Patent Publication Number: US-2017361038-A1

Title: Assembly for a Drug Delivery Device

Description:
This disclosure relates to an assembly for a drug delivery device. Furthermore, the disclosure relates to a drug delivery device comprising the assembly. The drug delivery device may be an inhalator, in particular a dry powder inhaler. An inhalation device is usually activated by a user&#39;s suction airstream and is intended for the inhalation of a substance, in particular a powdery substance. An inhalation device is described in document WO 2009/065707 A1, for example. 
     However, the assembly may also be suitable for other drug delivery devices, e.g. an injector such as an injection pen. In particular, the assembly may be used in a fixed-dose drug delivery device, i.e. a device in which the size of the dose of the drug which is delivered may not be varied by the user. Rather, in a fixed-dose device the size of the dose is set by the design of a dispensing mechanism. 
     It is an object of the present disclosure to provide an improved assembly for a drug delivery device, e.g. a mechanism preventing a further operation of the device after a given number of operation which requires only a low number of components. 
     This object may, inter alia, be achieved by the subject-matter of the independent claim. Advantageous embodiments and refinements are the subject-matter of the dependent claims. However, further advantageous concepts may be disclosed herein besides the ones which are claimed. 
     One aspect of the present disclosure relates to an assembly for a dry powder inhaler comprising a housing, a detachable member which is detachable from the housing and attachable to the housing, a mechanism configured to be transferred from one state to a subsequent state when the detachable member is detached from the housing. 
     The mechanism may be a step switching mechanism wherein the step switching mechanism comprises a finite number of states defining a chain of states such that the step switching mechanism is configured to be subsequently in each of the states of the chain of states, wherein the step switching mechanism is configured to be transferred from one state to a subsequent state of the chain of states when the detachable member is detached from the housing. 
     The dry powder inhaler may be a metering inhaler. A metering inhaler is designed to deliver a metered quantity of a drug with each dose delivery operation. The metering inhaler comprises a reservoir containing multiple doses of the metered quantity. The metering inhaler is designed such that the metered quantity is separated from the reservoir by the inhaler itself. Either the metered quantity may be separated from the reservoir in an initial part of each dose delivery operation or the metering quantity intended to be delivered in a subsequent dose delivery operation may be separated from the reservoir at a final part of a present dose delivery operation. The dry powder inhaler may be adapted for dispensing a plurality of doses of a drug or substance. 
     The mechanism may be defined by a first and a second abutment surface. In particular, each state of the step switching mechanism may correspond to a specific relative position between the first and the second abutment surface. With every detachment of the detachable member from the housing, the first and the second abutment surface may be moved closer together along a helical path. 
     The mechanism may be designed such that the first and the second abutment surface may only be moved into a specific relative position with respect to each other when they have passed a previous relative position with respect to each other, thereby defining the chain of states. 
     The finite number of states may correspond to a predetermined number N. 
     One aspect of the present disclosure relates to an assembly. The assembly may be suitable to be used in a lock-out mechanism for a drug delivery device. The device may be an inhalation device, in particular a dry powder inhalator. The device may be adapted for dispensing a plurality of doses of a medication or substance. 
     An assembly for a drug delivery device is provided which comprises a housing, a first abutment surface, a second abutment surface and a detachable member. The detachable member is detachable from the housing and attachable to the housing, wherein the assembly is configured such that, during detachment of the detachable member from the housing for an Nth time, N being a predetermined number, the first abutment surface is brought into abutment with the second abutment surface, wherein the assembly is configured such that, when the first abutment surface abuts with the second abutment surface, the detachable member is enabled to be reattached to the housing and, afterwards, the detachable member is prevented from being detached from the housing. 
     Accordingly, the assembly may be configured to ensure a lock-out of the drug delivery device after the detachable member has been detached from the housing N times and, afterwards, has been reattached to the housing. In particular, the assembly may be configured to prevent a user from trying to further use the device after the detachable member has been detached and reattached to the device N times. 
     The term “lock-out” may be understood in this context such that a further operation of the drug delivery device, e.g. a drug dispense operation, is prevented when the device is locked-out. The further operation may be prevented by the assembly in particular by preventing the detachment of the detachable member from the housing. A drug dispense operation may not be possible when the detachable member is attached to the housing. 
     Typically, every time the detachable member is detached from the device and afterwards reattached to the device, one drug dispense operation is carried out. In particular, the drug delivery device may be configured such that not more than one drug dispense operation can be carried out after the detachable member is detached from the device and before the detachable member is reattached to the device. Accordingly, the assembly may be configured to lock-out the drug delivery device after a maximum number of N drug delivery operations can be carried out. 
     The assembly may be an assembly for a lock-out mechanism configured to lock out the drug delivery device, i.e. to prevent a further operation of the device when the device is considered to be empty. The assembly may also be an assembly for a counter mechanism configured to count the number of doses left in the device or, alternatively, to count the number of possible drug dispense operations which may be carried before the device is considered to be empty wherein the counter-mechanism additionally has a lock-out feature preventing a further operation of the device when the device is considered to be empty. 
     The housing may be an external component of the drug delivery device. In particular, the housing may cover further elements of the drug delivery device. 
     The first abutment surface and the second abutment surface may be provided on different members of the drug delivery device. During normal operation of the drug delivery device, i.e. during a dose setting operation and/or a drug dispense operation before the device is considered to be empty, the first and the second abutment surface may be spaced apart from each other. The first and the second abutment surface may be configured to rotationally lock the a first member comprising the first abutment surface to each a second member comprising the second abutment surface when the first and the second abutment surface abut each other. 
     The detachable member being detachable from the housing may mean in this context that the detachable member can be completely removed from the housing such that it has no contact at all to the housing. When the detachable member is attached to the housing, the detachable member may cover at least a part of the housing. In particular, the detachable member may cover a part of the housing which comprises a mouthpiece such that no drug can be dispensed from the mouthpiece when the detachable member is attached to the housing. Thereby, the detachable member effectively prevents a drug dispense operation when attached to the housing. The detachable member may be a cap. 
     Attachment of the detachable member to the housing may be an operation which is carried out by a user. In this operation, the user may attach the previously detached detachable member to the housing, i.e. by screwing. Vice versa, detachment of the detachable member from the housing may be an operation wherein the detachable member is removed from the housing by the user, e.g. by screwing. 
     In one embodiment, the detachable member can be attached to the housing by screwing and detached from the housing by unscrewing. However, in alternative embodiments other means for attaching and detaching the detachable member are possible, e.g. the detachable member may be engageable with the housing via a bayonet connection or via a snap-fit mechanism. 
     The assembly provides the advantage of preventing a detachment from the housing with a minimal number of components. In particular, the first and the second abutment surface may be provided on members of the drug delivery device which are present in the drug delivery device anyway. Therefore, the assembly requires only minimal modifications of few elements of the drug delivery device and no further additional elements. 
     The design of the assembly ensuring that the detachable member can be reattached to the housing after it has been detached for the Nth time and is further prevented from being detached from the housing afterwards ensures that a user is warned that the device is considered to be empty. Thereby the user is prevented from trying to perform a drug delivery operation when no drug is left in the device. 
     The detachable member may be allowed to be rotated by a small angle relative to the housing when the detachable member is prevented from being detached from the housing. The small angle may be smaller than 10°, preferably smaller than 5°. The small angle may be in the range of 1° to 10°, preferably in the range of 1° to 5°. This feature may provide a very good warning to the user showing to the user that the operation of the drug delivery device is intentionally prevented. In particular, this design makes it obvious to the user that the drug delivery device is not damages as the detachable member is still movable by the small angle and, further, that the user is not supposed to operate the device any further as the range of motion of the detachable member has intentionally been limited to the small angle to indicate that the device is considered to be empty. 
     The detachable member may be rotatable relative to the housing by the small angle without damaging the detachable member or the housing. However, the detachable member may be prevented to be rotated by an angle bigger than the small angle relative to the housing in a way that such a rotation would result in a damaging of the detachable member and/or the housing. 
     In one embodiment, the first abutment surface is provided on a counting member comprising indicia and the second abutment surface is provided on a counter drive member. The counting member may be configured to follow a rotation of the counter drive member in the second rotational direction relative to the housing. The counting member may be prevented from following a rotation of the counter drive member in the first rotational direction relative to the housing. 
     In particular, a rotation of the counting member may increase or decrease a counted number. Further, the counter drive member may be configured to follow a rotation of the detachable member every time the detachable member is detached or attached to the housing. Thus, the assembly may be configured such that the counter drive member increases or decreases the counted number each time the detachable member is attached to the housing. The counter drive member may be constrained to rotate between a first and a second position. The first position of the counter drive member may corresponding to a configuration wherein the detachable member is attached to the housing. The second position of the counter drive member may correspond to a configuration wherein the detachable member is detached from the housing. Each time the detachable member alters its state from being attached to the housing to being detached from the housing, or vice versa, the counter drive member may be rotated. 
     In one embodiment, the counting member may be arranged such that one of the indicia is visible at any time through a window in the housing. Accordingly, this indicium may correspond to the currently counted number. As the counting member may be configured only to be rotated when the counter drive member rotates in the second rotational direction, the counting member may increase or decrease the counted number every time the counter drive member is moved from its second position to its first position. This may correspond to the counting member amending the counted number each time the detachable member is attached to the housing. 
     The predetermined number N may be determined by the position of the counting member relative to the housing. In particular, the predetermined number N may be determined by the initial position of the counting member relative to the housing, wherein the initial position is the position of the counting member relative to the housing after the assembly of the device is completed. This may be the position before the device is operated for the first time, i.e. before the first drug dispense operation is carried out. Accordingly, the assembly allows to set N to different values depending on the relative position of the counting member to the housing. Therefore, different drug delivery devices with different values of N may be constructed from the same components wherein the assembly process is modified in the respective relative position of the counting member to the housing to allow for different numbers N of possible operations. 
     The counter drive member and the counting member may be configured such that, when the first abutment surface abuts the second abutment surface, the counter drive member is prevented from rotating relative to the counting member. 
     The counter drive member may be rotated relative to the counting member during detachment of the detachable member from the housing. Further, the counter drive member may not be rotated relative to the counting member during attachment of the detachable member to the housing. Therefore, this design may ensure that the detachable member can be attached to the housing after it is detached for the Nth time and is further prevented from being detached from the housing afterwards. 
     The assembly may be configured such that, when the counter drive member is prevented from rotating relative to the counting member in the first rotational direction, the detachable member is prevented from rotation in the first rotational direction relative to the housing, thereby also being prevented from being detached from the housing. 
     Accordingly, the assembly is configured such that an abutment of two internal members, i.e. the counting member and the counter drive member, may prevent the detachment of the detachable member. As the counter drive member and the counting member are internal members, it is hardly possible for the user to override this mechanism preventing a detachment of the detachable member. Thus, the device is secure against operational mistakes of the user. 
     The drug delivery device may be configured such that a drug dispense operation is permitted only when the detachable member is detached from the housing. Accordingly, the abutment of the first and the second abutment surfaces may effectively prevent a further drug dispense operation. 
     The drug delivery device may be configured such that after a drug dispense operation has been carried out, the detachable member has to be reattached to the housing and, afterwards, the detachable member has to be detached from the housing to enable a subsequent drug dispense operation. 
     In particular, the detachable member may be configured to cover a mouthpiece of the drug delivery device when the detachable member is attached to the housing. 
     The detachable member may be configured such that, during detachment of the detachable member from the housing, the detachable member is rotated in a first rotational direction relative to the housing, wherein the detachable member is configured such that, during attachment of the detachable member to the housing, the detachable member is rotated in a second rotational direction relative to the housing which is opposite to the first rotational direction. 
     The detachable member may comprises a first projection and a second projection, wherein the counter drive member may comprise a protrusion, wherein the detachable member is configured such that, when the detachable member is rotated in the first rotational direction relative to the housing, the first projection engages the protrusion of the counter drive member such that the counter drive member follows the rotation of the detachable member in the first rotational direction, and wherein the detachable member is configured such that, when the detachable member is rotated in the second rotational direction relative to the housing, the second projection engage the protrusion of the counter drive member such that the counter drive member follows the rotation of the detachable member in the second rotational direction. 
     Accordingly, the counter drive member may be engaged with a different projection of the detachable member depending on the direction of the rotational movement of the detachable member. In particular, when the detachable member is first rotated in one direction and afterwards rotated in another rotational direction, the counter drive member may be disengaged from the detachable member for a short period of time wherein one of the projections is disengaged from the protrusion until the other of the projections engages the protrusion. This may be advantageous in case of a lock-out of the mechanism wherein the counter drive member may be prevented from moving and the detachable member is allowed to be rotated by a small angle before being prevented by the counter drive member from being rotated any further. As discussed above, this feature may provide a very good warning to the user showing to the user that the operation of the drug delivery device is intentionally prevented. 
     Further, the detachable member may be configured to engage with a metering rod during attachment of the detachable member to the housing. The assembly may be configured such that, during the attachment of the detachable member to the housing, the detachable member engages with the metering rod in a second relative position to said housing, and wherein said second relative position not being reachable during attachment before having passed a first relative position where a counted number is caused to be incremented or decremented either directly or during subsequent detachment. Thus, the assembly may be configured such that the detachable member engages with the metering rod after the incrementing or decrementing of a counted number has been initiated. 
     The engagement of the detachable member and the metering rod may be configured such that the metering rod follows a movement of the detachable member in the distal direction once the metering rod is engaged with the detachable member. Before engaging in this manner with each other, the detachable member may move the metering rod to its most proximal position during attachment of the detachable member. The engagement of the detachable member and the metering rod may be a snap-fit engagement. 
     In particular, the detachable member may comprise a snap-fit element that is configured to engage with the metering rod during attachment of the detachable member to the housing and that it is configured to be detached from the metering rod during detachment of the detachable member from the housing. The snap-fit element may force the metering rod to follow an axial movement of the detachable member when the snap-fit element is engaged with the metering rod. 
     In particular, the metering rod may be an element of a dose setting mechanism. The metering rod may have to be moved by the detachable member in the distal direction in order to set a subsequent dose of the drug. Thus, it may be ensured that it is impossible to set a subsequent dose, and thus to dispense a subsequent dose, after a drug dispense operation without previously incrementing or decrementing the counted number. The increment or decrement of the counted number may also correspond to a movement of the first and the second abutment surface closer to each other. 
     This design improves the safety of the assembly. In particular, this design may prevent a user from carrying out two subsequent drug dispense operations without incrementing or decrementing the counted number in between, i.e. without moving the first and the second abutment surface closer to each other. Accordingly, this design may ensure that it is not possible for the user to carry out more than N drug dispense operations. Accordingly, the safety of the device may be ensured by this feature as it is ensured that the lock-out of the mechanism cannot be prevented by the user. Thus, the user may be prevented from carrying out a drug dispense operation when the device is empty such that no drug or a too low dose of a drug would otherwise be dispensed. 
     The assembly may be configured such that during the attachment of the detachable member to the housing after the detachable member has been detached N times, the second relative position is not reachable during attachment before the detachable member has reached a configuration wherein it is no longer possible to detach the detachable member from the housing. 
     In particular, the assembly may be configured such that a projection projecting inwardly from the detachable member may engage with a corresponding outwardly protruding protrusion of a counter drive member before the detachable member engages with the metering rod in the second position during the attachment operation. The above-mentioned configuration may allow a movement of the detachable member relative to the housing but may prevent a detachment of the detachable member from the housing. 
     The detachable member may be allowed to be rotated by a small angle relative to the housing when the detachable member is prevented from being detached from the housing, and wherein the second relative position is within the small angle relative to the housing by which the detachable member is allowed to be rotated when the detachable member is prevented from being detached from the housing. This may ensure that the detachable member engages with the metering rod in a way that the metering rod follows a distal movement of the detachable member only after the counted number has been amended in the first N attachment operations. Further, this may ensure that the detachable member engages with the metering rod in a state wherein a detachment of the detachable member from the housing is no longer possible in the N+1th attachment operation. Accordingly, a user cannot manipulate the mechanism. In particular, it is not possible to remove a sub-quantity of the drug by partly attaching the detachable member and by, afterwards, removing the partly attached detachable member without incrementing or decrementing the counted number. 
     The detachable member may be configured to engage with the metering rod in such a manner that the metering rod removes a sub-quantity of a drug from a storage chamber during detachment of the detachable member from the housing, thereby setting the sub-quantity as a dose for the next drug dispense operation. 
     The metering rod may be configured to travel in the proximal direction during attachment of the detachable member from the housing. The metering rod may be in a most proximal position when the detachable member is fully attached to the housing. The detachable member may be configured to engage with the metering rod in a manner such that the metering rod follows a distal movement of the detachable member only when the metering rod is in its most proximal position. 
     The most proximal position of the metering rod may be a position wherein the metering rod has entered into the storage chamber. Accordingly, when the detachable member is fully attached to the housing, the metering rod may be in a position wherein it has entered into a storage chamber which comprises the drug. The assembly may be configured such that, after a drug dispense operation has been carried out, the metering rod has to be moved into its most proximal position to enable a subsequent drug dispense operation. Only when the metering rod has been moved into its most proximal position, the metering rod may be enabled to remove a sub-quantity of the drug from the storage chamber. 
     According to another aspect the present invention concerns a drug delivery device comprising the above-described assembly. 
     The assembly may be integrated in the device. In this way an improved, e.g. a compact and/or reliable and/or user-friendly, device may be achieved. 
     In the following text, a set of advantageous aspects is described. The aspects are numbered to facilitate referencing features of one aspect in other aspects. Features from the aspects are not only relevant in connection with the specific aspects they relate to but are also of relevance on their own. 
     1. An assembly for a drug delivery device comprising
         a housing,   a first abutment surface,   a second abutment surface, and   a detachable member which is detachable from the housing and attachable to the housing,   wherein the assembly is configured such that, during detachment of the detachable   member from the housing for an Nth time, N being a predetermined number, the first abutment surface is brought into abutment with the second abutment surface,   wherein the assembly is configured such that, when the first abutment surface abuts with the second abutment surface, the detachable member is enabled to be reattached to the housing and, afterwards, the detachable member is prevented from being detached from the housing.       

     2. The assembly according to aspect 1,
         wherein the detachable member is allowed to be rotated by a small angle relative to the housing when the detachable member is prevented from being detached from the housing.       

     3. The assembly according to one of the preceding aspects,
         wherein the first abutment surface is provided on a counting member comprising indicia,   wherein the second abutment surface is provided on a counter drive member,   wherein the counting member is configured to follow a rotation of the counter drive member in the second rotational direction relative to the housing and wherein the counting member is prevented from following a rotation of the counter drive member in the first rotational direction relative to the housing.       

     4. The assembly according to aspect 3,
         wherein the predetermined number N is determined by the position of the counting member relative to the housing.       

     5. The assembly according to one of aspects 3 or 4,
         wherein the counter drive member and the counting member are configured such that, when the first abutment surface abuts the second abutment surface, the counter drive member is prevented from rotating relative to the counting member.       

     6. The assembly according to one of aspects 3 to 5,
         wherein the assembly is configured such that, when the counter drive member is prevented from rotating relative to the counting member in the first rotational direction, the detachable member is prevented from rotation in the first rotational direction relative to the housing, thereby also being prevented from being detached from the housing.       

     7. The assembly according to one of the preceding aspects,
         wherein the drug delivery device is configured such that a drug dispense operation is permitted only when the detachable member is detached from the housing.       

     8. The assembly according to one of the preceding aspects,
         wherein the drug delivery device is configured such that, after a drug dispense operation has been carried out, the detachable member has to be reattached to the housing and, afterwards, the detachable member has to be detached from the housing to enable a subsequent drug dispense operation.       

     9. The assembly according to one of the preceding aspects,
         wherein the detachable member is configured to cover a mouthpiece of the drug delivery device when the detachable member is attached to the housing.       

     10. The assembly according to one of the preceding aspects,
         wherein the detachable member is configured such that, during detachment of the detachable member from the housing, the detachable member is rotated in a first rotational direction relative to the housing,   wherein the detachable member is configured such that, during attachment of the detachable member to the housing, the detachable member is rotated in a second rotational direction relative to the housing which is opposite to the first rotational direction.       

     11. The assembly according to one of the preceding aspects,
         wherein the detachable member comprises a first projection and a second projection,   wherein the counter drive member comprises a protrusion,   wherein the detachable member is configured such that, when the detachable member is rotated in the first rotational direction relative to the housing, the first projection engages the protrusion of the counter drive member such the counter drive member follows the rotation of the detachable member in the first rotational direction, and   wherein the detachable member is configured such that, when the detachable member is rotated in the second rotational direction relative to the housing, the second projection engages the protrusion of the counter drive member such the counter drive member follows the rotation of the detachable member in the second rotational direction.       

     12. The assembly according to one of the preceding aspects,
         wherein the detachable member is configured to engage with a metering rod during attachment of the detachable member to the housing, and   wherein the assembly is configured such that, during the attachment of the detachable member to the housing, the detachable member engages with the metering rod in a second relative position to said housing, and wherein said second relative position not being reachable during attachment before having passed a first relative position where a counted number is caused to be incremented or decremented either directly or during subsequent detachment.       

     13. The assembly according to aspect 12,
         wherein the assembly is configured such that during the attachment of the detachable member to the housing after the detachable member has been detached N times, the second relative position is not reachable during attachment before the detachable member has reached a configuration wherein it is no longer possible to detach the detachable member from the housing.       

     14. The assembly according to aspect 12 or 13,
         wherein the detachable member is allowed to be rotated by a small angle relative to the housing when the detachable member is prevented from being detached from the housing, and   wherein the second position of the detachable member relative to the housing is within the small angle relative to the housing by which the detachable member is allowed to be rotated when the detachable member is prevented from being detached from the housing.       

     15. The assembly according to one of aspects 12 to 14,
         wherein the detachable member is configured to engage with the metering rod in such a manner that the metering rod removes a sub-quantity of a drug from a storage chamber during detachment of the detachable member from the housing, thereby setting the sub-quantity as a dose for the next drug dispense operation.       

     16. The assembly according to one of aspects 12 to 15,
         wherein the metering rod is configured to travel in the proximal direction during attachment of the detachable member to the housing,   wherein the metering rod is in a most proximal position when the detachable member is fully attached to the housing,   wherein the detachable member is configured to engage with the metering rod in a manner such that the metering rod follows a distal movement of the detachable member only when the metering rod is in its most proximal position.       

     17. Drug delivery device comprising an assembly according to one of the preceding aspects. 
     Another aspect of the present disclosure related to an improved assembly for a drug delivery device, e.g. a mechanism allowing to count a counted number requiring a low number of components. This aspect of the present disclosure relates to an assembly. 
     This aspect may be present in an assembly for a drug delivery device, in particular in an assembly for a dry powder inhaler or a metering inhaler, additionally or alternatively to the above discussed aspects. 
     The assembly according to this aspect may be suitable to be used in a counter mechanism for a drug delivery device. The device may be an inhalation device, in particular a dry powder inhalator. The device may be adapted for dispensing a plurality of doses of a drug or substance. 
     An assembly for a drug delivery device is provided which comprises a housing, a counter drive member configured to increase or decrease a counted number when the counter drive member is rotated in a second rotational direction relative to the housing, and a detachable member which is detachable from the housing and attachable to the housing, wherein the detachable member is configured such that, during detachment of the detachable member from the housing, the detachable member is rotated in a first rotational direction relative to the housing and the counter drive member follows the rotation of the detachable member in the first rotational direction, and wherein the detachable member is configured such that during attachment of the detachable member to the housing the detachable member is rotated in the second rotational direction relative to the housing which is opposite to the first rotational direction and the counter drive member follows the rotation of the detachable member in the second rotational direction. 
     Accordingly, the assembly may be configured such that the counter drive member increases or decreases the counted number each time the detachable member is attached to the housing. The assembly may be configured to provide information regarding the number of attachment processes carried out. In particular, each time the detachable member is detached and afterwards reattached to the housing, a drug dispense operation may be performed. Therefore, the counted number may correspond to the number of drug dispense operations which have been carried out or, alternatively, the counted number may correspond to the number of drug dispense operations which are still possible before the device is considered to be empty. 
     The drug delivery device may be configured such that after detachment of the detachable member and before reattachment of the detachable member to the housing, at the most one drug dispense operation can be carried out. Accordingly, if the counted number is increased or decreased every time the detachable member is attached, the counter drive member may provide information about the minimum number of possible drug dispense operations. In this case, the counted number may corresponds to the minimum number of doses left in the device. 
     The assembly may be an assembly for a counter mechanism configured to count the number of doses left in the device or, alternatively, to count the number of possible drug dispense operations which may be carried out before the device is considered to be empty. 
     The housing may be an external component of the drug delivery device. In particular, the housing may cover further elements of the drug delivery device. 
     The counter drive member may be configured to interact with further elements of a counting mechanism, e.g. with a counting member comprising indicia. The indicia may be numbers printed on an outer surface of the counting member. 
     In an alternative design, the counter drive member may itself comprise indicia and may be configured to display the counted number. 
     The counter drive member may be constrained to rotate between a first and a second position. The first position of the counter drive member may correspond to a configuration wherein the detachable member is attached to the housing. The second position of the counter drive member may correspond to a configuration wherein the detachable member is detached from the housing. Each time the detachable member alters its state from being attached to the housing to being detached from the housing or vice versa, the counter drive member may be moved. In particular, the counter drive member may follow a rotation of the detachable member in this situation. 
     The counter drive member may be configured to trigger a counting of a counting member, i.e. to trigger an increase or a decrease of the counted number. The counter drive member may be configured to transfer a movement of the detachable member into a movement of the counting member. 
     The detachable member being detachable from the housing may mean in this context that the detachable member can be completely removed from the housing such that it has no contact at all to the housing. When the detachable member is attached to the housing, the detachable member may cover at least a part of the housing. In particular, the detachable member may cover a part of the housing which comprises a mouthpiece such that no drug can be dispensed from the mouthpiece when the detachable member is attached to the housing. Thereby, the detachable member may effectively prevent a drug dispense operation when attached to the housing. The detachable member may be a cap. 
     Attachment of the detachable member to the housing may be an operation which is carried out by a user. In this operation, the user may attach the previously detached detachable member to the housing, e.g. by screwing. Vice versa, detachment of the detachable member from the housing may be an operation wherein the detachable member is removed from the housing by the user, e.g. by screwing. 
     In one embodiment, the detachable member can be attached to the housing by screwing and detached from the housing by unscrewing. However, in alternative embodiments other means for attaching and detaching the detachable member are possible, e.g. the detachable member may be engageable with the housing via a bayonet connection or via a snap-fit mechanism. 
     The assembly provides the advantage of allowing the counting of a counted number with a minimal number of components. In particular, only the counter drive member and the counting member are required as additional components compared to a drug delivery device not comprising a counting mechanism. Moreover, this design of the counting mechanism requires only minimal modifications of other elements of the drug delivery device. 
     The counter drive member may be constrained such that it can only carry out a helical movement relative to the housing. The detachable member may be constrained such that it can only out a helical movement relative to the housing. The counter drive member and the detachable member may be configured such that, when the counter drive member follows a rotational movement of the detachable member, the counter drive member carries out a helical movement with an axial component being directed opposite to an axial component of the helical movement carried out by the detachable member. 
     Each helical movement comprises a rotational component and an axial component. The detachable member may be constrained in its movement to carry out a helical movement relative to the housing only when the detachable member is in contact to the housing. After the detachable member is completely detached from the housing, the detachable member may be free to carry out any arbitrary movement relative to the housing. However, during attachment to and detachment from the housing, the detachable member may be constrained such that it can only carry out a helical movement relative to the housing of the drug delivery device. 
     As the counter drive member and the detachable member may move in different axial directions when the counter drive member follows a rotational movement of the detachable member, they may be designed such that they are disengaged at a predefined point during this rotational movement of the detachable member. Further, the axial component of the helical movement carried out by the counter drive member and the axial component of the helical movement carried out by the detachable member may differ in their amplitude. The amplitude of the respective axial component may be defined by a slope of a thread along which the respective element runs. 
     The counter drive member may comprise a protrusion. The detachable member may comprise a first projection and a second projection. The detachable member may be configured such that, when the detachable member rotates in the first rotational direction, the first projection engages the protrusion of the counter drive member such that the counter drive member follows the rotation of the detachable member in the first rotational direction. The detachable member may be configured such that, when the detachable member rotates in the second rotational direction, the second projection engages the protrusion of the counter drive member such that the counter drive member follows the rotation of the detachable member in the second rotational direction. 
     Accordingly, the counter drive member may be engaged with a different projection of the detachable member depending on the direction of the rotational movement of the detachable member. In particular, when the detachable member is first rotated in one direction and afterwards rotated in another rotational direction, the counter drive member may be disengaged from the detachable member for a short period of time wherein one of the projections is disengaged from the protrusion until the other of the projections engages the protrusion. This may be advantageous in case of a lock-out of the mechanism wherein the counter drive member may be prevented from moving and the detachable member is allowed to be rotated by a small angle before being blocked by the counter drive member from being rotated any further. The small angle may be in the range of 1° to 10°, preferably in the range of 1° to 5°. This feature may provide a very good warning to the user showing to the user that the operation of the drug delivery device is intentionally prevented. 
     The protrusion of the counter drive member be inclined relative to an azimuthal direction. The azimuthal direction is a direction defined by a circle around a rotational axis of the drug delivery device wherein the circle lies in a plane that is perpendicular to the rotational axis of the drug delivery device. 
     In particular, when the counter drive member is constrained to carry out a helical movement, the protrusion may slide along a correspondingly inclined ramp of the housing, thereby allowing the counter drive member to move along its helical path relative to the housing with a minimal friction. The angle of inclination may define the amplitude of the axial component of a helical movement carried out by the counter drive member. 
     The first and the second projection of the detachable member may be spaced apart in the azimuthal and in the axial direction. This design may ensure that the first projection engages with the protrusion of the counter drive member during detachment of the detachable member and that the second projection engages with the counter drive member during attachment of the detachable member. The projections may be arranged at an inner surface of the detachable member. 
     The housing may comprise a cut-out. The counter drive member may be arranged at least partially inside the housing. The detachable member may be arranged outside of the housing. The protrusion of the counter drive member may protrude through the cut-out of the housing. 
     The cut-out of the housing may have an inclined form. Thus, if the protrusion is also inclined relative to the azimuthal direction, the protrusion and the inclined cut-out are configured to interact with each other with a minimal friction wherein the cut-out forces the counter drive member to travel along a helical path when rotated relative to the housing. As the protrusion of the counter drive member may protrude through the cut-out of the housing, the counter drive member may be allowed to interact with the detachable member which may be arranged outside of the housing. 
     During the detachment of the detachable member from the housing, the detachable member may be configured to carry out a detachment movement comprising a first part wherein the detachable member rotates in the first rotational direction relative to the housing and a subsequent second part wherein the detachable member rotates in the first rotational direction relative to the housing. The detachable member and the counter drive member may be configured such that, during detachment of the detachable member from the housing, the counter drive member follows only the first part of the detachment movement of the detachable member. The first part may be an initial part of the detachment movement. 
     Further, during the attachment of the detachable member to the housing, the detachable member may be configured to carry out an attachment movement comprising a first part wherein the detachable member rotates in the second rotational direction relative to the housing and a subsequent second part wherein the detachable member rotates in the second rotational direction relative to the housing. The detachable member and the counter drive member may be configured such that, during attachment of the detachable member to the housing, the counter drive member follows only the second part of the attachment movement of the detachable member. The second part may be a final part of the attachment movement. 
     The counter drive member may comprise a spring element biasing the counter drive member in an axial direction. This may ensure that the counter drive member stays in its second position when the detachable member is detached from the housing. 
     The counter drive member may comprise a slot in the axial direction. The slot may ensure that the counter drive member can be compressed during a manufacturing process such that it can be inserted into the housing. Once the manufacturing is completed, the counter drive member may be allowed to release its tension and to extend in the radial direction, thereby enlarging the slot and engaging properly with the housing. Accordingly, the counter drive member may be a C-shaped element. 
     The assembly may further comprise a counting member having indicia which correspond to the counted number. The counting member may be configured to follow a rotation of the counter drive member in the second rotational direction relative to the housing. The counting member may be prevented from following a rotation of the counter drive member in the first rotational direction relative to the housing. 
     In one embodiment, the counting member may be arranged such that one of the indicia is visible at any time through a window in the housing. Accordingly, this one of the indicia may correspond to the currently counted number. As the counting member may be configured only to be rotated when the counter drive member rotates in the second rotational direction, the counting member may increase or decrease the counted number every time the counter drive member is moved from its second position to its first position. This may correspond to the counting member amending the counted number each time the detachable member is attached to the housing. 
     The counting member may be constrained such that it can only carry out a helical movement relative to the housing of the drug delivery device. The counting member may be configured such that the helical movement has an axial component in the distal direction. Accordingly, the counting member may be move closer towards the distal end of the drug delivery device every time the detachable member is attached. 
     The counting member may be arranged inside the housing. The housing may comprise an inner surface having axially extending ribs. The counting member may comprise a claw being engaged with the axially extending ribs. The axially extending ribs of the housing and the claw of the counting member may be configured to allow a rotation of the counting member in the second rotational direction relative to the housing and to prevent a rotation of the counting member in the first rotational direction relative to the housing. 
     For this purpose, the claw and the axially extending ribs may comprise correspondingly tapered surfaces. This configuration may prevent that the counting member is rotated in the first rotational direction, thereby unintentionally amending the counted number. 
     The assembly may be configured such that the drug dispense operation is permitted only when the detachable member is detached from the housing. The assembly may be configured such that, after a drug dispense operation has been carried out, the detachable member has to be reattached to the housing and, afterwards, the detachable member has to be detached from the housing to enable a subsequent drug dispense operation. This design may ensure that the counted number is incremented or decremented at least each time a drug dispense operation is carried out. In particular, the counter drive member may rotate in the second rotational direction every time the detachable member is attached to the housing. 
     In the following text, a set of advantageous aspects is described. The aspects are numbered to facilitate referencing features of one aspect in other aspects. Features from the aspects are not only relevant in connection with the specific aspects they relate to but are also of relevance on their own. 
     1. Assembly for a drug delivery device, comprising
         a housing,   a counter drive member configured to increase or decrease a counted number when the counter drive member is rotated in a second rotational direction relative to the housing, and   a detachable member which is detachable from the housing and attachable to the housing,   wherein the detachable member is configured such that, during detachment of the detachable member from the housing, the detachable member is rotated in a first rotational direction relative to the housing and the counter drive member follows the rotation of the detachable member in the first rotational direction, and   wherein the detachable member is configured such that, during attachment of the detachable member to the housing, the detachable member is rotated in the second rotational direction relative to the housing which is opposite to the first rotational direction and the counter drive member follows the rotation of the detachable member in the second rotational direction.       

     2. Assembly according to aspect 1,
         wherein the counter drive member is constrained such that it can only carry out a helical movement relative to the housing,   wherein the detachable member is constrained such that it can only carry out a helical movement relative to the housing, and   wherein the counter drive member and the detachable member are configured such that, when the counter drive member follows a rotational movement of the detachable member, the counter drive member carries out a helical movement with an axial component being directed opposite to an axial component of the helical movement carried out by the detachable member.       

     3. Assembly according to one of the preceding aspects,
         wherein the counter drive member comprises a protrusion,   wherein the detachable member comprising a first projection and a second projection, and   wherein the detachable member is configured such that, when the detachable member rotates in the first rotational direction, the first projection engages the protrusion of the counter drive member such the counter drive member follows the rotation of the detachable member in the first rotational direction, and   wherein the detachable member is configured such that, when the detachable member rotates in the second rotational direction, the second projection engages the protrusion of the counter drive member such that the counter drive member follows the rotation of the detachable member in the second rotational direction.       

     4. Assembly according aspect 3,
         wherein the protrusion of the counter drive member is inclined relative to an azimuthal direction.       

     5. Assembly according to one of aspects 3 or 4,
         wherein the first and the second projection of the detachable member are spaced apart in an azimuthal direction and in an axial direction.       

     6. Assembly according to one of aspects 3 to 5,
         wherein the housing comprises a cut-out,   wherein the counter drive member is arranged at least partially inside the housing,   wherein the detachable member is arranged outside of the housing, and   wherein the protrusion of the counter drive member protrudes through the cut-out of the housing.       

     7. Assembly according to one of the preceding aspects,
         wherein, during the detachment of detachable member from the housing, the detachable member is configured to carry out a detachment movement comprising a first part   wherein the detachable member rotates in the first rotational direction relative to the housing and a subsequent second part wherein the detachable member rotates in the first rotational direction relative to the housing,   wherein the detachable member and the counter drive member are configured such that, during detachment of the detachable member from the housing, the counter drive member follows only the first part of the detachment movement of the detachable member.       

     8. Assembly according to one of the preceding aspects,
         wherein, during the attachment of detachable member to the housing, the detachable member is configured to carry out an attachment movement comprising a first part   wherein the detachable member rotates in the second rotational direction relative to the housing and a subsequent second part wherein the detachable member rotates in the second rotational direction relative to the housing,   wherein the detachable member and the counter drive member are configured such that, during attachment of the detachable member to the housing, the counter drive member follows only the second part of the attachment movement of the detachable member.       

     9. Assembly according to one of the preceding aspects,
         wherein the counter drive member comprises a spring element biasing the counter drive member in an axial direction.       

     10. Assembly according to one of the preceding aspects,
         wherein the counter drive member comprises a slot in an axial direction.       

     11. Assembly according to one of the preceding aspects,
         further comprising a counting member having indicia which correspond to the counted number,   wherein the counting member is configured to follow a rotation of the counter drive member in the second rotational direction relative to the housing, and   wherein the counting member is prevented from following a rotation of the counter drive member in the first rotational direction relative to the housing.       

     12. Assembly according to aspect 11,
         wherein the counting member is constrained such that it can only carry out a helical movement relative to the housing.       

     13. Assembly according to one of aspects 11 or 12,
         wherein the counting member is arranged inside the housing,   wherein the housing comprises an inner surface having axially extending ribs,   wherein the counting member comprises a claw being engaged with the axially extending ribs, and   wherein the axially extending ribs of the housing and the claw of the counting member are configured to allow a rotation of the counting member in the second rotational direction relative to the housing and to prevent a rotation of the counting member in the first rotational direction relative to the housing.       

     14. The assembly according to one of the preceding aspects,
         wherein the assembly is configured such that a drug dispense operation is permitted only when the detachable member is detached from the housing, and   wherein the assembly is configured such that, after a drug dispense operation has been carried out, the detachable member has to be reattached to the housing and, afterwards, the detachable member has to be detached from the housing to enable a subsequent drug dispense operation.       

     15. Drug delivery device comprising an assembly according to one of the preceding aspects. 
     The term “drug” or “substance”, as used herein may mean a pharmaceutical formulation containing at least one pharmaceutically active compound, for example for the treatment of obstructive airway or lung diseases such as asthma or chronic obstructive pulmonary disease (COPD), local respiratory tract oedema, inflammation, viral, bacterial, mycotic or other infection, allergies, diabetes mellitus. 
     The active pharmaceutical compound is preferably selected from the group consisting of active pharmaceutical compounds suitable for inhalation, preferably antiallergenic, antihistamine, anti-inflammatory, antitussive agents, bronchodilators, anticholinergic drugs, and combinations thereof. 
     The active pharmaceutical compound may for example be chosen from: 
     an insulin such as human insulin, e.g. a recombinant human insulin, ora human insulin analogue or derivative, a 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; 
     an adrenergic agent such as a short acting β2-agonists (e.g. Salbutamol, Albuterol, Levosalbutamol, Fenoterol, Terbutaline, Pirbuterol, Procaterol, Bitolterol, Rimiterol, Carbuterol, Tulobuterol, Reproterol), a long acting β2-agonist (LABA, e.g. Arformoterol, Bambuterol, Clenbuterol, Formoterol, Salmeterol), an ultra LABA (e.g. Indacaterol) or another adrenergic agent (e.g. Epinephrine, Hexoprenaline, Isoprenaline (Isoproterenol), Orciprenaline (Metaproterenol)); 
     a glucocorticoid (e.g. Beclometasone, Budesonide, Ciclesonide, Fluticasone, Mometasone, Flunisolide, Betamethasone, Triamcinolone); 
     an anticholinergic agent or muscarinic antagonist (e.g. Ipratropium bromide, Oxitropium bromide, Tiotropium bromide); 
     a mast cell stabilizer (e.g. Cromoglicate, Nedocromil); 
     a xanthine derivative (e.g. Doxofylline, Enprofylline, Theobromine, Theophylline, Aminophylline, Choline theophyllinate); 
     an eicosanoid inhibitor, such as a leukotriene antagonist (e.g. Montelukast, Pranlukast, Zafirlukast), a lipoxygenase inhibitor (e.g. Zileuton) or a thromboxane receptor antagonist (e.g. Ramatroban, Seratrodast); 
     a phosphodiesterase type- 4  inhibitor (e.g. Roflumilast); 
     an antihistamine (e.g. Loratadine, Desloratadine, Cetirizen, Levocetirizine, Fexofenadine); 
     an allergen immunotherapy (e.g. Omalizumab); 
     a mucolytic (e.g. Carbocisteine, Erdosteine, Mecysteine); an antibiotic or antimycotic; 
     or a combination of any two, three or more of the above-mentioned compound classes or compounds (e.g. Budesonide/Formoterol, Fluticasone/Salmeterol, Ipratropium bromide/Salbutamol, Mometasone/Formoterol); 
     or a pharmaceutically acceptable salt or solvate or esters of any of the above named compounds. 
     Pharmaceutically acceptable salts are for example acid addition salts and basic salts. Acid addition salts are e.g. a chloride, bromide, iodide, nitrate, carbonate, sulfate, methylsulfate, phosphate, acetate, benzoate, benzenesulfonate, fumarate, malonate, tartrate, succinate, citrate, lactate, gluconate, glutamate, edetate, mesylate, pamoate, pantothenate or a hydroxy-naphthoate salt. Basic salts are for example salts having a cation selected from alkali or alkaline, e.g. Na+, or K+, or Ca2+, or an ammonium ion N+(R1)(R2)(R3)(R4), wherein R1 to R4 independently of each other mean: hydrogen, an optionally substituted C1 C6-alkyl group, an optionally substituted C2-C6-alkenyl group, an optionally substituted C6-C10-aryl group, or an optionally substituted C6-C10-heteroaryl group. Further examples of pharmaceutically acceptable salts are described in “Remington&#39;s Pharmaceutical Sciences” 17. ed. Alfonso R. Gennaro (Ed.), Mark Publishing Company, Easton, Pa., U.S.A., 1985 and in Encyclopedia of Pharmaceutical Technology. Pharmaceutically acceptable ester may for example be acetates, propionates, phosphates, succinates or etabonates. 
     Pharmaceutically acceptable solvates are for example hydrates. 
    
    
     
       Further features and refinements become apparent from the following description of the exemplary embodiments in connection with the accompanying figures. 
         FIGS. 1A and 1B  schematically show a perspective view of a drug delivery device, 
         FIG. 10  schematically shows a sectional side view of the drug delivery device of  FIGS. 1A and 1B , 
         FIG. 2  shows a perspective view of a counting member, 
         FIG. 3  shows a perspective view of a counter drive member, 
         FIG. 4  shows a cross-sectional view of a detachable member, 
         FIG. 5A  and  FIG. 5B  show perspective views of a housing, 
         FIG. 5C  shows an enlarged view of a part of the housing, 
         FIG. 6  shows a perspective view of a storage chamber, 
         FIG. 7  shows a perspective view of a spring housing, 
         FIG. 8  shows a perspective view of a bottom lid, 
         FIG. 9  shows an exploded view of the drug delivery device, 
         FIGS. 10, 11 and 12  indicate the assembly process of the device, 
         FIG. 13  shows an enlarged view of a part of the device in a state wherein the detachable member is completely attached to the housing, 
         FIG. 14  shows an enlarged view of a part of the device in a state wherein the detachable member is partly detached from the housing, 
         FIGS. 15 and 16  show details of the interaction of the counter drive member and the counting member during the detachment of the detachable member, 
         FIG. 17  shows details of the interaction of the counting member and the housing, 
         FIG. 18  shows a detailed view of a part of the device at the end of the first part of the attachment movement, 
         FIG. 19  shows a detailed view of a part of the device at the end of the attachment movement, 
         FIG. 20  shows the interaction of the counter drive member and the counting member during the attachment of the attachable member to the housing, 
         FIG. 21  shows a perspective view of the interaction of the counter drive member and the counting member when the detachable member has been detached N times, 
         FIG. 22  shows the interaction of the counter drive member and the detachable member in a configuration wherein the detachable member has been detached N times and, afterwards, has been reattached to the housing, and 
         FIGS. 23 and 24  show a transportation lock of a bottom unit. 
     
    
    
     Like elements, elements of the same kind and identically acting elements may be provided with the same reference numerals in the figures. 
     In  FIGS. 1A, 1B and 10 , an inhalation device  1  is shown. The inhalation device  1  comprises a housing  3 . The device  1  comprises an outer cylinder  4 . The outer cylinder  4  is secured against axial movement with respect to the housing  3 . The outer cylinder  4  is rotatable with respect to the housing  3 . The inhalation device  1  further comprises a mouthpiece  6 . The device  1  and the housing  3  have a distal end  41  and a proximal end  42 . The term “distal end” designates that end of the device  1  or a component thereof which is or is to be arranged closest to the mouthpiece  6 . The term “distal end” designates that end of the device  1  or a component thereof which is or is to be arranged closest to the dispensing end. The term “proximal end” designates that end of the device  1  or a component thereof which is or is to be arranged furthest away from the mouthpiece  6 . The term “proximal end” designates that end of the device  1  or a component thereof which is or is to be arranged furthest away from the dispensing end. The distal end  41  and the proximal end  42  are spaced apart from one another in the direction of an axis  16 . The axis  16  may be the main longitudinal axis or rotational axis of the device  1 . 
     The inhalation device  1  comprises a detachable member  7 . In particular, the detachable member  7  is a cap. The detachable member  7  is used for covering the mouthpiece  6 . In  FIGS. 1B and 10 , the detachable member  7  is mounted onto the device  1  for covering the mouthpiece  6 . In  FIG. 1A , the detachable member  7  is removed from the device  1 . The detachable member  7  may comprise a thread, preferably a screw thread. The detachable member  7  may be rotatable with respect to the housing  3  for screwing the detachable member  7  onto the device  1  and for unscrewing the detachable member  7  from the device  1 . The outer cylinder  4  is rotationally fixed to the detachable member  7 . In particular, the outer cylinder  4  follows rotation of the detachable member  7  with respect to the housing  3 . For the detailed description of the components of the inhalation device  1  and their mechanical cooperation it is referred to document WO 2009/065707 A1. 
     The device  1  comprises a storage chamber  15 . The storage chamber  15  holds one dose, preferably a plurality of doses, of a medical substance  2 . The substance  2  may be a powder. In particular, the plurality of doses may correspond to a predefined number of doses, such that after the predefined number of doses has been delivered a lock-out mechanism (not explicitly shown in the Figures) may prevent a further operation of the device. 
     A numerical value corresponding to the predefined number of doses is a starting value of a counting mechanism. Before delivery of a first dose, the counting mechanism displays this predefined number as the number of available doses and with every dose delivery the number is decremented. Alternatively, the counting mechanism may display the number of doses that already have been delivered. In this case, the counting mechanism displays “0” as predefined number before delivery of the first dose and with every dose delivery the number is incremented. The counting mechanism is not shown in  FIGS. 1A, 1B, 1C , but the dose counting mechanism will be discussed later on in detail. 
     The storage chamber  15  is terminated by a chamber sealing  24 . The chamber sealing  24  is formed integrally with a top wall of the storage chamber  15 . The device  1  further comprises a rotary part  25 . The rotary part  25  is of substantially plate-like configuration and is connected in a rotationally fixed manner to the outer cylinder  4 . Accordingly, the rotary part  25  follows rotation of the detachable member  7  and, hence, of the outer cylinder  4  about the main longitudinal axis or rotational axis  16  of the device  1  with respect to the storage chamber  15 . However, the rotary part  25  is axially fixed relative to the housing  3 . 
     The device  1  further comprises a metering rod  33 . The metering rod  33  may be connected to the detachable member  7  by a snap fit element  34  when the detachable member  7  is attached to the housing  3 . When the detachable member  7  is re-attached to the housing  3 , the metering rod  33  travels axially in the proximal direction such that a most proximal part of the metering rod  33  comprising a metering chamber  40  enters the storage chamber  15 . When the detachable member  7  is detached from the housing  3  the metering rod  33  travels axially in the distal direction such that the most proximal part of the metering rod  33  exits the storage chamber  15 . The metering rod  33  is configured for functioning as a moving metering chamber  40  for a sub-quantity  14  of the substance  2  which is to be dispensed during a specific delivery action. The metering chamber  40  is provided in that end section of the metering rod  33  which projects into the substance  2 , e.g. the proximal end section. 
     The inhalation device  1  further comprises a flow path comprising a flow channel  60  and an intermediate channel portion  61 . The inhalation device  1  further comprises an actuation element  54 . The actuation element  54  is arranged within an actuator housing  35 . The actuator housing  35  is configured substantially as a hollow body. The actuator housing  35  is secured against axial movement with respect to the housing  3 . The actuator housing  35  is adapted and arranged to guide an axial movement of the actuation element  54 . The actuator housing  35  is arranged within the inner cylinder  4 . The actuation element  54  and the actuator housing  35  are prevented from rotation with respect to one another. 
     The actuation element  54  comprises a piston comprising tongues  77  and a head  76 . The actuation element  54  has a first and a second position. The first position is more proximal than the second position. In the first position, the tongues  77  of the actuation element  54  are configured to block the flow path between the flow channel  60  and the intermediate channel portion  61 . In the second position, the actuation element  54  is positioned more distally, i.e. closer to the mouthpiece  6 , such that the tongues  77  no longer block the flow path between the flow channel  60  and the intermediate channel portion  61 . 
     The detachable member  7  is removed from the housing  3  by unscrewing the detachable member  7  from the housing  3 . Accordingly, the detachable member  7  performs a concurrent axial movement in the distal direction and a rotational movement. The detachable member  7  and the rotary part  25  are in a splined engagement when the detachable member  7  is attached to the housing  3 . During detachment of the detachable member  7  from the housing  3 , the rotational movement of the detachable member  7  is transferred into a rotation of the rotary part  25  around the longitudinal axis  16  due to their splined engagement. The rotation of the rotary part  25  is transferred into a rotation of the actuation element  54 . Furthermore, the concurrent axial and rotational movement of the detachable member  7  is transferred to the metering rod  33  concurrently performing an axial movement in the distal direction and a rotational movement around the longitudinal axis  16 . As the detachable member  7  approaches the end of the threaded connection to the housing  3 , the snap fit element  34  disengages from the metering rod  33 . During detachment of the detachable member  7  from the housing  3 , the actuation element  54  is not moved in an axial direction with respect to the housing  3 . Accordingly, the actuation element  54  is in the first position before and after detachment of the detachable member  7  from the housing  3 . 
     When the detachable member  7  is fully detached from the housing  3 , the metering chamber  40  is in a first condition. The first condition of the metering chamber  40  is defined by the tongues  77  of the actuation element  54  closing the metering chamber  40  such that the metering chamber  40  is not in contact with the flow path. Accordingly, when the actuation element  54  is in the first position and the detachable member  7  is detached from the housing  3 , the metering chamber  40  is in the first condition. In the first condition of the metering chamber  40 , the tongues  77  of the actuation element  54  cover the metering chamber  40  on each side. Accordingly, in this first condition, it is not possible for the sub-quantity  14  of substance to trickle out. Rather, the substance  2  is reliably retained in the metering chamber  40 . 
     After the detachable member  7  has been demounted or detached from the housing, the user may trigger an inhalation operation by subjecting the device to a suction airstream, in the simplest case by the user breathing in. Air is sucked in via the mouthpiece  6 , and this, in first instance, by virtue of the head  76  being subjected to the action of air, results in the actuation element  54  being displaced axially towards the mouthpiece  6 , i.e. in the distal direction. By virtue of the axially displaced actuation element  54 , the tongues  77  are likewise displaced axially, in order to release the metering chamber  40 . The metering chamber  40  is then in a second condition. The second condition of the metering chamber  40  is defined by the actuation element  54  being in the second position. In the second condition, the metering chamber  40  lies freely in the flow path between the flow channel  60  and the intermediate channel portion  61 . The metering chamber  40  is cleared out with air being sucked from the flow channel  60 . 
     After the inhalation operation was finished, the detachable member  7  can be re-attached to the housing  3 . During attachment of the detachable member  7  to the housing  3 , the detachable member  7  is moved axially in the proximal direction and concurrently rotated around the longitudinal axis  16 . During this movement of the detachable member  7 , the detachable member  7  abuts the metering rod  33  and pushes the metering rod  33  in the proximal direction. In an initial part of the attachment movement of the detachable member  7 , the detachable member  7  does not engage with the metering rod  33  via the snap fit element  34 , but only pushes the metering rod  33  in the proximal direction. Accordingly, if the user tried to move the detachable member in the distal direction during this initial part of the movement, the metering rod  33  would not follow such a movement of the detachable member  7  in the distal direction. Therefore, if the user only partly attached the detachable member  7  and then detached the detachable member  7 , the user could not move the metering rod  33  in the distal direction in this way. 
     During the initial part of the attachment movement, the detachable member  7  passes a first position relative to the housing  3 . In the first relative position, the detachable member  7  interacts with the counter drive member  19 , thereby a counted number is caused to be incremented or decremented either directly or during subsequent detachment. 
     During a second part of the attachment movement of the detachable member  7  to the housing  3 , the detachable member  7  engages with the metering rod  33  via the snap fit element  34 . The second part of the movement follows after the initial part of the movement is finished. In particular, at the end of the initial part which corresponds to the beginning of the second part, the metering rod  33  has been moved in the proximal direction so far that it abuts an end of travel face preventing a further pushing of the metering rod  33  in the proximal direction. Further, at the beginning of the second part of the attachment movement, the detachable member  7  is in a second position relative to the housing  3 . This second position cannot be reached without having passed the first relative position previously. In the second part of the attachment movement, the detachable member  7  continues to travel in the proximal direction. This causes the engagement of the snap fit element  34  with the metering rod  33 . 
     Accordingly, the metering rod  33  is moved into the proximal direction when the detachable member  7  is attached to the housing  3 . Further, the metering rod  33  follows a rotation of the detachable member  7  in the second part of the attachment movement. During re-attachment of the detachable member  7  to the housing  3 , the metering rod  33  is moved in the proximal direction due to the interaction with the detachable member  7 . Movement of the metering rod  33  in the proximal direction is transferred to the actuation element  54  (if the actuation element  54  is in the second position). Thereby, the actuation element  54  is moved from the second position to the first position. However, in case that the detachable member  7  is detached from the housing  3  and, afterwards, re-attached to the housing  3  without a drug delivery being performed in the meantime, the actuation element  54  remains in the first position the whole time. Accordingly, as the actuation element  54  is already in the first position, it cannot be moved axially during attachment of the detachable member  7  to the housing  3 . 
       FIG. 2  shows a perspective view of a counting member  5 . The counting member  5  has a tubular shape. The counting member  5  defines a longitudinal axis which is parallel to the rotational axis  16  of the inhalation device  1 . The counting member  5  comprises an outer surface  8  and an inner surface  9 . The counting member  5  comprises indicia  10 . The indicia  10  are arranged on the outer surface  8  of the counting member  5 . The counting member  5  is configured to be arranged inside the housing  3  such that at least one of the indicia  10  is visible through a window  89  of the housing  3 . The indicia  10  are numbers corresponding to the number of doses left in the device  1  or to the numbers of dispensed doses. Alternatively or additionally, the indicia  10  may be color-coded. For example, the indicia  10  may be coloured such that, when only a low number of doses is left in the device, e.g. five doses, the colour of the indicia  10  visible in the window may change, warning the user that the device  1  will have to be replaced soon. 
     Moreover, the counting member  5  comprises gear teeth  11  which are arranged on the outer surface  8 . The gear teeth  11  are arranged along a helical path. As will be described in detail later on, the gear teeth  11  are configured to interact with an engagement feature of a counter drive member. In particular, the gear teeth  11  are shaped such that the counting member  5  follows a rotation of the counter drive member in a second rotational direction. 
     Further, the counting member  5  comprises a claw  12 . The claw  12  protrudes outwardly from the outer surface  8  of the counting member  5 . The claw  12  is arranged at a proximal end of the counting member  5 . The claw  12  has a first surface  13  and a second surface  17 . The first surface  13  of the claw  12  is roughly perpendicular to an azimuthal direction around the rotational axis of the counting member  5 . The first surface  13  of the claw  12  extends roughly in a radially outward direction away from the rotational axis of the counting member  5 . The second surface  17  of the claw  12  forms a flatter angle to the azimuthal direction than the first surface  13 . 
     As will be described later in detail, the claw  12  is configured to interact with axially extending ribs arranged at an inner surface of the housing  3 . The first surface  13  of the claw  12  are shaped such that the counting member  5  is prevented from rotating in a first rotational direction relative to the housing  3  due to the engagement of the claw  12  and the axially extending ribs. Further, the second surface  17  of the claw  12  is shaped such that the counting member  5  is enabled to rotate in the second rotational direction relative to the housing  3  as the second surface  17  of the claw  12  is enabled to slide over a correspondingly tapered surface of the axially extending ribs in this case. 
     Further, the counting member  5  comprises a slide rail  18 . The slide rail  18  is arranged at the inner surface  9  of the counting member  5 . The slide rail  18  has a helical shape. The slide rail  18  of the counting member  5  is configured to be engaged with a corresponding slide rail of the storage chamber  15 . Thereby, the counting member  5  is enabled to travel along a helical path relative to the storage chamber  15  and relative to the housing  3  as the storage chamber  15  is fixed to the housing  3 . The position of the counting member  5  relative to the housing  3  along this path corresponds to the current value of the counted number. This position also determines which one of the indicia  10  is visible in the window  89  of the housing  3 . 
     Moreover, a first abutment surface is provided on the counting member  5  which is not visible in  FIG. 2 . The first abutment surface is arranged at the outer surface  8  of the counting member  5 . The first abutment surface is arranged in the vicinity of the distal end of the counting member  5 . The first abutment surface is configured to be abutted by a second abutment surface provided on a counter drive member, thereby preventing a further rotation of the counting member  5  relative to the counter drive member. The first abutment surface faces in the azimuthal direction. 
       FIG. 3  shows a perspective view of a counter drive member  19 . The counter drive member  19  is an essentially ring-shaped element. The counter drive member  19  comprises a slot  20  which extends in an axial direction. Thus, the ring-shape of the counter drive member  19  is not closed, thereby forming a C-shape. As will be discussed later on, the slot  20  facilitates the manufacturing process. 
     Further, a second abutment surface  21  is provided on the counter drive member  19 . In particular, the counter drive member  19  comprises a lug  22  protruding in the distal direction wherein the second abutment surface  21  is provided on the lug  22 . The second abutment surface  21  faces in the azimuthal direction around a rotational axis of the counter drive member  19 . The rotational axis of the counter drive member  19  is parallel to the rotational axis of the inhalation device  1 . As will be discussed later, the second abutment surface  21  is configured to abut the first abutment surface of the counting member  5 , thereby preventing a further rotation of the counter drive member  19  relative to the counting member  5 . 
     Further, the counter drive member  19  comprises a spring element  23 . When the counter drive member  19  is assembled to the inhalation device  1 , the spring element  23  is configured to bias the counter drive member  19  in the axial direction, in particular in the proximal direction. Thereby, the spring element  23  ensures that the counter drive member  19  remains in its second position when the detachable member  7  is detached from the housing  3 . 
     In particular, the spring element  23  comprises four spring arms wherein a first pair of two spring arms form a V-shape and a second pair of two spring arms is arranged opposite to the first pair of spring arms and also forms a V-shape. This design further stabilizes the counter drive member  19 . In an alternative design, which is not shown in  FIG. 3 , the spring element  23  comprises two spring arms which are arranged opposite to each other. 
     The counter drive member  19  comprises an inner surface  26  and an outer surface  27 . An engagement feature  28  is arranged at the inner surface  26  of the counter drive member  19 . The engagement feature  28  is a tooth. The engagement feature  28  of the counter drive member  19  is configured to interact with the gear teeth  11  of the counting member  5 . The engagement feature  28  is shaped such that the counter drive member  19  is enabled to rotate in the first rotational direction relative to the counting member  5 . In this case, the engagement feature  28  slides over a side surface of the respective tooth and engages with the next tooth. Further, the engagement feature  28  is shaped such that the counter drive member  19  is prevented from rotating in the second rotational direction relative to the counting member  5  wherein the second rotational direction is opposite to the first rotational direction. 
     Further, the counter drive member  19  comprises a protrusion  29 . The protrusion  29  is arranged on the outer surface  27  of the counter drive member  19 . The protrusion  29  protrudes in the radially outward direction. The protrusion  29  has a first side surface  30  and a second side surface  31  which are spaced apart from each other in the azimuthal direction. The azimuthal direction circles around the rotational axis of the counter drive member  19 . 
     Further, the protrusion  29  comprises a third surface  32  which connects the first and the second side surface  30 ,  31 . The third surface  32  extends essentially in the azimuthal direction. The third surface  32  is inclined relative to the azimuthal direction. Moreover, the protrusion  29  also comprises a fourth surface  36  which is parallel to the third surface  32  and also connects the first and the second side surface  30 ,  31 . 
     The third surface  32  is configured to slide along a cut-out in the housing  3  when the counter drive member  19  travels along a helical path relative to the housing  3 . Due to the inclination of the third surface  32 , the friction of the counter drive member  19  and the housing  3  can be kept to a minimum. The first and the second surface  30 ,  31  are configured to abut a respective end face of the cut-out, thereby limiting the range of motion of the counter drive member  19 . 
     In particular, the counter drive member  19  may be constrained such that it can only be moved from a first to a second position and vice versa. The counter drive member  19  is in its first position when the detachable member  7  is fully attached to the housing  3 . The counter drive member  19  is moved into its first position during the incrementing or decrementing the counted number. The counter drive member  19  is in its second position when the detachable member  7  is partially or fully detached from the housing  3 . The second position of the counter drive member  19  is position wherein the counter drive member  19  is ready to increment or decrement a counted number. 
     The protrusion  29  of the counter drive member  19  is configured to be engaged by a first and a second projection of the detachable member  7 . Thereby, the protrusion  29  and the respective projection are configured to transfer a movement of the detachable member  7  into a movement of the counter drive member  19 . In particular, the counter drive member  19  is configured to follow a rotation of the detachable member  7  when the projection  29  is engaged with one of the protrusions. 
     The counter drive member  19  further comprises an identical second protrusion  29 ′ which is arranged opposite to the first protrusion  29  and which is not visible in the perspective view shown in  FIG. 3 . As the function of the identical second protrusion  29 ′ is essentially identical to the protrusion  29 , only the protrusion  29  is referred to in the following. 
       FIG. 4  shows a cross-sectional view of the detachable member  7 . The detachable member  7  comprises a thread  37  arranged at its inner surface. The detachable member  7  can be detached, e.g. unscrewed, from the housing  3  of the inhalation device  1 . The thread  37  of the detachable member  7  is engaged with a thread on the housing  3  when the detachable member  7  is attached to the housing  3 . 
     The detachable member  7  comprises axially extending splines  38 . When the detachable member  7  is attached to the housing  3 , the detachable member  7  and the rotary part  25  are in a splined engagement due to an engagement of the splines  38  of the detachable member  7  with corresponding elements of the rotary part  25 . 
     The detachable member  7  comprises the first projection  39  and the second projection  43 . The first projection  39  and the second projection  43  are arranged at the inner surface of the detachable member  7 . The first and the second projection  39 ,  43  protrude inwardly from the inner surface. The first and the second projection  39 ,  43  are spaced apart in the azimuthal direction and in the axial direction. In particular, the first projection  39  is arranged more distally than the second projection  43 . Moreover, the detachable member  7  comprises a second pair of a first projection  39 ′ and a second projection  43 ′ which are identical to the previously described first and second projection  39 ,  43 . The second pair of projections  39 ′,  43 ′ is arranged opposite to the first and the second projection  39 ,  43 . 
     The first and the second projection  39 ,  43  of the detachable member  7  are configured to engage with the protrusion  29  of the counter drive member  19 . Further, the second pair of projections  39 ′,  43 ′ is configured to engage with the second protrusion  29 ′ of the counter drive member  19 . As the second pair of projections  39 ′,  43 ′ is substantially identical to the first and the second projection  39 ,  43 , only the first and the second projection  39 ,  43  are described in the following. 
     In particular, the detachable member  7  is configured such that the detachable member  7  is rotationally locked to the counter drive member  19  when one of the first or the second projection  39 ,  43  is engaged with the protrusion  29  of the counter drive member  19 . In other words, the counter drive member  19  follows a rotation of the detachable member  7  when one of the first or the second projection  39 ,  43  is engaged with the protrusion  29  of the counter drive member  19 . 
     The detachable member  7  is further configured to seal the inhalation device  1  against moisture when the detachable member  7  is completely attached to the housing  3 . 
       FIG. 5A  and  FIG. 5B  show perspective views of the housing  3 .  FIG. 5C  shows an enlarged view of a part of the housing  3 . 
     The housing  3  comprises a thread  44 . The thread is arranged at the distal part of the housing  3 . The detachable member  7  can be screwed along the thread  44 . 
     Further, the housing  3  comprises the window  89 . A part of the counting member  5  is visible through the window  89 . In particular, the window  89  is configured such that one indicia  10  at a time is visible through the window  89 . The window  89  is arranged such that the window  89  is visible when the detachable member  7  is attached to the housing  3  and when the detachable member  7  is detached from the housing  3 . 
     Further, the housing  3  comprises a cut-out  45 . The cut-out  45  is arranged such that it is inclined relative to an azimuthal direction which circles around a longitudinal axis defined by the housing  3 . The longitudinal axis of the housing  3  is parallel to the rotational axis  16  of the inhalation device  1 . 
     The inclination of the cut-out  45  corresponds to the inclination of the protrusion  29  of the counter drive member  19 . The counter drive member  19  is configured to be arranged at least partially inside the housing  3 . Further, when the counter drive member  19  is arranged inside the housing  3 , the protrusion  29  protrudes out of the cut-out  45  of the housing  3 . 
     Further, as can be seen in  FIG. 5B , an orientation segment  46  is arranged at a distal end of the housing  3  protruding inwardly. The orientation segment  46  ensures that the storage chamber  15  can be fixed to the housing  3  only in one orientation. 
     Further, the housing  3  comprises axially extending ribs  47 . The axially extending ribs  47  are arranged at the inner surface of the housing  3 . The axially extending ribs  47  are configured to cooperate with the claw  12  of the counting member  5 . In particular the claw  12  and the axially extending ribs  47  are configured to allow a rotation of the counting member  5  relative to the housing  3  in the second rotational direction and to prevent a rotation of the counting member  5  relative to the housing  3  in the first rotational direction. 
       FIG. 6  shows a perspective view of the storage chamber  15 . The storage chamber  15  is configured to be fixed relative to the housing  3 . 
     Moreover, the storage chamber  15  comprises a slide rail  48 . The slide rail  48  has a helical shape. The slide rail  48  is arranged at an outer surface of the storage chamber  15 . The slide rail  48  of the storage chamber  15  is configured to engage with the slide rail  18  arranged at the inner surface of the counting member  5 . Accordingly, the counting member  5  can be screwed up and down the storage chamber  15 . The counting member  5  is constrained such that it can only carry out a helical movement relative to the storage chamber  15  and, as the storage chamber  15  is fixed to the housing  3 , the counting member  5  is constrained such that it can only carry out a helical movement relative to the housing  3 . 
     The storage chamber  15  comprises a cut-out segment  49  at its distal end which is configured to engage with the orientation segment  46  of the housing  3 , thereby ensuring that the storage chamber  15  is correctly aligned with the housing  3 . 
     Further, the storage chamber  15  comprises a centering device  50  which is arranged at a proximal end of the storage chamber  15 . In particular, a first and a second centering device  50  are arranged at opposite surface sides. The centering devices  50  align the storage chamber  15  inside the housing  3 . 
     Further, a chamfered surface  51  is provided at the proximal end of the storage chamber  15 . As will discussed later on, the chamfered surface  51  is configured to engage the storage chamber  15  with a snapper of a bottom lid. The snapper and the chamfered surface  51  form a transportation lock mechanism which ensures that a spring is allowed to release its tension only when a bottom unit comprising the spring, a spring housing, a spring housing seal and a bottom lid are attached to the remainder of the inhalation device  1 . 
     Further,  FIG. 7  shows a perspective view of the spring housing  52  which is configured to be arranged inside the storage chamber  15 . The spring can be arranged inside the spring housing  52 . The spring housing  52  comprises an opening  53 . When the transportation lock mechanism is activated, the spring housing is fixed to the bottom lid. 
       FIG. 8  shows a perspective view of the bottom lid  55 . The bottom lid  55  comprises a stabilizing element  56  which is configured to stabilize the spring housing  52  when the spring housing  52  is attached to the bottom lid  55 . Further, the bottom lid  55  comprises a snapper  57 . 
       FIG. 9  shows an exploded view of the inhalation device  1 . 
       FIGS. 10 and 11  indicate the assembly process of the inhalation device  1 . In one step, the counter drive member  19  is entered into the housing  3 . Thereby, a tool is used to press the counter drive member  19  such that the slot  20  is narrowed. Thereby, the radius of the counter drive member  19  is slightly reduced. This allows entering the counter drive member  19  into the housing  3 . Once the counter drive member  19  has reached its predetermined position, the tool is separated from the counter drive member  19 , thereby allowing the counter drive member  19  to release its tension and to expand such that the width of the slot  20  increases. Now, the counter drive member  19  is fixed to the housing  3  as the protrusion  29  protrudes through the cut-out  45  of the housing  3 . The counter drive member  19  is now constrained to move between its first position and its second position relative to the housing  3 .  FIG. 10  shows a stage before the counter drive member  19  is entered into the housing  3  and  FIG. 11  shows a later stage of the assembly process wherein the counter drive member  19  has been entered into the housing  3 . 
     Further, the counting member  5  is screwed onto the storage chamber  15  during the assembly process. The initial value of the counted number depends on the axial position of the counting member  15  relative to the storage chamber  15  at the end of the assembly process. As the storage chamber  15  is fixed to the housing  3 , the initial value of a counted number is determined by the axial position of the counting member  5  relative to the housing  3  at the end of the assembly process. This position determines how many counting operations can be carried out before the first abutment surface and the second abutment surface  21  abut each other. 
     The counted number corresponds to the indicia  10  visible through the window  89  of the housing  3 . A large range of counted numbers is printed on the counting member  5 , e.g. a range from “120” to “0”. However, the number of operations N is determined by the position of the counting member  5  relative to the housing  3 . Thus, the same assembly can be used wherein the predetermined number N is set to different values during the assembly process by positioning the counting member  5  differently relative to the storage chamber  15  and relative to the housing  3 . For example, in one embodiment, the counting member  5  is positioned such that the initial value of the counted number is a first value, e.g. “60”, and in another embodiment, the counting member  5  is positioned such that the initial value of the counted number is a different second value, e.g. “120”.  FIG. 10  shows a stage before the counting member  5  is screwed onto the storage chamber  15  and  FIG. 11  shows a later stage of the assembly process wherein the counting member  5  has been screwed onto the storage chamber  15 . 
       FIG. 12  shows a last step of the assembly process wherein the bottom unit  58  comprising the bottom lid  55 , the spring housing  52 , the spring (not visible) and a spring housing seal  59  is entered into the remained of the inhalation device  1 . 
     To perform a drug dispense operation, the detachable member  7  has to be detached from the housing  3 . Thereby, the mouthpiece  6  is uncovered. Moreover, the detachable member  7  is connected with the metering rod  33 . The detachment of the detachable member  7  results in the metering rod  33  traveling axially in the distal direction such that a dose of the substance  2  is prepared for inhalation. 
       FIGS. 13 to 17  show the process of detaching the detachable member  7  from the housing  3 .  FIG. 13  shows an enlarged view of a part of the inhalation device  1  in a state wherein the detachable member  7  is completely attached to the housing  3 . In the configuration shown in  FIG. 13 , the counter drive member  19  is in its first position. The protrusion  29  of the counter drive member  19  is engaged with the first projection  39  of the detachable member  7 . In particular, the protrusion  29  of the counter drive member  19  abuts the first projection  39  of the detachable member  7 . 
     To detach the detachable member  7  from the housing  3  the detachable member  7  has to carry out a detachment movement. The detachment movement is a rotation of the detachable member  7  relative to the housing  3  in the first rotational direction. The detachment movement comprises a first part and a second part. The first part is an initial part of the movement. The second part is a final part of the movement. 
     In the first part of the detachment movement, the detachable member  7  is rotated in the first rotational direction and the protrusion  29  remains engaged with the first projection  39 . Thus, the counter drive member  19  follows the rotation of the detachable member  7  in the first rotational direction. The counter drive member  19  and the detachable member  7  are configured such that they are moved in different axial directions when rotated in the same rotational direction. This is due to the fact that the threads  37 ,  44  of the detachable member  7  and the housing  3  are oppositely orientated to the inclination of the cut-out  45  in the housing  3  and the inclination of the protrusion  29  of the counter drive member  19 . 
     Accordingly, a can be seen in  FIG. 14  which shows a configuration at the end of the first part of the detachment movement, the detachable member  7  travels in the distal direction. At the same time, the counter drive member  19  travels from its first position to its second position, i.e. in the proximal direction. Thereby, at the end of the first part of the detachment movement, the protrusion  29  disengages from the first projection  39 . 
     In a second part of the detachment movement, the detachable member  7  continues to rotate in the first rotational direction relative to the housing  3 . At the end of the second part, the detachable member  7  is completely unscrewed from the housing  3  and detached from the housing  3 . 
     The protrusion  29  is not engaged with the first projection  39  of the detachable member  7  in the second part of the detachment movement. Thus, the counter drive member  19  does not follow the rotation of the detachable member  7  in the second part of the detachment movement. The counter drive member  19  remains in its second position. 
       FIGS. 15 and 16  show details of the interaction of the counter drive member  19  and the counting member  5  during the detachment of the detachable member  7 .  FIG. 15  corresponds to the configuration shown in  FIG. 13  when the detachable member  7  is completely attached to the housing  3 .  FIG. 16  corresponds to the configuration shown in  FIG. 14  at the end of the first part of the detachment movement. 
     In  FIG. 15 , the engagement feature  28  of the counter drive member  19  is engaged with one of the teeth of the gear teeth  11 . During a rotational movement of the counter drive member  19 , the engagement feature  28  slides over a ramp-shaped side surface of the tooth and snaps into the next tooth of the gear teeth  11 . Each tooth of the gear teeth  11  comprises a ramp-shaped first side surface, thereby ensuring that the counter drive member  19  is enabled to rotate relative to the counting member  5  in the first rotational direction. Accordingly, the counter drive member  19  is rotated in the first rotational direction relative to the counting member  5  during detachment of the detachable member  7 . 
       FIG. 17  shows details of the interaction of the counting member  5  and the housing  3 . In particular, it can be seen that the claw  12  of the counting member  5  abuts one of the axially extending ribs  47  of the housing  3 , thereby preventing a rotation of the counting member  5  in the first rotational direction relative to the housing  3 . This ensures that the counting member  5  is not moved relative to the housing  3  during a detachment of the detachable member  7 . 
     In particular, the first surface  13  of the claw  12  abuts a first surface  62  of the axially extending rib  47  wherein the first surface  13  of the claw  12  and the first surface  62  of the axially extending rib  47  are parallel to each other, thereby preventing the claw  12  from sliding over the axially extending rib  47 . 
     It can also be seen in  FIG. 17  that the second surface  17  of the claw  12  is enabled to slide over a tapered second surface  63  of the axially extending rib  47  such that a rotation of the counting member  5  relative to the housing  3  in the second rotational direction is enabled. 
     Once the detachable member  7  has been detached completely from the housing  3 , the mouthpiece  6  is free from the detachable member  7  and the user can perform an inhalation. 
     After the inhalation has been performed, the detachable member  7  has to be reattached to the housing  3  and, afterwards, be detached from the housing  3  again before a subsequent inhalation can be performed. To reattach the detachable member  7  to the housing  3 , the detachable member  7  can be screwed onto the housing  3  along the thread  44  of the housing  3 . Thereby the detachable member  7  carries out an attachment movement. The attachment movement comprises a first part and a subsequent second part. 
     During the first part of the attachment movement, the detachable member  7  is not attached to the counter drive member  19  such that the detachable member  7  carries out a helical movement with a rotational component in the second rotational direction relative to the counter drive member  19  and relative to the housing  3 . The counter drive member  19  remains in its second position during the first part of the attachment movement. 
       FIG. 18  shows a detailed view of a part of the inhalation device  1  at the end of the first part of the attachment movement. At the end of the first part of the attachment movement, the second projection  43  abuts the protrusion  29  of the counter drive member  19 , thereby engaging the detachable member  7  and the counter drive member  19 . In the second part of the attachment movement, the detachable member  7  is rotated further in the second rotational direction. Due to the engagement of the second projection  43  and the protrusion  29 , the counter drive member  19  follows the rotation of the detachable member  7  in the second rotational direction. As the counter drive member  19  is constrained to carry out a helical movement, it is moved from its second position back to its first position. Accordingly, the counter drive member  19  is moved in the distal direction. The detachable member  7  travels in the proximal direction during the attachment movement. 
       FIG. 19  shows the assembly at the end of the attachment process. The counter drive member  19  has reached its first position and the detachable member  7  is fully reattached to the housing. 
       FIG. 20  shows the interaction of the counter drive member  19  and the counting member  5  during the attachment of the attachable member  7  to the housing  3 . The engagement feature  28  of the counter drive member  19  and the gear teeth  11  of the counting member  5  are configured such that the counting member  5  follows a rotation of the counter drive member  19  in the second rotational direction. Accordingly, the counting member  5  is rotated in the second rotational direction when the detachable member  7  is attached to the housing  3 . Thereby, a counted number counted by the counting member  5  is increased or decreased. In particular, as the counting member  5  is rotated, another indicia  10  is now visible through the window  89  of the housing  3 . 
     Accordingly, the counted number is incremented or decremented each time the detachable member  7  is attached to the housing  3 . During normal use of the inhalation device  1 , this will correspond to a drug dispense operation having been carried out. 
     The mechanism is configured such that the incrementing or decrementing of the counted number will stop shortly before the snap fit element  34  snaps into the metering rod  33  such that it is impossible to carry out a drug dispense operation without incrementing or decrementing the counted number. 
     Furthermore, the inhalation device  1  is configured such that no drug dispense operation can be performed after N operations have been carried out, wherein N is a predefined number which is determined by the initial relative position of the counting member  5  relative to the housing  3 . This lock-out mechanism is described in detail with reference to  FIGS. 21 and 22 . 
     The lock-out mechanism prevents the user from trying to perform a drug dispense operation when the device is empty. Accordingly, it increases the safety and usability. In particular, the assembly is designed such that the detachable member is prevented from being detached from the housing after it has been detached N times. Thus, it is ensured that a maximal number of N drug delivery operations can be carried out as only one drug delivery operation can be carried out after the detachable member is detached before it is reattachted to the housing. 
       FIG. 21  shows a perspective view of the interaction of the counter drive member  19  and the counting member  5  when the detachable member  7  has been detached N times.  FIG. 22  shows the interaction of the counter drive member  19  and the detachable member  7  in a configuration wherein the detachable member  7  has been detached N times and, afterwards, has been reattached to the housing  3 . 
     In particular, the assembly is configured such that, after detachment of the detachable member  7  from the housing  3  for an Nth time, the detachable member  7  is enabled to be reattached to the housing  3  and, afterwards, the detachable member  7  is prevented from being detached from the housing  3  again. In particular, the detachable member  7  being prevented from being detached from the housing  3  again is to be understood such that the detachable member  7  can only be detached from the housing  3  by damaging the inhalation device  1 . 
     The first abutment surface  64  is provided on the counting member  5 . The second abutment surface  21  is provided on the counter drive member  19 . Every time the counted number is incremented or decremented, the first and the second abutment surface  64 ,  21  are moved closer together along a helical path. After the detachable member  7  is detached from the housing  3  an Nth time, the first and the second abutment surface  64 ,  21  abut each other. It should be noted that the detachable member  7  is detached from housing  3  in this state and, therefore, the detachable member  7  is also disengaged from the metering rod  33 .  FIG. 21  shows the abutment of the first and the second abutment surface  64 ,  21 . Thereby, the first and the second abutment surface  64 ,  21  prevent that the counter drive member  19  is rotated relative to the counting member  5  in the first rotational direction. Moreover, as the counter drive member  19  is in its first position, it cannot be rotated further in the second rotational direction. 
     Then, the detachable member  7  is re-attached to the housing  3 . The assembly is thereby moved into the configuration shown in  FIG. 22 . As discussed above, the detachable member  7  engages the metering rod  33  via the snap fit element  34  during this movement when the detachable member reaches the second position relative to the housing  3 . The assembly is configured such that the second relative position can only be reached during the reattachment of the detachable member  7  to the housing  3  after the Nth detachment when the assembly is in a configuration wherein it is no longer possible to detach the detachable member  7  from the housing  3 . In particular, the second position is reached only after an abutment of second projection  43  of the detachable member  7  with the the protrusion  29  of the counter drive member  19  has happened. 
     The detachable member  7  cannot be detached from the housing  3  anymore as the counter drive member  19  is prevented from being moved out of its first position. To move the counter drive member  19  out of its first position, the counter drive member  19  has to be rotated in the first rotational direction relative to the housing  3  which is prevented by the abutment of the first and the second abutment surface  64 ,  21 . Further, the detachable member  7  is prevented from rotating in the first rotational direction as it is rotationally locked to the counter drive member  19 . 
     However, the detachable member  7  can be rotated by a small angle until the first projection  39  abuts the protrusion  29  of the counter drive member  19  as shown in  FIG. 22 . The small angle is smaller than 10°, preferably smaller than 5°. The metering rod  33  which is engaged with the detachable member  7  via the snap fit element  34  in this state cannot be moved in the distal direction far enough to remove a sub-quantity  14  of the drug from the storage chamber  15  as the detachable member  7  can only be rotated by the small angle. The second relative position at which the detachable member  7  engages with the metering rod  33  lies within the range by which the detachable member  7  is allowed to be rotated. 
     As the metering rod  33  engages with the detachable member  7  via the snap fit element  34  only after the first position has been passed, it is prevented that the user only partly reattaches the detachable member  7  and afterwards detaches the partly detachable member  7  and, thereby, tries to move a sub-quantity of the dose out of the dosing chamber without incrementing or decrementing the counted number. This is not possible as the counted number is incremented or decremented before an engagement of the detachable member  7  with the metering rod  33  which results in the metering rod  33  following a movement of the detachable member  7  in the distal direction. 
     This configuration corresponds to an orientation of the counting member  5  wherein the indicia “0” is visible through the window  89 , thereby indicating to a user that the device  1  is empty. As the detachable member  7  cannot be detached from the housing  3  anymore, the user is warned that the device  1  is empty. The fact that the detachable member  7  is allowed to rotate by a small angle before being locked makes it obvious for the user that the detachment is prevented on purpose. 
       FIGS. 23 and 24  show the transportation lock of the bottom unit  58 . Before the assembly of the bottom unit  58  to the remainder of the inhalation device, the snapper  57  based in the bottom lid  55  are engaged with the opening  53  in the spring housing  52 , thereby preventing release of the tension of the spring, as shown in  FIG. 23 . 
     When the bottom unit  58  is attached to the remainder of the inhalation device  1 , as shown in  FIG. 24 , the chamfered surface  51  of the storage chamber  15  engages the snapper  57  and pushes the snapper  57  in the radial outward direction. Thereby, the snapper  57  is disengaged from the spring housing  52 . Now, the spring is free to release its tension, thereby moving the powder reservoir in the distal direction. 
     REFERENCE NUMERALS 
     
         
         
           
               1  inhalation device 
           
         
       
    
       2  substance 
       3  housing 
       4  outer cylinder 
       5  counting member 
       6  mouthpiece 
       7  detachable member 
       8  outer surface of the counting member 
       9  inner surface of the counting member 
       10  indicia 
       11  gear teeth 
       12  claw 
       13  first surface of the claw 
       14  sub-quantity of substance 
       15  storage chamber 
       16  rotational axis 
       17  second surface of the claw 
       18  slide rail of the counting member 
       19  counter drive member 
       20  slot 
       21  second abutment surface 
       22  lug 
       23  spring element 
       24  chamber sealing 
       25  rotary part 
       26  inner surface of the counter drive member 
       27  outer surface of the counter drive member 
       28  engagement feature 
       29  protrusion 
       30  first side surface of the protrusion 
       31  second side surface of the protrusion 
       32  third surface of the protrusion 
       33  metering rod 
       34  snap fit element 
       35  actuator housing 
       36  fourth surface of the protrusion 
       37  thread of the detachable member 
       38  spline 
       39  first projection 
       40  metering chamber 
       41  distal end 
       42  proximal end 
       43  second projection 
       44  thread of the housing 
       45  cut-out 
       46  orientation segment 
       47  axially extending rib 
       48  slide rail of storage chamber 
       49  cut-out segment 
       50  centering device 
       51  chamfered surface 
       52  spring housing 
       53  opening of the spring housing 
       54  actuating element 
       55  bottom lid 
       56  stabilizing element 
       57  snapper 
       58  bottom unit 
       59  spring housing seal 
       60  flow channel 
       61  intermediate channel portion 
       62  first surface of the axially extending rib 
       63  second surface of the axially extending rib 
       64  first abutment surface 
       76  head 
       77  tongues 
       89  window