Abstract:
Handheld drug injection device ( 10 ) for setting and dispensing of a dose of a medicament, having a housing ( 20 ) extending in an axial direction ( 1, 2 ) and a dose setting and drive mechanism ( 3 ) comprising: —a rotatable dose setting member ( 50 ) in a sidewall of the housing and engaging two dose indicating wheels ( 54,56 ), —a drive member ( 70 ) axially displaceable relative to a drive spindle ( 80 ) and the housing against the action of a spring element ( 78 ) during dose setting and having a sleeve-shaped part ( 72 ) being threadedly engaged with the drive spindle ( 80 ) to form a spindle gear, and having a rack portion ( 71 ) engaged with a gear wheel ( 58 ) of the dose setting member, —the drive spindle ( 80 ) being linked on its proximal end to a ratchet mechanism ( 140,150 ) which is releasable via an axially shiftable trigger button ( 40 ) for dose dispensing, and on its distal end via a pinion ( 86 ) to a —drive sleeve ( 90 ), the latter being axially shiftable to form a clutch for engagement with —a threaded piston rod ( 120 ), which engages a piston ( 14 ) of a cartridge ( 12 ) to displace the piston ( 14 ) in a distal axial direction ( 1 ), the trigger button ( 40 ) releasing the ratchet holding the drive spindle ( 80 ) to free it for rotation, and closing the clutch between drive sleeve ( 90 ) and piston rod ( 120 ), such that the drive spring ( 78 ) can push the drive member ( 70 ) forward, thereby rotating the spindle ( 80 ), which in turn rotates the drive sleeve ( 90 ), which in turn produces spiral forward movement of the piston rod ( 120 ). A dose limiter element ( 130 ) is also included between piston rod and coaxial drive sleeve.

Description:
[0001]    The present invention relates to a drive mechanism for a drug delivery device and to a respective drug delivery device. In particular, the invention relates to an injection device such like a pen-type injector inter alia comprising a single and/or a last-dose limiting mechanism and further comprising a comparatively large dose indicating display. 
       BACKGROUND AND PRIOR ART 
       [0002]    Drug delivery 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. 
         [0003]    Drug delivery 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 drug delivery 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. 
         [0004]    Typically, such devices comprise a housing or a particular cartridge holder, which is adapted to receive a cartridge at least partially filled with the medicament to be dispensed. The device further comprises a drive mechanism, usually having a displaceable piston rod which is adapted 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 or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the drug delivery device. 
         [0005]    The medicament to be dispensed by the drug delivery 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 drug delivery devices an empty cartridge is replaceable by a new one. In contrast to that, drug delivery devices of disposable type are to be entirely discarded when the medicament in the cartridge has been completely dispensed or used-up. 
         [0006]    With such multi-dose drug delivery devices at least a last dose limiting mechanism is required to inhibit setting of a dose exceeding the amount of medicament left in the cartridge. This is to avoid a potentially dangerous situation for the user believing that a set dose is entirely injected. There already exist some drug delivery devices with end-of-content mechanisms or last dose mechanisms. 
         [0007]    Drug delivery devices such like pen type injectors also provide a dose indicating mechanism which is operable to display the size of a set dose to a user. Typically, the housing of such drug delivery devices comprises a dose indicating window in which a number representing the size of the dose shows up. 
         [0008]    Especially with elderly patients or users suffering impaired vision, reading of such dose indicating numbers is sometimes difficult. With devices adapted for injection of e.g. insulin, typical dose sizes may vary between 0 and 120 I.U. (International Units) of insulin. Due to the rather compact design and limited geometrical dimensions of typical drug delivery devices the size of such dose indicating numbers is fairly small. For visually impaired persons correct reading of comparatively tiny numbers may therefore be rather difficult. However, since such drug delivery devices are intended for self-medication treatment, it is of importance, that the user is able to correctly determine the size of dose actually set. 
       OBJECTS OF THE INVENTION 
       [0009]    It is therefore an object of the present invention to avoid disadvantages of known drug delivery devices and to provide a drive mechanism of a drug delivery device allowing for an intuitive operation, both for setting and for dispensing of a dose. It is another object to provide a dose indicating mechanism which is easy and unequivocal to read even for persons suffering impaired vision. 
         [0010]    In another object, the invention serves to provide a drive mechanism of a drug delivery device for setting and dispensing of a dose of a medicament and further featuring a single and/or a last dose limiting mechanism. 
         [0011]    It is a further aim to provide a drug delivery device comprising such a drive mechanism and comprising a cartridge sealed with a piston and being operably engaged with a piston rod of such drive mechanism. The drug delivery device should be rather easy and intuitive to handle. 
       SUMMARY OF THE INVENTION 
       [0012]    In a first aspect a drive mechanism for a drug delivery device is provided for dispensing of a dose of a medicament. The drive mechanism comprises a housing extending in an axial direction. The housing may be of substantially tubular or cylindrical shape that allows gripping and operating of the drive mechanism, hence of the entire drug delivery device by one hand of a user. The housing may also be of rectangular or cubic shape which may smoothly fit into a palm of a user&#39;s hand. 
         [0013]    The drive mechanism further comprises a piston rod to operably engage with a piston of a cartridge containing the medicament to be dispensed by the drive mechanism. The cartridge comprises a piston, which, by means of a displacement in axial distal direction, serves to expel an amount of the medicament from the cartridge corresponding to the axial displacement of the piston. The piston typically seals the cartridge in axial proximal direction. The piston rod serves to displace the piston of the cartridge in an axial distal direction. The piston rod is therefore operable to apply distally directed thrust or pressure to the piston of the cartridge for displacing the same in distal direction for a predetermined distance that corresponds to a respective amount of the medicament to be dispensed. 
         [0014]    Furthermore, the drive mechanism comprises a drive spindle operably engageable with the piston rod during dose dispensing. The drive spindle is rotatably supported in the housing and is preferably axially fixed. It is exclusively operable to be rotated in a dose incrementing direction during setting of a dose and to rotate in an opposite, hence in a dose decrementing direction during dispensing of a dose. Preferably, the drive spindle is selectively engageable with the piston rod only during dose dispensing. 
         [0015]    For dose setting drive spindle and piston rod are operably disengaged from each other. In this way, a required dose of the medicament can be set without any interaction with the piston rod. It is only during dose dispensing that the drive spindle is operably engaged with the piston rod for advancing the same in a distal, hence dose dispensing direction. 
         [0016]    The drive mechanism is further equipped with a drive member axially displaceable relative to the drive spindle against the action of a spring element during dose setting. The drive member is threadedly engaged with the drive spindle to form a kind of a spindle gear. Preferably, the drive member is axially displaceable relative to the drive spindle and relative to the housing. The drive member is further rotatably locked to the housing and is therefore only allowed to slidably displace relative to the housing. 
         [0017]    Since drive member and drive spindle are threadedly engaged, an axial displacement of the drive member relative to the drive spindle sets the drive spindle, which is axially fixed, in rotation. A dose setting axial displacement of the drive member is operable against the action of a spring element, typically in form of a compression spring. However, for dose dispensing or dose injection, the biased or tensioned spring element may serve as a drive element to return the drive member to its initial position. 
         [0018]    Hence, during dose dispensing, the drive member will be axially displaced by the action of the spring thereby inducing a counter-directed rotation to the drive spindle. Since the drive spindle is operably engageable with the piston rod during such a dose dispensing rotation, the piston rod will advance accordingly. 
         [0019]    By means of the mutual engagement of the axially displaceable drive member and the spring element, mechanical energy can be stored in the drive mechanism by inducing an axially-directed sliding motion onto the drive member. Hence, for setting of a dose an axially-directed sliding displacement of the drive member is generally sufficient. 
         [0020]    Additionally and depending on the lead of the threaded engagement of drive member and drive spindle, different transmission ratios between the drive member and the drive spindle can be realised allowing to adapt the drive mechanism to different specific application scenarios. Since it is only the drive member which is biased by the spring element, a variety of different transmission ratios between drive member and drive spindle can be realised by implementing respective leads without the necessity to modify the spring element. 
         [0021]    Preferably, the drive member is displaceable in axial proximal direction against the action of the spring element for setting of a dose. The drive spindle will then rotate in a dose incrementing direction. For dose correction or during dose dispensing, which comes along with a decrementing of a set dose, the drive member is driven in distal direction under the action of the spring element. Consequently and due to the threaded engagement of drive member and drive spindle, the drive spindle then rotates in the opposite, hence in a dose decrementing or dose dispensing direction. 
         [0022]    In a further embodiment, the drive member comprises a hollow sleeve portion threadedly engaged with the drive spindle and further comprises an axially extending toothed rack portion. Typically, the hollow sleeve portion and the toothed rack portion are separated from each other in radial direction by means of an interconnecting bar. In axial direction the hollow sleeve portion and the toothed rack portion may at least partially overlap. 
         [0023]    The hollow sleeve portion comprises an inner thread to engage with an outer thread of the drive spindle. In this way, axially-directed displacement of the drive member relative to the drive spindle induces a dose incrementing or dose decrementing rotation of the drive spindle. The toothed rack portion is typically of elongated shape and extends in axial-direction featuring a number of teeth arranged side-by-side in axial-direction to mate with a pinion of a dose mechanism or of a dose setting member. The design of the drive member with the hollow sleeve portion and the radially-offset toothed rack portion enables a rather flat or slim design of the housing of the drive mechanism since toothed rack portion and hollow sleeve portion may be arranged next to each other as seen in radial direction. 
         [0024]    In a further embodiment the drive mechanism also comprises a dose setting member rotatably mounted to a sidewall of the housing. The dose setting member is preferably operably engageable with the drive member, in particular with its toothed rack portion. Arranging a dose setting member to a sidewall of the housing provides a very intuitive and easy handling of the drive mechanism for setting of a dose as well as for displaying the size of a set dose to a user. Integration of the dose setting member into the sidewall of the housing is also beneficial for a rather flat-shaped, rectangular or cubic design of the housing. Given that the housing comprises a substantially rectangular cross-section perpendicular to the axial direction, the dose setting member may be mounted to or in the larger sidewall portion of the rectangular cross-section. 
         [0025]    In a further embodiment the rack portion of the drive member is engaged with a pinion of a gear wheel. Typically, the gear wheel is further operably engaged with the dose setting member. The gear wheel may be directly engaged with the dose setting member. It may be a component of the dose setting member or it may be operably engaged with the rotatable dose setting member, e.g. by some kind of transmission gear. 
         [0026]    For instance, a rack and pinion gear can be provided for transferring a rotatable displacement of a gear wheel of a dose setting arrangement into an axial sliding displacement of the drive member against the action of the spring element. The gear wheel engaged with the rack portion and/or a respective transmission gear may also support a rather flat design of the drive mechanism and its housing. 
         [0027]    In another embodiment, the drive member is axially slidably disposed in the housing from above. For this purpose, the drive member and the housing may comprise mutually engaging guiding structures supporting a well-defined axial displacement of the drive member relative to the housing. For instance, the drive member may comprise a ridge portion protruding from a lateral side of the toothed rack portion which is slidably received in a correspondingly-shaped guiding structure of the housing. Moreover, also the hollow sleeve portion may comprise a radially outwardly extending protrusion to engage with a correspondingly-shaped groove of the housing. 
         [0028]    Preferably, both, the toothed rack portion as well as the sleeve portion of the drive member comprise a guiding structure which is operable to engage with a correspondingly-shaped axially extending guiding structure of the housing, respectively. In this way, both portions of the drive member hence rack portion and sleeve portion can be separately and securely guided in the housing. By a twofold sliding support of the drive member in the housing, an axial displacement of the drive member relative to the housing effectively free of tilt or cant can be effectively provided. 
         [0029]    In a further embodiment, the drive member is axially displaceable relative to the housing between a distal stop and a proximal stop. Hence, axially-directed displacement of the drive member relative to the housing is delimited in both axial directions. In this way, a dose incrementing as well as a dose decrementing axial displacement of the drive member relative to the housing can be confined between predefined margins. 
         [0030]    Typically, the distal stop corresponds to a zero dose configuration whereas the proximal stop correlates to and defines a maximum dose configuration, which in case of a drive mechanism for an insulin injecting device may correspond to 120 I.U. By means of the proximal stop, a maximum dose to be set can be effectively limited. When the drive member engages and abuts with the proximal stop, a further proximally-directed displacement of the drive member can be effectively impeded. Since the drive member is typically engaged with a gear wheel of the dose setting member, a further dose incrementing rotation of the dose setting member is effectively blocked. 
         [0031]    Moreover, due to the axially delimited displacement of the drive member relative to the drive spindle also a further dose incrementing rotation of the drive spindle is effectively impeded or blocked. 
         [0032]    When reaching the opposite distal stop configuration, which may correspond to a zero dose configuration, either the distal stop itself or an additional clicking member may audibly interact with the drive member in order to generate an audible click sound indicating to a user, that the end of a dose dispensing procedure has been reached and that dose dispensing has just terminated. 
         [0033]    The distal stop and/or the proximal stop typically provided by the housing may preferably engage with the hollow sleeve portion of the drive member. In typical embodiments, proximal stop and distal stop of the housing may be arranged at respective proximal and distal ends of a groove of the housing which is adapted to slidably receive a radially outwardly extending protrusion of the sleeve portion of the drive member. With such an implementation, the radially outwardly extending protrusion of the hollow sleeve portion provides a double function. It serves to axially guide the drive member relative to the housing and to define proximal and distal stop positions of the drive member relative to the housing. 
         [0034]    In a further embodiment, the spring element comprises a compression spring extending around the drive spindle. In this way, a nested or interleaved arrangement of spring element, drive spindle and drive member can be obtained. Preferably, the spring element also at least partially extends around the drive member. In this way, the spring element and the drive member may mutually stabilise to support a smooth axial displacement of the drive member relative to the drive spindle. 
         [0035]    In a further embodiment, the spring element axially extends between the drive member and the drive spindle. Here, the drive spindle may comprise a radially outwardly extending rim or flange portion, which may serve as a proximal stop for the spring element. Preferably also the drive member comprises a correspondingly-shaped radially outwardly extending rim to receive an opposite end of the spring element. 
         [0036]    The spring element may be positively engaged with the drive member and/or with the drive spindle. However, a mutual axial abutment of the opposite axial end sections of the spring element to respective radially outwardly extending rim portions or flange portions of drive spindle and drive member may be sufficient to keep the spring element in place. Moreover, it is intended that the spring element is tensioned to a minimum degree when the drive member is in its distal stop position. 
         [0037]    Additionally and according to a further embodiment, the drive spindle comprises a toothed rim rotatably engaged with a ratchet member. The toothed rim is preferably provided at a proximal end of the drive spindle. The toothed rim may equally serve as a radially outwardly extending flange portion adapted to axially support a proximal end of the spring element. Preferably, the toothed rim of the drive spindle is rotatably engaged with a ratchet member. In this way rotation in dose incrementing and/or dose decrementing direction of the drive spindle can be rotatably locked or rotatably secured by the ratchet member. 
         [0038]    Therefore, a proximally-directed displacement of the drive member against the action of the spring can be locked in place since the drive spindle threadedly engaged with the sleeve portion of the drive member is effectively hindered by the ratchet member to rotate freely. 
         [0039]    The ratchet member serves to provide a clutch mechanism operable to lock a rotational movement of the drive spindle. In this way, mechanical energy can be stored in the spring element when compressed by the proximally-directed displacement of the drive member relative to the drive spindle or relative to the housing. 
         [0040]    Preferably, the ratchet member is configurable to selectively interlock or to release the toothed rim of the drive spindle. In an interlocking configuration, the drive spindle is rotatably locked by the ratchet member. However, in a release configuration, the toothed rim and hence the drive spindle is free to rotate relative to the latch element and relative to the housing. Then, mechanical energy stored in the tension spring element can be released because the drive spindle is free to rotate, thereby allowing the drive member to be displaced in distal direction under the action of the previously-tensioned spring element. 
         [0041]    In another embodiment, the ratchet member comprises at least one arc-shaped latch element which is variably stressable in radial direction to selectively engage or disengaged with the toothed rim of the drive spindle. Releasing and interlocking of the drive spindle and the ratchet member may be exclusively obtained by a modification of the latch element of the ratchet member. 
         [0042]    Preferably, the latch element is either pivotally supported in radial direction or it is resiliently deformable in radial direction to engage with the toothed rim of the drive spindle with variable and adjustable strength. Hence, by modifying a degree of engagement of the latch element with the toothed rim of the drive spindle, rotation of the drive spindle can either be interlocked or released, respectively. 
         [0043]    Moreover, by means of a variably stressable latch element of the ratchet member also intermediate configurations are conceivable, in which the toothed rim and the drive spindle are generally allowed to rotate while still being in mechanical engagement with the latch element. In such configurations, the latch element only partially and/or gradually obstructs the rotational movement of the drive spindle, thereby retarding the angular velocity of the drive spindle, e.g. during a dose dispensing procedure. Consequently, an angular velocity of the drive spindle can be regulated or modified by means of the ratchet member. 
         [0044]    It is generally conceivable, that the ratchet member comprises several latch elements homogeneously distributed around the outer circumference of the ratchet member. Typically, the ratchet member comprises a cup-shaped receptacle to receive the toothed rim of the drive spindle therein. The arc-shaped latch element then forms a portion of the sidewall of the cup-shaped ratchet member or it is integrated into the sidewall of the ratchet member. 
         [0045]    In another embodiment the dose setting member is rotatably engaged with a first dose indicating wheel and with a second dose indicating wheel to display at least first and second digits of a number in a dose indicating window of the housing. First and second dose indicating wheels may be coaxially arranged in the housing of the drive mechanism. First and second dose indicating wheels may be of disc-like shape and may feature a series of dose indicating numbers at an outer side face thereof. Hence, the axis of rotation of the first and second dose indicating wheel will be radially offset from the dose indicating window of the housing. 
         [0046]    The first dose indicating wheel may be adapted to display numbers 0-9, whereas the second dose indicating wheel may display numbers from 0-12, thereby representing together the numbers 0, 1, 2, 3, 4, up to 119 and 120. First and second dose setting members are typically geared, e.g. by mutually engaging sprockets and pinions. First and second dose indicating wheels may either be directly geared or there may be provided at least one additional gear wheel that serves to provide a required transmission ratio between first and second dose indicating wheels. 
         [0047]    Transmission of a rotational movement to the second gear wheel is typically provided by a gear wheel having a reduced number of cogs that are separated from each other in such a way, that the second gear wheel is rotated one step further every time the first gear wheel has rotated by an angular distance that corresponds to an interval of 10 digits. 
         [0048]    According to another embodiment, the drive mechanism further comprises a pinion fixed to a distal end of the drive spindle. Said pinion is further geared with a drive sleeve rotatably supported in the housing. In this way, a dose incrementing as well as a dose decrementing rotation of the drive spindle can be directly transferred to a drive sleeve. The drive sleeve comprises a hollow shape and is adapted to receive the piston rod therein. Since the pinion is geared with the drive sleeve, the drive spindle and the drive sleeve can be arranged radially offset, thereby allowing for a rather flat but laterally elongated design of the drive mechanism and its surrounding housing. 
         [0049]    Preferably, the drive sleeve is arranged at a radial offset from the drive spindle facing away from the radially outwardly extending toothed rack portion of the drive member. Axial dimensions of the pinion and the gear wheel or geared rim of the drive wheel is such that the drive sleeve is axially displaceable relative to the pinion and hence relative to the drive spindle to a certain extent. By means of an axial displacement of the drive sleeve, a clutch mechanism can be implemented, by way of which the drive mechanism can be switched between a dose setting configuration and a dose dispensing configuration. 
         [0050]    In a further embodiment, the drive sleeve is axially displaceable between a distal stop position and a proximal stop position. In its distal stop position, the drive sleeve is rotatably engaged with the piston rod in order to drive the same in distal direction. However, in the proximal stop position, the drive sleeve is disengaged from the piston rod. In this way, the drive sleeve may rotate with the drive spindle during a dose setting procedure without any impact on the piston rod. It is only due to the distally-directed displacement of the drive sleeve, that a respective clutch mechanism is activated. 
         [0051]    The clutch mechanism provides a double function. In a first aspect, the clutch mechanism serves to operably engage the drive sleeve with the piston rod. In a second aspect, the clutch mechanism serves to release the drive spindle from the ratchet member. Since drive sleeve and drive spindle are permanently geared, in both, the dose dispensing configuration as well as in the dose setting configuration, a release of the drive spindle may lead to a dose decrementing rotation of the drive spindle, which is transferred to a respective rotation of the drive sleeve by means of the pinion located at the distal end of the drive spindle. 
         [0052]    The twofold function of the clutch mechanism is preferably operable sequentially. During switching of the drive mechanism from the dose setting mode into the dose dispensing mode, a mutual engagement of drive sleeve and piston rod is to be established before a rotation of the drive spindle relative to the housing or relative to the drive member is allowed. In this way, mechanical energy stored in the spring element biased by the axially displaceable drive member can be saved and is therefore effectively hindered to dissipate in a rather uncontrolled way. 
         [0053]    In a further embodiment, the drive mechanism also comprises an axially displaceable dose dispensing button located at a proximal end of the housing. Distally-directed displacement of the dose dispensing button, which is typically conductible by a thumb of a user, may activate the clutch mechanism in order to rotatably engage drive sleeve and piston rod and in order to release the ratchet mechanism of the drive spindle. 
         [0054]    The dose dispensing button is typically depressible in distal direction against the action of another spring element, e.g. an injection spring. A respective spring element may for instance be disposed axially between an inside facing portion of a proximal end face of the dose dispensing button and a proximal end face of the ratchet member. 
         [0055]    Here, it may be of particular benefit, when the dose dispensing button separately engages with the ratchet member and with the drive sleeve for switching the drive mechanism from a dose setting mode into a dose dispensing mode. 
         [0056]    The dose dispensing button may particularly extend across the entire cross-section of the rectangular-shaped housing. The dose dispensing button may comprise a hollow cupped shape to receive the compression spring, by way of which the dose dispensing button can be axially biased with respect to the ratchet member. 
         [0057]    Additionally, the dose dispensing button may comprise a distally extending strut or a respective extension, to directly engage with a proximally-facing flange portion of the drive sleeve. By means of the distally extending strut, the drive sleeve can be displaced in distal direction by a distally-directed depression of the dose dispensing button, e.g. against the action of the injection spring. The drive sleeve may be additionally engaged with another spring element which serves to return the drive sleeve into its proximal stop position as soon as a distally-directed thrust exerted by the dose dispensing button is no longer present. 
         [0058]    Generally, by means of the spring element operably engaged with the drive member, a semi-automated drug delivery device can be provided. During a dose setting procedure the spring element can be strained or tensioned to such a degree, that a dose dispensing action of the drug delivery device can be exclusively driven by the relaxing action of the biased spring element. Hence, dose dispensing is completely governed by the action of a spring element previously tensioned and strained in a dose setting procedure. 
         [0059]    According to another aspect, the invention also relates to a drug delivery device for dispensing of a dose of a medicament. The drug delivery device comprises a drive mechanism as described above and a cartridge at least partially filled with the medicament to be dispensed by the drug delivery device. The cartridge is arranged in the housing of the drive mechanism or in a cartridge holder of the drug delivery device which is fixed to the housing either releasably or non-releasably. Consequently, the drug delivery device comprises a cartridge holder to receive and to accommodate a cartridge filled with the medicament. 
         [0060]    In case of a disposable drug delivery device the cartridge is not to be replaced when empty but the entire device is intended to be discarded. With a reusable device, the drive mechanism can be reset and an empty cartridge can be generally replaced by a new one. 
         [0061]    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. 
         [0062]    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 drug delivery 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. 
         [0063]    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 proteine, 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, 
         [0000]    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.
 
         [0064]    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. 
         [0065]    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. 
         [0066]    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. 
         [0067]    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), 
       [0068]    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(02)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, 
       [0069]    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(02)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; 
       [0070]    or a pharmaceutically acceptable salt or solvate of any one of the afore-mentioned Exendin-4 derivative. 
         [0071]    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. 
         [0072]    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. 
         [0073]    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. 
         [0074]    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. 
         [0075]    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. 
         [0076]    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. 
         [0077]    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. 
         [0078]    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. 
         [0079]    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). 
         [0080]    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. 
         [0081]    Pharmaceutically acceptable solvates are for example hydrates. 
         [0082]    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 signs used in the appended claims are not to be construed as limiting the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0083]    In the following, various embodiments of the invention will be described by making reference to the drawings, in which: 
           [0084]      FIG. 1  schematically illustrates a front view of the drug delivery device, 
           [0085]      FIG. 2  shows a side view of the drug delivery device, 
           [0086]      FIG. 3  shows another side view as seen from the opposite side compared to  FIG. 2 , 
           [0087]      FIG. 4  shows a transverse cross-section through the drug delivery device according to A-A according to  FIG. 2 , 
           [0088]      FIG. 5  is an exploded view of the components of the drive mechanism, 
           [0089]      FIG. 6  shows a perspective isolated view of a dose indicating arrangement as seen from the front, 
           [0090]      FIG. 7  shows the dose indicating arrangement according to  FIG. 6  from the back side, 
           [0091]      FIG. 8  shows an enlarged view of the dose indicating and dose setting arrangement according to  FIG. 7 , 
           [0092]      FIG. 9  shows a transverse cross-section B-B according to  FIG. 2 , 
           [0093]      FIG. 10  is an isolated view of the interleaved first and second dose indicating wheels as seen from the front, 
           [0094]      FIG. 11  shows the wheels according to  FIG. 10  from the back side, 
           [0095]      FIG. 12  shows a perspective and partially cut view of the dose indicating wheels assembled in the housing, 
           [0096]      FIG. 13  shows a partially cut and perspective view of the drive spindle arranged in the housing, 
           [0097]      FIG. 14  is a partially cut- and enlarged view of the drive sleeve, 
           [0098]      FIG. 15  is a perspective view of the mutual engagement of drive sleeve, drive spindle and drive member, 
           [0099]      FIG. 16  shows a perspective view of a drive wheel engaged with the piston rod, 
           [0100]      FIG. 17  shows an isolated side view of the drive mechanism without the housing, 
           [0101]      FIG. 18  schematically shows the mutual interaction of the drive spindle with the drive sleeve, 
           [0102]      FIG. 19  shows a configuration of the drive mechanism with the drive member in its proximal stop position, 
           [0103]      FIG. 20  schematically illustrates the assembly of the drive mechanism inside a lower housing portion, 
           [0104]      FIG. 21  shows a cross-section along B-B together with the dose dispensing button, 
           [0105]      FIG. 22  shows an enlarged perspective view of the mutual engagement of the dose setting button with a regulating member, 
           [0106]      FIG. 23  shows a cross-section B-B according to  FIG. 2  with the regulating member in a release configuration, 
           [0107]      FIG. 24  shows a perspective view according to  FIG. 22  with the dose dispensing button fully depressed, 
           [0108]      FIG. 25  shows a partially cut view of the assembled drug delivery device, 
           [0109]      FIG. 26  shows a longitudinal cross-section of the drive member before reaching a zero dose configuration and 
           [0110]      FIG. 27  is indicative of the drive member reaching the zero dose configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0111]    As illustrated in  FIGS. 1 and 2  the drug delivery device  10  comprises a rather rectangular or cubic-shaped housing  20  comprising an upper housing portion  21  and a lower housing portion  22 . In the present embodiment, the upper housing portion  21  may serve as a mounting base to assemble the components of the drive mechanism  3  thereon. The lower housing portion  22  may then serve as a cover, which preferably stabilises and keeps the various components of the drive mechanism  3  at their positions. However, the roles of upper and lower housing portions may also be interchanged in alternative embodiments. 
         [0112]    The rectangular shape of the housing  20  is particularly adapted to take and to clasp the device  10  by one hand of a user. The drug delivery device  10  therefore comprises an elongated shape extending in axial direction. In the present context, the axial distal direction is denoted with reference number  1  and the opposite proximal direction is denoted with reference number  2 . The housing  20 , in particular both of its halves  21 ,  22 , comprises a cartridge window  23 . 
         [0113]    The cartridge window  23  may comprise a recess in the upper and/or lower housing portion  21 ,  22  and may be at least partially transparent to allow visual inspection of a filling level of a cartridge  12  assembled inside the housing. The distal end of the housing  20  is further provided and protected by a removable cap  24 . The cap  24  may positively engage with a distal end of upper and lower housing portions  21 ,  22  in order to protect a threaded socket  25  formed by upper and lower housing portions  21 ,  22 . 
         [0114]    The threaded socket  25  is adapted to receive a needle assembly  15 , in particular a cup-shaped needle hub  16  providing a double-tipped injection needle. In the various Figures, in particular in  FIGS. 1 ,  2  and in  FIGS. 6 and 7 , the needle assembly  15  is illustrated with a needle cap  17 , which is to be removed from the needle assembly  15  prior to conducting a dose dispensing procedure. The cartridge  12  to be fixed in the housing  20  comprises a tubular-shaped barrel filled with a medicament to be dispensed by the drug delivery device  10 . 
         [0115]    The barrel is sealed in proximal direction  2  by means of a piston  14 , which is slidably disposed in axial direction  1 ,  2  inside the barrel of the cartridge  12 . The piston  14  of the cartridge  12  is operably engageable with a piston rod  120 . The piston rod  120  of the drive mechanism  3  is operable to apply distally-directed thrust or pressure to the piston  14  in order to drive the same in distal direction  1 . In this way, a fluid pressure may build up inside the cartridge  12 . 
         [0116]    When the distal dispensing end of the cartridge  12  is connected with the needle assembly  15  in such a way, that a proximally extending tipped portion of the needle penetrates a distally-located seal of the cartridge, e.g. a septum, a predefined amount of the medicament can be expelled from the cartridge  12  via the needle assembly  15  and into biological tissue. 
         [0117]    As indicated in  FIG. 1 , the housing  20  comprises a compartment  29  adapted to receive the protective cap  24 . For this purpose, the distal end face of the housing  20  comprises a slit  29   a  as indicated in  FIG. 5  allowing to slidably receive the protective cap therein. Here, the slit  29   a  may serve as a hinge to pivot and to slidably receive the cap  24  when the device is in use. In this way, the cap  24  is non-removably attached to the housing  20  and cannot get lost. 
         [0118]    In the following, setting of a dose is described. 
         [0119]    For setting of a dose, the user typically takes or clasps the housing  20  in one hand and starts to rotate, in particular to dial a dose setting member  50  located in the upper housing portion  21 . The dose setting member  50  as illustrated in detail in  FIG. 10  comprises a circular-shaped button comprising an outer rim and a central gripping bar  52  extending across the disc-shaped dose setting member  50 . The gripping bar  52  divides the dose setting member  50  into two recesses allowing for an intuitive and easy gripping thereof. 
         [0120]    As indicated by the arrows in  FIG. 10 , the dose setting member  50  can be rotated either clockwise  5 , e.g. in a dose incrementing way or counter-clockwise, e.g. in a dose decrementing way for incrementing or decrementing a dose to be dispensed by the drug delivery device  10 . The dose setting member  50  is directly coupled to a dose indicating arrangement as illustrated in  FIGS. 10 and 11 . The dose setting member  50  as illustrated in cross-section of  FIG. 12  is rotatably coupled with a dose indicating wheel  54 . 
         [0121]    As indicated in  FIG. 12 , the dose indicating wheel  54  comprises an axially extending shaft received in a correspondingly-shaped receptacle of the dose setting member  50 . Even though not illustrated, the shaft and the receptacle are splined. Shaft and receptacle of the dose indicating wheel  54  and the dose setting member  50  comprise at least one protrusion engaged with a correspondingly-shaped groove. 
         [0122]    As further illustrated in  FIG. 12 , the receptacle  51  of the dose setting member  54 , in particular its sidewall is positively engaged with an inwardly extending fixing rim of the housing  20 , thereby fixing the dose setting member  50  in axial direction relative to the housing  20  but allowing the dose setting member  50  to rotate in either direction relative to the housing  20 . 
         [0123]    The dose indicating wheel  54  serves as a first dose indicating wheel and comprises a series of dose indicating numbers at its outer circumference as illustrated in  FIG. 10 . Here, the dose setting member  50  and the first dose indicating wheel  54  are coaxially aligned. The dose indicating wheel  54  may feature an outer rim substantially enclosing the outer circumference of the dose setting member  50 . 
         [0124]    Due to the splined and direct engagement of the dose setting member  50  and the first dose indicating wheel  54 , a rotation of the dose setting member  50  in either direction directly transfers to a respective rotation of the first dose indicating wheel  54 . As a consequence, a respective number printed on a side of the dose indicating wheel  54  shows up in a dose indicating window  26  of the housing  20  as illustrated in  FIG. 25 . 
         [0125]    The first dose indicating wheel  54  comprises a sprocket  55  to engage with an outer geared rim  59  of a gear wheel  58 . The gear wheel  58  as illustrated in  FIG. 11  comprises a further sprocket or pinion  60  axially offset from the geared rim  59  of the gear wheel  58 . As will be explained later on, the sprocket  60  is engaged with a toothed rack portion  71  of a drive member  70 . 
         [0126]    On the side opposite to the sprocket  60  the gear wheel  58  comprises a rim structure  61  featuring isolated and separated cogs  62 . Said cogs  62  are operable to engage with a geared rim  57  or sprocket of a second dose indicating wheel  56 . As illustrated in  FIGS. 10 and 11 , the second dose indicating wheel  56  provides a second series of ten digit representing numbers of 10, 20, 30 and so on. By means of the isolated and circumferentially separated cogs  62 , a stepwise incrementing rotation of the second dose indicating wheel  56  can be attained when the first dose indicating wheel  54  rotates. 
         [0127]    In effect, by means of the two dose indicating wheels  54 ,  56  all numbers of for instance between 0 and 120 can be illustrated in the dose indicating window  26  of the housing  20 . Implementation of the two interleaved dose indicating wheels  54 ,  56  allows for a rather large scale display so that even persons suffering impaired vision are enabled to read the illustrated numbers. 
         [0128]    The first and the second dose indicating wheels  54 ,  56  further comprise a crown wheel  53 ,  57   a  engaging with clicking members  31 ,  30  provided on the inside of the oppositely disposed housing portion  21 . As illustrated in  FIG. 12 , an inwardly extending pin-shaped clicking member  31  engages with a crown wheel  53  located on a side face of the first dose indicating wheel  54 . Correspondingly also the second dose indicating wheel  56  comprises a crown wheel  57   a  to mate with a correspondingly-shaped clicking member  30  of the housing  20 . 
         [0129]    Mutual engagement of the first and second dose indicating wheels  54 ,  56  with respective clicking members  31 ,  30  provides an audible click sound when the dose setting member  50  is rotated either in dose incrementing direction or in dose decrementing direction. In this way, an audible feedback can be provided to the user when dialling the dose setting member  50  in either direction. 
         [0130]    As illustrated for instance in  FIGS. 7 ,  8 ,  19  and  20  the centrally-located sprocket  60  of the gear wheel  58  meshes with a toothed and elongated rack portion  71  of a drive member  70 . The drive member  70  is axially displaceable relative to a drive spindle  80  extending therethrough. The drive member  70  comprises a sleeve portion  72  to receive the drive spindle  80 , which is axially fixed in the housing  20  by means of a bearing  33  as for instance illustrated in  FIGS. 13 and 20 . 
         [0131]    As illustrated in detail in  FIG. 15 , the toothed rack portion  71  is connected with the sleeve portion  72  via an interconnecting bar  73 . The toothed rack portion  71  therefore radially outwardly extends from the sleeve portion  72  of the drive member  70 . The drive member  70  is axially displaceable relative to the drive spindle  80  and relative to the housing  20  against the action of a spring element  78 . 
         [0132]    As illustrated in  FIG. 15 , the spring element  78  helically winds around the drive spindle  80 . The spring element  78  is preferably designed as a compression spring and can be tensioned by an upward, hence proximally-directed displacement of the drive member  70  relative to the drive spindle  80 . As further illustrated in  FIG. 15 , the sleeve portion  72  of the drive member  70  comprises a radially outwardly extending rim  76  at its distal end, which serves as a distal stop for the spring element  78 . 
         [0133]    Furthermore, the rim  76  comprises a radially outwardly extending protrusion  77  by way of which the drive member  70  can be axially guided relative to the housing  20 . Moreover, the protrusion  77  may act as an axial stopper for the drive member  70 . As shown in  FIG. 13 , the housing  20  comprises a proximal stop  27  and a distal stop  28  that are operable to engage with the radially outwardly extending protrusion  77  of the drive member  70 . In this way, axial displacement of the drive member  70  relative to the housing  20  can be delimited in distal direction  1  as well as in proximal direction  2 . 
         [0134]    The drive member  70  is further threadedly engaged with the drive spindle  80 . As illustrated in  FIG. 13 , the flange portion or rim  76  of the drive member  70  comprises an inner thread  79  engaging with an outer thread  81  of the drive spindle  80 . Due to this threaded engagement and due to the axial fixing of the drive spindle  80  to the housing  20 , a displacement of the drive member  70  in proximal direction  2  against the action of the spring element  78  comes along with a dose incrementing rotation  5  of the drive spindle  80 . 
         [0135]    Proximally-directed displacement of the drive member  70  relative to the housing  20  can be induced by a dose incrementing rotation of the dose setting member  50  and accordingly by a respective rotation of the gear wheel  58  and its sprocket  60 . The axial length of the toothed rack portion  71  typically corresponds to the maximum distance the drive member  70  is allowed to be displaced in distal direction  1  according to the distance of the two stops  27  and  28 . 
         [0136]    Additionally, as illustrated in  FIGS. 4 and 15 , there is provided a protruding ridge portion  75  on the side face of the toothed rack portion  71 . Said ridge portion  75  can be guided in a guiding structure  38  of the housing  20  forming an elongated groove supporting the drive member  70  and guiding the drive member  70  in axial direction. 
         [0137]    The toothed rack portion  71  comprises consecutive teeth  74  at its lateral side portion to engage with the sprocket  60  of the gear wheel  58 . 
         [0138]    Drive member  70  and drive spindle  80  form a kind of a spindle gear. Proximally-directed displacement of the drive member  70  comes along with a tensioning of the spring element  78  thereby rotating the drive spindle  80  in a dose incrementing direction  5 . The drive spindle  80  comprises a toothed rim  82  at its proximal end. As illustrated in cross-section of  FIG. 9 , said toothed rim  82  engages with a radially outwardly extending latch element  153  of a ratchet member  150 . The cup-shaped ratchet member  150  receives the toothed rim  82  of the drive spindle  80  and inhibits a counter-directed, hence, a dose decrementing rotation  6  of the drive spindle  80 . 
         [0139]    For this purpose, the latch element  153  comprises an arc-shape and at least partially extends along the outer circumference of the toothed rim  82  of the drive spindle  80 . The latch element  153  serves as a clutch element and the ratchet member  150  serves as a clutch member to selectively inhibit a rotation of the drive spindle  80 . Typically, during dose setting, the latch or clutch element  153  meshes with a radially inwardly extending lug  154  with the teeth  83  of the toothed rim  82 . 
         [0140]    The latch element  153  is either pivotal in radial direction (r) and/or is resiliently deformable in radial direction to engage with the teeth  83  of the toothed rim  82  of the drive spindle  80 . Depending on the slope and geometry of mutually engaging teeth  83  and the lug  154 , a dose incrementing rotation  5  as well as a dose decrementing rotation  6  of the drive spindle  80  requires application of a respective actuation force above a predefined level or threshold. 
         [0141]    The mutual engagement of the latch element  153  with the toothed rim  82  is in any case sufficient to counterbalance the relaxing force of a biased spring element  78 . In this way, the ratchet member  150  is operable to keep the drive spindle  80  fixed, independent of the axial position of the drive member  70  and the degree of tension of the spring element  78 . 
         [0142]    The spring element  78  may abut with its proximal end at the radially outwardly extending toothed rim  82  of the drive spindle  80 . In this way, the spring element  78  is axially constrained between the drive spindle  80  and the drive member  70 . 
         [0143]    The distal end of the drive spindle  80  is provided with a pinion  86  featuring a bearing portion  89  in form of a circumferential groove or recess. As illustrated in  FIGS. 13 and 20 , the pinion  86  is supported by a bearing  33  of the housing  20 , thereby axially and radially fixing the drive spindle  80  in the housing  20 . The pinion  86  comprises various cogs or teeth  88  engaging with a geared rim  93  of a drive sleeve  90 . The drive sleeve  90  as illustrated in detail in  FIGS. 14 and 15  comprises a tubular-shaped sleeve portion and a radially extending flange portion  92  at its distal end. 
         [0144]    The flange portion  92  is provided with a geared rim  93  that meshes with the pinion  86  of the drive spindle  80 . Here, drive spindle  80  and drive sleeve  90  are permanently geared. Therefore, a dose incrementing as well as a dose decrementing rotation of the drive spindle  80  always leads to a corresponding rotation of the drive sleeve  90 . 
         [0145]    Furthermore, the drive sleeve  90  at least partially encloses the piston rod  120 . The drive sleeve  90  is operably releasable from the piston rod  120  during dose setting but is operably engageable with the piston rod  120  for dispensing of a dose, as will be explained later on. 
         [0146]    Radially sandwiched between the drive sleeve  90  and the piston rod  120  there is provided a dose limiting member  130 . The dose limiting member  130  as illustrated in  FIG. 14  comprises a sleeve portion  132  featuring an outer thread  133  engaged with an inner thread  95  of the drive sleeve  90 . Moreover, the dose limiting member  130  comprises a proximally extending bracket portion  137  featuring two axially extending and parallely-oriented branches  138 ,  139  that are mutually interconnected with their proximal ends to form a closed frame structure. 
         [0147]    As illustrated for instance in  FIG. 15 , a proximal end of the bracket portion  137  extends in proximal direction from a proximal end of the drive sleeve  90 . By means of the bracket portion  137 , the dose limiting member  130  can be rotatably fixed to the housing  20 . 
         [0148]    For instance, a correspondingly extending pin that may e.g. radially extend from the housing  20  may protrude through the closed frame structure of the bracket portion  137  in radial direction, thereby effectively inhibiting that the dose limiting member  130  rotates as the drive sleeve  90  is set in rotation by means of the drive spindle  80 . Due to the threaded engagement of the dose limiting member  130  and the drive sleeve  90  the dose limiting member  130  experiences a proximally-directed displacement relative to the drive sleeve  90  when the drive sleeve  90  is rotated in a dose incrementing direction  5 . 
         [0149]    Since a direct mechanical interaction or contact between the drive sleeve  90  and the piston rod  120  is not required, the dose limiting member  130  can be arranged inside the drive sleeve  90  in a rather contactless configuration relative to the piston rod  120 , which also extends therethrough. Internal friction of the drive mechanism  3  can therefore be reduced. 
         [0150]    Moreover and as illustrated in  FIG. 14 , the piston rod  120  comprises a stop member  124  which is adapted to engage with the dose limiting member  130  when a maximum number of doses has been dispensed by the drive mechanism  3 . In the present embodiment, the stop member  124  of the piston rod  120  comprises a radially outwardly extending flange portion to engage with the proximally-located rim  136  of the sleeve portion  132  of the dose limiting member  130 . Preferably, the faces of the stop member  124  and the sleeve portion  132  that face towards each other and which get in direct mutual contact when a last dose configuration is reached comprise a geared structure. 
         [0151]    Hence, a distally-facing portion of the stop member  124  may comprise a geared flange, e.g. in form of a crown wheel  128 . Correspondingly, also the proximal face of the sleeve portion  132  may comprise a geared rim or a crown wheel portion  136  to mate with the crown wheel  128  of the piston rod  120 . Such a configuration may be beneficial with such embodiments, where the piston rod  120  rotates when it is driven in distal direction  1  during dose dispensing. 
         [0152]    Mutually engaging crown wheels  128 ,  136  of the piston rod  120  and the dose limiting member  130  may then immediately inhibit any further rotation of the piston rod  120  relative to the rotatably fixed dose limiting member  130 . Said mutual engagement is of particular benefit, when the complete content of the cartridge  12  has been expelled. Then, dose limiting member  130  and piston rod  120  are securely interlocked and effectively impede any further incrementing dose setting. 
         [0153]    The dose limiting member  130  effectively serves as a last dose limiter. In an initial configuration of the drive mechanism  3  as for instance illustrated in  FIG. 15 , the dose limiting member  130  will travel in proximal direction  2  during a dose incrementing rotation of drive spindle  80  and drive sleeve  90 . Since the dose setting of a single dose is limited by the axially confined displacement of the drive member  70 , the dose limiting member  130  will at maximum reach a proximal end position, in which the sleeve portion  132  still remains in the drive sleeve  90 . 
         [0154]    In such a configuration the dose limiting member  130  will be separated from the stop member  124  of the piston rod  120 . During a consecutive dose dispensing action, the piston rod  120  will advance in distal direction  1  relative to the drive sleeve  90 . Since a distally-directed dispensing displacement of the piston rod  120  comes along with a dose decrementing rotation of the drive sleeve  90 , also the dose limiting member  130  will return into its initial zero dose configuration as for instance illustrated in  FIG. 14 . 
         [0155]    There may be provided a stop member inside the drive sleeve  90  to provide a well-defined distal stop for the dose limiting member  130 . However, such a zero dose stop is not necessarily required for the dose limiting member  130  since the dose decrementing rotation  6  of the drive sleeve  90  is already delimited by the drive member  70  engaging with a distal stop  28  of the housing  20 . 
         [0156]    With a consecutive dose setting procedure, the dose limiting member  130  will repeatedly displace in axial direction  2 . Since the piston rod  120  has moved in distal direction  1  during the previous dose dispensing procedure, the stop member  124  of the piston rod  120  continuously approaches to the axial range in which the dose limiting member  130  is displaceable. If the position of the piston rod  120  corresponds to a dose size smaller than the maximum size of a single dose, e.g. smaller than 120 I.U., the stop member  124  of the piston rod  120  may enter the drive sleeve  90  as for instance illustrated in  FIG. 14 . 
         [0157]    In a proceeding dose setting procedure, the dose incrementing rotation of the drive sleeve  90  is immediately stopped, when the proximally-advancing dose limiting member  130  axially engages with the stop member  124  of the piston rod  120 . In this way, it can be assured, that the sum of consecutive doses set and dispensed does not exceed the total amount of doses of the medicament contained in the cartridge  12 . 
         [0158]    The stop member  124  may comprise a lateral recess in order to receive and to pass by the bracket portion  137  of the dose limiting member  130 . Additionally or alternatively, it is also conceivable, that the dose limiting member  130  is splined to the piston rod  120  itself. As for instance illustrated in  FIG. 4 , the dose limiting member  130  may comprise a radially inwardly extending protrusion  135  to engage with an axially extending groove  122  of the piston rod  120 . In this way, the dose limiting member  130  can be rotatably locked to the piston rod  120 . In such an alternative embodiment, the piston rod  120  should be rotatably fixed to the housing. Here, the piston rod  120  could be splined to the housing  20 . 
         [0159]    In the following dispensing of a dose will be described. 
         [0160]    For dispensing of a dose the drive sleeve  90  rotates in a dose decrementing direction  6  in such a way, that the torque of the drive sleeve  90  is transferred to a distally-directed displacement of the piston rod  120 . As illustrated in  FIG. 14 , the drive sleeve  90  is coaxially aligned with a drive nut or drive wheel  100 . The drive wheel  100  comprises a radially outwardly extending geared rim  102 . The teeth of said rim  102  comprise a saw tooth profile and engage with a ratchet member  32  of the housing  20  as illustrated in  FIG. 16 . 
         [0161]    By means of the mutual engagement of the ratchet member  32  with the geared rim  102  rotation of the drive wheel  100  is only allowed in a dose dispensing or dose decrementing direction. A counter-directed movement is effectively blocked and inhibited by said engagement. Moreover, during a dose decrementing or dose dispensing rotation of the drive wheel  100 , the ratchet member  32  generates an audible click sound thereby providing an audible feedback to the user, that the injection or dose dispensing is in progress. 
         [0162]    The drive wheel  100  further comprises a through opening to receive the piston rod  120  therethrough. The piston rod comprises an outer thread  121  and/or a longitudinally extending groove  122 . By means of a groove  122  the piston rod  120  could be rotatably fixed to the housing  20 . By means of a threaded engagement of the piston rod  120  with an inner thread  104  of the drive wheel  100 , the rotation of the axially fixed drive wheel  100  can be transferred into a distally-directed displacement of the piston rod  120 . 
         [0163]    In an alternative but not illustrated embodiment, it is also conceivable, that the piston rod  120  is splined to the drive wheel  100  and that the piston rod  120  is threadedly engaged with a housing portion. In such a technically equivalent configuration, rotation of the drive wheel  100  equally transfers into a distally-directed displacement of the piston rod  120  relative to the housing  20  and relative to the barrel of the cartridge  12 . 
         [0164]    A torque to rotate the drive wheel  100  is provided by the drive sleeve  90 , which is axially displaceable between a proximal stop position, in which the drive sleeve  90  is decoupled or disengaged from the drive wheel  100  and hence from the piston rod  120 . In its distal stop position, the drive sleeve  90  operably engages with the drive wheel  100  in a torque transmissive way. 
         [0165]    As for instance illustrated in  FIG. 15 , the drive sleeve  90  comprises a radially outwardly extending flange portion  92  at its distal end. From said flange portion  92 , there extends a geared rim  93  radially outwardly. The distal end face of the geared rim comprises a ring structure to mate with a correspondingly-shaped flange portion of drive wheel&#39;s geared rim  102 . Between the rim  102  and the rim  93  there is provided a disc spring  110  which serves to displace the drive sleeve  90  in proximal direction  2 . 
         [0166]    Hence, drive sleeve  90  and drive wheel  100  can be axially coupled against the action of the disc spring  110  positioned there between. The rim portions  93 ,  102  of drive sleeve  90  and drive wheel  100  carrying and supporting the disc spring  110  are substantially flat-shaped. In order to transfer angular momentum between the drive sleeve  90  and the drive wheel  100  the drive sleeve  90  comprises a crown wheel portion  94  radially inwardly from the geared rim  93 . Correspondingly, the drive wheel  100  comprises a proximally extending socket featuring a correspondingly-shaped crown wheel  106 . 
         [0167]    When the drive sleeve  90  is displaced in distal direction  1  to get in direct contact with the drive wheel  100 , said crown wheels  94 ,  106  mutually engage and angular momentum acting on the drive sleeve  90  may equally transfer to the drive wheel  100 , thereby leading to a distally-directed displacement of the piston rod  120 . A distally-directed displacement of the drive sleeve  90  against the action of the disc spring  110  is inducible by a dose dispensing button  40  provided at a proximal end of the housing  20 . 
         [0168]    As for instance illustrated in  FIG. 17 , the dose dispensing button  40  comprises a distally extending strut  41  to but against a proximal-facing portion of the radially outwardly extending flange portion  92  of the drive sleeve  90 . The strut  41  comprises a proximal rather axially extending strut portion  41   a  and a distal strut portion  41   b  which extends at a predefined angle with respect to the axial direction. In this way, the strut  41  is at least resiliently deformable to a certain degree so that a clutch between the drive sleeve  90  and the drive wheel  100  remains engaged even when the position of the dose dispensing button  40  in axial direction varies to a certain extent. 
         [0169]    Depression of the dose dispensing button  40  in distal direction  1  not only engages the drive sleeve  90  and the drive wheel  100 . Additionally, distally-directed displacement of the dose dispensing button  40  leads to a release of the drive spindle  80  relative to the ratchet member  150 . 
         [0170]    As becomes apparent from a comparison of  FIGS. 21 and 23 , the latch element  153  is resiliently deformable in radial direction. As shown in the released configuration according to  FIG. 23 , the latch element  153  radially protrudes from the outer circumference of the sidewall  156  of the cup-shaped ratchet member  150 . In this configuration, the radially inwardly extending lug  154  provided at the free end of the resiliently deformable latch element  153  is no longer engaged with the teeth  83  of the toothed rim  82  of the drive spindle  80 . 
         [0171]    In the released configuration the drive spindle  80  is effectively free to rotate under the action of the relaxing spring element  78  and the spindle gear of drive spindle  80  and drive member  70  which is driven by said spring element  78 . 
         [0172]    In the locked or engaged configuration according to  FIG. 21 , the arc-shaped latch element  153  is biased radially inwardly so that its radially inwardly extending lug  154  engages with the teeth  83  of the drive spindle  80 . Radially-directed displacement of the latch element  153  is governed by a biasing member  144  provided at a proximal end of a sleeve-shaped regulating member  140 . 
         [0173]    The regulating member  140  is rotatably and coaxially arranged to the ratchet member  150  as for instance illustrated in  FIGS. 22 and 24 . The regulating member  140  comprises a sleeve portion  141  featuring at least one inclined slit  142  or a respective groove on its outer circumference. As illustrated in  FIG. 21  the dose dispensing button  40  comprises an inwardly extending guiding member  42  featuring a radially inwardly extending pin  43  engaging with the inclined slit  142  of the regulating member  140 . 
         [0174]    Due to the inclined orientation of the slit  142  relative to the axial direction, a distally-directed displacement of the dose dispensing button  40  leads to continuous rotation of the regulating member  140 . As a consequence, the biasing member  144  travels along the outer circumference of the arc-shaped latch element  153 . Here, the biasing member  144  comprises a radially inwardly extending bulged portion  146  which abuts with an outer circumference of the arc-shaped latch element  153 . 
         [0175]    In the interlocked configuration, which corresponds to the dose dispensing button  40  in its proximal stop position, the biasing member  144  is fairly close to the free end of the arc-shaped latch element  153 . A depression of the dose dispensing button  40  in distal direction  1  comes along with a corresponding rotation of the regulating member  140  and leads to a continuous displacement of the biasing member  144  along the outer circumference of the arc-shaped latch element  153 . 
         [0176]    As a consequence and as illustrated in  FIG. 23 , the free end of the latch element  153  may extend radially outwardly. Due to the engagement of the guiding member  42  of the dose dispensing button  40  with the inclined slit  142  of the regulating member  140 , the degree of rotation of the regulating member  140  and its biasing member  144  is directly correlated to the degree of axial depression of the dose dispensing button  40 . 
         [0177]    Due to the resiliently deformable properties of the arc-shaped latch element  153 , the holding force provided by the latch element  153  and acting on the toothed rim  82  of the drive spindle  80  can be continuously and steplessly reduced or modified. In this way, mutual friction and gliding behaviour of the latch element  153  and the toothed rim  82  of the drive spindle  80  can be modified in dependence of the depth or degree of axial depression of the dose dispensing button  40 . 
         [0178]    Depending on the degree of rotation of the regulating member  140 , the holding force acting on the drive spindle  80  during an injection procedure can be continuously modified, thereby allowing to regulate the angular velocity of the drive spindle  80  when rotating in a dose decrementing, hence in a dose dispensing orientation  6 . 
         [0179]    It is to be mentioned here, that the dispensing velocity regulation provided by the mutual interaction of drive spindle  80  and ratchet member  150  can be realized in a variety of different ways. The orientation of the drive spindle  80  serving as a rotatable member and/or the concrete mechanical interaction between the drive spindle  80  and the ratchet member  150  may vary from the illustrated embodiment. 
         [0180]    It is only required that the ratchet member  153 , generally serving as a clutch member  153 , is at least partially radially displaceable with respect to the orientation of the axis of rotation  4  of the drive spindle  80  or of a respective rotatable element  80 . Moreover, the mutual retarding interaction of ratchet member  150  and drive spindle  80  can be frictionally based. Additionally, a positive engagement of ratchet member  150  and drive spindle  80  may also exhibit a combined friction-based and positively engaging interaction. 
         [0181]    As further illustrated by a comparison of  FIGS. 22 and 24 , the dose dispensing button  40  is coupled with the proximal end of the ratchet member  150  by means of a spring element  45 , e.g. an injection spring  45 , typically designed as a compression spring. As further illustrated in  FIG. 21  the dose dispensing button  40  is intersected by a strut  44  having a half shell shape which at least partially adopts the outer circumference of the ratchet member  150 . In the half shell-shaped portion the strut  44  further comprises an additional pin  46  to engage with a further slit  142  of the regulating member  140 . 
         [0182]    The regulating member  140  may therefore comprise two oppositely disposed slits  142  to engage with correspondingly arranged radially inwardly extending pins  43 ,  46  of the dose dispensing button  40 . The inwardly extending guiding member  42  of the dose dispensing button  40  further comprises an outer guiding portion  42   a , which also adopts the outer shape of the ratchet member  150 . By means of the outer guiding portion  42   a  and the half shell strut  44 , the dose dispensing button  40  can be axially guided along the ratchet member  150 . 
         [0183]    For a secure fastening of the spring element  45 , the proximal end of the ratchet member  150  comprises a stepped portion  151  to receive the spring element  45  therein. 
         [0184]    As becomes further apparent from  FIGS. 21 and 22 , the ratchet member  150  comprises axially extended notches  155  that allow to guide the radially inwardly extending pins  43 ,  46  of the dose dispensing button  40  past the ratchet member  150  during final assembly of the drive mechanism  3 . 
         [0185]    Depression of the dose dispensing button  40  in distal direction  1  for dispensing of a dose may then be divided into two consecutive steps. In a first step the dose dispensing button  40  is displaced in distal direction by a distance so that the pins  43 ,  46  advance in distal direction  1  into the slits  142  of the regulating member  140 . During this initial displacement the axially extending strut  41  already serves to mutually engage the drive sleeve  90  and the drive wheel  100 . 
         [0186]    In this way, a torque transmissive coupling of the drive sleeve  90  with the piston rod  120  can be attained even before the drive spindle  80  and hence the drive member  70  are released from the ratchet member  150 . It is only due to a further depression of the dose dispensing button  40  in distal direction  1 , that the pins  43 ,  46  run along the slit or groove  142  leading to a releasing rotation of the regulating member  140  and to a gradual and continuous release of the latch element  153 . The torque transmissive coupling of drive sleeve  90  and piston rod prior to a release of the drive spindle  80  from the ratchet member can be controlled and governed by the flexural behaviour and by the geometric design of the latch element  153 . As already explained above, the depth of depression of the dose dispensing button  40  may determine or may at least influence the angular velocity of the drive spindle  80  during dose dispensing. 
         [0187]    Under the action of the relaxing spring element  78 , the drive member  70  will return into its initial zero dose configuration. Since the toothed rack portion  71  of the drive member  70  is geared with the sprocket  60  of the gear wheel  58 , the dose indicating wheel  54 ,  56  will count down accordingly. Just before approaching an initial zero dose configuration, the drive member  70  may audibly engage with a clicking member  36  of the housing  20 . 
         [0188]    As shown in  FIG. 26 , the drive member  70  comprises a ledge  75   a  to engage with an inwardly extending pin-like clicking member  36 . Just before reaching a zero dose configuration at the end of a dose dispensing procedure, the bevelled ledge  75   a  engages with the correspondingly bevelled clicking member  36 , thereby generating an audible click sound, in particular when the resiliently deformable clicking member  36  returns into an initial abutment configuration with the bevelled ledge  75   a  as illustrated in  FIG. 27 . This audible feedback indicates to the user that a dispensing procedure has terminated. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  distal direction 
           2  proximal direction 
           3  drive mechanism 
           4  axis of rotation 
           5  dose incrementing direction 
           6  dose decrementing direction 
           10  drug delivery device 
           12  cartridge 
           14  piston 
           15  needle assembly 
           16  needle hub 
           17  needle cap 
           20  housing 
           21  upper housing portion 
           22  lower housing portion 
           23  cartridge window 
           24  cap 
           25  socket 
           26  dose indicating window 
           27  proximal stop 
           28  distal stop 
           29  receptacle 
           29   a  slit 
           30  clicking member 
           31  clicking member 
           32  ratchet member 
           33  bearing 
           36  clicking member 
           37  fixing rim 
           38  guiding structure 
           40  dose dispensing button 
           41  strut 
           41   a  proximal strut portion 
           41   b  distal strut portion 
           42  guiding member 
           42   a  outer guiding portion 
           43  pin 
           44  strut 
           45  spring element 
           46  pin 
           50  dose setting member 
           51  receptacle 
           52  gripping bar 
           53  crown wheel 
           54  dose indicating wheel 
           55  sprocket 
           56  dose indicating wheel 
           57  geared rim 
           57   a  crown wheel 
           58  gear wheel 
           59  geared rim 
           60  sprocket 
           61  ring structure 
           62  cog 
           70  drive member 
           71  toothed rack portion 
           72  sleeve portion 
           73  bar 
           74  tooth 
           75  ridge portion 
           75   a  ledge 
           76  rim 
           77  protrusion 
           78  spring element 
           79  inner thread 
           80  drive spindle 
           81  outer thread 
           82  toothed rim 
           83  tooth 
           86  pinion 
           88  tooth 
           89  bearing portion 
           90  drive sleeve 
           92  flange portion 
           93  geared rim 
           94  crown wheel 
           95  inner thread 
           100  drive wheel 
           102  geared rim 
           104  inner thread 
           106  crown wheel 
           110  disc spring 
           120  piston rod 
           121  thread 
           122  groove 
           124  stop member 
           126  pressure piece 
           128  crown wheel 
           130  dose limiting member 
           132  sleeve portion 
           133  outer thread 
           135  protrusion 
           136  geared rim 
           137  bracket portion 
           138  branch 
           139  branch 
           140  regulating member 
           141  sleeve portion 
           142  slit 
           144  biasing member 
           146  bulged portion 
           150  ratchet member 
           151  stepped portion 
           153  latch element 
           154  lug 
           155  notch 
           156  sidewall