portion. 
     As the latch element is urged further into the first through recess in distal direction the wedge-shaped side faces of the first latch element will start to widen the neck receiving portion of the first through recess in tangential direction due to the continuously increasing width of the wedge-shaped latch element, in particular due to the wedge-shaped geometry of the latch portion thereof. 
     According to a another embodiment the receptacle comprises a first protrusion in addition to the first latch element. The first protrusion is axially elongated and extends inwardly from the sidewall of the receptacle at a first distance from the first latch element. As seen in axial or longitudinal direction the first protrusion and the first latch element may be located at the same axial position. They are separated along a tangential or circumferential direction of the e.g. tubular-shaped sidewall of the receptacle. The first protrusion is configured to prevent disengagement of body and cartridge holder once these components are mutually assembled. 
     In another embodiment the insert section comprises a first slit adjoining the proximal end of the insert section and extends in distal direction from the proximal end of the cartridge holder. The first slit is located at the first distance from the first through recess. It is therefore configured to receive the first protrusion on the inside of the receptacle of the body. The first slit as well as the first protrusion may be rather straight-shaped. A tangential or lateral width of the first slit may exactly match with a tangential or lateral width of at least a portion of the first protrusion. Once the cartridge holder and the body are in a final assembly configuration the first protrusion may at least occupy a portion of the first slit in tangential direction. In this way, the first protrusion and the first slit provide a rotational interlock of cartridge holder and body with regard to a rotation axis coinciding with the longitudinal axial direction of the cartridge holder or the body. 
     Since the tangential distance between the first through recess and the first slit is identical to the tangential distance between the first protrusion and the first latch element the first through recess and the latch element as well as the first slit and the first protrusion simultaneously engage during insertion of the insert section of the cartridge holder into the receptacle of the body. Furthermore, the first slit engaging with the first protrusion provides an axial guiding function during insertion of the insert section into the receptacle of the body. 
     The radial extension of the first protrusion may be substantially identical to the width of thickness of the sidewall of the insert section. Likewise the first through recess the first slit is also configured as a through opening in the sidewall of the insert section. The first slit is also open towards the proximal end so as to receive the first protrusion extending in distal direction along the inside of the sidewall of the receptacle. 
     In a further embodiment a first sidewall section of the insert section, which is confined by the first through recess and the first slit is flexible in a tangential direction from an initial unbiased state towards a biased state when the latch element actually enters into the first through recess. In the biased state the neck receiving portion of the first through recess is in engagement with the wedge-shaped latch portion of the first latch element. Consequently and since the sidewall of the insert section is subject to a tangentially directed deformation the first slit located at the predefined first distance from the first through recess will be subject to a temporary narrowing in tangential direction. 
     In the biased state in which the sidewall of the insert section is subject to an elastic deformation the first through recess tangentially widens at the expense of the first slit. In order to allow a tangential narrowing of the first slit, at least one of the first slit and the first protrusion or both may comprise a wedge-shaped geometry as seen in axial direction. Apart from that it is also conceivable that the first slit and the first protrusion are somewhat straight-shaped or rectangular-shaped. Then, and as will be explained later on, a tangential temporary flexing of the first sidewall section of the insert section may be accompanied by a well-defined but tiny radial deflection. 
     According to another embodiment a transverse size of the first protrusion is substantially equal to a transverse size of the first slit when the first sidewall section is in the unbiased state. The insert section will be in the unbiased or initial configuration prior to an assembly process as well as after a final assembly configuration has been reached. Since the transverse or tangential size or a maximal tangential width of the first protrusion exactly matches with the transverse size or tangential width of the first slit the mutual engagement of the first protrusion and the first slit provides an effective rotational interlock of cartridge holder and body when in the final assembly configuration. 
     It is generally conceivable, that the first protrusion has a minimal transverse size or tangential width at a distal end and comprises a maximal transverse size at or near a proximal end. In this way the widest portion of the first protrusion will just enter the first slit at the end of the assembly process of body and cartridge holder. That section of the first protrusion comprising a maximal tangential width may engage with the first slit substantially simultaneously with the completion of the snap-fit engagement of the first latch element with the first through recess. 
     In another embodiment the first protrusion further comprises a lateral abutment face to abut with a lateral abutment face of the first sidewall section of the insert section. The lateral abutment face of the first sidewall section confines the first slit. Typically, the first protrusion comprises two tangentially oppositely located lateral abutment faces having a lateral distance, i.e. a distance in tangential direction, that substantially matches with the lateral distance between oppositely located lateral abutment faces confining the first slit in tangential or lateral direction. In this way and as a final assembly configuration is reached the first protrusion entirely occupies a lateral or tangential cross-section of the first slit of the insert section. Hence, oppositely located lateral abutment faces of the first protrusion get in direct abutment with lateral abutment faces laterally confining the first slit in the sidewall of the insert section. A tangential size or width of the first protrusion matches with and is substantially identical with a tangential or circumferential size or width of the slit provided in the insert section. 
     The first protrusion entirely occupying at least a portion of the first slit in tangential direction effectively prevents any further tangentially or laterally directed deformation of the first sidewall section of the insert section or even prevents any further tangential or lateral deflection of the insert section as a whole. In this way, the first protrusion engaged with and located inside the first insert section effectively prevents a release of the positive engagement of the first through recess and the latch element located therein. 
     According to another embodiment the first protrusion comprises a ramp section with a beveled surface extending inwardly from the inside of the sidewall of the receptacle as seen in proximal direction. The ramp section with its beveled surface facing in distal direction and having a smoothly and continuously increasing distance from the inside of the sidewall of the receptacle towards the proximal direction provides a small but distinct radially inwardly directed deflection of the first sidewall section of the insert section of the cartridge holder during the assembly process. Due to the biasing and/or tangentially directed deformation of the first sidewall section during insertion of the first latch element into the first through recess the lateral or tangential width of the first slit is inevitably narrowed compared to the initial unbiased state. 
     Since the first slit is only capable to receive the first protrusion when it is in the initial unbiased state the ramp section with its beveled surface provides a well-defined radial deflection at least of a tangential corner section of the first sidewall section. Here, at least that lateral edge of the first sidewall section engaging with the ramp section is subject to a slight but distinct radially inwardly directed deflection so as to radially overlap with the first protrusion during the assembly process. As soon as the final assembly configuration has been reached and when the latch portion of the first latch element engages with the latch receiving portion of the first through recess the first sidewall section and hence the first through recess will return into its initial configuration or into the unbiased state. 
     The first sidewall section will be subject to a tangential relaxation and the first slit will approach its initial unbiased state. The lateral or tangential width of the first slit will widen to such an extent that it is able to receive the first protrusion in its entirety. Then, the lateral abutment face of the first protrusion will laterally or tangentially abut with the lateral abutment face of the first sidewall section of the insert section. Once the first protrusion occupies the first slit a repeated tangential deformation of the first sidewall section so as to narrow the first slit is effectively prevented. Consequently, a disengagement of the latch element and the first through recess is effectively inhibited and prevented. In this way, a long-lasting, durable and non-releasable connection of cartridge holder and body is provided. 
     According to a further embodiment the ramp section is located at or near a proximal end of the receptacle. It may be located and positioned at or near a proximal end of the first protrusion. In this way it will be only a proximal end section of the insert section of the cartridge holder that will become subject to a temporary radially inwardly directed deflection. In this way the total degree of a radially inwardly directed elastic deformation of the cartridge holder can be limited to a proximal end section thereof. Moreover, and since only a lateral edge of the first sidewall section of the insert section engages with the ramp section and its beveled surface it is only a small portion of the first sidewall section that is subject to a radial deflection. Having a radial deflection of the insert section only at a proximal end leaves any further sections of the insert section of the sidewall of the cartridge holder rather unaffected in terms of a radial deformation. 
     The area of the sidewall of the insert section that is subject to a radial deformation can be minimized, which is beneficial for reducing eventual mechanical load acting in radial direction onto the cartridge located inside the cartridge holder. Moreover, it is conceivable, that the proximal end of the insert section of the cartridge holder which is subject to a temporary radially inwardly directed deflection is located proximally offset from a proximal end of the cartridge. In this way a radially inwardly directed mechanical load to the cartridge can be completely avoided during the assembly process of body and cartridge holder. 
     Furthermore and according to another embodiment the lateral abutment face of the first protrusion adjoins the ramp section. The lateral abutment face typically faces in tangential direction. It may extend perpendicular to the beveled surface of the ramp section. The beveled surface typically faces in distal direction as well as radially inwardly. The lateral abutment face typically extends in radial and longitudinal direction. The surface normal of the lateral abutment face typically faces towards the tangential direction so as to engage with the correspondingly-shaped lateral abutment face of the first sidewall section of the insert section confining the first slit. 
     References made to the axial or radial as well as to a tangential direction typically refer to a substantially tubular or cylindrical geometry of the body and of the cartridge holder. However, these expressions equally relate to other elongated geometries of body and cartridge holder. If for instance the body and the cartridge holder, in particular the receptacle of the body and the insert section of the cartridge holder comprise a somewhat oval cross-section, terms like ‘axial’, ‘tangential’ and ‘radial’ are to be understood as if the insert section and the receptacle were of cylindrical shape. Hence the axial direction coincides with the main longitudinal axis of body or cartridge holder. The radial direction points from a center axis outwardly and perpendicular to the elongation of cartridge holder and body and the tangential direction or lateral is perpendicular to the radial direction and the longitudinal direction. 
     Furthermore, the above described positive engagement and interconnection of body and cartridge holder principally works with a single first through recess engaging with a single first latch element, it may be of particular benefit to have a second through recess as well as a second latch element. Typically, the cartridge holder may comprise a first through recess and a second through recess at a oppositely located sidewall section, e.g. at diametrically opposite sidewall sections. 
     Correspondingly, also the body may comprise a first latch element to engage with the first through recess and a second latch element to engage with the second through recess. Likewise, the cartridge holder may also comprise not only a single first slit but a first and a second slit that may be also located opposite to each other on or in the sidewall of the insert section. 
     Correspondingly, also the body may comprise not only a single first protrusion but may comprise a first protrusion and a second protrusion, wherein the first and the second protrusions are located opposite to each other on the inside of the sidewall of the receptacle. By increasing the number of mutually engaging through recesses, latch elements, slits and protrusions the stability and durability of the interconnection of cartridge holder and body can be further improved. 
     Typically, and as seen in tangential direction through recesses and slits are arranged in an alternating way at the sidewall of the insert section. Correspondingly, the latch elements and protrusions located on the inside of the sidewall of the receptacle are arranged alternately as seen in tangential direction. An alternating and eventually symmetrical arrangement of mutually engaging latch elements, through recesses, protrusions and slits further improves the durability and stability of the interconnection of the body and the cartridge holder. 
     According to another aspect there is also provided an injection device for administering an injectable medicament into biological tissue. The injection device, which is typically configured as a handheld injection device such as an injection pen comprises a housing as described above. The injection device further comprises a drive mechanism assembled inside the body of the housing and further comprises a cartridge that is assembled inside the cartridge holder. Typically, the injection device is configured as a pre-filled injection device or as a disposable injection device with the cartridge radially assembled therein. The injection device may be configured for a one-time use or for several consecutive usages. 
     After the content of the cartridge has been used up the entire device may be intended to be discarded in its entirety. Hence, the drive mechanism is not configured for a reset operation nor is the cartridge intended to be replaced by a new one. When configured and designed as a disposable or prefilled injection device the positively engaging first and second latch elements of the body and of the cartridge holder are configured to be of permanent and non-releasable type. 
     Once the first and second latch elements positively engage there is no way of disengaging the same except when destroying one of the housing components&#39; body or cartridge holder. 
     In the present context, the distal direction points in the direction of the dispensing and of the device, where, preferably a needle assembly is provided having a double-tipped injection needle that is to be inserted into biological tissue or into the skin of a patient for delivery of the medicament. 
     The proximal end or proximal direction denotes the end of the device or a component thereof, which is furthest away from the dispensing end. Typically, an actuating member is located at the proximal end of the injection device, which is directly operable by a user to be rotated for setting of a dose and which is operable to be depressed in distal direction for dispensing of a dose. 
     The term “drug” or “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound, 
     wherein in one embodiment the pharmaceutically active compound has a molecular weight up to 1500 Da and/or is a peptide, a protein, a polysaccharide, a vaccine, a DNA, a RNA, an enzyme, an antibody or a fragment thereof, 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 exendin-3 or exendin-4 or an analogue or derivative of exendin-3 or exendin-4.
 
     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. 
     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. 
     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. 
     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 Exendin-4(1-39), 
     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), 
     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
 
     des Pro36 Exendin-4(1-39)-Lys6-NH2 (AVE0010), 
     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; 
     or a pharmaceutically acceptable salt or solvate of any one of the afore-mentioned Exendin-4 derivative. 
     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. 
     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. 
     Antibodies are globular plasma proteins (˜150 kDa) that are also known as immunoglobulins which share a basic structure. As they have sugar chains added to amino acid residues, they are glycoproteins. The basic functional unit of each antibody is an immunoglobulin (Ig) monomer (containing only one Ig unit); secreted antibodies can also be dimeric with two Ig units as with IgA, tetrameric with four Ig units like teleost fish IgM, or pentameric with five Ig units, like mammalian IgM. 
     The Ig monomer is a “Y”-shaped molecule that consists of four polypeptide chains; two identical heavy chains and two identical light chains connected by disulfide bonds between cysteine residues. Each heavy chain is about 440 amino acids long; each light chain is about 220 amino acids long. Heavy and light chains each contain intrachain disulfide bonds which stabilize their folding. Each chain is composed of structural domains called Ig domains. These domains contain about 70-110 amino acids and are classified into different categories (for example, variable or V, and constant or C) according to their size and function. They have a characteristic immunoglobulin fold in which two β sheets create a “sandwich” shape, held together by interactions between conserved cysteines and other charged amino acids. 
     There are five types of mammalian Ig heavy chain denoted by α, δ, ε, γ, and μ. The type of heavy chain present defines the isotype of antibody; these chains are found in IgA, IgD, IgE, IgG, and IgM antibodies, respectively. 
     Distinct heavy chains differ in size and composition; α and γ contain approximately 450 amino acids and δ approximately 500 amino acids, while μ and ε have approximately 550 amino acids. Each heavy chain has two regions, the constant region (C H ) and the variable region (V H ). In one species, the constant region is essentially identical in all antibodies of the same isotype, but differs in antibodies of different isotypes. Heavy chains γ, α and δ have a constant region composed of three tandem Ig domains, and a hinge region for added flexibility; heavy chains μ and ε have a constant region composed of four immunoglobulin domains. The variable region of the heavy chain differs in antibodies produced by different B cells, but is the same for all antibodies produced by a single B cell or B cell clone. The variable region of each heavy chain is approximately 110 amino acids long and is composed of a single Ig domain. 
     In mammals, there are two types of immunoglobulin light chain denoted by λ and κ. A light chain has two successive domains: one constant domain (CL) and one variable domain (VL). The approximate length of a light chain is 211 to 217 amino acids. Each antibody contains two light chains that are always identical; only one type of light chain, κ or λ, is present per antibody in mammals. 
     Although the general structure of all antibodies is very similar, the unique property of a given antibody is determined by the variable (V) regions, as detailed above. More specifically, variable loops, three each the light (VL) and three on the heavy (VH) chain, are responsible for binding to the antigen, i.e. for its antigen specificity. These loops are referred to as the Complementarity Determining Regions (CDRs). Because CDRs from both VH and VL domains contribute to the antigen-binding site, it is the combination of the heavy and the light chains, and not either alone, that determines the final antigen specificity. 
     An “antibody fragment” contains at least one antigen binding fragment as defined above, and exhibits essentially the same function and specificity as the complete antibody of which the fragment is derived from. Limited proteolytic digestion with papain cleaves the Ig prototype into three fragments. Two identical amino terminal fragments, each containing one entire L chain and about half an H chain, are the antigen binding fragments (Fab). The third fragment, similar in size but containing the carboxyl terminal half of both heavy chains with their interchain disulfide bond, is the crystalizable fragment (Fc). The Fc contains carbohydrates, complement-binding, and FcR-binding sites. Limited pepsin digestion yields a single F(ab′)2 fragment containing both Fab pieces and the hinge region, including the H—H interchain disulfide bond. F(ab′)2 is divalent for antigen binding. The disulfide bond of F(ab′)2 may be cleaved in order to obtain Fab′. Moreover, the variable regions of the heavy and light chains can be fused together to form a single chain variable fragment (scFv). 
     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. 
     Pharmaceutically acceptable solvates are for example hydrates. 
     It will be further apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Further, it is to be noted, that any reference numerals used in the appended claims are not to be construed as limiting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, a non-limiting embodiment of the invention is described in detail by making reference to the drawings, in which: 
         FIG. 1  shows a perspective and partially cut view of the distal end of a body of a housing of an injection device, 
         FIG. 2  shows a perspective view of a cartridge holder to be connected to the body according to  FIG. 1 , 
         FIG. 3  is an enlarged perspective view of the insert section of the cartridge holder, 
         FIG. 4  is an enlarged and partially cut view of the cartridge holder and of the body at the beginning of an insertion of the cartridge holder&#39;s insert section into the receptacle of the body, 
         FIG. 5  is a view according to  FIG. 4  but with cartridge holder and body in a final assembly configuration, 
         FIG. 6  is a view according to  FIGS. 4 and 5  with the assembly of body and cartridge holder rotated by 90 degrees with respect to the longitudinal axis, 
         FIG. 7  is an enlarged and partial view of a slit in the sidewall of the insert section of the cartridge holder in an initial unbiased state, 
         FIG. 8  is the same view as  FIG. 7  but with the sidewall section of the cartridge holder in a biased state in which the first slit is narrowed due to a tangentially directed deflection of the sidewall section, 
         FIG. 9  is a partially cut and perspective view during insertion of the insert section of the cartridge holder into the receptacle prior to or at the beginning of a tangential deflection of a sidewall section of the cartridge holder&#39;s insert section, 
         FIG. 10  is the same view as  FIG. 9  but with cartridge holder and body during a tangential deflection and deformation of a sidewall section of the insert section of the cartridge holder prior to reach a final state of assembly, 
         FIG. 11  is a perspective view according to  FIGS. 9 and 10  when the cartridge holder and the body have reached the final assembly configuration, 
         FIG. 12  is an exploded view of an exemplary injection device equipped with a housing in accordance to  FIGS. 1-11  and 
         FIG. 13  is a longitudinal cross-section through the injection device according to  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     The injection device  10  as shown in  FIGS. 12 and 13  is configured as a pen-type injector. It comprises an elongated housing  11  extending in a longitudinal or axial direction. Towards a distal direction  1  the injection device  10  comprises a distal housing component denoted as cartridge holder  20 . In the opposite longitudinal direction the housing  11  comprises a second housing component denoted as body  30 . Both housing components, namely cartridge holder  20  and body  30  are of tubular and elongated shape. The cartridge holder  20  is configured to accommodate a cartridge  50  comprising a tubular-shaped barrel  51  filled with a liquid medicament  53 . At a distal end the cartridge  50  comprises a pierceable seal  54  typically inform of a pierceable septum of an elastomeric material. 
     At the opposite proximal end the cartridge  50  is sealed by a piston  52  slidably arranged inside the barrel  51  of the cartridge  50 . For dispensing of a dose of the liquid medicament  53  the cartridge holder  20  comprises a threaded socket  19  at its distal end to receive a correspondingly threaded needle assembly with a double-tipped injection needle. A proximal tipped end of the injection needle of the needle assembly, which is presently not illustrated, is configured to pierce the distal seal  54  of the cartridge  50  thereby gaining access to the interior of the cartridge  50 . The distal end of the injection needle is then configured to puncture biological tissue to deliver the medicament into biological tissue. For medicament delivery the piston  52  is to be displaced in distal direction  1  under the action of a distally advancing piston rod  110  of a drive mechanism  5  of the injection device  10 . The drive mechanism  5  is accommodated and fixed in the body  30  of the injection device  10 . There is further provided a protective cap  40  covering the distal portion of the cartridge holder  20  when assembled and attached thereto. 
     The cartridge holder  20  and the body  30  are to be interconnected by means of a positive connection as it is explicitly shown in  FIG. 4 . As illustrated in  FIGS. 1 and 2  the cartridge holder  20  comprises a proximal end  23  to interconnect non-releasable with a distal end  33  of the body  30 . The cartridge holder  20  and the body  30  are interconnectable in an interleaved or nested way. In the presently illustrated embodiment the proximal connecting end of the cartridge holder  20  comprises an insert section  21  axially confined in distal direction  1  by a radially outwardly extending annular ridge or flange section  27 . The distal connecting end of the body  30  comprises a receptacle  31  to axially receive the insert section  21  of the cartridge holder  20 . The outer diameter of the insert section  21  exactly matches with the inner diameter of the receptacle  31  so that the insert section  21  can be inserted into the receptacle  31  by means of a sliding motion in proximal direction  2  relative to the body  30 . 
     From the combination of the  FIGS. 2-4  it is immediately apparent, that the insert section  21  of the cartridge holder  20  is located at a proximal end  23  of the cartridge holder  20  and that the receptacle  31  is located at a distal end  33  of the body  30 . Once mutually assembled the insert section  21  of the cartridge holder  20  is fully or entirely located inside the receptacle  31  of the body  30 . 
     The annular flange section  27  radially outwardly protruding from the sidewall  22  of the insert section  21  comprises an abutment face  28  facing in proximal direction  2 . When assembled with the body  30  the abutment face  28  is in axial abutment with a distal end face  38  of the sidewall  32  of the body  30 . Additionally and as it is apparent from  FIG. 4  the proximal end  23  of the cartridge holder  20  may optionally also axially abut with a web  36  extending across the inner diameter of the tubular-shaped body  30 . The web  36  comprises a central through opening  37  that may be threaded. The threaded through opening  37  may be threadedly engaged with the piston rod  110 , in particular with a distal thread  112  of the piston rod  110  of the drive mechanism  5  as illustrated in  FIGS. 12 and 13 . The web  36  may comprise a closed surface and confines the receptacle  31  of the body  30  in proximal direction. 
     As further illustrated in  FIG. 2  the cartridge holder  20  comprises a cartridge receiving space  25  in its interior that is typically completely occupied by the cartridge  50 . Near a distal end or in an intermediate section the sidewall  22  of the cartridge holder  20  further comprises at least one transparent window  26  or a respective through recess in order to provide visual inspection of the cartridge  50  located therein. There is further shown a radially outwardly extending protrusion  29  in close proximity to the flange section  27 . The protrusion  29  which is located distally from the flange section  27  and which is hence visible from outside when the injection device  10  is configured to engage with a correspondingly-shaped protrusion or snap feature on the inside of the sidewall of the protective cap  40 . In this way a snap-fit or positive engagement of cartridge holder  20  and protective cap  40  can be provided. 
     As it is apparent from  FIGS. 1 and 2  as well as from  FIGS. 4 and 5  there is provided at least a first through recess  24  in the sidewall  22  of the insert section  21  of the cartridge holder  20 . The first through recess comprises a neck receiving portion  24   a  having a first width w 1 . The neck receiving portion  24   a  axially extends into a laterally or tangentially widened latch receiving portion  24   b  of the first through recess  24 . The latch receiving portion  24   b  comprises a second width w 2  that is larger than the first width w 1 . 
     As further shown in  FIGS. 2 and 3  the first through recess  24  adjoins the proximal end  23  of the cartridge holder  20 . The first through recess  24  is hence open towards the proximal direction  2 . It is configured to receive a latch element  34  protruding radially inwardly from the inside  35  of the sidewall  32  of the receptacle  31 . 
     The radial extension or radial protrusion of the first latch element  34  substantially matches with the thickness of the sidewall  22  of the insert section  21  of the cartridge holder  20 . So when fully assembled as illustrated in  FIG. 5  the first latch element  34  entirely occupying the first through recess  24  forms a somewhat even and closed inner surface with the inside of the sidewall  22  of the insert section  21 . 
     The latch element  34  comprises a latch portion  34   b  and an adjoining neck portion  34   a . The neck portion  34   a  extends in axial distal direction into the latch portion  34   b . As illustrated in  FIGS. 1, 4 and 5  the latch portion  34   b  is wedge-shaped and comprises an increasing tangential width in proximal direction  2 . Hence, the latch portion  34   b  comprises a minimal width w 4  at a distal end as shown in  FIG. 4 . Near a proximal end and close or in direct vicinity to the neck portion  34   a  the latch portion  34   b  comprises a maximal width w 3  in tangential direction. The maximal width w 3  matches with the second width w 2  of the latch receiving portion  24   b  of the first through recess  24 . 
     As it is exemplary illustrated in  FIG. 4 , the minimal width w 4  at the distal end of the latch element  34   b  is smaller than the first width w 1  of the neck receiving portion  24   a  of the first through recess  24 . So for inserting the first latch element  34  into the first through recess  24  along the axial longitudinal direction, and in particular in distal direction  1  the distal end of the wedge-shaped first latch element  34  will easily enter the narrowed neck receiving portion  24   a  of the first through recess  24 . Upon a further distally directed displacement of the body  30  relative to the cartridge holder  20  the side faces  34   c  and  34   d  of the latch element  34  will engage with correspondingly-shaped side faces  24   c  of the insert section that laterally or tangentially confine the neck receiving portion  24   a.    
     Since the latch portion  34   b  continuously and smoothly widens in tangential direction towards the proximal direction and since the latch portion  34   b  is urged further into the neck receiving portion  24   a  the side faces  34   c ,  34   d  of the latch portion  34   b  will start to abut and to engage with the side faces  24   c ,  24   d  of the insert section  21 . Consequently and as the maximal width w 3  of the latch portion  34   b  is larger than the first width w 1  and since the first latch element  34 , in particular its latch portion  34   b  is substantially inelastic the insertion of the latch portion  34   b  into the first through recess  24  leads to a temporary deformation of the insert section  21  of the cartridge holder  20 . Consequently, the neck receiving portion  24   a  of the first through recess  24  will be subject to a widening in tangential or lateral direction. 
     As a consequence a first sidewall section  122  of the insert section  21  that tangentially confines the first through recess  24  will be subject to a lateral or tangential deformation so as to give way for the widened latch portion  34  of the first latch element. When reaching a final assembly configuration in which the latch element  34  is completely received inside the first through recess  24  abutment faces  34   e  and  34   f  at the proximal end of the latch portion  34   b  will engage with correspondingly-shaped abutment faces  24   e  and  24   f  that are located at the proximal end of the latch receiving portion  24   b  of the first through recess  24 . The abutment faces  34   e  and  34   f  face in proximal direction  2  and extend in tangential direction inwardly from the proximal end of the latch portion  34   b . Via the abutment faces  34   e  and  34   f  the latch portion  34   b  extends into the tangentially narrowed neck portion  34   a.    
     The correspondingly-shaped abutment faces  24   e  and  24   f  of the first through recess  24  face in distal direction  1  so as to axially abut with the abutment faces  34   e  and  34   f . Once a final assembly configuration has been reached as shown in  FIG. 5 , the abutment faces  24   e  and  34   e  as well as the abutment faces  24   f  and  34   f  are in axial abutment so as to prevent a sliding movement of the cartridge holder  20  in distal direction relative to the body  30 . In this way an axial interlock of cartridge holder  20  and body  30  is obtained. The mutual engagement of the first through recess  24  with the first latch element  34  provides an axial interlock that inhibits a separation of cartridge holder  20  and body  30  in axial direction. The engagement of the end face  38  with the abutment  28  of the annular flange section  27  as well as an eventual axial abutment of the proximal end  23  of the cartridge holder  20  with the web  36  extending across the inner cross-section of the body  30  prevent a further insertion of the insert section  20  into the body  30 . This abutment therefore provides a kind of an axial interlock that prevents a further movement of the cartridge holder  20  in proximal direction relative to the body  30 . 
     Since the first through recess  24  is open towards the proximal direction  2  the positive engagement of the first through recess  24  with the first latch element  34  can be obtained without any radial deformation of the insert section  21  of the cartridge holder. In this way the cartridge  50  already assembled inside the cartridge holder  20  prior to the final assembly step of interconnecting body  30  and cartridge holder  20  will not be subject to mechanical load acting in radial direction. In this way mechanical stress eventually applied to the cartridge during the final step of assembly of body  30  and cartridge holder  20  can be effectively reduced. A likelihood of cartridge breakage can be also reduced which enhances production quality and patient safety. 
     From  FIG. 2  as well as from  FIG. 6  it is immediately apparent that the cartridge holder comprises not only the first through recess  24  but also a second through recess  224 . In the present embodiment the second through recess  224  is located diametrically opposite to the first through recess  24 . Correspondingly also the body  30  comprises not only a first latch element  34  but also a second latch element which is not shown explicitly in the Figures but which is identically shaped and configured as the first latch element  34 . The second latch element is also located opposite to the first latch element  34 . By having two pairs of through recesses and latch elements, a twofold positive interconnection of body  30  and cartridge holder  20  can be provided thus improving the stability and durability of the positive interconnection of body  30  and cartridge holder  20 . 
     In addition to the mutual engagement of at least the first through recess  24  with the first latch element  34  the insert section  21  of the cartridge holder  20  further comprises a first slit  124  that adjoins the proximal end  23  and which extends in distal direction  1  from the proximal end  23 . The first slit  124  is located at a first tangential or lateral distance t 1  from the first through recess  24  as illustrated in  FIG. 2 . Correspondingly to the first slit  124  also the receptacle  31  comprises a first protrusion  134  that is axially elongated and which extends inwardly from the inside  35  of the sidewall  32  of the receptacle  31 . The first protrusion  134  is located at the first tangential or lateral distance t 1  from the first latch element  34 . 
     A transverse size S 1  of the first protrusion  134  is substantially equal to a transverse size S 2  of the second through recess  124  when the first sidewall section  122  is in an unbiased state. At least an axial section of the first protrusion, typically a proximal end section of the first protrusion  134  comprises a transverse size S 1 , hence an expansion in tangential direction that is substantially identical to the transverse size S 2  of the first slit  124 . Upon final assembly of body  30  and cartridge holder  20  not only the first latch element  34  engages with the first through recess  24  but also the first protrusion  134  axially enters the first slit  124 . The first slit  124  and the first protrusion  134  may engage simultaneously with the engagement of the first latch element  34  and the first through recess  24 . The engagement of the first protrusion  134  with the first slit  124  provides an additional axial and longitudinal guiding for the insert section  21  sliding into the receptacle  31  in proximal direction  2  relative to the body  30 . 
     Apart from that and when reaching a final assembly configuration as shown in  FIGS. 6 and 11  a lateral abutment face  125  of a first sidewall section  122  of the insert section  21  that confines the first slit  124  is in tight tangential or circumferential engagement with a lateral abutment face  135  of the first protrusion  134 . As shown in  FIG. 11  and when a final assembly configuration has been reached the sidewall section  122  located laterally or tangentially between the first slit  124  and the first through recess  24  is tangentially sandwiched between the first latch element  34  and the first protrusion  134 . Hence, when fully assembled the first sidewall section  122  of the insert section  21  of the cartridge holder  20  entirely occupies a free space  39  laterally or tangentially between the first latch element  34  and the first protrusion  134 . The lateral abutment of abutment faces  125  and  135  actually prevent a deformation of the first sidewall section  122  towards the tangential or lateral direction. 
     This serves to prevent a release or disengagement of the first latch element  34  and the first through recess  24 . Once the positive interconnection of body  30  and housing  20  is attained it cannot be abrogated without destroying at least one of the housing component&#39;s cartridge holder  20  or body  30 . 
     Since the geometric shape, especially the tangential width of the first sidewall section  122  exactly matches with the free space  39  between the first latch element  34  and the first protrusion  134  it would be quite difficult to arrive at the final assembly configuration as shown in  FIG. 11  since the first sidewall section  122  is subject to a tangentially directed elastic deformation during the process of assembly as described above. In  FIGS. 7 and 8  the degree of tangential deformation of the first sidewall section  122  is apparent. In  FIG. 7  the initial unbiased state is illustrated that corresponds to the geometry of the insert section  21  according to  FIG. 4 . In  FIG. 8  a biased state of the first sidewall section  122  is shown that substantially corresponds to the configuration of  FIG. 10 , in which a final assembly configuration has been almost reached. 
     Since the neck receiving portion  24   a  of the first through recess  24  is subject to a tangential widening, the first sidewall section  122  is subject to a respective tangential deformation at the expense of the tangential width of the first slit  124 ′. From a comparison of  FIGS. 7 and 8  it is immediately apparent that the first slit  124 ′ in  FIG. 8  is narrower in tangential or circumferential direction compared to the first slit  124  with the first sidewall section  122  being in the unbiased initial state. 
     Since the tangential width of the first slit  124  exactly matches with the tangential width of the first protrusion  134  the first protrusion  134  will be unable to completely enter the first slit  124  as long as the first sidewall section  122  is subject to an elastic deformation. For enabling and facilitating the process of assembly, i.e. the sliding motion of the insert section  21  into the receptacle  31 , the first protrusion  134  comprises a ramp section  136  as best seen in  FIG. 1 . Typically, the longitudinally extending first protrusion  134  comprises two ramp sections  136  near its proximal end, hence near or adjoining the web  36 . The at least one ramp section  136  comprises a beveled surface  138  facing in distal direction  1 . The beveled surface  138  extends from the inside  35  of the sidewall  32  of the receptacle radially inwardly as seen in proximal direction  2 . 
     Hence, as seen from the distal end towards the proximal end of the first protrusion the ramp section  136  comprises a gradually and continuously increasing extension radially inwardly from the inside  35  of the sidewall  32 . The distal end of the ramp section  136  is integrally formed with the inside  35  of the sidewall  32 . The distal end of the ramp section  136  is flush with the inside  35  of the sidewall  32 . As the insert section  21  of the cartridge holder  20  is pushed into the receptacle  31  as shown in the sequence of  FIGS. 9-11  a proximal and lateral edge  126  of the first sidewall section  122  engages with the ramp section  136  of the first protrusion  134 . In this way the proximal and lateral edge  126  of the first sidewall section  122  is subject to a small but distinct radially inwardly directed deformation and deflection. Prior to reach a final state of assembly the lateral edge  126  of the first sidewall section  122  radially overlaps with at least the ramp section  136  of the first protrusion  134 . This radial overlap persists during the process of assembly and as long as the first sidewall section is subject to a tangential deflection from its initial unbiased state. 
     Due to the radial deformation of the edge  126  the first sidewall section  122  is allowed to flex and to deform in tangential or lateral direction towards the first protrusion  134  and to radially overlap at least in sections with the first protrusion  134 . When the final assembly configuration has been reached as shown in  FIG. 11  the first sidewall section  122  returns into its unbiased state thereby increasing the lateral or tangential size of the first slit  124  to the initial size. Consequently and due to the mutually matching geometries of the first sidewall section  122  and the free space  39  between the first latch element  34  and the first protrusion  134  the first sidewall section, in particular the proximal and lateral edge  126  thereof is free to relax radially outwardly so as to enter and to occupy the free space  39 . 
     As it is shown in  FIGS. 1 and 11  the ramp portion  136  with its beveled surface  138  is located at a proximal end of the receptacle  31 . It is hence operable to deflect only a limited proximal and lateral edge  126  of the insert section  21  of the cartridge holder  20 . Positioning of the ramp section  136  towards a proximal end of the interface of insert section  21  and receptacle  31  is beneficial to reduce any radially inwardly directed mechanical load that may otherwise be present to the cartridge  50 . If the radially inwardly directed deflection of the proximal and lateral edge  126  of the first sidewall section  122  should be of such a magnitude that the inside of the first sidewall section  122  gets in mechanical contact with the barrel  51  of the cartridge  50  the mechanical load will be present to a proximal end of the cartridge, which is stabilized by the piston  54  as well as by an enamel edge of the vitreous body  51  of the cartridge. 
     In the present embodiment there are provided two protrusions,  134  and  334 , that are provided on opposite, e.g. geometrically opposite portions on the inside  35  of the sidewall  32  of the receptacle  31 . Likewise and corresponding to the position and shape of the first protrusion  134  and the second protrusion  334  there are provided a first slit  124  to receive the first protrusion  134  as well as a second slit  324  to receive the second protrusion  334 . 
     In the illustrated embodiment the first and the second protrusions  134  and  334  are located diametrically opposite. Correspondingly, also the first slit  124  and the second slit  324  are located diametrically opposite on the insert section  21 . Logically, there is not only a first sidewall section  122  as described above, but there exists altogether four sidewall sections  122 ,  222 ,  322  and  422  that are simultaneously subject to a tangential deformation as the first and second latch elements  34  engage with correspondingly-shaped first and second through recesses  24 ,  224 . In this context it is further to be mentioned, that the present concept of establishing a snap-fit connection of cartridge holder  20  and body  30  is not limited to only two pairs of through recesses and latch elements or two pairs of slits and protrusions but may be expanded to an arbitrary number of mutually positively engaging structures. 
     In the following the general functionality and features of the drive mechanism  5  is described. The drive mechanism  5  is only exemplary for one of a plurality of differently configured drive mechanisms that are generally implementable in a disposable pen-injector. The drive mechanism as described above is explained in more detail e.g. in WO2004/078239A1, WO 2004/078240A1 or WO 2004/078241A1 the entirety of which being incorporated herein by reference. The interface and interconnection of housing components, such like the cartridge holder  20  and the body  30  as explained above can be generally implemented with a large variety of different drive mechanisms  5  and injection devices. 
     The drive mechanism  5  comprises numerous mechanically interacting components. A flange like web  36  or support of the body  30  comprises a threaded axial through opening  37  threadedly engaged with a distal thread  112  of the piston rod  110 . The distal end of the piston rod  110  comprises a bearing  115  on which a pressure foot  116  is free to rotate with the longitudinal axis of the piston rod  110  as an axis of rotation. The pressure foot  116  is configured to axially abut against the proximally facing thrust receiving surface of the piston  52  of the cartridge  50 . During a dispensing action the piston rod  110  rotates relative to the body  30  thereby experiencing a distally directed advancing motion relative to the body  30  and hence relative to the barrel  51  of the cartridge  50 . As a consequence, the piston  52  of the cartridge  50  is displaced in distal direction by a well-defined distance due to the threaded engagement of the piston rod  110  with the body  30 . 
     The piston rod  110  is further provided with a second thread  114  at its proximal end. The distal thread  112  and the proximal thread  114  are oppositely handed. 
     There is further provided a drive sleeve  100  having a hollow interior to receive the piston rod  110 . The drive sleeve  100  comprises an inner thread threadedly engaged with the proximal thread  114  of the piston rod  110 . Moreover, the drive sleeve  100  comprises an outer threaded section  105  at its distal end. The threaded section is axially confined between a distal flange portion  102  and another flange portion  104  located at a predefined axial distance from the distal flange portion  102 . Between the two flange portions  102 ,  104  there is provided a last dose limiting member  106  in form of a semi-circular nut having an internal thread matching the threaded section  105  of the drive sleeve  100 . 
     The last dose limiting member  106  further comprises a radial recess or protrusion at its outer circumference to engage with a complementary-shaped recess or protrusion at an inside of the sidewall  32  of the body  30 . In this way the last dose limiting member  106  is splined to the body  30 . A rotation of the drive sleeve  100  in a dose incrementing or clockwise direction during consecutive dose setting procedures leads to an accumulative axial displacement of the last dose limiting member  106  relative to the drive sleeve  100 . There is further provided an annular spring  96  that is in axial abutment with a proximally facing surface of the flange portion  104 . Moreover, there is provided a tubular-shaped clutch member  90 . At a first end the clutch member  90  is provided with a series of circumferentially directed saw teeth. Towards a second opposite end of the clutch member  90  there is located a radially inwardly directed flange. 
     Furthermore, there is provided a dose dial or dose indicating sleeve  80 . The dose indicating sleeve  80  is provided outside of the spring  96  and the clutch member  90  and is located radially inward of the body  30 . A helical groove  81  is provided about an outer surface of the dose indicating sleeve  80 . The body  30  is provided with a window  44  through which a part of the outer surface of the dose indicating sleeve  80  can be seen. The body  30  is further provided with a helical rib at an inside sidewall portion of an insert piece  70 , which helical rib is to be seated in the helical groove  81  of the dose indicating sleeve  80 . The tubular shaped insert piece  70  is inserted into the proximal end of the body  30 . It is rotationally and axially fixed to the body  30 . There are provided first and second stops on the body  30  to limit a dose setting procedure during which the dose indicating sleeve  80  is rotated in a helical motion relative to the body  30 . 
     A dose dial grip  66  is disposed about an outer surface of the proximal end of the dose indicating sleeve  80 . An outer diameter of the dose dial  66  typically corresponds to the outer diameter of the body  30 . The dose dial  66  is secured to the dose indicating sleeve  80  to prevent relative movement there between. The dose dial  66  is provided with a central opening. 
     Furthermore, a dose button  60  of generally T-shape is provided at a proximal end of the injection device  10 . A stem  62  of the dose button  60  extends through the opening in the dose dial  66  through an inner diameter of extensions of the drive sleeve  100  and into a receiving recess at the proximal end of the piston rod  110 . The stem  62  is retained for limited axial movement in the drive sleeve  100  and against rotation with respect thereto. A head  64  of the dose button  60  is generally circular. A skirt extends from a periphery of the head  64  and is further adapted to be seated in a proximally accessible annular recess of the dose dial  66 . 
     To dial a dose a user rotates the dose dial  66 . With the spring  96  also acting as a clicker and the clutch member  90  engaged, the drive sleeve  100  the spring or clicker  96 , the clutch member  90  and the dose indicating sleeve  80  rotate with the dose dial  66 . Audible and tactile feedback of the dose being dialed is provided by the spring  96  and by the clutch member  90 . Torque is transmitted through saw teeth between the spring  96  and the clutch member  90 . The helical groove  81  on the dose indicating sleeve  80  and a helical groove in the drive sleeve  100  have the same lead. This allows the dose indicating sleeve  80  to extend from the body  30  and the drive sleeve  100  to climb the piston rod  110  at the same rate. At a limit of travel a radial stop on the dose indicating sleeve  80  engages either with a first stop or a second stop provided on the body  30  to prevent further movement. Rotation of the piston rod  110  is prevented due to the opposing directions of the overall and driven threads on the piston rod  110 . 
     The last dose limiting member  106  keyed to the body  30  is advanced along the threaded section  105  by the rotation of the drive sleeve  100 . When a final dose dispensed position is reached, a radial stop formed on a surface of the last dose limiting member  106  abuts a radial stop on the flange portion  104  of the drive sleeve  100 , preventing both, the last dose limiting member  106  and the drive sleeve  100  from rotating further. 
     Should a user inadvertently dial beyond the desired dosage, the pen-injector  10  allows the dosage to be dialed down without dispense of the medicament from the cartridge  50 . For this the dose dial  66  is simply counter-rotated. This causes the system to act in reverse. A flexible arm of the spring or clicker  96  then acts as a ratchet preventing the spring  96  from rotating. The torque transmitted through the clutch member  90  causes the saw teeth to ride over one another to create the clicks corresponding to dialed dose reduction. Typically, the saw teeth are so disposed that a circumferential extent of each saw tooth corresponds to a unit dose. 
     When the desired dose has been dialed the user may simply dispense the set dose by depressing the dose button  60 . This displaces the clutch member  90  axially with respect to the dose indicating sleeve  80  causing dog teeth thereof to disengage. However, the clutch member  90  remains keyed in rotation to the drive sleeve  100 . The dose indicating sleeve  80  and the dose dial  66  are now free to rotate in accordance with the helical groove  81 . 
     The axial movement deforms the flexible arm of the spring  96  to ensure the saw teeth cannot be overhauled during dispense. This prevents the drive sleeve  100  from rotating with respect to the body  30  though it is still free to move axially with respect thereto. The deformation is subsequently used to urge the spring  96  and the clutch member  90  back along the drive sleeve  100  to restore the connection between the clutch member  90  and the dose indicating sleeve  80  when the distally directed dispensing pressure is removed from the dose button  60 . 
     The longitudinal axial movement of the drive sleeve  100  causes the piston rod  110  to rotate through the through opening  133  of the support  132  of the body  30 , thereby to advance the piston  52  in the cartridge  50 . Once the dialed dose has been dispensed, the dose indicating sleeve  80  is prevented from further rotation by contact of a plurality of members extending from the dose dial  66  with a corresponding plurality of stops. A zero dose position is finally determined by the abutment of one of axially extending edges of members of the dose indicating sleeve  80  with a corresponding stop of the body  30 . 
     REFERENCE NUMBERS 
     
         
           1  distal direction 
           2  proximal direction 
           5  drive mechanism 
           10  injection device 
           11  housing 
           19  threaded socket 
           20  cartridge holder 
           21  insert section 
           22  sidewall 
           23  proximal end 
           24  through recess 
           24   a  neck receiving portion 
           24   b  latch receiving portion 
           24   c  side face 
           24   d  side face 
           24   e  abutment face 
           24   f  abutment face 
           25  cartridge receiving space 
           26  windows 
           27  flange section 
           28  abutment face 
           29  protrusion 
           30  body 
           31  receptacle 
           32  sidewall 
           33  distal end 
           34  latch element 
           34   a  neck portion 
           34   b  latch portion 
           34   c  side face 
           34   d  side face 
           34   e  abutment face 
           34   f  abutment face 
           35  inside 
           36  web 
           37  through opening 
           38  end face 
           39  free space 
           40  cap 
           44  window 
           50  cartridge 
           51  barrel 
           52  piston 
           53  medicament 
           54  seal 
           60  dose button 
           62  stem 
           64  head 
           66  dose dial 
           70  insert piece 
           80  dose indicating sleeve 
           81  helical groove 
           90  clutch member 
           96  spring 
           100  drive sleeve 
           102  distal flange portion 
           104  flange portion 
           105  threaded section 
           106  last dose limiting member 
           110  piston rod 
           112  distal thread 
           114  proximal thread 
           115  bearing 
           116  pressure foot 
           122  sidewall section 
           124  slit 
           125  abutment face 
           126  edge 
           134  protrusion 
           135  abutment face 
           136  ramp section 
           138  beveled surface 
           222  sidewall section 
           224  through recess 
           322  sidewall section 
           324  slit 
           334  protrusion 
           422  sidewall section