HK1158997B

HK1158997B - Drive assembly suitable for use in a medication delivery device and medication delivery device

Info

Publication number: HK1158997B
Application number: HK11113509.4A
Authority: HK
Inventors: David Plumptre
Original assignee: 赛诺菲-安万特德国有限公司
Priority date: 2008-12-02
Filing date: 2009-12-01
Publication date: 2014-06-27

Description

Drive assembly suitable for use in a drug delivery device and drug delivery device

Technical Field

The present invention relates to a drive assembly suitable for use in a drug delivery device, in particular a pen-type device, such as a pen-type injector. In particular, the present invention may relate to a drive assembly suitable for use in a drug delivery device, wherein a plurality of predetermined doses may be administered. Further, the invention may relate to a drug delivery device wherein the user may activate the drug delivery device.

Background

The drug delivery device described above may be used when a person (e.g., a patient) that has not been trained in a formal medicine needs to administer an accurate and predetermined dose of a drug product. In particular, the above-described device may be used when the pharmaceutical product is administered regularly or irregularly, both short-term and long-term.

These conditions set a number of requirements for such drug delivery devices. The device should have a robust construction, but should be easy to use in terms of part manipulation, user understanding of its operation, and delivery of the required dose of medication. Dose setting should be easy and unambiguous. Where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose of (preferably being suitable for recycling). To meet these requirements, the number of parts required to assemble the device and the number of types of materials from which the device is made should be as small as possible.

A drug delivery device operated by a user is for example seen in US 7,316,670.

In addition, if the drug is a fluid or the fluid contains a drug, gaseous inclusions such as bubbles are typically present in the fluid. Such inclusions can be detrimental to the health of the user if they are not removed from the fluid prior to administration. Additionally, some elements in the drug delivery device, such as the needle, may be filled with a gas before the first dose of drug is removed from the device. The gas can also be detrimental to the health of the user if not removed. To minimize the risk of health damage, gas may be removed from the fluid prior to the first administration of the drug ("device preparation"). This can be achieved, for example, as follows: when the device is brought into a predetermined orientation, such as needle up, a small dose of fluid (a "priming dose") is expelled from the device. Thus, gas may be removed from the fluid and the needle and the risk of injecting gas into the user is minimized and/or manufacturing tolerances may be eliminated and/or the initial gas gap between the piston rod and the piston in the sleeve may be removed. Of course, the amount of fluid expelled cannot be used for subsequent drug administration. Since the medication is generally expensive, priming should be minimized.

In addition, the dimensions of the device, e.g. its length, should be as small as possible, since drug delivery devices, especially devices for regular administration of drugs, are usually carried by the user, and the space for storing the device is therefore significant for the user. In addition, smaller devices are more attractive than larger devices.

Disclosure of Invention

One aspect of the present invention provides a drive assembly adapted for use in a drug delivery device, the drive assembly comprising:

a housing having a proximal end and a distal end,

a drive member movable relative to the housing in a direction towards the proximal end for setting a dose of medicament to be delivered and movable relative to the housing in a direction towards the distal end for delivering the dose,

-a piston rod adapted to be driven by the drive member in a direction towards the distal end with respect to the housing during movement of the drive member in a direction towards the distal end for delivering the dose,

-a stop member for limiting the proximal movement of the piston rod relative to the housing during the proximal movement of the drive member by a mechanical interaction between the stop member and the stopper of the piston rod, wherein the stop member and the stopper are arranged to move the piston rod proximally a first distance before the stop member and the stopper mechanically interact during a first proximal movement of the drive member, wherein the first distance the piston rod is moved proximally during the first proximal movement of the drive member (e.g. for setting a ready dose of medicament to be delivered) is larger than the distance the piston rod is subsequently moved proximally during a subsequent proximal movement of the drive member for setting a dose of medicament to be delivered.

The stop member may be arranged to abut the stopper to prevent proximal movement of the piston rod beyond the first distance during the first proximal movement of the drive member.

According to at least one aspect, the drug delivery device comprises a drive assembly and a cartridge comprising a plurality of drug doses, in particular at least one preparation dose and at least one drug dose to be delivered. The device includes a piston preferably retained within a sleeve. The piston rod is advantageously arranged to drive the piston distally relative to the cartridge to expel a dose of medicament from the cartridge.

The mechanical interaction between the drive member and the piston rod may be adapted to move the piston rod proximally during proximal movement of the drive member to set a dose. This movement proximally relative to the housing is stopped when the stop and stop feature interact.

In an initial state of the drive assembly, the stop member and the stopper may be arranged to move the piston rod proximally a first distance during a first proximal movement of the drive member, which is performed starting from the initial state of the drive assembly or the drug delivery device, respectively. The initial state may be a state in which the drive assembly or the drug delivery device is provided by the manufacturer, i.e. unused but assembled, preferably with an unused and filled cartridge. In particular, the initial state may be a state of the drive assembly or device in which the piston rod is in an initial position relative to the housing. That is, when the piston rod is in the initial position, the piston rod has not been moved distally relative to the housing, for example to deliver a dose or to prepare an assembly or device. Thus, the drive assembly may be arranged to allow the piston rod to move in the proximal direction during a first execution of the drive member to set a dose. In addition, the drive assembly may be arranged to prevent proximal movement of the piston rod during a second proximal movement of the drive member, and preferably any subsequent proximal movement to set a subsequent dose. In particular, in the initial state, before the first execution, the stopper and the stop member may be arranged at a distance from each other, said distance defining a first distance, said first distance being the distance the piston rod moves proximally during the first proximal movement of the drive member.

The features described in the context of the present application with respect to the drive assembly may also relate to the drug delivery device, since the device advantageously comprises a corresponding drive assembly. Similarly, features described in the context of the present application with respect to the drug delivery device may also relate to the drive assembly.

In a preferred aspect, the piston rod is coupled with the drive member such that the piston rod follows the movement of the drive member distally relative to the housing for delivering a dose. The piston rod may or may not follow the movement of the drive member in a gear ratio (ratio transmission). Thus, the piston rod is movable with respect to the housing by the same distance as the drive member, by a smaller distance than the drive member or by a larger distance than the drive member. The medicament may be expelled from the cartridge by moving the piston distally relative to the cartridge by means of the piston rod. The piston rod is advantageously coupled with the drive member to drive the piston rod in a distal direction relative to the housing during a first and any subsequent distal movement of the drive member to deliver a dose.

Since the piston rod follows the proximal movement of the drive member during the first proximal movement of the drive member, the piston rod is in particular adapted to move proximally a first distance away from the piston in a distal movement of the piston rod towards the proximal end relative to the surface of the piston rod that the sleeve pushes the piston inside the sleeve in a distal direction during the distal movement of the drive member. Thus, when the piston rod is moved a given distance during a distal movement of the drive member, if the piston rod is moved proximally before its distal movement, the distal displacement of the piston relative to the sleeve during the first distal movement of the piston rod may be reduced, e.g. compared to a piston rod which is only moved in the distal direction when the drive member is moved in the proximal and distal directions. This is particularly advantageous for preparing the device, since the amount of prepared dose expelled from the cartridge should be kept small.

The total distance that the piston is moved in the distal direction relative to the housing during the first distal movement of the drive member is advantageously smaller than the total distance that the piston rod is moved in the distal direction relative to the housing during the first distal movement of the drive member. Preferably, a first distance of proximal movement of the piston rod relative to the housing during a first proximal movement of the drive member is smaller than a total distance of proximal movement of the drive member relative to the housing during said first proximal movement to set a dose. The total distance that the piston rod is moved in the distal direction with respect to the housing during the first distal movement of the drive member with respect to the housing is larger than the first distance.

In a preferred aspect, the priming movement of the drive member, i.e. the movement of the drive member for setting and delivering a priming dose, comprises a first proximal movement of the drive member. The priming dose may be set during a first proximal movement of the drive member. The priming dose may be delivered during the first distal movement of the drive member.

In a preferred aspect, the piston rod is arranged at a distance from the piston, in particular before a first proximal movement of the drive member. The piston rod may be separated from the piston by a gap, such as an air gap, between the piston and the piston rod. The piston rod may already be mechanically connected with the piston before setting and/or delivering a subsequent dose.

Agent expelled from the device during a first distal movement of the drive memberThe amount corresponds to the distal displacement of the piston relative to the sleeve. The distal displacement of the piston relative to the sleeve corresponds to d_DM-d_PP-d_FWherein d is_DMFor the distance the piston rod moves in the distal direction during the first distal movement of the drive member, d_PPA distance between the piston rod and the piston before a first proximal movement of the drive member, and d_FThe piston rod is moved proximally a first distance corresponding to the first distance during a first proximal movement of the drive member. It will be appreciated that the piston rod may also abut the piston before said first proximal movement. Thus, d_PPAnd may be zero or greater than zero.

Thus, the distal displacement of the piston within the sleeve may be reduced by moving the piston rod a first distance in the proximal direction before the piston rod is moved distally to deliver a dose. Thus, the drive assembly may expel a prepared dose from the drug delivery device that may be smaller than one or all doses subsequently expelled from the device, in particular when the distal displacement of the piston rod during distal movement of the drive member is fixed for all doses to be delivered (including the prepared dose). In addition, the size of the drug delivery device may be reduced, in particular the length in case of a pen-type device, since it is not necessary to arrange the piston rod at a distance from the piston in the initial state of the device, thereby allowing the piston rod to move only in the distal direction during the priming movement of the drive member and to expel only a small priming dose from the cartridge.

In a preferred aspect, the drug delivery device is adapted to deliver a fixed dose of drug after the device has been prepared. For this purpose, the drive assembly may be arranged to move the piston rod a fixed distance in the distal direction during the distal movement of the drive member. The piston rod may be moved the above-mentioned fixed distance during the first, second and preferably any subsequent distal movement of the drive member to deliver a dose. However, considering that the piston rod is moved proximally a first distance before it moves distally, the dose expelled from the device during the first distal movement of the piston rod (the priming dose) is preferably smaller than any subsequent dose. During the second and any subsequent proximal movement of the drive member, the proximal movement of the piston rod is limited to a small distance. During the second and any subsequent proximal movement of the drive member, the piston rod may even be prevented from moving proximally completely.

According to the invention, the first distance is in any case larger than the distance the piston rod is subsequently moved proximally during a subsequent proximal movement of the drive member. According to a first embodiment, the piston rod is not moved proximally during a subsequent proximal movement of the drive member to set a dose of medicament to be delivered. The proximal movement of the piston rod during subsequent movement of the drive member may be derived from tolerances of components within the drug delivery device. Thus, the piston rod may for example move a first distance of at least 3mm in the proximal direction during a first proximal movement of the drive member and at least 0.1mm in the proximal direction during a subsequent proximal movement of the drive member. According to a preferred embodiment, the relationship of the subsequent distance to the first distance is in the range of 1: 50 to 1: 5, most preferably in the range of 1: 10 to 1: 7.

Preferably, the difference between the first distance the piston rod is moved proximally during setting of the first (ready) dose and the subsequent distance the piston rod is moved proximally during setting of the subsequent dose is substantially equal to the difference between the movement of the piston distally during delivery of the subsequent dose and the movement of the piston distally during delivery of the first (ready) dose.

In a preferred aspect, the piston rod comprises a plurality of stops. The drive assembly is advantageously arranged to mechanically interact with the stop member after distal movement of the drive member to deliver a dose. Preferably, the drive assembly is arranged such that the stop member interacts with a different stop after each distal movement of the piston rod to deliver a dose.

In a preferred aspect, the drive assembly is arranged such that the piston rod follows the proximal movement of the drive member relative to the housing during a first proximal movement of the drive member and such that the piston rod limits the proximal movement of the piston rod relative to the housing during a second proximal movement of the drive member and preferably also during any subsequent proximal movement of the drive member.

In a preferred aspect, the piston rod and the stop member are arranged to limit proximal movement of the piston rod during a second proximal movement of the drive member, and preferably any subsequent proximal movement to set a dose. This may be achieved, for example, by the stop member mechanically interacting with one of the stops before the drive member has made a second proximal movement and preferably any subsequent proximal movement to set a dose. A small movement of the piston rod proximally during a second proximal movement or any other subsequent proximal movement of the drive member to set a dose may then result from tolerances of the inner member of the drug delivery device.

In particular, in other states of the drive assembly than the initial state, the stop member and the associated stop member, which advantageously differs from the one with which the stop member interacts during the first proximal movement of the drive member, may be arranged at a distance from each other before setting of a dose, said distance being smaller than the first distance. The stop member and the associated stop member may interact mechanically already before the drive member is moved proximally to set the respective dose, which is particularly useful for preventing a significant movement of the piston rod proximally due to the mechanical interaction between the stop member and the drive member.

According to a preferred aspect, the piston rod is allowed to move a small distance proximally (which is smaller than the first distance) after each distal drug delivery movement of the piston rod has ended to reduce the piston rod to piston pressure.

In a preferred aspect, the respective stop is provided on an outer surface of the piston rod. The stops may be, for example, protrusions (e.g., teeth) on the outer surface of the plunger rod

In a preferred aspect, the stops are arranged equidistantly along the piston rod. In particular, the stops protruding on the longitudinal axis of the plunger rod may be arranged equidistantly. The distance between the raised stops may correspond to the distance the piston rod moves in a distal direction relative to the housing during distal movement of the drive member to deliver a dose.

In a preferred aspect, the stop member is fixed to prevent at least one or both of rotational movement and axial movement relative to the housing. The movement limiting means can be arranged on the housing, in particular on an inner surface of the housing. The movement limiting means can be fixed to the housing as a separate element or integrated into the housing. The housing and the stop feature may be integrally formed.

In a preferred aspect, the piston rod and the drive member are releasably coupled, e.g. releasably engaged, such that the piston rod may be (fully) uncoupled by proximal movement of the drive member relative to the housing during a second and preferably any subsequent proximal movement of the drive member to set a dose.

In a preferred aspect, the drive component comprises a drive system or drive sleeve. The drive system may include a rack movable relative to the housing and a rotatable element (e.g., a gear wheel) engaged with the movable rack. The drive sleeve may include internal threads. The piston rod may be threadedly engaged with the internal thread of the drive sleeve.

In a preferred aspect, the stop member engages the piston rod. The motion limiting member may be a flexible member or a non-flexible member. The stop feature may be a ratchet feature, a protrusion, a thread, or a partial thread.

In a preferred aspect, the drive assembly is arranged to limit or prevent rotational movement of the piston rod relative to the housing. The drive assembly may be arranged to provide a pure axial movement of the piston rod relative to the housing.

In another preferred aspect, the drive assembly is arranged such that the piston rod is rotatable relative to the housing. Thus, the piston rod is rotatable when translated in a distal direction relative to the housing.

Preferably, in this aspect, the piston rod includes a thread and the stop member engages the thread of the piston rod. Advantageously, the stop means are in this case threads or partial threads. The thread of the piston rod may comprise respective stops. Each stop is preferably a threaded region having a different thread angle than the adjacent threaded region. In particular, the stopper thread region may have a smaller thread angle than the adjacent region. Smaller thread angles may form thread regions with a smaller lead or even zero lead. Each stop may be, for example, a shoulder, step or recess in the thread of the piston rod.

The term "drug delivery device" refers to a single-dose, multi-dose, or pre-determined dose, disposable or reusable device designed to deliver a selectable or pre-determined dose (e.g., 7 pre-determined doses) of a drug to a user. The drug may include insulin, growth hormone, low molecular weight heparin and/or their analogues and/or derivatives and the like. The device may have any shape, for example compact or pen-shaped. Additionally, the device may or may not include a needle. In particular, the term "drug delivery device" refers to a needle-based disposable pen-type device with mechanical and manual dose delivery and dose selection mechanisms providing a plurality of pre-determined doses, the device being designed for use by personnel (e.g. patients) who have not received formal medical training. Preferably, the drug delivery device is of the syringe type.

The term "housing" refers to any outer housing ("main housing", "body" or "outer housing") or inner housing ("insert" or "inner body") that preferably has a unidirectional axial coupling to prevent proximal movement of certain components. The housing may be designed to enable safe, accurate and comfortable handling of the drug delivery device or any of its mechanisms. Generally, it is designed to house, fix, protect, guide and/or engage any internal member (e.g. a sleeve, a piston or a piston rod) of the drug delivery device by limiting exposure to contaminants such as liquid, dust, dirt etc. Generally, the housing may be a one-piece or multi-piece member having a tubular shape or a non-tubular shape.

The term "mesh" especially refers to the interlocking between two or more members of a drug delivery device (e.g. a spline, thread or a ratcheting tooth connection), preferably the interlocking between the ratcheting teeth of the members.

The term "drive member" refers to any member adapted to run through/within the housing, which is designed to transfer axial movement through/within the drug delivery device, preferably to the piston rod by the actuation member. In a preferred embodiment, the drive member is releasably coupled to the piston rod. The drive member may have a one-piece or multi-piece construction.

The term "drive sleeve" refers to a substantially tubular member of substantially circular cross-section, which is releasably connected to the piston rod. The drive sleeve may have a one-piece or multi-piece construction. In a more particular embodiment, the drive sleeve may be disposed proximally with the user activation device. In more specific embodiments, the user activated device may include a ribbed surface designed to enable the user to firmly grip the drive sleeve when setting the device and a smoothly recessed proximal surface designed to provide comfortable handling when delivering the device.

The term "releasably engaged" preferably means that the two components of the present device are engaged to transmit force or movement in only one direction, preferably during delivery.

The term "piston rod" refers to a member adapted to run through/within the housing, which is designed to transfer axial movement through/within the drug delivery device, preferably by the drive means to the piston, for the purpose of expelling/delivering the injectable product. The piston rod may be flexible or rigid. It may be a simple rod, screw, rack and pinion system, worm gear system, etc. The term "piston rod" also refers to a member having a circular or non-circular cross-section. It may be made of any suitable material known to those skilled in the art and may have a one-piece or multi-piece construction.

In a preferred embodiment, the piston rod includes one or more sets of longitudinally spaced ribs, teeth and/or recesses. In another preferred embodiment, the piston rod comprises at least one, more preferably two, external and/or internal helical threads. In another preferred embodiment of the piston rod a first helical thread is located at the distal end of the piston rod and a second helical thread is located at the proximal end of the piston rod, wherein the threads may have the same or preferably opposite alignment. In another preferred embodiment, the piston rod comprises a thread with the same lead at the proximal and distal end. Preferably, one of said threads is designed to engage with the drive sleeve. Alternatively or additionally, a thread engaging the drive sleeve is formed on the flexible region and/or regions of the piston rod. Preferably, the other of said threads is designed to engage with the housing, preferably with the inner housing.

The term "gear" refers to a wheel having teeth, which is used with a rack, preferably a rack that transmits force and/or movement. Preferably, the term "gear" refers to a geared wheel mounted in a carrier. In alternative embodiments, the term "gear" refers to a lever used with a support element within the housing, such as a rib, tooth, or notch, to transmit force and/or movement. Preferably, one support element is located on an interior surface of the housing and the other support element is located on a surface of the drive component.

The term "rack" refers to any member having a linear arrangement of ribs and/or notches and/or teeth. In a preferred embodiment, the first rack is located within the housing or the first rack is part of the housing and the second rack is located within the drive component or the second rack is part of the drive component. In another preferred embodiment, one and/or both of the racks on the housing or the drive member, more preferably one, is flexible and/or pivotable and/or movable in one or more axial directions, more preferably in one axial direction.

The "distal end" of the device or device member refers to the end closest to the delivery end of the device.

The "proximal end" of a device or device component refers to the end furthest from the delivery end of the device.

The term "mechanical interaction" refers to any mechanical interaction adapted to prevent the piston rod from moving further proximally with respect to the housing during proximal movement of the drive member, e.g. by the stop member having moved into abutment with the stop. The plunger rod may be moved proximally during the first proximal movement of the drive member until the stop member abuts the stopper and additional proximal movement of the plunger rod with respect to the housing is prevented by the stop member abutting the stopper. The drive member may be further moved in the proximal direction with respect to the plunger rod and the housing after the stop member and the stopper have been moved into abutment.

Other features, advantages and benefits will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.

Drawings

Fig. 1 shows a cross-sectional view of a first embodiment of a drug delivery device in a first, full cartridge position;

fig. 1A shows another cross-sectional view of the first embodiment of the drug delivery device in a first, full cartridge position;

fig. 1B shows an enlarged, fragmentary, simplified view of a first embodiment of a drug delivery device in a first, full-cartridge position;

fig. 2 shows a cross-sectional view of a first embodiment of a drug delivery device in a second, ready-to-dose setting position;

fig. 2A shows an enlarged, simplified view of a part of the first embodiment of the drug delivery device in a second, ready-dose setting position;

fig. 3 shows an enlarged, simplified view of a part of the first embodiment of the drug delivery device in a third, ready-dose delivery position;

fig. 4 shows a cross-sectional view of the first embodiment of the drug delivery device in a fourth, final dose delivery position;

fig. 5 shows a cross-sectional view of the second embodiment of the drug delivery device in the first, full cartridge position;

fig. 5A shows an enlarged, fragmentary, simplified view of a second embodiment of a drug delivery device in a first, full-cartridge position;

fig. 5B shows another enlarged, fragmentary, simplified view of the second embodiment of the drug delivery device in the first, full-cartridge position;

fig. 6 shows an enlarged, fragmentary, simplified view of the second embodiment of the drug delivery device shown in fig. 5A during preparation for dose setting;

fig. 7 shows a cross-sectional view of the second embodiment of the drug delivery device in a second, ready-to-dose setting position;

fig. 7A shows an enlarged, simplified view of a part of a second embodiment of a drug delivery device in a second, ready-dose setting position;

fig. 8 shows a cross-sectional view of the second embodiment of the drug delivery device in a fourth, final dose delivery position.

Similar elements, elements of the same type and elements performing the same function are labeled with the same reference numeral throughout the drawings.

Detailed Description

Fig. 1 to 4 show a drug delivery device according to a first embodiment.

The drug delivery device 1 comprises a cartridge retaining part 2 and a main (outer) housing part 3. The proximal end of the sleeve retaining portion 2 and the distal end of the main housing portion 3 are secured together by any suitable means known to those skilled in the art. In the embodiment shown, the sleeve retaining portion 2 is secured within the distal end of the main housing portion 3.

The sleeve 4 is held in the sleeve holding portion 2. A medicament 5, such as the fluid medicament described above, is disposed within the sleeve 4. The piston 6 is held within the sleeve 4. The piston 6 seals the medicament within the sleeve 4 at the proximal side of the sleeve. When in use, movement of the piston 6 distally within the sleeve 4 expels medicament from the sleeve.

A removable cap 7 is releasably retained on the distal end of the cartridge retaining portion 2. The removable cap 7 may optionally be provided with one or more windows 30 through which the position of the piston 6 within the sleeve 4 can be viewed. The distal end of the cartridge retaining portion 2 is provided with a distal threaded region 8 designed for attachment of a suitable needle assembly to enable expulsion of the medicament 5 from the cartridge 4.

The main housing part 3 is provided with an inner housing 9. The inner housing 9 is fixed against rotational and axial movement relative to the main housing part 3. Alternatively, the inner housing 9 may be integrally formed with the main housing portion 3. The inner housing 9 is equipped with a toothed rack 15. The toothed rack 15 extends along the main axis of the inner housing 9 and/or along the main axis of the outer housing part 3. The main shaft of the outer housing part 3 may extend between the proximal and distal ends of the main housing part.

In addition, the inner housing 9 is equipped with a plurality of guide lugs (not explicitly shown) and one or more stop members 10 (see fig. 1A), which are for example a pawl-type arrangement and/or a ratchet arrangement, such as ratchet pawls. For example, each stop feature 10 may be an integral part of the inner housing 9 or may be a separate component as shown in fig. 1A. The respective stop members 10 are fixed against rotational and axial movement relative to the main housing portion 3. Each of the motion limiting members may be an elastic motion limiting member. The respective stop elements may be arranged to deform in the radial direction.

The drug delivery device 1 comprises a piston rod 11. The piston rod 11 is arranged within the main housing part 3. The piston rod extends along the main length of the main housing part 3. The stop member 10 engages the outer surface of the piston rod 11. The surfaces are arranged opposite to each other.

The piston rod 11 is provided with a first set of recesses 12 on its outer surface. Preferably, two external surfaces arranged opposite each other are provided with respective first sets of recesses 12. The recess 12 is arranged in the main length direction of the piston rod 11. Each stop member 10 is arranged to engage a notch 12 in each first set of notches. Each stop member 10 is arranged to limit proximal movement of the piston rod 11 relative to the main housing part 3 during setting of a dose. This can be achieved, for example, as follows: each stop member 10 abuts a projection 27 forming the distal end of the recess of the first set of recesses 12 in which the stop member 10 is located. Thus, the distal end of each notch in the first notch set acts as a stop as further described in the context.

The inner surface of the piston rod 11 is provided with a second set of recesses 13. Two inner surfaces arranged opposite each other may be provided with a respective second set 13 of recesses. The recesses 13 are arranged side by side in the main length direction of the piston rod 11.

The piston rod 11 is arranged to drive the piston 6 in a distal direction to deliver a dose of the drug 5. The bearing surface 14 at the distal end of the piston rod 11 is arranged to abut the proximal end face of the piston 6 and in particular to advance the piston 6 further into the sleeve 4 to deliver a dose of medicament 5. As shown in fig. 1 and 1A, i.e. before the device is prepared, the bearing surface 14 is arranged at a distance from the piston 6, for example with an air gap formed between the bearing surface 14 and the piston 6. Alternatively, the bearing surface 14 may abut the proximal end face of the piston 6 before the device 1 is prepared, thereby bringing the piston rod 11 and the piston 6 into direct mechanical contact.

The drug delivery device 1 comprises a gear wheel 16 comprising a carrier 17 and a gear wheel 18. The gear wheel 18 and the carrier 17 are connected to each other. A gear wheel 18 is arranged to rotate in the carrier 17. The gear wheel is rotatable relative to the main housing part 3 and/or the inner housing 9. The gear 16 is located in a groove in the piston rod 11. The claw arm 19 is disposed on the carrier 17. The claw arms 19 project from the carrier 17 in the radial direction. The pawl arm 19 is releasably engaged with the second set of recesses 13 of the piston rod 11. The pawl arms 19 of the carrier 17 are designed to transfer a force to the piston rod 11 in the distal direction when delivering a dose and to move the gear wheel 16 relatively to the piston rod 11 in the proximal direction when setting a dose. The teeth of the gear wheel 18 can be permanently engaged with the teeth of the toothed rack 15 of the inner housing 9.

The drive member 20 extends around the piston rod 11. The driving part 20 includes a rack portion 21. The drive member 20 further comprises an activation portion 22. The rack portion 21 and the activation portion 22 are fixed to each other to prevent rotational and axial movement therebetween. Alternatively, the drive component 20 may be a unitary member that includes an integrated rack portion 21 and an integrated activation portion 22. The drive member 20 is movable in a proximal direction relative to the main housing part 3 to set a dose and in a distal direction relative to the main housing part 3 to deliver a dose.

The rack portion 21 is provided with a rack 23. The rack 23 may extend along a major axis of the rack portion 21. The teeth of the rack 23 of the rack portion 21 may be permanently engaged with the teeth of the pinion wheel 18.

The drive member 20 has a plurality of guide slots (not explicitly shown) in which guide tabs (not explicitly shown) of the inner housing 9 are located. These guide slots define the extent of axial movement permitted for the drive member 20 relative to the main housing portion 3. In the embodiment shown, the guide slots may also prevent rotational movement of the drive member 20 relative to the main housing portion 3.

The activation portion 22 of the drive member 20 has an application face 25 and a plurality of gripping surfaces 24.

To improve the intuitiveness of the operation of the device, the main housing portion 3 may optionally be provided with a window 26 through which a graphical status indicator provided on the drive member 20 may be viewed.

Fig. 1B shows a simplified partial cross-sectional view of the above-described drug delivery device, i.e. before the ready dose is expelled (delivered) from the cartridge 4. The device is arranged to expel a small prepared dose of medicament during a first distal movement of the drive member 20 and the piston rod 11.

The bearing surface 14 of the piston rod 11, e.g. the distal end of the piston rod, is arranged at a distance d from the proximal end of the piston 6_PP. Alternatively, the piston rod may abut the piston. A motion limiting member 10, such as an elastic ratchet pawl, engages the piston rod 11 and is fixed against rotational and axial movement relative to the main housing part (not explicitly shown). Biasing the stop member 10 radially inward. Each stopper member 10 is disposed in a first notch 12a in a first notch group 12 disposed outside the piston rod 11. Each stop member 10 engages with the piston rod 11. The distal end of each stopper member 10 is disposed at a first distance d from the distal end (projection 27) of the first recess 12a_F. The piston rod 11 is proximally movable a first distance d during proximal movement of a drive member (not explicitly shown) for setting a dose_FUntil stop member 10 abuts the stopper (protrusion 27) and prevents further proximal movement of the plunger rod.

The first recess 12a may extend deeper into the piston rod 11 in the radial direction than one or all of the other recesses 12b, 12c and 12d in the first set of recesses, which are arranged further from the distal end of the piston rod 11 than the first recess 12 a. In case the drug delivery device is storable in the state shown in fig. 1B, each stop member is subjected to less stress when it is arranged in the first recess 12a than when it is arranged in another recess, i.e. the recess 12B, 12c or 12d. Since the mechanical stress on the stop element 10 can be reduced in this way during storage of the device, the risk of material fatigue of the elastic stop element 10 is reduced. The distal ends of the recesses 12a to 12d may be equidistantly arranged on the piston rod 11.

The drive element, e.g. a claw arm 19, of the carrier 17 engages with the first recess 13a in the second set of recesses 13, which are arranged inside the piston rod. The drive element abuts the distal end of the first recess 13 a. The second set of recesses 13 further comprises recesses 13b, 13c, 13d and 13e, said recesses 13b, 13c, 13d and 13e being arranged further from the distal end of the piston rod 11 than the first recess 13 a. The distal end of the first notch 13a and the distal end of the next notch 13b are preferably arranged closer to each other than the distance between the distal ends of other pairs of notches, preferably than the distance between the distal ends of all other adjacent pairs of notches in the second set of notches 13.

The operation of the drug delivery device of fig. 1 to 3 will now be described.

To set the priming dose, the drive member 20 is moved proximally. For this purpose, the user grips the gripping surface 24 of the drive member 20. Then, the user pulls the drive member 20 in the proximal direction away from the main housing portion 3, thereby moving the rack portion 21 in the proximal direction.

Since the teeth of the gear wheel 18 of the gear 16 are meshed with the teeth of the rack 23 of the rack portion 21 and the teeth of the rack 15 of the inner housing 9, proximal movement of the rack portion 21 causes the gear wheel 18 to rotate and move proximally, thereby moving the gear 16 in a proximal direction relative to the inner housing.

Since the stop member 10 allows the piston rod 11 to move proximally relative to the inner housing 9 during a first proximal movement of the drive member 20 to set a prepared dose, the piston rod follows the proximal movement of the drive member, preferably only during a part of the total proximal movement of the drive member 20. Proximal movement of the piston rod 11 may be achieved by friction between the radially outwardly biased claw arms 19 of the carrier 17 and the piston rod within the recess 13a and/or mechanical contact between the claw arms 19 and the proximal side of the recess 13 a. Thus, the piston rod 11 follows the proximal movement of the gear wheel 16 relative to the inner housing 19.

The piston rod 11 is moved in the proximal direction until the stop members 10 abut the protrusions 27 on the distal end of the respective first recesses 12a, i.e. the piston rod 11 is moved proximally a distance d during setting of the priming dose_F. After the stop member 10 has abutted the protrusion 27, the drive member 20 is moved proximally with respect to the piston rod 11. After the respective stop means 10 has moved into abutment with the protrusion 27, the piston rod is prevented from further proximal movement relative to the inner housing 9. The gear wheel 16 follows the proximal movement of the drive member 20 relative to the inner housing 9 and the piston rod 11. When the gear wheel 16 is moved proximally relative to the piston rod 11, the claw arm 19 of the carrier 17 is moved proximally in a proximal direction from the first notch 13a of the second set of notches into the next notch 13 b. The claw arms 19 of the carrier 17 are pressed radially inwards due to the mechanical interaction between the claw arms 19 and the bevel provided on the proximal side of the first recess 13 a. The claw arm 19 slides over the ramp and engages the next notch 13b (see fig. 2A). When the claw arm 19 slides into the recess 13b, an audible and/or tactile feedback may be generated. Thus, the user is informed that the prepared dose is set. In addition, visual feedback regarding the ready dose being set may be provided by a graphical status indicator provided on the drive member 20, which is viewable through the window 26 in the main housing portion 3.

This embodiment therefore has the advantage of allowing the piston rod 11 to move backwards a distance d during the first proximal movement of the drive member 20_FThis minimizes the length of the drug delivery device (e.g., pen injector). At the same time, this also coincides with the click sound at the end of this first dose (e.g. priming dose) setting and the end of the first dose setting stroke of the drive member 20, also for any subsequent dose setting stroke (which stroke also preferably coincides with the graphical state indication).

The proximal movement of the driving member 20 is restricted by the guide groove of the rack portion 21. When the movement of the drive member 20 is finished, the claw arm 19 of the carrier 17 engages with the next recess in the second set of recesses 13 of the piston rod 11, as shown in fig. 2 and 2A. The pawl arm 19 remains in the first recess 13a until the one or more motion limiting members 10 prevent further proximal movement of the plunger rod 11 due to the mechanical interaction between the respective motion limiting member and the stopper (protrusion 27) of the plunger rod 11. The piston rod 11 is moved proximally a distance d during setting of a priming dose_F. Thus, the distance between the piston 6 and the piston rod 11 increases d after the priming dose has been set_F. The distance between the piston rod and the piston after the set preparation dose has been d_PP+d_F。

After the prepared dose has been set, the user may deliver the dose by pressing the administration face 25 of the activation part 22 of the drive member 20. The drive member 20 and the rack portion 21 are axially moved in the distal direction relative to the main housing portion 3 by this action. Since the teeth of the pinion 18 of the pinion 16 mesh with the teeth of the rack 23 of the rack portion 21 and the teeth of the rack 15 of the inner housing 9, the pinion 18 of the pinion 16 is rotated and moved in the distal direction. Thus, the gear 16 moves longitudinally relative to the housing in a distal direction. As the pawl arms 19 of the carrier 17 of the gear wheel 16 engage with the second set of recesses 12 of the piston rod 11, the piston rod 11 is moved longitudinally in a distal direction relative to the inner housing 9. The gear 16, in particular the claw arm 19, abuts the distal side of the recess 13b such that a distal movement of the gear causes a distal movement of the piston rod 11. The piston rod 11 is only moved longitudinally. The piston rod 11 does not rotate relative to the housing.

The piston rod has moved in the distal direction with respect to the housing d_PP+d_FThereafter, the bearing surface 14 of the piston rod 11 bears against the piston 6 of the sleeve 4, wherein continued distal movement of the piston rod 11 causes distal movement of the piston 6, thereby delivering a prepared dose of medicament, for example through an attached needle (not explicitly shown). In this manner, gaseous inclusions within the hub and needle are removed. Preferably, the drug is deliveredThe delivery device is oriented with its distal end up (i.e., needle up) for preparation.

The distal movement of the drive member 20 may be limited to a guide slot (not explicitly shown) of the rack portion 21.

When the piston rod 11 is moved distally, the stopper member 10 is pressed radially outwards and slides along the ramp, and the stopper member 10 then engages the next recess 12b in the first set of recesses. When the piston rod is moved relative to the stop means 10 and the stop means is guided with the piston rod 11 into the next (second) recess 12b (see fig. 3), an audible and/or tactile feedback may be generated indicating that a ready dose has been delivered due to the mechanical interaction between the stop means 10 and the piston rod 11. In addition, visual feedback regarding the dose being delivered may be provided by a graphical status indicator provided on the drive member 20, which may be viewed through a window 26 in the main housing portion 3.

After distally moving the piston rod 11 to deliver a dose, the piston rod 11 may be moved proximally a short distance to reduce the pressure of the piston rod 11 on the piston 6 of the sleeve 4. The distance between the distal end of the stop member 10 and the distal end of the recess 12b, 12c, 12d before setting the next dose is advantageously smaller than d_FThe distal end of the notch 12b, 12c, 12d. Preferably, the stop member 10 already abuts the distal end of the second recess before the next dose is set. Thus, the proximal movement of the piston rod after priming is limited to the stop member having interacted with the stopper before the next dose is set.

The distal displacement of the piston rod 11 may be equal for all doses to be delivered. In particular, the device 1 may be a fixed dose device, i.e. a predetermined fixed dose is delivered after a first distal movement of the piston rod 11, e.g. after the device has been prepared. Since the piston rod 11 moves proximally (away from the piston 6) during the priming movement of the drive member 20, the priming dose is thus reduced, since the displacement of the piston distally in the sleeve is reduced by d_F. For the preparation dose and the subsequent dose to be deliveredThe distal displacement of the piston rod during delivery of a dose may be equal.

The distal movement of the piston 6 relative to the sleeve 4 for a second dose to be delivered, preferably for all doses to be subsequently delivered, is preferably greater than the distal movement of the piston to deliver a prepared dose from the sleeve. When the drive member is moved proximally after priming for setting a dose, the piston rod 11 is moved significantly proximally (e.g. d is moved)_FOr larger) is advantageously avoided.

Since the piston rod is moved proximally before delivering the priming dose, the length of the device may be reduced, e.g. compared to a device in which the piston rod has been arranged at a distance from the piston in an initial setting (e.g. when an unused pen-type device is administered to a patient) and no proximal movement of the piston rod away from the piston occurs before a given priming dose is expelled.

For the prepared and subsequent doses to be delivered, audible and tactile feedback about the dose having been set or delivered may occur at respective points in time.

Other doses may be delivered as needed until a predetermined maximum number of doses is reached. Fig. 4 shows the drug delivery device in a state where the maximum number of doses has been delivered. In this state, the proximal end face 28 of the carrier 17 abuts the inner distal end face 29 of the piston rod 11 to prevent further axial movement of the gear wheel 16, and thereby the drive member 20, in the proximal direction. The device can be locked out and rendered inoperable in this manner after the maximum number of doses has been delivered.

WO 2008/058666 a1 describes a device similar to that described in relation to fig. 1 to 4, wherein the piston rod is only moved in the axial direction relative to the housing and not rotated, the entire content of the disclosure of said WO 2008/058666 a1 being expressly incorporated in the present application by reference.

Fig. 5 to 8 show a drug delivery device according to a second embodiment.

A sleeve 4 from which a number of medicament doses 5 can be delivered is arranged within the sleeve retaining portion 2. The piston 6 is held within the proximal end of the sleeve 4.

A removable cap 7 is releasably retained on the distal end of the cartridge retaining portion 2. The removable cap 7 is optionally provided with one or more windows 30 through which the position of the piston 6 within the sleeve 4 can be observed.

In the shown embodiment, the distal end of the cartridge retaining portion 2 is provided with a distal threaded region 8 designed for attachment of a suitable needle assembly (not shown) to enable expelling of the medicament 5 from the cartridge 4.

The main housing part 3 is provided with an inner housing 9. The inner housing 9 is fixed against rotational and axial movement relative to the main housing part 3. Alternatively, the inner housing 9 may be integrally formed with the main housing portion 3. The inner housing 9 is provided with a threaded opening 31 (preferably circular). The opening 31 may include a protrusion 35. The protrusion 35 may be threaded or partially threaded. The opening 31 may extend through the entire inner housing 9. In the illustrated embodiment, the threaded opening 31 includes a series of partial threads rather than full threads. In addition, the inner housing 9 may be equipped with a plurality of guide slots and claw means (not explicitly shown).

The piston rod 11 is disposed within the main housing 3. A first thread 32 is formed at the distal end of the piston rod 11. The piston rod 11 may have a substantially circular cross-section. The first thread 32 of the piston rod 11 extends through the threaded opening 31 of the inner housing 9 and is threadedly engaged with the threaded opening 31 of the inner housing 9. The first thread 32 is formed on the outside of the piston rod 11. A pressure foot 33 is located at the distal end of the piston rod 11. Arranging the presser foot 33 adjacent the piston 6A proximal end face. The piston rod 11 is arranged at a distance d from the piston 6_PP. Preferably, the distance d_PP0 and presser foot 33 abuts piston 6.

A second thread 34 is formed at the proximal end of the piston rod 11. The second thread 34 is formed on the outside of the piston rod 11. In the illustrated embodiment, the second threads 34 comprise a series of partial threads rather than full threads. The second thread 34 is formed on a flexible arm 36 of the piston rod 11.

The first and second threads 32, 34 are oppositely disposed.

A drive member 20, such as a drive sleeve, extends around the piston rod 11. The drive member 20 includes a threaded portion 37. The threaded portion 37 may be provided inside the drive member 20. The threaded portion 37 may have a substantially cylindrical cross-section. The drive member 20 further comprises an activation portion 22. The threaded portion 37 and the activation portion 22 are secured to one another to prevent rotational and/or axial movement therebetween. Alternatively, the drive component 20 may be a unitary member that includes an integrated threaded portion 37 and activation portion 22.

In the embodiment shown, the threaded portion 37 is provided with a longitudinally extending (helical) thread 38 formed on the inner surface of the drive member 20.

The flank (flank) on the distal side of the thread 38 is designed to remain in contact with the second thread 34 of the piston rod 11 when delivering a dose. The flanks on the proximal side of the thread 38 are designed to allow the second thread 34 of the piston rod 11 to disengage from the thread 38 when setting a dose. The thread 38 of the threaded portion 37 releasably engages with the second thread 34 of the piston rod 11 in this manner. Thus, the drive member 20 is releasably engaged with the piston rod.

The drive member 20 has a plurality of features formed on an outer surface thereof that are designed to move axially within guide slots (not expressly shown) in the inner housing 9. These guide slots define the extent of axial movement permitted for the drive member 20 relative to the main housing portion 3. The guide slots may also prevent rotational movement of the drive member 20 relative to the main housing portion 3.

To improve the intuitiveness of the operation of the device, the main housing portion 3 may optionally be provided with windows through which graphical status indicia provided on the drive member 20 may be viewed.

As in the previous embodiment, the piston rod 11 is arranged at a distance d from the piston 6 before setting the priming dose_PP(see FIG. 5). Alternatively, the presser foot 33 may abut the piston 6 before setting the priming dose.

The first thread 32 of the piston rod 11 is equipped with a plurality of stops. The stopper is arranged to mechanically interact with the stop member 10 to limit or prevent proximal movement of the piston rod relative to the housing 3. Each stop may be a flattened step 39 of the first thread 32 (see fig. 5A). For example, each stop may be embodied as a region having a thread angle that is different than a thread angle in an adjacent region of the first thread 32. It should be understood that a shoulder or recess in the first thread 32 is also suitable as a stop. The protrusion 35 in the opening 31 may serve as the stopper 10.

Fig. 5A shows a partial view of the piston rod 11 in the above-mentioned region, in which the first thread 32 and the stop element 10 engage with each other. The side closest to the distal end is labeled D and the side closest to the proximal end is labeled P in fig. 5A. Fig. 5A shows only one step. However, the first thread 32 preferably includes a plurality of steps 39 that are equidistantly disposed (when viewed along the thread). After the dose has been delivered, i.e. after the piston rod 11 has advanced the piston 6 further into the sleeve 4, the stop feature 10 is arranged to mechanically interact with another stop (not shown) or the stop feature 10 has interacted with another stop (not shown) different from the one with which the stop feature mechanically interacts before the dose is delivered.

The motion limiting member 10 may have a parallelogram cross section or a trapezoidal cross section.Before setting the prepared dose, the stop member 10 is arranged at a distance d from the stop_F(see FIG. 5A). As described with respect to the previous embodiments, this allows the piston rod 11 to move proximally with respect to the stop feature 10 before the ready dose is delivered. In contrast to the previous embodiments, the piston rod 11 is adapted to rotate and translate relative to the housing when the piston rod is moved distally to deliver a dose. It will be appreciated that during the first proximal movement of the drive member, the piston rod is also caused to rotate and translate when the piston rod is caused to move proximally.

The operation of the drug delivery device according to the present embodiment will now be described.

To set the prepared dose, the user grips the gripping surface 24 of the drive member 20. The user then pulls the drive member 20 in a proximal direction away from the main housing portion 3. The drive member 20 does not rotate during this proximal movement.

The piston rod 11 follows a part of the proximal movement of the drive member 20 relative to the housing, because the piston rod interacts with the drive member 20 and because the stop member 10 does not prevent this first proximal movement. The turn (turn)38a of the thread 38 may include a ramp 40 that rises as it extends in a distal direction. The ramp 40 may extend distally only over a portion of the thread turn 38 a. Before setting (preparing) a dose, the second thread 34 of the piston rod 11 is arranged on the proximal side of the bevel 40. Due to the friction between the piston rod and the drive member 20, in particular between the second thread 34 and the ramp 40 of the piston rod, the piston rod follows the first movement of the drive member 20 in the proximal direction.

The piston rod 11 follows the proximal movement of the drive member 20 relative to the housing until the stop member 10 mechanically interacts (e.g. by mechanical contact) with the stop, i.e. the step 39, of the first thread 32. During proximal movement of the piston rod relative to the housing, the piston rod is rotated relative to the housing and the drive member. The piston rod 11 moves a distance d towards the proximal end_FUntil the piston rod 11 is proximally displaced with respect to the housing 3Is limited to a stop that mechanically interacts with the stop member 10 (see fig. 5A and 6).

As drive member 20 continues to move proximally, stopper 39 and stop member 10 remain in mechanical interaction and the drive member moves proximally relative to plunger rod 11. The interaction between the stopper and the stop member 10 prevents further proximal movement of the piston rod 11 relative to the housing 3 and the piston 6. Thus, the initial distance d between the piston rod 11 and the piston 6_PPCan increase d_FTo d_PP+d_F。

When the drive member 20 is moved proximally relative to the piston rod 11, the flexible arms 36 of the piston rod are displaced radially inwards and move past the distal end of the ramp 40. Thus, the next turn 38b of the thread 38 of the drive member 20 may engage the thread 34 of the piston rod under the action of the flexible arm 36. When the proximal end of the plunger rod slides over the distal end of ramp 40, audible and tactile feedback may be generated regarding the ready dose to be set.

In addition, visual feedback regarding the setting of a dose may be provided by a graphical status indicator provided on the drive member 20, which is viewable through a window in the main housing portion 3.

The chamfer 40' in the next turn 38b of the thread 38 may have a smaller slope than the chamfer 40 in turn 38 a. The ramp 40' may extend distally over the entire thread turn 38 b. Thus, after the device 1 has been prepared, the play between the drive member 20 and the piston rod 11 may be reduced.

After the prepared dose has been set, the user may deliver the dose by pressing the administration face 25 of the activation part 22 of the drive member 20. The drive member 20 is axially displaced in the distal direction relative to the main housing part 3 by this action. Since the second thread 34 of the piston rod 11 positively engages the thread 38 of the drive member 20, an axial movement of the drive member 20 in the distal direction causes a rotation of the piston rod 11 relative to the inner housing 9. When the piston rod 11 is rotated, the first thread 32 of the piston rod 11 rotates within the opening 31 of the inner housing 9, thereby axially moving the piston rod 11 in a distal direction with respect to the inner housing 9.

The piston rod 11 has moved d_PP+d_FThe pressure foot 33 of the piston rod 11 then carries the piston 6. Further distal movement of the piston rod 11 causes the piston to move distally relative to the cartridge 4 and expel a dose of medicament from the cartridge 4.

The distal movement of the drive member 20 is limited by guide slots (not explicitly shown) in the inner housing 9. Audible and tactile feedback indicating that a ready dose has been delivered is provided by the interaction between the detents of the drive member (not explicitly shown) and the detent means (not explicitly shown) of the inner housing 9. In addition, visual feedback regarding the dose being delivered may be provided by a graphical status indicator provided on the drive member 20, which may be viewed through a window in the main housing portion 3.

Other doses may be delivered as needed until a predetermined maximum number of doses is reached.

In the embodiment shown, the first thread 32 is advantageously provided with a plurality of stops 39 which can cooperate with the stop member 10 within the opening 31 to limit the movement of the piston rod 11 in the proximal direction during setting of the second and any subsequent dose to be delivered. The stop member may interact with different stops before and during setting of a subsequent dose.

Thus, since the piston rod does not move significantly in the proximal direction when setting the second dose and preferably any dose after the prepared dose, the (fixed) dose that can be delivered after preparation may be larger than the prepared dose if the piston rod moves distally a fixed displacement during delivery of each dose.

Additional doses may be delivered from the cartridge until the maximum number of doses has been delivered. Fig. 8 shows the drug delivery device in a state where the maximum number of doses has been delivered. In this state, the flange means 41 on the piston rod 11 may be interlocked with the flange means 42 on the drive member 20 to prevent further axial movement of the drive member 20 in the proximal direction relative to the housing.

WO 2008/058665a1 describes a device similar to that described in relation to fig. 5 to 8, wherein the piston rod is moved and rotated in axial direction relative to the housing, the entire content of the disclosure of said WO 2008/058665a1 being expressly incorporated in the present application by reference.

Claims

1. A drive assembly for a drug delivery device, comprising:

a housing having a proximal end and a distal end,

-stop means for limiting the proximal movement of the plunger rod relative to the housing during the proximal movement of the drive means by a mechanical interaction between the stop means and the stopper of the plunger rod,

it is characterized in that

The stop member and the stop member are arranged to move the plunger rod proximally a first distance before the stop member and the stop member mechanically interact during a first proximal movement of the drive member, wherein the first distance the plunger rod is moved proximally during the first proximal movement of the drive member is larger than the distance the plunger rod is subsequently moved proximally during a subsequent proximal movement of the drive member.

2. The drive assembly of claim 1, wherein the priming movement of the drive member comprises the first proximal movement of the drive member.

3. The drive assembly according to claim 1 or 2, wherein the drive member and the piston rod are releasably engageable.

4. The drive assembly of claim 1, wherein the stop member engages the piston rod.

5. The drive assembly of claim 1, wherein the stop member is fixed to prevent at least one or both of rotational movement relative to the housing and axial movement relative to the housing.

6. The drive assembly according to claim 1, wherein the stopper is provided on an outer surface of the piston rod.

7. The drive assembly according to claim 1, wherein the piston rod comprises a plurality of stops, the drive assembly being arranged to mechanically interact the stop member with another stop after the drive member has been moved distally to deliver a dose.

8. The drive assembly according to claim 7, wherein the stops are equidistantly arranged along the piston rod.

9. The drive assembly according to claim 7 or 8, wherein the piston rod and the stop member are arranged such that during a second and any subsequent proximal movement of the drive member to set a dose, the proximal movement of the piston rod is prevented by the stop member, the stop member having mechanically interacted with one of the stop members prior to the second and any subsequent proximal movement of the drive member to set a dose.

10. The drive assembly according to claim 1, wherein the drive assembly is arranged such that the piston rod is limited in rotational movement relative to the housing.

11. The drive assembly according to claim 1, wherein the drive assembly is arranged such that the piston rod is rotatable relative to the housing.

12. The drive assembly according to claim 1, wherein the piston rod comprises a thread and the stop member engages the thread of the piston rod.

13. The drive assembly of claim 12, wherein the stop feature is a thread.

14. The drive assembly of claim 12, wherein the stop feature is a partial thread.

15. The drive assembly according to claim 12 or 13 or 14, wherein the thread of the piston rod comprises the stop, wherein the stop is a threaded region having a different thread angle than an adjacent threaded region.

16. The drive assembly according to claim 1, wherein the first distance is greater than a distance that the piston rod moves proximally after the piston rod moves distally to deliver a dose.

17. The drive assembly according to claim 1, wherein the piston rod (11) and the stop member (10) are arranged to limit proximal movement of the piston rod (11) during the second and any subsequent proximal movement of the drive member (20) to set the dose.

18. The drive assembly according to claim 1, wherein the distal end of the housing (3) is arranged to be fixed with the proximal end of the cartridge retaining portion (2).

19. The drive assembly according to claim 1, configured to deliver a predetermined fixed dose after a first distal movement of the piston rod (11).