Abstract:
The present invention relates a drug delivery device for dispensing of a dose of a medicament, comprising: an elongated body ( 20 ) extending in an axial direction ( 1, 2 ), a cartridge holder ( 13 ) to accommodate a cartridge ( 12 ) at least partially filled with the medicament and having an axially displaceable piston ( 14 ), a piston rod ( 110 ) to operably engage with the piston ( 14 ) of the cartridge ( 12 ) to displace the piston ( 14 ) in axial distal direction ( 1 ), a coupling member ( 100 ) connected with the cartridge holder ( 13 ) and being axially displaceably arranged in the body ( 20 ) for retracting the cartridge holder ( 13 ) into the body ( 20 ) during setting of a dose.

Description:
[0001]    The present invention relates to a drug delivery device and in particular to an injection device such like a pen-type injector. 
       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, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. They further comprise 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 or needle 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 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 dose actually set is entirely injected. 
         [0007]    There already exist some drug delivery devices with end of content mechanisms or last dose mechanisms. Most of these mechanisms require a rather complicated interaction of components of a drive mechanism. Typically, a separate last dose limiting member is required that successively propagates either in distal or proximal direction every time a dose is set or dispensed. When reaching an end of content configuration, a last dose limiting member typically engages with a corresponding stop to inhibit a further dose incrementing operation or actuation of the delivery device. 
         [0008]    Numerous last dose limiting implementations are non-visibly integrated somewhere in the drive mechanism of such drug delivery or injection devices. A user not being aware that the content of a cartridge is almost used up may be fairly surprised or confused when being suddenly confronted with an end of content situation. In circumstances in which the residual amount of medicament left in a cartridge is smaller than a prescribed dose to be administered the user may be in need of a spare cartridge. However, when being unaware, that such an end of content situation is likely to occur, a new cartridge may be unavailable to the user when the end of content is actually reached. 
         [0009]    In order to avoid such situations it is an object of the present invention to provide an improved drug delivery device configured to clearly, unambiguously and intuitively indicate to a user the actual filling level of a cartridge. It is a further aim to provide an improved end of content mechanism without making use of a separate last dose limiting member. In this regard it is a further object to reduce the number of parts of the drug delivery device. 
       SUMMARY OF THE INVENTION 
       [0010]    In a first aspect a drug delivery device for dispensing, in particular for injecting of a dose of a medicament is provided. The drug delivery device, typically designed as an injection device comprises an elongated body extending in an axial direction. Typically, the body is of substantially tubular or cylindrical shape that allows gripping and operating of the device by one hand of a user. 
         [0011]    The drug delivery device further comprises a cartridge holder to accommodate and to receive a cartridge that is at least partially filled with the medicament to be dispensed. The cartridge further has an axially displaceable piston, typically serving as a proximally located seal of the cartridge. The piston is displaceable in axial distal direction, thereby inducing a respective pressure in the inside volume of the cartridge in order to expel an amount of the medicament from the cartridge. For such a dispensing action, the distal seal of the cartridge, typically in form of a pierceable septum is in fluid connection with a piercing assembly or needle assembly. Axial displacement of the piston relative to the barrel of the cartridge directly corresponds to the size of a dose and hence correlates to the amount of medicament dispensed therefrom. 
         [0012]    The body and the cartridge holder typically form the housing of the drug delivery device and define its outer shape, which may be further completed by a removable protective cap that is typically releasably engageable with a distal portion of the body and which encapsulates the cartridge holder and the cartridge located therein when the device is not in use. 
         [0013]    The drug delivery device further comprises a piston rod to operably engage with the piston of the cartridge. By way of the piston rod, distally directed thrust can be exerted to the piston in order to displace the piston in distal direction relative to the cartridge&#39;s barrel. Displacement of the piston rod in distal direction exclusively takes place during dose dispensing and is typically controlled and conducted by a drive mechanism of the drug delivery device that is located in the body. The body typically forms a proximal portion of the housing of the drug delivery device while the cartridge holder forms a distal end thereof. Since the drive mechanism is located in the body, the drug delivery device is operable and configurable by a user at its proximal end. 
         [0014]    Additionally, the drug delivery device comprises a coupling member connected with the cartridge holder. The coupling member is further axially displaceably arranged in the body for retracting the cartridge holder into the body during setting of a dose. Typically, a coupling member is retractable in proximal direction into the body for retracting the cartridge holder in proximal direction at least during or for a respective dose setting procedure. 
         [0015]    During dose dispensing the coupling member is substantially inactive and rests at the position previously occupied at the end of the dose setting procedure. Hence, during dose dispensing the coupling member and also the cartridge holder interconnected therewith are substantially immobile relative to the body. Since coupling member and cartridge holder are subject to proximally directed displacement during dose setting, the overall axial extension of the drug delivery device shortens during and after each successive dose setting procedure. 
         [0016]    Moreover, the magnitude of the displacement of the coupling member and hence of the cartridge holder relative to the body in proximal direction is directly correlated to the size of the dose actually set. In this way, the axial displacement of the cartridge holder relative to the body during dose setting is a direct measure and indication of the size of the dose. 
         [0017]    Since the cartridge holder and the coupling member do not return into an initial position during a subsequent dose dispensing procedure the cartridge holder is successively retracted into the body until an end of content configuration correlating to a substantially empty cartridge has been reached. It is here of particular benefit that an end of content mechanism can be implemented by a mutual interaction and/or by a relative axial displacement of cartridge holder and housing. In this way, implementation of a separate last dose limiting member is no longer required and the number of components of the drug delivery device can be effectively reduced. Additionally, retraction of the cartridge holder into the body provides a very intuitive and unambiguous approach to visually or even to haptically indicate the filling level of a cartridge to a user. By successively retracting the cartridge holder into the body the overall length of the housing of the drug delivery device is inherently indicative of the cartridge&#39;s filling level. 
         [0018]    According to an embodiment the cartridge holder is non-rotatably connected to the body and is further radially and axially guided in and by a through opening at the body&#39;s distal end. In effect, the cartridge holder and the body are slidingly connected to allow a sliding displacement or a sliding retraction of the cartridge holder into the body. Typically, the inner diameter or inner geometry of the body&#39;s through opening matches with the outer circumference of the cartridge holder. 
         [0019]    In order to retract the cartridge holder into the body, the cartridge holder comprises an elongated shape, extends in axial direction and features a substantially constant cross-section perpendicular to the axial direction. Radial and axial guidance of the cartridge holder is therefore provided by the through opening located in a distal end face of the body. Additionally and in order to improve axial guiding of the cartridge holder the body may comprise an axially extending shaft portion at the circumference of the through opening. By means of said shaft portion, typically extending in proximal direction, a precise sliding displacement of the cartridge holder relative to the body, substantially free of tilt or cant can be provided. 
         [0020]    According to another embodiment body and cartridge holder are keyed engaged in order to prevent mutual rotation of cartridge holder and body with regard to a central axis extending in axial direction. The keyed engagement is typically obtained by at least one pair of mutually corresponding radially extending protrusions and recesses of body and cartridge holder. Hence, the cartridge holder may comprise at least one symmetry breaking protrusion or recess to engage with a correspondingly shaped recess or protrusion of the body, typically provided at the outer circumference of its through opening. 
         [0021]    In another embodiment the body comprises at least one radially inwardly extending protrusion extending into an axially extending through opening of the cartridge holder. Instead of a through opening the cartridge holder may comprise a recess at its outer circumference that does not completely penetrate the cartridge holder&#39;s sidewall portion. The axially extending through opening of the cartridge holder is typically provided in a sidewall portion of the substantially tubular-shaped cartridge holder. 
         [0022]    The through opening may further serve as an inspection window providing visual access to the cartridge arranged in the cartridge holder. By way of the through opening, the content of the cartridge may be visually inspected by the user. Typically, the circumferential size of the body&#39;s protrusion and of the cartridge holder&#39;s through opening mutually match so that protrusion and through opening effectively inhibit mutual rotation of cartridge holder and body. 
         [0023]    In typical embodiments the body comprises two diametrically positioned radially inwardly extending protrusions mating with two diametrically oppositely located through openings of the cartridge holder. By providing two or even more pairs of inter-engaging protrusions and through openings of body and cartridge holder a multiple rotational interlock of cartridge holder and body can be provided that may support a smooth sliding displacement of cartridge holder and body. 
         [0024]    Moreover, when having several pairs of mutually engaged protrusions and through openings or recesses, forces or torque acting between cartridge holder and body in circumferential direction may be evenly distributed among the pairs of inter-engaging protrusions and through openings. 
         [0025]    According to an alternative embodiment it is the cartridge holder featuring a radially outwardly extending protrusion engaged and guided in a correspondingly shaped axially extending recess or through opening of the body. 
         [0026]    According to another embodiment, the through opening of the cartridge holder or a correspondingly acting recess thereof comprises a stop edge at its distal end to delimit a proximally directed displacement of the cartridge holder relative to the body when reaching an end of content configuration. Typically, the through opening or recess of the cartridge holder terminates at the distal stop edge. In this way, the stop edge inherently provides a stop face to abut with the body&#39;s protrusion when reaching an end of content configuration of the cartridge. 
         [0027]    When the radially inwardly extending protrusion of the body abuts with said stop edge of the cartridge holder, the cartridge holder cannot be displaced any further in proximal direction relative to the body. Since the proximally directed displacement of the cartridge holder is directly coupled to a dose setting, a respective dose setting procedure is delimited and stopped. In this way, the mutual interaction, in particular the mutual axial abutment of the body&#39;s protrusion and the cartridge holder&#39;s stop edge effectively provides an end of content mechanism. 
         [0028]    According to another embodiment the drug delivery device, in particular its drive mechanism comprises drive sleeve rotatably supported in the body and being operably engageable with the piston rod to induce a distally directed displacement of the piston rod for dispensing of a dose. Moreover, the drive sleeve may not only be operable for dose dispensing but also for dose setting. The drive sleeve may rotate in a dose incrementing direction during dose setting. It may rotate in the opposite direction, hence in a dose decrementing direction during dispensing of a dose. 
         [0029]    Typically, for dispensing of a dose the drive sleeve is operably connectable to the piston rod in order to drive the piston rod in distal direction. During dose setting, the drive sleeve may be effectively disengaged from the piston rod. The drive sleeve may further be engaged with a spring element, typically with a helically-shaped spring element that is configured to transfer a driving torque to the drive sleeve during a dose dispensing procedure. The spring element may either be selectively or permanently coupled to the drive sleeve. When permanently coupled to the drive sleeve the spring element may be strained or biased during a dose setting procedure when the drive sleeve is rotated in dose incrementing direction. By some kind of clutch or ratchet mechanism the energy transferred to the spring element may then be stored and saved in or by said spring element until a dose dispensing action is triggered during which the energy stored in the spring element is to be released to exert a driving torque to the drive sleeve, i.e. to induce a rotation of the drive sleeve in dose decrementing direction. 
         [0030]    In another embodiment, wherein the drive sleeve is only selectively coupled or engaged with the spring element, the spring element may be pre-tensioned in such a way, that the energy or torque stored in the spring element is sufficient for subsequent dispensing procedures. In particular, the spring element may be charged or biased for the entire lifetime of a respective drug delivery device. 
         [0031]    According to another embodiment the piston rod is displaceable in proximal direction relative to the body and/or relative to the drive sleeve for setting of the dose. Here, the piston rod may be in permanent contact with the piston of the cartridge. Since the cartridge holder and the cartridge located therein is retracted in proximal direction relative to the body during setting of a dose, the same may also be valid for the piston rod. In a subsequent dose dispensing procedure cartridge holder and the cartridge located therein are immobilized relative to the body while the piston rod is driven in distal direction relative to the body and hence relative to the cartridge holder and relative to the cartridge. 
         [0032]    Typically, the piston rod is subject to proximally and distally directed displacement relative to the body during dose setting and dose dispensing, respectively. Typically, the magnitude or distance of a proximally directed displacement during dose setting is substantially equal to a subsequent distally directed displacement of the piston rod during dose dispensing. Hence, at the end of a dose dispensing procedure the piston rod returns into an initial configuration relative to the body. 
         [0033]    Drive sleeve and piston rod are mutually engaged by some kind of clutch mechanism that allows proximally directed displacement of the piston rod relative to the drive sleeve when the device is in dose setting mode. However, in dose dispensing mode drive sleeve and piston rod are mutually engaged in such a way, that a rotation of the drive sleeve transfers into a distally directed displacement of the piston rod. 
         [0034]    According to another embodiment the drug delivery device further comprises a sleeve-shaped retraction member rotatably supported in the body and being threadedly engaged with the coupling member. The retraction member is typically axially constrained or axially fixed in the housing and may therefore only rotate relative to the housing, at least during dose setting or for dose setting. Moreover, the coupling member and the cartridge holder are typically non-rotatably connected. 
         [0035]    Additionally, coupling member and cartridge holder are typically axially and rotatably fixed relative to each other. Since the cartridge holder is further non-rotatably connected to the body also the coupling member is non-rotatable relative to the body. Since the retraction member and the coupling member are threadedly engaged, a rotation of the retraction member relative to the housing therefore leads to an axial displacement of the coupling member relative to the housing, thereby retracting the cartridge holder into said housing. 
         [0036]    Typically, the retraction member is rotatable only during dose setting but is decoupled from the drive mechanism during dose dispensing. It is of particular benefit here, when the retraction member is rotatably locked to the housing in order to impede and to block any axial displacement of the cartridge holder relative to the body during dose dispensing. During dose setting, the retraction member is rotatable in both directions, i.e. in dose incrementing direction for increasing of a dose size as well as in dose decrementing direction for decreasing or for correcting a dose previously set. 
         [0037]    When the retraction member rotates in a dose incrementing direction the coupling member is displaced in proximal direction relative to the housing and/or relative to the retraction member. In the opposite case, when the retraction member rotates in a dose decrementing direction, the coupling member is subject to a corresponding distally directed axial displacement relative to the housing and/or relative to the retraction member. 
         [0038]    According to another embodiment, the drive sleeve and the retraction member are rotatably coupled for dose setting. Moreover, for dose dispensing the drive sleeve and the retraction member are rotatably disengaged. In this way, the retraction member is rotatable by means of the drive sleeve when the drug delivery device is in dose setting mode whereas the retraction member is substantially inactive or even immobilized relative to the body when the device is in dose dispensing mode. 
         [0039]    Typically, the drive sleeve is at least partially inserted into the hollow retraction member. Here, the drive sleeve typically comprises an outer geared rim or an outer toothing engaged with a correspondingly shaped toothing provided on an inwardly facing sidewall portion of the retraction member. In this way, a torque acting on the drive sleeve during dose setting can be unalterably transferred to the retraction member. For dose dispensing the mutually corresponding toothings of drive sleeve and retraction member are disengaged, e.g. by an axial displacement of the drive sleeve relative to the retraction member. 
         [0040]    Typically, the drive sleeve is engaged with a proximal end of the retraction member while a distal end section of the retraction member is threadedly engaged with the coupling member. The hollow and sleeve-shaped retraction member comprises an inner thread and an inside-facing tubular sidewall portion. In this way, the coupling member having an outer thread to threadedly engage with said inner thread of the retraction member is initially located near a distal end of the retraction member. 
         [0041]    During successive dose setting procedures the coupling member is therefore displaced in proximal direction, thereby retracting the cartridge holder into the hollow retraction member. Consequently, the retraction member is adapted to almost completely receive the cartridge holder, typically, until the stop edge of the cartridge holder provided at a distal end thereof engages with the radially inwardly extending protrusion of the body, which is typically located at the body&#39;s distal end. In said end of content configuration cartridge holder and body are arranged in an interleaved, hence in an axially and/or radially overlapping configuration. 
         [0042]    According to another embodiment the drive sleeve is rotatably engageable with a drive member threadedly engaged with the piston rod. Drive member and drive sleeve may be permanently rotatably engaged or rotatably coupled. Alternatively, drive member and drive sleeve may be selectively rotatably engaged or rotatably coupled or selectively rotatably connected. The drive member typically comprises or forms a drive nut rotatably or threadedly supported on the outer circumference of the piston rod. The drive member comprises an inner thread that corresponds and mates with an outer thread of the piston rod. Typically, the drive member is axially secured or axially constrained in the housing. The drive member may be for instance axially coupled with the drive sleeve. Since the drive member is either axially immobilized or axially constrained, rotation of the drive member then leads to an axial displacement of the piston rod, given that the piston rod is rotatably fixed relative to the body. 
         [0043]    The threaded engagement of drive member and piston rod may be of non-self-locking type, i.e. an axial displacement of the piston rod, in particular a proximally directed axial displacement of the piston rod, may then transfer into or induce a rotation of the drive member, which is axially fixed in the housing. This type of threaded engagement between piston rod and drive member would allow and support a selective rotational engagement of drive member and drive sleeve. Especially during setting of a dose, which is accompanied by a proximally directed displacement of the piston rod relative to the housing, the drive member could rotate independent from the drive sleeve. In other embodiments it is conceivable that the drive member and the drive sleeve are permanently rotatably engaged. During setting of a dose the drive member would then rotate in unison with the drive sleeve. 
         [0044]    In particular, the drive sleeve is rotatably engageable with the drive member in order to transfer a driving torque to the drive member. Due to the threaded engagement of drive member and piston rod and due to the axial coupling of the drive member relative to the body the piston rod, when rotatably locked to the body, experiences a distally directed displacement as the drive member is rotated in a dose decrementing direction by means of a correspondingly rotating drive sleeve. 
         [0045]    Typically, drive sleeve and drive member are rotatably engaged at least only during dose dispensing or only during dose dispensing. During dose setting drive sleeve and drive member may be operably disengaged. Drive sleeve and drive member may provide a kind of a clutch mechanism, by way of which the drive sleeve can be selectively engaged and coupled with the piston rod. By operably disengaging drive sleeve and drive member during dose setting, the drive sleeve can be rotated for setting of a dose without any interaction with the piston rod. In this way, the piston rod remains completely unaffected by a rotation of the drive sleeve for dose setting purpose. 
         [0046]    According to another embodiment the piston rod axially extends through a coupling member&#39;s through opening. Typically, piston rod and coupling member are keyed engaged. Hence, the piston rod is non-rotatably coupled to the coupling member. For this, the piston rod typically comprises a longitudinal groove engaging with a radially inwardly extending pin or a respective protrusion pointing radially inwardly from the inner circumference of the coupling member&#39;s through opening. In this way, the piston rod is axially but non-rotatably guided in or by the coupling member. 
         [0047]    Moreover, since the piston rod is rotatably locked to the coupling member and since the coupling member is rotatably locked to the cartridge holder, which in turn is rotatably locked to the body, the piston rod cannot rotate relative to the body. Since the piston rod is further threadedly engaged with the drive member, a rotation of the drive member transfers to an axial displacement of the piston rod relative to the body and hence relative to the cartridge holder and relative to the cartridge arranged therein. 
         [0048]    In still another embodiment the drug delivery device further comprises a single dose limiting member threadedly engaged with the piston rod and being non-rotatably but axially displaceably engaged with the drive sleeve. By means of the dose limiting member axial displacement of the piston rod can be delimited or restricted in at least one axial direction. Typically, the dose limiting member provides at least a zero dose stop by way of which a distally direction displacement of the piston rod can be stopped when the piston rod approaches an initial configuration at the end of a dose dispensing procedure. 
         [0049]    The single dose limiting member typically comprises a dose limiting disc or a respective dose limiting nut non-rotatably engaged, hence rotatably locked with the drive sleeve. For this, the dose limiting member comprises a radially extending protrusion or a radial recess at its outer circumference to mate with a correspondingly shaped recess or protrusion at an inward facing sidewall portion of the drive sleeve. 
         [0050]    The single dose limiting member may axially abut with a proximal end face of the drive member. Furthermore, the dose limiting member may comprise a radial or axial stop to engage with a correspondingly, typically radially outwardly extending radial or axial stop provided on the outer circumference of the piston rod. When the mutually corresponding stops of the single dose limiting member and the piston rod get in direct abutment, a rotation of the dose limiting member relative to the piston rod can be blocked. Such a blocking typically coincides with a zero dose configuration. By means of this zero dose stop function it can be effectively prevented, that a negative dose is set, e.g. by turning or twisting a respective dose setting member in a wrong direction for setting of a dose. 
         [0051]    The drug delivery device further comprises a maximum dose limiting feature. This may be implemented by a mutual interaction of the piston rod and the drive member. For instance, the piston rod comprises a second radially outwardly extending radial or axial stop element to engage with a correspondingly shaped stop of the drive member. The respective stop of the drive member may be located at a distal end face thereof. Typically, when implemented as a drug delivery device for injecting insulin, a stop configuration of the second or distal stop of the piston rod with the distal end face of the drive member serves to limit the maximum size of a dose to e.g. 120 international units (IU) of insulin. 
         [0052]    According to another embodiment the threaded engagement of the coupling member and the retraction member and the threaded engagement of the piston rod and the drive member comprise an equal pitch. Moreover, also the threaded engagement of the piston rod and the single dose limiting member and the threaded engagement of the piston rod and the drive member may comprise an equal pitch. Additionally or alternatively also the threaded engagement of the piston rod and the single dose limiting member and the threaded engagement of the coupling member and the retraction member comprise a substantially equal pitch. 
         [0053]    In this way axial displacement of the coupling member relative to the retraction member is substantially the same as the axial displacement of the piston rod relative to the drive member and relative to the single dose limiting member during setting of a dose, i.e., when the retraction member is subject to a dose incrementing or dose decrementing rotation. 
         [0054]    Since the piston rod is threadedly engaged with the drive member and since the drive member is axially constrained or even axially fixed relative to the body and/or relative to the drive sleeve it is of particular benefit, when the drive member rotates in unison with the drive sleeve during dose setting. In this way the piston rod can be displaced in proximal direction relative to the drive member and relative to the drive sleeve in the same way as the cartridge holder is retracted into the body. 
         [0055]    According to another embodiment the drug delivery device further comprises a blocking member engaged with a pretensioned spring element. The blocking member is further alternately engageable with the body or with the drive sleeve. Typically, the blocking member is engaged with the body and is disengaged from the drive sleeve during dose setting. In this way, the drive sleeve can be rotated for dose setting purpose without any interaction with the spring element. It is only due to dose dispensing, that the blocking member is disengaged from the body and is simultaneously engaged with the drive sleeve. 
         [0056]    In this way, mechanical energy stored and provided by the spring element can be released in order to exert a driving torque to the drive sleeve, e.g. to trigger and to conduct a spring-biased dose dispensing procedure. 
         [0057]    By selectively or alternately engaging the blocking member either with the body or with the drive sleeve a pretensioned spring element can be used that is operable to store such an amount of mechanical energy that is sufficient for completely dispensing the entire content of the cartridge during subsequent dose dispensing procedures. Especially when implemented as a disposable drug delivery device, a spring element being ‘charged for life’, hence for the entire life cycle of the device, can be applied here. 
         [0058]    According to another embodiment the drive sleeve is axially displaceable between a proximal stop position and a distal stop position for switching between a dose setting mode and a dose dispensing mode. Displacement of the drive sleeve in distal direction is such, that the drive sleeve rotatably engages with the blocking member and further disengages the blocking member from the body. At the same time the axial displacement of the drive sleeve, e.g. in distal direction serves to disengage the drive sleeve from the retraction member. Moreover, by means of a distally directed displacement of the drive sleeve from its proximal stop position into its distal stop position the drive sleeve may rotatably engage or may rotatably interlock with the drive member for transferring a driving torque from the relaxing spring element via the blocking member to the drive sleeve, to the drive member and hence to the piston rod for driving the same in distal direction. 
         [0059]    Axial displacement of the drive sleeve therefore fulfils three functions. First of all, the blocking member can be selectively engaged and disengaged to and from the body. Second, the drive sleeve could be rotatably engaged and disengaged with the drive member and third, the drive sleeve can selectively engage and disengage with or from the retraction member. In this way, three different clutch mechanisms are integrated or realized by a single element of the drug delivery device or of its drive mechanism, namely by the drive sleeve. 
         [0060]    Distally directed displacement of the drive sleeve may act against a retraction spring, which may either be integrated or engaged with the drive sleeve itself or with a clutch element axially fixed to the drive sleeve and being further supported by the body. 
         [0061]    In still another embodiment the drug delivery device further comprises a cartridge that is at least partially filled with the medicament to be dispensed. Said cartridge is arranged in the cartridge holder and is displaceable relative to the body together with the cartridge holder. Here, it is particularly due to the axial abutment of the piston of the cartridge with the piston rod, that the piston rod experiences a proximally directed displacement relative to the drive member and/or relative to the drive sleeve during setting of a dose, i.e. when the cartridge holder together with the cartridge disposed therein is retracted in proximal direction relative to the body. 
         [0062]    The drug delivery device may be designed as a disposable drug delivery device which is intended to be completely discarded upon consumption of the medicament initially provided in the cartridge. Alternatively, the drug delivery device may be designed as a reusable device, wherein the cartridge holder is releasably connected to the coupling member. Additionally, there may be implemented a reset function, to return the piston rod into an initial configuration upon replacement of a cartridge. 
         [0063]    By means of the pretensioned spring element the user does not have to provide a driving force to induce a driving torque on the drive sleeve. Instead, the user may only have to axially displace the drive sleeve from its proximal dose setting position into its distal dose dispensing position. The mechanical energy or torque necessary to displace the piston rod in distal direction for expelling of a predefined amount of the medicament from the cartridge may be completely provided by the pretensioned spring element. 
         [0064]    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. 
         [0065]    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. 
         [0066]    The term “drug” or “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound, 
         [0000]    wherein in one embodiment the pharmaceutically active compound has a molecular weight up to 1500 Da and/or is a peptide, a proteine, a polysaccharide, a vaccine, a DNA, a RNA, 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.
 
         [0067]    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. 
         [0068]    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. 
         [0069]    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. 
         [0070]    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.
   
 
         [0120]    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. 
         [0121]    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. 
         [0122]    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. 
         [0123]    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. 
         [0124]    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. 
         [0125]    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. 
         [0126]    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. 
         [0127]    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. 
         [0128]    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). 
         [0129]    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. 
         [0130]    Pharmaceutically acceptable solvates are for example hydrates. 
         [0131]    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 
         [0132]    In the following, a brief description of the drawings is provided, in which: 
           [0133]      FIG. 1  schematically illustrates the drug delivery device in a longitudinal cut, 
           [0134]      FIG. 2  shows a cross-section along A-A according to  FIG. 1 , 
           [0135]      FIG. 3  shows a cross-section B-B according to  FIG. 1 , 
           [0136]      FIG. 4  shows a cross-section along C-C of  FIG. 1 , 
           [0137]      FIG. 5  shows a cross-section along D-D of  FIG. 1 , 
           [0138]      FIG. 6  shows another cross-section E-E according to  FIG. 1 , 
           [0139]      FIG. 7  shows a longitudinal cross-section of the proximal end of the drug delivery device, 
           [0140]      FIG. 8  shows a longitudinal cross-section through the drive sleeve, 
           [0141]      FIG. 9  shows an exploded view of the various components of the drug delivery device, without the body 
           [0142]      FIG. 10  shows a perspective and partially cut view through the assembled drug delivery device, 
           [0143]      FIG. 11  shows a partially cut and perspective illustration of the proximal end of the drug delivery device, 
           [0144]      FIG. 12  shows a longitudinal cross-section through the drive mechanism of the drug delivery device in an initial configuration, 
           [0145]      FIG. 13  is indicative of the device according to  FIG. 12  after setting of a dose, 
           [0146]      FIG. 14  shows an enlarged view of the drive sleeve in the configuration according to  FIG. 12 , 
           [0147]      FIG. 15  shows an enlarged view of the drive sleeve in the configuration according to  FIG. 13 , 
           [0148]      FIG. 16  shows a partially cut and perspective illustration of the interface of cartridge holder and body in an initial configuration and 
           [0149]      FIG. 17  shows the interface of cartridge holder and body in an end of content configuration, 
           [0150]      FIG. 18  shows a longitudinal cut through the drive mechanism in the dose setting mode 
           [0151]      FIG. 19  shows the drive mechanism in dose dispensing mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0152]    In  FIGS. 1, 9 and 10 , the complete drug delivery device  10  is illustrated in a longitudinal cross-section and in an exploded view. The drug delivery device  10  of pen-injector type comprises a substantially cylindrical and axially elongated shape. The device  10  comprises a central axis  4  extending in axial direction. Throughout the various Figures, the axial distal direction is denoted with reference number  1  and the opposite proximal direction is denoted with reference number  2 . 
         [0153]    The drug delivery device  10  comprises a body  20  and a cartridge holder  13 . Body  20  and cartridge holder  13  form a housing of the drug delivery device  10 , which may be completed by a protective cap  19  that is releasably engageable with a distal end portion of the body  20  and which is adapted to completely cover the cartridge holder  13  and a cartridge  12  disposed therein. 
         [0154]    The drug delivery device  10  further comprises a drive mechanism  3  featuring at least a piston rod  110  that is operably engageable with a piston  14  of the cartridge  12 . The drive mechanism  3  is operable to displace the piston rod  110  in distal direction  1  in order to displace the piston  14  relative to the cartridge  12  accordingly for dispensing of a dose of the liquid medicament contained in said cartridge  12 . The cartridge  12  typically comprises a vitreous barrel of cylindrical or tubular shape and is further sealed at its distal end by a pierceable sealing member, such like a septum. 
         [0155]    In proximal direction  2  or at its proximal end, the cartridge  12  is sealed by means of the piston  14  slidably arranged in the cartridge  12 . The piston  14  typically comprises an elastomeric material, by way of which the proximal end of the cartridge is effectively sealed in a fluid- and gas-tight manner. Distally-directed displacement of the piston  14  induced by a respective displacement of the piston rod  110  typically leads to the build up of a fluid pressure inside the cartridge  12 . The distal outlet of the cartridge  12  is typically connected with a piercing member or with a needle assembly  16  as illustrated in  FIGS. 1, 16 and 17 . Since the needle assembly  16  comprises a double-tipped injection needle  17 , a dose of the medicament can be expelled from the cartridge  12  through the needle assembly  16  and can be injected into biological tissue. Typically, as illustrated in  FIGS. 1, 16 and 17 , the injection needle  17  is covered by an inner needle cap  18  that is to be removed prior to an injection procedure. 
         [0156]    The needle assembly  16  is typically removably attached to the distal end portion of the cartridge holder  13 . Here, a distally-located socket of the cartridge holder  13  and the needle assembly  16  may comprise mutually corresponding threads to screw the needle assembly  16  onto the cartridge holder  13  in a releasable way. 
         [0157]    Prior to conduct an injection procedure, the protective cap  19  has to be removed while the needle assembly  16  has to be attached to the cartridge holder  13 . After completion of a dose dispensing or injection procedure, the needle assembly  16  is to be removed and to be discarded and the protective cap  19  is to be assembled to the body  20  for protecting and for receiving the cartridge holder  13 . 
         [0158]    The drive mechanism  3  as illustrated in the various  FIGS. 1-19  comprises numerous functional and mechanically inter-engaging components by way of which a dose of variable size can be set and subsequently dispensed. The drive mechanism  3  is of semi-automated type. It comprises a means for storing mechanical energy either during a dose setting procedure or it is even equipped with an energy storage means, such like a pretensioned helical spring element  86  that is charged or biased in such a way, that it does not have to be biased or strained any further during dose setting. In particular with a disposable drug delivery device the spring element may be initially ‘charged for life’. 
         [0159]    The mechanical energy stored and provided by the helical spring element  86  is exploited for driving the piston rod  110  in distal direction  1  during a dose dispensing procedure. Consequently, an injection force or injection torque does not have to be provided by a user of the device  10  during the dose dispensing process. 
         [0160]    The body  20  comprises a tubular or cylindrical shape and features a window  21  near its proximal end, where a display assembly  140  is arranged. Near its distal end or in its distal end face the body  20  comprises a through opening  34  to receive the outer circumference of the tubular-shaped cartridge holder  13 . Adjacent to said central through opening  34  there is located a proximally extending shaft portion  36  as illustrated in  FIG. 16 . Additionally, the through opening  34  features a radially inwardly extending protrusion  35  that mates and engages with a correspondingly shaped through opening  13   a  of the cartridge holder  13 . The through opening  13   a  serves as an inspection window in order to visually inspect the medicament provided in the transparent cartridge  12 . 
         [0161]    By means of the radially inwardly extending protrusion  35  of the body  20  engaging with the correspondingly shaped recessed portion or through opening  13   a  of the cartridge  13 , a rotational interlock of cartridge holder  13  and body  20  is provided. In this way, the cartridge holder  13  is translationally displaceable relative to the body  20 , e.g. in proximal direction  2  until the radially inwardly extending protrusion  35  of the body  20  axially abuts with a distal stop edge  13   b  at the distal end of the through opening  13   a  as indicated in the respective end of content configuration of  FIG. 17 . 
         [0162]    As will be explained below, the cartridge holder  13  is retracted in proximal direction  2  into the body  20  during a dose setting procedure while it remains in the retracted position during a subsequent dose dispensing. The radially inwardly extending protrusion  35  of the body  20  and the correspondingly shaped longitudinal or slit-like through opening  13   a  of the cartridge holder  13  provide two functions. First of all, the cartridge holder  13  is rotatably interlocked to the body  20  and second, a rather simple but robust and intuitive end of content mechanism can be provided. 
         [0163]    As the content, hence the medicament provided in the cartridge reduces in the course of subsequent dispensing procedures the overall axial extension of the drug delivery device  10  reduces as well. Moreover, the axial distance the cartridge holder  13  is retracted into the body  20  during a dose setting procedure is directly related or equivalent to the size of the dose actually set. In this way, the actual dose size but also the total amount of medicament left in the cartridge is directly discernible from the axial position of the cartridge holder  13  in relation to the body  20 . 
         [0164]    The tubular-shaped body  20  further serves as a mount for a proximal base member  22  located at a proximal end of the body  20 . The proximal base member  22  serves as a mount for a first wheel  150  of the display assembly  140 . Furthermore, the proximal base member  22  features a central bore to receive and to axially and to radially guide a proximal shaft portion  61  of a clutch member  60 . 
         [0165]    Additionally, there is also provided a distal base member  26  axially separated from the proximal base member  22 . The distal base member  26  serves as a mount for a second wheel  160  of the display assembly  140 . Additionally, also the distal base member  26  comprises a central through opening  32  to axially and/or to radially guide a distal shaft portion  65  of the clutch member  60 . 
         [0166]    Both, the proximal as well as the distal base members  22 ,  26  are permanently fixed to the body  20 . They may even be integrally formed with the body  20 . As illustrated in cross-section according to  FIG. 3 , the distal base member  26  comprises radially inwardly extending recesses  30  to receive correspondingly shaped radially inwardly extending protrusions  24  located at the inward-facing sidewall portion of the body  20 . 
         [0167]    The proximal base member  22  may be permanently and rigidly attached to the body  20  in a similar way, which is not particularly illustrated here. 
         [0168]    The body  20  further serves as a mount for an annular fixing element  88  as illustrated in the cross-section of  FIG. 6 . The fixing element  88  comprises numerous radially inwardly extending recesses  89  at its outer circumference to engage with correspondingly shaped and radially inwardly extending protrusions  25  of the body  20 . By means of mutually corresponding protrusions  25  and recesses  89 , the fixing element  88  can be clamped or otherwise fixed inside the body  20 . As illustrated in  FIGS. 12 and 13 , the fixing element  88  is positioned near the distal end of the body  20 . 
         [0169]    The fixing element  88  further serves as a mount for the helical spring element  86 , that winds or extends along the outer circumference of a tubular or sleeve-shaped retraction member  90 . The opposite, hence the proximal end of said helical spring element  86  is connected with a blocking member  80 , which is of arched shape as indicated in  FIGS. 3 and 9  and which is adapted to alternately engage either with the body  20 , in particular via the distal base member  26 , or with a drive sleeve  70  as becomes apparent from a comparison of  FIGS. 18 and 19 . 
         [0170]    The distal base member  26  as for instance illustrated in  FIG. 8  comprises a central through opening  32  to axially and radially guide the distal shaft portion  65  of the clutch member  60 . Said through opening  32  is provided in a flange-like portion of the distal base member  26  that extends across the cross-section of the body  20 . At the outer circumference of said flange portion the distal base member  26  features a sleeve portion  29  substantially extending along the inward-facing side wall of the body  20 . By means of the sleeve portion  29 , a tight fitting or clamping-like engagement between body  20  and distal base member  26  can be attained. 
         [0171]    The retraction member  90  as for instance indicated in  FIGS. 12 and 13  is axially fixed to the body  20  by means of a fastening portion  96  located at a distal end thereof. As indicated in  FIG. 16 , the snap-shaped fastening portion  96  engages with a circumferential and outwardly extending rim located on the shaft portion  36  of the body  20 . In this way, the retraction member  90  is free to rotate with respect to the body  20 . 
         [0172]    Additionally, the retraction member  90  features a radially outwardly extending abutment portion  93  at its distal end  95 . This abutment portion  93  axially engages with the fixing element  88  to axially and/or to radially fix the fixing element  88  to the body  20 . As indicated in  FIG. 12 , the fixing element  88  is axially constricted or axially clamped between a radially stepped portion of the body  20  and the abutment portion  93  of the retraction member  90 . 
         [0173]    Moreover, the retraction member  90  comprises an inner thread  92  by way of which it is threadedly engaged with a coupling member  100  featuring a corresponding outer thread  102  at its outer circumference. The retraction member  90  further comprises a toothing  91  or a geared structure at its proximal end  94  at an inward-facing portion of its tubular sidewall. Said toothing  91  is selectively engageable with a correspondingly shaped distal toothing  71  of the drive sleeve  70 . In this way, the drive sleeve  70  and the retraction member  90  are rotatably engaged so that a rotation of the drive sleeve  70  equally transfers into a respective rotation of the retraction member  90 . 
         [0174]    The coupling member  100  as illustrated in cross-section according to  FIG. 5  features a flange portion  101  extending substantially perpendicular to the central axis  4 . The coupling member  100 , in particular its flange portion  101 , comprises a central through opening  105  to receive the piston rod  110  extending there through. The through opening  105  comprises two diametrically oppositely-located and radially inwardly extending protrusions  103  engaging with a correspondingly shaped notch or groove  112  of the piston rod  110 . Additionally, the coupling member  100  is fixed to the cartridge holder  13 . The coupling member  100  comprises a distally and/or proximally extending connecting portion  104  to receive a proximal end of the cartridge holder  13  as illustrated in  FIG. 13 . Hence, the proximal end of the cartridge holder  13  and the sleeve-like shaped coupling member  100  are arranged in an overlapping or nested configuration. 
         [0175]    As becomes apparent from  FIGS. 12 and 13 , the cartridge holder  13  comprises two or even more through openings  13   c  at its proximal end to receive radially inwardly extending connecting portions  104  of the coupling member  100 . The connecting portions  104  may comprise radially inwardly biased snap elements by way of which the coupling member  100  and the cartridge holder  13  can be mutually engaged in a non-rotative way. Moreover, coupling member  100  and cartridge holder  13  are also axially engaged, so that any axial displacement of the coupling member  100 , e.g. inside the retraction member  90  is directly transferred into a corresponding displacement of the cartridge holder  13 . 
         [0176]    Additionally, since the cartridge holder  13  is rotatably locked to the body  20  and since the cartridge holder  13  is also rotatably locked to the coupling member  100 , the coupling member  100  is hindered from rotating relative to the body  20 . Consequently, a rotation of the retraction member  90  leads to an axial displacement of the coupling member  100  and hence of the cartridge holder  13  due to the threaded engagement of coupling member  100  and retraction member  90 . 
         [0177]    The drive sleeve  70  as illustrated in detail in  FIGS. 8, 14 and 15  comprises a radially inwardly extending flange portion  77  at a distal end. Said radially extending flange portion  77  is located in a radial recess  122  of a drive member  120 . The drive member  120  serves as a drive nut and features a central bore with an inner thread  121  by way of which it is threadedly engaged with the outer thread  111  of the piston rod  110 . As indicated in  FIGS. 14 and 15 , the piston rod  110  axially extends through the drive member  120  and extends into the drive sleeve  70 . The recess  122  of the drive member  120  comprises an axial extension that is larger than the axial width of the drive sleeve&#39;s  70  distal flange portion  77 . In this way, the drive sleeve  70  can be axially displaced relative to the drive member  120 , in particular for switching the drive mechanism  3  between a dose dispensing and a dose setting mode. 
         [0178]    The drive member  120  comprises a radially widened head  126  that is located proximal to the radially inwardly extending distal flange portion  77  of the drive sleeve  70 . The radially widened head  126  is wider than the through opening of the distal flange portion  77 , so that drive sleeve  70  and drive member  120  are axially engaged in such a way, that the drive sleeve  70  axially constricted and is displaceable relative to the drive member  120  between a proximal stop position as indicated in  FIG. 18  and a distal stop position as shown in  FIG. 19 . 
         [0179]    Additionally, the distal end face of the drive sleeve  70  comprises a crown wheel  74  that matches with a correspondingly shaped crown wheel  124  of the drive member  120 . Typically, the crown wheel  124  of the drive member  120  is located on a radially widened portion of the drive member  120 . 
         [0180]    When the drive sleeve  70  is in its distal stop position as shown in  FIG. 19 , the crown wheels  74 ,  124  of drive sleeve  70  and drive member  120  mutually engage in a torque transferring way. In this way, a rotation of the drive sleeve  70  is equally transferable into a respective rotation of the drive member  120 . Due to the threaded engagement of piston rod  110  and drive member  120 , a dose decrementing rotation of the drive member  120  during dose dispensing transfers into a distally directed displacement of the piston rod  110  relative to the body  20  and hence relative to the cartridge holder  13  and the cartridge  12 , thus leading to a respective displacement of the piston  14  relative to the cartridge  12  thereby expelling a predefined dose of the medicament. 
         [0181]    The drive sleeve  70  further comprises a proximal flange portion  76  at its proximal end. By means of the radially outwardly extending proximal flange portion  76  the drive sleeve  70  axially abuts with the distal base member  26 , as indicated in  FIG. 15 . At a distally facing portion the proximal flange portion  76  comprises a second crown wheel  75  or a respective toothing that is selectively engageable with a corresponding crown wheel  82  or toothing of the blocking member  80 . 
         [0182]    The blocking member  80  further comprises a proximally extending rim portion having a gliding surface  84   a  facing radially inwardly. Additionally, the blocking member  80  also comprises a distally extending rim portion  83  with a radially inwardly facing gliding surface  83   a . As indicated for instance in  FIG. 15 , the distal rim portion  83  is radially supported by an intermediate and radially outwardly extending flange portion  78  of the drive sleeve  70  featuring a gliding surface  79 . 
         [0183]    Additionally, the proximal rim portion  84  is radially supported by the proximal flange portion  76  of the drive sleeve  70  having a respective outer gliding surface  79   a . The blocking member  80  further comprises a radially outwardly extending toothing  81  to engage with a correspondingly shaped toothing  31  provided at an inward facing sidewall portion of the distal base member  26  as illustrated in  FIG. 3 . When the toothings  81 ,  31  mutually engage as it is the case in the dose setting configuration shown in  FIGS. 14, 15 and 18 , the blocking member  80  is rotatably fixed to the proximal base member  26  and hence to the body  20 . 
         [0184]    It is upon a distally directed displacement of the blocking member  80 , that the toothings  81 ,  31  disengage as shown in  FIG. 19 , thereby allowing the blocking member  80  to rotate under the action of the relaxing helical spring element  86 . The blocking member  80  is displaceable in distal direction  1  by means of the drive sleeve  70 . In the dose setting mode as for instance indicated in  FIG. 18 , the drive sleeve  70  is free to rotate relative to the blocking member  80 . Here, the gliding surface  79  of the drive sleeve  70  glides along the gliding surface  83   a  of the blocking member  80 . Additionally, also the gliding surface  79   a  of the drive sleeve  70  slides or glides along the correspondingly and even shaped gliding surface  84   a  of the blocking member  80 . 
         [0185]    A rotation of the drive sleeve  70  in the dose setting mode as illustrated in  FIGS. 14, 15 and 18  further transfers into a respective rotation of the retraction member  90  by means of the mutually corresponding toothings  71 ,  91  of the drive sleeve  70  and the retraction member  90 , respectively. 
         [0186]    The drive sleeve  70  as shown in cross-section in  FIG. 3  further comprises radially outwardly extending recesses  73  to receive correspondingly shaped radially outwardly extending protrusions  66  provided on the distal shaft portion  65  of the clutch member  60 . Additionally but not illustrated here, the clutch member  60 , which is inserted into the proximal end portion of the drive sleeve  70  is also axially fixed to the drive sleeve  70 , e.g. by means of some kind of snap fit engagement, symbolized by a fixing member  67  in  FIGS. 18 and 19 . In this way, any rotational or axial displacement of the clutch member  60  equally transfers to the drive sleeve  70  and vice versa. 
         [0187]    The clutch member  70  is axially guided and radially supported by the proximal base member  22  and in the distal base member  26 . Additionally, the clutch member  60  comprises a proximal shaft portion  61 . As indicated in  FIG. 7  as well as in  FIGS. 18 and 19 , the hollow proximal shaft portion  61  receives a distally extending central shaft portion  51  of a dose dispensing member  50 . The button-shaped dose dispensing member  50  features a stepped portion  52  in its shaft portion  51  such that the stepped portion  52  axially abuts with a proximal end of the proximal shaft portion  68  of the clutch member  60 . 
         [0188]    Additionally and as indicated in  FIG. 18 , the dose dispensing member&#39;s shaft portion  51  comprises a fixing member  53 , axially engaged with the clutch member  60 . The fixing member  53  may comprise a resilient latch element to engage with a corresponding recessed portion of the clutch member  60 , or vice versa. By means of the fixing member  53  the clutch element  60  and the dose dispensing member  50  are axially fixed so that any axially directed displacement of the dose dispensing member  50  is transferred to clutch member  60 , and vice versa. 
         [0189]    In this way, a distally directed displacement of the dose dispensing member  50  can be unalterably transferred to the clutch member  60  and hence to the drive sleeve  70 . Typically, the distally directed displacement of the dose dispensing member  50  and/or of the clutch member  60  may act against the action of a retention spring element which is not particularly illustrated here. Typically, such spring element could be integrally formed in the clutch member  60 . It may be further supported on or at a proximal end face of the proximal base member  22 . A release of the dose dispensing member  50 , e.g. during or at the end of a dose dispensing procedure may then lead to an immediate proximally directed displacement of the clutch member  60  in order to switch the drug delivery device  10  into the dose setting mode. 
         [0190]    As further indicated in  FIG. 2 , the clutch member  60  comprises a toothing  68  at its proximal end engaged with a corresponding toothing  42  of a dose setting member  40 . The dose setting member  40  of tubular or knob-like shape features a central through opening  41  to receive the proximal shaft portion  61  of the clutch member  60  as well as to receive the distally extending shaft portion  51  of the dose dispensing member  50 . The dose setting member  40  is further axially supported by the base member  22 . It may be axially fixed to the base member  22  and may form a proximal end of the housing and hence of the drug delivery device  10 . 
         [0191]    The dose setting member  40  further comprises a rippled gripping surface  44  along its outer circumference as indicated in  FIG. 2 . Furthermore, as illustrated in  FIG. 7  it comprises a cylindrically-shaped receptacle  43  at its proximal end face to receive the outer circumference of the dose dispensing member  50 . Since the dose setting member  40  is rotatably engaged via the toothing  42  with the clutch member  60 , a rotation of the dose setting member  40  equally transfers to the clutch member  60  and hence to the drive sleeve  70  interconnected therewith. 
         [0192]    Additionally but not necessarily the outer circumference of the button shape dose setting member  50  also comprises a toothing  55  that is in engagement with a correspondingly shaped toothing  45  of an inward facing sidewall of the dose setting member&#39;s  40  receptacle  43 . In this way, the dose dispensing member  50  rotates in unison with the dose setting member  40  during a dose setting procedure. 
         [0193]    However, when depressing the dose dispensing member  50  in distal direction  1 , the clutch member  60  is displaced in distal direction  1  accordingly, thereby disengaging the toothing  68  of the clutch member  60  from the toothing  41  of the dose setting member  40 . In this way, and during dose dispensing, the dose setting member  40  may be further rotatable. Since the rotational engagement of dose setting member  40  and clutch member  60  is abrogated a rotation or dialing of the dose setting member  40  during dose dispensing is substantially effectless. 
         [0194]    The clutch member  60  is further permanently engaged with the display assembly  140 . As illustrated in  FIGS. 18 and 19 , the display assembly  140  comprises a first dose indicating member  141  and a second dose indicating member  142 . Both sleeve-shaped dose indicating members  141 ,  142  comprise an inner toothing  143 ,  144 , respectively. Radially outwardly, hence at its outer circumference, the first dose indicating member  141  comprises a first display surface  145  adapted to illustrate various digits 0, . . . , 9, whereas the second dose indicating member  142  comprises a second display surface  146  adapted to display consecutive digits 1, . . . , 12. 
         [0195]    In this way, the combination of first and second dose indicating members  141 ,  142  is applicable to illustrate consecutive numbers from 0-120, thereby representing e.g. 0-120 IU. The first wheel  150  as illustrated comprises a proximally extending central shaft  153  located in a correspondingly shaped receptacle or blind hole  23  of the proximal base member  22 . The first wheel  150  further comprises a first geared rim  151  that meshes with the toothing  143  on the inside facing sidewall portion of the first dose indicating member  141 . 
         [0196]    Axially adjacent to said first geared rim  151 , the first wheel  150  comprises a second geared rim  152 , which is reduced in diameter compared to the first geared rim  151 . The outer circumference of the second geared rim  152  is engaged and meshes with an inwardly facing toothing or with a respective inner gear axially extending at the radially outwardly located portion of a disc-shaped flange portion  62  of the clutch member  60 . Said radially outwardly extending disc-like flange portion  62  of the clutch member  60  further provides axial abutment for the second wheel  160  that features a central bore  163  to receive a proximally extending shaft  27  of the distal base member  26 . 
         [0197]    Also the second wheel  160  is provided with a geared rim  162 , which directly meshes with an outer gear  64  of the clutch member  60 . But in contrast to the first wheel  150 , the second wheel  160  is engaged with the second dose indicating member  142  by means of a single or several isolated tappets  161 , only frequently meshing with the toothing  144  of the second dose indicating member  142 . For instance, the second wheel  160  comprises only one tappet or two diametrically oppositely located tappets radially outwardly extending from the outer circumference of the second wheel  160 . 
         [0198]    Then, during a complete revolution of the second wheel  160 , said tappet  161  only engages once or twice with the toothing  144  of the second dose indicating member  142 . In this way, the second dose indicating member  142  is step-wise rotated in discreet steps every time the first display surface  145  changes from 9 to 0 when dialed in a dose incrementing direction  5 , as for instance illustrated in  FIG. 11 . 
         [0199]    The distal base member  26  further comprises a proximally extending retaining member  28  engaging with the sidewall portion of the second dose indicating member  142 . In particular, the second dose indicating member  142  may comprise radially extending notches to receive or to engage with the retaining member  28 . In this way and in situations in which the tappet  161  is not in engagement with the second dose indicating member  142  the second dose indicating member  142  is substantially immobilized or fixed to the body  20 . 
         [0200]    In effect, the first dose indicating member  141  represents single digits or the last digit of a two or three digit number whereas the second dose indicating member  142  is operable to represent the first or the first and the second digits of a two or three digit number. Hence, the second display surface  146  of the second dose indicating member  142  represents integer multiples of ten, and hence numbers such like 10, 20, 30, . . . , 120. 
         [0201]    As becomes apparent from  FIGS. 18 and 19 , the axial extension of the inner gear  63  and the outer gear  64  is larger than the maximum axial displacement path of the clutch member  60 . In this way, the clutch member  60  remains permanently engaged with the first and second wheels  150 ,  160 . Consequently, any rotation of the clutch member  60  leads to a respective dose incrementing or dose decrementing rotation of the first and the second dose indicating members  141 ,  142 . 
         [0202]    In the following, setting of a dose is described. 
         [0203]    Per default the drug delivery device  10  is in dose dispensing mode as for instance illustrated in  FIGS. 12, 13 and 18 . When a user starts dialing the dose setting member  40  in a dose incrementing direction  5  as indicated in  FIG. 11 , the rotation of the dose setting member  40  is equally transferred to the clutch member  60  via the mutually corresponding toothings  42 ,  68  of dose setting member  40  and clutch member  60 , respectively. 
         [0204]    The respective rotation of the clutch member  60  transfers to the two wheels  150 ,  160  of the display assembly  140 . Accordingly, respective dose indicating numbers of the first and second display surfaces  145 ,  146  will show up in the window  21  of the body. Additionally, the rotation of the clutch member  60  is equally transferred to the drive sleeve  70  and to the retraction member  90  via the mutually corresponding toothings  71 ,  91  of drive sleeve  70  and retraction member  90 , respectively. A rotation of the retraction member  90  in dose incrementing direction  5  leads to a retraction of the coupling member  100  and hence to a respective proximally directed retraction of the cartridge holder  13  as becomes apparent from  FIG. 13 . 
         [0205]    Since the piston rod  110  with its distal pressure piece  113  is in direct axial abutment with a proximal end face of the piston  14 , also the piston rod  110  is translationally displaced in proximal direction  2  relative to the drive member  120  and relative to the drive sleeve  70 . A proximally directed displacement of the piston rod  110  relative to the drive member  120  is possible when the drive member  120  rotates in unison with the drive sleeve  70  during dose setting. Moreover, the threaded engagement of the coupling member  100  and the retraction member  90  may comprises a pitch equal to the threaded engagement of piston rod  110  and drive member  120 . In an alternative embodiment the threaded engagement of piston rod  110  and drive member  120  may be of non-self-locking type. Hence a proximally directed axial displacement of the piston rod as it is induced through a dose increasing rotation of the drive sleeve  70  leads to a rotation of the drive member  120 . Here, the drive member  120  may be rotatably decoupled from the drive sleeve  70  and may rotate independently from the drive sleeve, i.e. with a different angular velocity. 
         [0206]    The piston rod  110  as illustrated in  FIG. 15  axially enters the distal shaft portion  65  of the clutch member  60  as indicated in  FIG. 15 . A proximally directed displacement of the piston rod  110  is delimited by a distal stop  115  provided at the outer circumference of the piston rod as indicated in  FIG. 15 . Said distal stop  150  may either axially and/or radially engage with a correspondingly shaped but not illustrated stop of the drive member  120 . When mutually corresponding stops of drive member  120  and piston rod  110  get in abutment, a further dose incrementing rotation of the drive member  120  relative to the piston rod  110  is substantially inhibited, thus leading to a blocking of the rotation of the drive sleeve  70 , of the clutch member  60  and hence of the dose setting member  40 . 
         [0207]    As indicated in  FIG. 14  the piston rod  110  further comprises another radially extending proximal stop  114  at a proximal end portion. Said proximal stop  110  is adapted to engage with a correspondingly shaped stop of a single dose limiting member  130  as illustrated in  FIG. 14 . Said single dose limiting member  130  is operable to prevent dialing of a negative dose and to stop a distally directed displacement of the piston rod  110  during or at the end of a dose dispensing procedure. 
         [0208]    The single dose limiting member  130  is of disc-like shape and comprises two radially outwardly extending protrusions  132  engaged with two correspondingly shaped axially extending grooves or recesses  72  of the drive sleeve  70 . In this way, the single dose limiting member  130  is permanently rotatably engaged with the drive sleeve  70  but is allowed to axially move relative to the drive sleeve  70 . The single dose limiting member  130  also comprises a central bore through which the threaded piston rod  110  extends in axial direction. 
         [0209]    The outer thread  111  of the piston rod  110  is threaded with a correspondingly shaped inner thread  131  of the single dose limiting member  130 . The pitch of the threaded engagement of the single dose limiting member  130  and the piston rod  110  might be also equal to the pitch of the threaded engagement of the drive member  120  and the piston rod  110 . It is also equal to the pitch of the threaded engagement of the coupling member  100  and the retraction member  90 . 
         [0210]    Given that a selected dose is too large, the dose setting member  40  can be rotated in the opposite direction, hence in dose decrementing direction  6  as indicated in  FIG. 11 . Then, the rotatable components as mentioned above will rotate in the opposite direction, thus leading to an axial displacement of the coupling member  100  and the piston rod  110  together with the cartridge  12  in distal direction  1 . Accordingly, the dose indicating numbers showing up in the window  21  will decrement. Once a dose has been correctly set, the drug delivery device  10  is ready for dose dispensing. 
         [0211]    In the following, dispensing of a dose will be described. 
         [0212]    Dispensing of a dose is simply triggered by depressing the dose dispensing member  50  in distal direction  1  as becomes apparent from a comparison of  FIGS. 18 and 19 . The distally directed displacement of the dose dispensing member  50  leads to a corresponding displacement of the clutch member  60  and of the drive sleeve  70  connected therewith. Consequently, the toothing  68  of the clutch member  60  disengages from the correspondingly shaped toothing  42  of the dose setting member  40 . 
         [0213]    Hence, any further rotation of the dose setting member  40  is substantially effectless when the dose dispensing procedure in progress. The distally directed displacement of the drive sleeve  70  leads to a decoupling or disengagement of drive sleeve  70  and retraction member  90 . Consequently, during dose dispensing the cartridge holder  13  will remain in its position. 
         [0214]    Furthermore, by displacing the drive sleeve  70  in distal direction  1 , the crown wheel  75  located at the proximal flange portion  76  of the drive sleeve  70  engages with the correspondingly shaped crown wheel  82  of the blocking member  80  facing in proximal direction  2 . In this way, blocking member  80  and drive sleeve  70  are rotatably interlocked. Shifting further of the drive sleeve  70  towards its distal stop position then leads to a corresponding distally directed displacement of the blocking member  80 . 
         [0215]    Consequently, the toothing  81  of the blocking member  80  disengages from the toothing  31  of the body  20 . In this way, the blocking member  80  is free to rotate under the action of the relaxing helical spring element  86  that is permanently connected to the blocking member  80 . Since the blocking member  80  is rotatably interlocked or rotatably engaged with the drive sleeve  70  also the drive sleeve  70  starts to rotate in a dose decrementing direction  6 . Additionally and prior to a release of the blocking member  80  from the body  20 , the drive sleeve  70  also rotatably engages with the drive member  120 . 
         [0216]    Here, the distal crown wheel  74  of the drive sleeve  70  engages with the correspondingly shaped crown wheel  124  of the drive member  120  facing in proximal direction. In this way, the spring-induced rotation of the blocking member  80  and of the drive sleeve  70  equally transfers to a respective rotation of the drive member  120 . Since the piston rod  110  threadedly engaged with the drive member  120  is rotatably interlocked with the coupling member  110  via its longitudinally extending groove  112  the piston rod  110  cannot rotate but is driven in distal direction instead until the initial configuration as illustrated in  FIG. 14  is reached, in which the proximal stop  114  of the piston rod  110  engages with the single dose limiting member  130 . 
         [0217]    Reaching of this initial configuration may be further accompanied by a visual or audible feedback. For instance, the proximal stop  114  and the single dose limiting member  130  may audibly engage, e.g. by way of a particular click sound generating element, such like a resilient latch element. In this way, the end of a dispensing procedure can be audibly indicated to a user. 
         [0218]    When releasing the dose dispensing member  50  during or after termination of a dose dispensing procedure, an axially acting retraction spring, e.g. located between the clutch member  60  and one of the proximal base member  22  or distal base member  26  serves to immediately displace the clutch member  60  in proximal direction  2 . Since the clutch member  60  is also axially interlocked or axially connected to the drive sleeve  70 , the proximally directed retraction of the clutch member  60  equally transfers to the drive sleeve  70 . 
         [0219]    Consequently, since the drive member  120  is threadedly engaged with the piston rod  110 , the crown wheels  74 ,  124  of the drive sleeve  70  and of the drive member  120  will immediately disengage, thereby interrupting any further distally directed displacement of the piston rod  110 . With the proximally directed retraction of the drive sleeve  70  also the blocking member  80  returns into its proximal stop position as indicated in  FIG. 18 . Here, the intermediate flange portions  78  of the drive sleeve  70  may serve to exert a respective axially and proximally directed displacement force to the blocking member  80 . Additionally, it is conceivable, that the blocking member  80  returns into its proximal stop position under the effect of the helical spring  86 . 
         [0220]    For not losing mechanical energy stored in the helical spring  86  it is of particular benefit that the drive sleeve  70  consecutively engages and disengages with the drive member  120  and the blocking member  80  as described in the following. For switching the drive mechanism  3  from dose setting mode as illustrated in  FIG. 18  into dose dispensing mode as shown in  FIG. 19 , the drive sleeve  70  is displaced in distal direction  1 . 
         [0221]    During this distally directed displacement of the drive sleeve  70 , the drive sleeve first engages with the drive member  120  before the blocking member  80  disengages from the body  20 . Additionally, the drive sleeve  70  should disengage from the retraction member  90  before the blocking member  80  is released to rotate under the action of the helical spring  86 . When releasing the button-shaped dose dispensing member  50  engagement and disengagement of drive sleeve  70 , retraction member  90 , drive member  120 , blocking member  80  and body  20  or distal base member  26  should take place in the reverse order. 
         [0222]    The single dose limiting member  130  is axially shiftable relative to the drive sleeve  70  which is of particular benefit during switching of the drive mechanism  3  between dose setting and dose dispensing mode as becomes apparent from the comparison of  FIGS. 18 and 19 . Generally, the single dose limiting member  130  is in axial abutment with a proximal end of the drive member  120 . But since the drive member  120  is free to rotate relative to the drive sleeve  70  in the dose setting mode, it is the single dose limiting member  130  which effectively provides a rotational blocking of piston rod  110  and drive sleeve  70  in the zero dose configuration as illustrated in  FIG. 14 . 
         [0223]    In the embodiment as illustrated, the blocking member  80  is either engaged with the body  20  via the distal base member  26  or it is engaged with the drive sleeve  70 . In particular, since the blocking member  80  is operably disconnected from the drive sleeve  70  during dose setting, the dose setting can take place without any interaction with the helical spring  86 . Moreover, when the helical spring  86  extending radially between the body  20  and the retraction member  90  is ‘charged for life’ sufficient energy can be provided to repeatedly transfer a driving torque to the drive sleeve  70  during subsequent dose dispensing procedures until an end of content configuration as shown in  FIG. 17  has been reached. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  distal direction 
           2  proximal direction 
           3  drive mechanism 
           4  longitudinal axis 
           5  dose incrementing direction 
           6  dose decrementing direction 
           10  drug delivery device 
           12  cartridge 
           13  cartridge holder 
           13   a  through opening 
           13   b  stop edge 
           13   c  through opening 
           14  piston 
           16  needle assembly 
           17  injection needle 
           18  needle cap 
           19  protective cap 
           20  housing 
           21  window 
           22  proximal base member 
           23  blind hole 
           24  protrusion 
           25  protrusion 
           26  distal base member 
           27  shaft 
           28  retaining member 
           29  sleeve portion 
           30  recess 
           31  toothed structure 
           32  through opening 
           34  through opening 
           35  protrusion 
           36  shaft portion 
           40  dose setting member 
           41  through opening 
           42  toothing 
           43  receptacle 
           44  gripping surface 
           45  toothing 
           50  dose dispensing member 
           51  shaft 
           52  stepped portion 
           53  fixing member 
           55  toothing 
           60  clutch member 
           61  proximal shaft portion 
           62  flange portion 
           63  inner gear 
           64  outer gear 
           65  distal shaft portion 
           66  protrusion 
           67  fixing member 
           68  toothing 
           70  drive sleeve 
           71  toothing 
           72  recess 
           73  recess 
           74  crown wheel 
           75  crown wheel 
           76  flange portion 
           77  flange portion 
           78  flange portion 
           79  gliding surface 
           79   a  gliding surface 
           80  blocking member 
           81  toothing 
           82  crown wheel 
           83  rim portion 
           83   a  gliding surface 
           84  rim portion 
           84   a  gliding surface 
           86  helical spring 
           88  fixing element 
           89  recess 
           90  retraction member 
           91  toothing 
           92  inner thread 
           93  abutment portion 
           94  proximal end 
           95  distal end 
           96  fastening portion 
           100  coupling member 
           101  flange portion 
           102  outer thread 
           103  protrusion 
           104  connecting portion 
           105  through opening 
           110  piston rod 
           111  outer thread 
           112  groove 
           113  pressure piece 
           114  proximal stop 
           115  distal stop 
           120  drive member 
           121  inner thread 
           122  recess 
           124  crown wheel 
           126  head portion 
           130  single dose limiting member 
           131  inner thread 
           132  protrusion 
           140  display assembly 
           141  first dose indicating member 
           142  second dose indicating member 
           143  toothing 
           144  toothing 
           145  first display surface 
           146  second display surface 
           150  first wheel 
           151  geared rim 
           152  geared rim 
           153  shaft 
           160  second wheel 
           161  tappet 
           162  geared rim 
           163  bore