WO2018078187A1

WO2018078187A1 - Drug delivery device

Info

Publication number: WO2018078187A1
Application number: PCT/EP2017/077928
Authority: WO
Inventors: Nikolaj Eusebius JACOBSEN
Original assignee: Novo Nordisk AS
Current assignee: Novo Nordisk AS
Priority date: 2016-10-31
Filing date: 2017-10-31
Publication date: 2018-05-03
Anticipated expiration: 2019-04-30

Abstract

A drug delivery device (1) comprising: a housing (10), - a piston rod (20) threaded to the housing, - a piston rod drive member (30) for driving the piston rod in an expelling direction, - a torsion spring (60) arranged for urging the piston rod drive member (30) in a rotational expelling direction, and a dose dial member (50) configured for defining a travel distance of the piston rod (20) during expelling, wherein one of the piston rod drive member (30) and the dose dial member (50) comprises a helical track (37) and the other of the piston rod drive member (30) and the dose dial member (50) comprises a track follower (57) that engages the helical track (37), and wherein, during dose setting, the track follower (57) is adapted to travel the helical track (37) between a first stop (37.1) corresponding to a minimum dose limiting position and a second stop (37.2) corresponding to a maximum dose limiting position, and wherein, during dose expelling, the track follower (57) travels towards the minimum dose limiting position as a set dose is being expelled.

Description

DRUG DELIVERY DEVICE

The present invention relates to an assembly of components for a drug delivery device that allows a user to adjust and set the quantity of at least one dose of an injectable liquid drug and to dispense the set dose of the product and to apply said product to a patient, preferably by injection. In particular, the present invention relates to a drug delivery device having an expelling mechanism controlled by a rotatable piston rod drive member.

BACKGROUND

In the disclosure of the present invention reference is mostly made to drug delivery devices used e.g. in the treatment of diabetes by delivery of insulin, however, this is only an exemplary use of the present invention.

Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicinal product, such as liquid drugs, and further providing administration of the liquid to a patient, are as such well-known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe. Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and the dose expelling must be simple and intuitive. The device should be inexpensive to manufacture and easy to dispose. These factors are of primary importance where the device is to be disposable rather than reusable. However, even for reusable devices, all these factors are still important. In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.

Pen-type drug delivery devices typically incorporate a dose scale component in the form of a scale sleeve which is in threaded engagement with a further component of the device. One example is shown in US patent No. 8,608,708. The dose scale component is typically a component separate from a dose dial member which is the component that the user grips and operates for dialling the size of a dose to be injected. The dose scale component typically includes geometries to engage with other cooperating geometries for providing a minimum dose limitation and/or a maximum dose limitation, the minimum dose limitation at the same time providing a dose stop during an expelling operation, i.e. a so-called end-of-dose stop. Document WO 2015/032770 Al discloses a drug delivery device which incorporates a number sleeve that is in threaded engagement with a housing thread and wherein a drive member moves axially with the number sleeve. The end-of dose condition is assumed when the drive member has been moved helically during the dose delivery state back to a rest state wherein ratchet teeth engage.

Relative to the drug delivery devices previously disclosed there remains a need for an improved drug delivery device.

SUMMARY

It is an object of the present invention to provide a drug delivery device comprising only a limited number of components. It is a further object to provide a drug delivery device having simplified means of providing a minimum dose limitation and/or a dose maximum limitation. It is a further object to provide a drug delivery which enable inclusion of an injection button that is arranged at a proximal end of the drug delivery device. In the disclosure of the present invention, embodiments and aspects will be described which will address one or more of the above objects or which will address objects apparent from the below disclosure as well as from the description of exemplary embodiments. In a first aspect, the present invention relates to a drug delivery device comprising :

a housing extending along an axis,

a piston rod axially movable in an expelling direction relative to the housing, a piston rod drive member coupled to the piston rod for driving the piston rod in the expelling direction as the piston rod drive member is rotated in a rotational expelling direction, the piston rod drive member being :

o prevented from rotating in the rotational expelling direction in a dose setting state, and

o capable of rotating in the rotational expelling direction in a dose expelling state, a torsion spring operatively coupled with the piston rod drive member and arranged to provide a force for urging the piston rod drive member in the rotational expelling direction,

a trigger release arrangement configured to:

o in the dose setting state, prevent the piston rod from moving in the expelling direction,

o in the dose expelling state, enable movement of the piston rod in the expelling direction,

a dose dial member for defining a travel distance of the piston rod, the dose dial member being :

o capable of rotation relative to the housing in the dose setting state, and o rotationally locked with respect to the housing in the dose expelling state, wherein one of the piston rod drive member and the dose dial member comprises a helical track and the other of the piston rod drive member and the dose dial member comprises a track follower that engages the helical track.

In accordance with such drug delivery device, the structure of the dose setting and expelling mechanism enables a particularly simple yet effective design requiring only a minimum number of components. Also, the traditional way of forming a dose stop, either at the zero dose position, at the maximum dose position, or at both the minimum and the maximum position, does not require a dedicated dose scale drum.

In some embodiments, the dose dial member forms a dialling member that at least partly is accessible from the exterior of the device and that may be gripped by the hand of a user of the drug delivery device.

In some embodiments the helical track and the track follower provides a direct engagement between the dose dial member and the piston rod drive member. In some embodiments, the helical track is formed integrally with the piston rod drive member and the track follower is formed integrally with the dose dial member.

In other embodiments, the helical track is formed integrally with the dose dial member and the track follower is formed integrally with the piston rod drive member. In still other embodiments, the drug delivery device is so configured that, in the dose setting state, the track follower is adapted to travel the helical track between a first stop corresponding to a minimum dose limiting position and a second stop corresponding to a maximum dose limiting position, and so that, in the dose expelling state, the track follower travels towards the minimum dose limiting position as a set dose is being expelled.

In some embodiments the track follower defines a first blocking geometry configured for engaging a first stop geometry at the minimum dose limiting position and wherein the first stop geometry is fixedly arranged relative to the helical track.

Also, in some embodiments, the track follower defines a second blocking geometry configured for engaging a second stop geometry at the maximum dose limiting position and wherein the second stop geometry is fixedly arranged relative to the helical track.

In some embodiments, in the dose setting state, the trigger release arrangement prevents the piston rod drive member from rotating in the rotational expelling direction whereas, in the dose expelling state, the trigger release arrangement allows rotation of the piston rod drive member in the rotational expelling direction.

In some embodiments, in the dose setting state, the trigger release arrangement prevents the piston rod drive member from rotating in any rotational direction.

In particular embodiments the piston rod drive member is axially movable from a first axial position to a second axial position, wherein the piston rod drive member is rotationally locked relative to the housing when the piston rod drive member assumes the first axial position, and wherein the piston rod drive member is free to rotate in the rotational expelling direction when the piston rod drive member assumes the second axial position. In some embodiments, when in the dose setting state, the piston rod drive member assumes the first axial position as a dose is being dialled up and/or a dose is being dialled down.

The trigger release arrangement may in some embodiments further comprise a trigger activator that is coupled to the piston rod drive member so that operation of the trigger activator by moving it axially moves the piston rod drive member axially from the first axial position to the second axial position. In particular embodiments, the trigger activator forms an injection button wherein the injection button is arranged at the proximal end of the housing, such as protruding axially relative to the housing. Said dose dial member and said injection button may in certain embodiments form a combined dose dial and injection button, and wherein the combined dose dial and injection button is mounted relative to the housing so as to be rotationally movable for setting a dose and axially movable for moving the piston rod drive member axially from the first axial position to the second axial position. The combined dose dial and injection button may in some embodiments be arranged to protrude axially from the proximal end of the housing.

In other embodiments, the dose dial member and the injection button are formed as two independently movable components, wherein the injection button is axially movable while the dose dial member is axially fixed but rotationally movable relative to the housing.

In still other embodiments, the trigger activator forms a needle shield which is configured to extend axially and shield a mounted injection needle, and wherein movement of the needle shield axially in the proximal direction, as the needle shield is pressed towards an injection site, the needle shield moves the piston rod drive member axially from the first axial position to the second axial position.

The piston rod may in some embodiments comprise a thread. A threaded nut member is either fixedly mounted or fixedly mountable relative to the housing. In such embodiments, the thread of the piston rod engages the threaded nut member.

Also, the piston rod drive member may be formed to comprise a rotational guide that connects to a longitudinal extending geometry of the piston rod so that, in the dose expelling state, the piston rod is forced to rotate through the threaded nut member as the piston rod drive member rotates.

The rotational guide of the piston rod drive member may be formed as an axially extending guide so configured that relative rotation between the piston rod and the piston rod drive member is prevented while axial relative movement is enabled. In further embodiments, there is provided a gearing between the piston rod drive member and the piston rod. Such gearing may include one or more threaded couplings that couples rotation of the piston rod drive member with rotation of the piston rod. The gearing may be provided with a gearing ratio that is either constant or varying during dose expelling.

In some embodiments, when in the dose setting state, the piston rod drive member maintains its axial position during dialling up a dose and/or dialling down a set dose. In the dose expelling state as the piston rod drive member rotates, the piston rod drive member is moved axially relative to the housing.

The helical track may be so configured that, in the dose expelling state as the piston rod drive member rotates, the piston rod drive member is moved distally relative to the housing. In alternative embodiments, the helical track is so configured that, in the dose expelling state as the piston rod drive member rotates, the piston rod drive member is moved proximally relative to the housing.

In still other embodiments, the piston rod drive member is held axially stationary in the second axial position as the piston rod drive member rotates in the dose expelling state. Due to the helical track, and in accordance with the particular design of the helical track, the dose dial member is moved either proximally or distally during dose expelling while the piston rod drive member rotates in its second axial position.

In some embodiments the drug delivery device does not comprise a mechanically operated dose dial scale component, i.e. does not include a component having a series of different dose size indications printed or disposed thereon.

As used herein, the term "insulin" is meant to encompass any drug-containing flowable medicine capable of being passed through a delivery means such as a cannula or hollow needle in a controlled manner, such as a liquid, solution, gel or fine suspension, and which has a blood glucose controlling effect, e.g. human insulin and analogues thereof as well as non-insulins such as GLP-1 and analogues thereof. In the description of exemplary embodiments reference will be made to the use of insulin. BRIEF DESCRIPTION OF DRAWINGS

In the following the invention will be further described with reference to the drawings, wherein : fig . 1 shows a perspective view of an embodiment of a medical injection device 1 in accordance with the invention, fig . 2 shows an exploded perspective view of the main components of the injection device 1 of fig . 1, fig . 3 shows a detailed exploded perspective view of a first sub-group of components of the injection device 1, fig . 4 shows a detailed exploded perspective view of a second sub-group of components of the injection device 1, fig . 5A and 5B show cross sectional side views oriented 90 degrees relative to each other of the device of fig . 1 in an initial state before the setting of a dose, fig . 5C and 5D are axial cross sectional views of section D-D and F-F indicated in fig . 5A, fig . 6A and 6B shows a cross section to each other of the device of fig . 1 in a state wherein a dose has been set, fig . 6C and 6D are axial cross sectional views of section D-D and E-E indicated in fig . 6A, fig . 6E show a side view corresponding to the view of fig . 6A but with the injection button partly cut, fig . 7A and 7B show cross sectional side views oriented 90 degrees relative to each other of the device of fig . 1 in a state after the set dose has been expelled and with the injection button still pressed-in, fig . 7C and 7D are axial cross sectional views of section G-G and F-F indicated in fig . 7A, fig. 8 is a magnified detailed view of the proximal part of the injection device 1 corresponding to the view shown in fig. 5B, fig. 9 is a magnified detailed view of a central section of the injection device 1 in a view slightly angled relative to the view shown in fig. 5B, wherein the piston rod drive member 30 is rotationally locked relative to the housing 10, fig. 10 is a detailed perspective view of spring base member 40, and fig. 11 is a side view of piston rod drive member 30.

DESCRIPTION

The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only. In the following, when the term member or element is used for a given component, it generally indicates that in the described embodiment the component is a unitary component, however, the same member or element may alternatively comprise a number of sub-components just as two or more of the described components could be provided as unitary components, e.g. manufactured as a single injection moulded part. The term "assembly" does not imply that the described components necessarily can be assembled to provide a unitary or functional assembly during a given assembly procedure but is merely used to describe components grouped together as being functionally more closely related. In the context of the following discussion it may be convenient to define that the term "distal end" in the appended figures is meant to refer to the end of the injection device which usually carries the injection needle whereas the term "proximal end" is meant to refer to the opposite end pointing away from the injection needle, i.e. the end carrying an injection button 50 as depicted in figure 1. The term "axial" refers to directions parallel with a central longitudinal axis of a held cylindrical drug cartridge.

Figs. 1 shows an embodiment of a drug delivery device according to the present invention in the form of a pen-formed auto-injection device 1, i.e. a so-called "injection pen" that includes an expelling mechanism incorporating a spring drive. Fig. 2 shows an exploded view of the parts included in the auto-injection device 1 shown in fig. 1. Figs. 3 and 4 provide magnified views of respective subgroups of the parts included in fig. 2. Referring to fig. 1, the injection device 1 is shown as a cartridge-based injection device wherein a drug filled cartridge 5 is accommodated within the housing (10, 15). The cartridge 5 has an elongated body and a pierceable septum (both non-referenced), the latter covering a distal outlet end of the body for cooperation with a replaceable subcutaneous injection needle (not shown). The cartridge 5 is provided with a piston driven by a piston rod forming part of the expelling mechanism and may for example contain an insulin, GLP-1 or growth hormone formulation. When a needle assembly (not shown) is mounted on the injection device 1, piston 6 may be forced in the distal direction along the expelling axis for expelling portions of the drug accommodated in the cartridge 5. Either the cartridge 5 or the housing 10/15 defines a needle mount adapted to releasably mount a needle assembly, e.g. a double pointed injection needle. In the shown embodiment, at the proximal end of injection device 1, a combined dose setting and injection button 50 is arranged facilitating both dose setting and dose expelling by a user operating the one and same operating knob/button.

The injection device 1 shown in fig. 1 may further include a cap (not shown in drawings) which detachably mounts relative to the distal end of distal part of housing 10 for protection of the contents of the cartridge 5 and optionally for protecting an injection needle which may be mounted at the distal end of the device. Fig. 2 provides an exploded perspective view of all components of injection device 1 whereas figs. 3 and 4 respectively show magnified views of a first and a second subgroup of components.

Fig. 3 mainly shows components of the housing and components arranged at the distal part of the injection device 1. The housing comprises a generally cylindrically formed main housing 10 which extends from the proximal end of the device to the distal end of the cartridge 5. A cartridge holder 15, formed as an end cap, attaches via a snap connection 15.2/10.2 to the main housing 10 in a manner to axially retain and protect the cartridge within the main housing 10. The cartridge holder 15 includes connection means 16 for replaceably receiving a needle assembly. In the shown example, the injection device forms a pre-filled drug delivery device wherein the cartridge 5 is irreplaceably accommodated in the housing 10/15, meaning that the device is to be discarded when the cartridge has been emptied. In alternative embodiments, and in accordance with the present invention, the drug delivery device may be designed to allow a loaded cartridge to be replaced. Main housing 10 includes a nut member having a threaded opening configured to receive a threaded rotatable piston rod. In the shown embodiment, the main housing 10 internally includes a partition wall 13 comprising a threaded central opening 17 that serves as the nut member. Fig. 3 further shows a piston washer 25 which serves as an axial bearing for the rotating piston rod and evens out the pressure exerted by the piston rod on the rubber piston.

Fig. 4 mainly shows components that make up the dose setting and expelling mechanism of injection device 1. The expelling mechanism mainly consist of a piston rod 20, a piston rod drive member 30 and a drive spring 60. Fig. 4 further shows components that mainly relates to a dial system of the dose setting mechanism, i.e. a spring base member 40, a dose dial member 50, a return spring 70 and an end-of-content limiter 80.

The piston rod 20 is a generally cylindrical elongated member that is formed with an external thread 27 extending along the length of the piston rod. Piston rod 20 further includes two opposing flattened longitudinally extending surfaces 21. The piston rod drive member 30 is formed as a generally tubular member having a longitudinal extending central opening. The opening includes two opposing flattened surfaces 31 adapted to slidably mate and engage with the two opposing flattened surfaces 21 of piston rod 20. In this way, when the device is in the assembled state as shown in fig. 5A and 5B, the piston rod 20 is received within the opening of the piston rod drive member 30 so that the piston rod 20 is axially movable relative to the piston rod drive member 30 but the two components rotates together. The distal end of piston rod drive member 30 is formed with an enlarged diameter disc-shaped geometry provided with a plurality of dog- teeth 32 arranged along the periphery. The disc-shaped geometry further includes a retaining feature 33 adapted to engage and retain a distal end portion of drive spring 60. As will be discussed further below, the piston rod drive member 30 is arranged inside housing 10/15 to be axially movable for a limited range of axial positions. When the piston rod drive member 30 assumes its extreme proximal position the dog-teeth 32 of piston rod drive member engages cooperating teeth 12 formed in the housing to prevent the piston rod drive member from rotating.

Spring base member 40 is formed as a generally tubular member comprising a reduced diameter tubular distal part configured to be inserted and received within a proximal opening formed in main housing 10 so that the spring base member 40 is rotatably movable within main housing 10. Spring base member 40 further includes an enlarged collar 45 with a diameter larger than the proximal opening formed in main housing 10. When the distal part of spring base member 40 is inserted into the proximal opening of main housing 10 a distally facing annular section of collar 45 engages a proximally facing annular section of main housing 10. The distally facing annular section of collar 45 includes a plurality of indexing protrusions 49 configured for engaging mating indexing depressions 19 of main housing 10 in a manner so that indexing protrusions 49 of spring base member 40 are slidingly movable relative to indexing depressions 19 of main housing 10 by rotational movements in discrete angular steps (cf. fig. 6E). The angular steps control the incremental size of each dose step and determine the number of rotational rest positions of the spring base member 40 relative to the main housing 10.

Dose dial member 50 is formed as a tubular element with a generally cylindrical outer surface adapted to be gripped for receiving a turning force from a user during dialling up a dose or during dialling down an initially set dose (dose cancelling). Dose dial member 50 is further formed with a proximally oriented end surface adapted to receive a distally oriented force from a finger of a user during dose injection of a set dose.

Dose dial member 50 further includes a tubular section 52 that connects to a proximal end portion of the dose dial member and extends in the distal direction. The tubular section 52 is configured for insertion into a proximally bore of spring base member 40. Tubular section 52 includes a pair of axially extending recesses or tracks 53. The pair of axially extending tracks 53 makes the tubular section being provided as two halves. Each axially extending track 53 is adapted to receive and cooperate with a spline element 43 extending radially inwards from the proximally bore of spring base member 40 so that the spring base member 40 is forced to rotate together with dose dial member 50. However, the provision of the spline elements 43 reaching radially into tracks 53 means that dose dial member 50 is axially movable relative to the spring base member 40 for a limited range of axial relative positions. The return spring 70 mentioned above is provided as a compression spring and performs as a mode switch controller which ensures that the injection device 1 is in dose setting state unless a distally directed force is exerted onto dose dial member 50 for pressing-in the dose dial member, in which case the injection device 1 enters into dose expelling state. As shown in fig. 5A and 5B, the return spring 70 is inserted in the proximal bore of spring base member 40 and rests with its distal end against a proximal facing annular section of spring base member 40. The proximal end of return spring 70 rests against a distally facing annular section of the dose dial member 50, i.e. it rests against the two halves of the tubular section 52. For all relative axial positions between the dose dial member 50 and the spring base member 40, the return spring 70 provides a biasing force for moving the dose dial member 50 towards the proximal end of the injection device 1 while biasing the spring base member 40 in the distal direction. Increasing bias is exerted by return spring 70 thus providing an increased retaining effect between indexing protrusions 49 and indexing depressions 19 upon increasing the dose setting amount. Referring to fig. 11, which shows a detailed view of the piston rod drive member 30, a track 37 extends helically on a proximal portion of the piston rod drive member. The helical track 37 extends between a first stop geometry 37.1 and a second stop geometry 37.2. The helical track 37 is in the shown embodiment formed as a recessed track configured for cooperating with a protruding track follower 57 arranged on the dose dial member 50. Referring back to fig. 4, the protruding track follower 57 is provided as two track followers, each forming a thread segment protruding radially inwards from each respective of the two half-sections of tubular section 52. The thread 57 formed by both thread segments protrude radially into and engage with helical track 37 so that rotational movement of dose dial member 50 relative to the piston rod drive member 30 results in relative axial movement between the dose dial member 50 and the piston rod drive member 30.

In the shown embodiment, a proximally oriented end section of the thread 57 is adapted to engage with the first stop geometry 37.1 of the piston rod drive member 30 for a specific rotational and axial relative position between the dose dial member 50 and the piston rod drive member 30. Also, a proximally oriented end section of the thread 57 is adapted to engage with the second stop geometry 37.2 of the piston rod drive member 30 for a different specific rotational and axial relative position between the dose dial member and the piston rod drive member. The position wherein the track follower 57 engages the first stop geometry 37.1 corresponds to the position that the dose dial member 50 assumes relative to the piston rod drive member 30 when a "0" dose has been adjusted, i.e. corresponding to the end-of-dose position. The position wherein the track follower 57 engages the second stop geometry 37.2, corresponds to the position that the dose dial member 50 assumes relative to the piston rod drive member 30 when a maximum dose is being adjusted. Non-limiting examples may include a fixed maximum dose of say 80 or 100 dose increments, for example spanning 4 total revolutions between the dose dial member 50 and piston rod drive member 30.

The skilled reader will readily appreciate that in alternative embodiments, in accordance with the present invention, the dose dial member 50 may define said helical track whereas the piston rod drive member 30 may define a track follower. Also contemplated are track and track followers which are differently formed than the shown helical track 37 and track follower, i.e. thread 57. For example, whereas the helical track 37 in the shown embodiment is formed in a way exhibiting a thread with a fixed lead, the helical track may instead be formed with a lead of variable pitch along its extension.

In the shown embodiment, the first stop geometry 37.1 and the second stop geometry 37.2 of the piston rod drive member 30 form the extreme end positions of helical track to engage geometries on the track follower 57. As such, these geometries form a rotational blocking limitation for preventing the dose dial member 50 from being adjusted beyond the intended operating range. However, as will be readily recognized by the skilled reader, in other embodiments the stop geometries on the component carrying or defining the helical track may be arranged on that component at locations other than at each end of the helical track while still enabling a blocking of movements outside the intended range of movements.

As for commonly available injection devices having a dose setting feature, a visual dose readout will typically be provided. However, for the shown embodiment, such visual dose readout will not be extensively described. Any known read-out principle may be incorporated in injection device 1. For example, a mechanical dial system may be provided between the dose dial member 50 and spring base member 40. Alternatively, the injection device 1 provides no mechanically based dose read-out. Instead, the user may be required to track the dialling by other means, such as by counting click sounds during dialling. In other embodiments, the design of the device may rely entirely on electronic dose sensing and an electronic display, either built into the device or relying on cooperation with an electronic add-on device, such as disclosed in WO 2007/107564 Al . In the shown injection device 1, dose dial clicks may be provided by forming longitudinally extending ribs 48 to cooperate with one or more click arms for example provided by the main housing. As best viewed on fig. 4, at the distal end of spring base member 40, a retaining feature 44 is formed to engage and retain a proximal end portion of drive spring 60. In the shown embodiment, the drive spring 60 is provided as a torque spring having helical windings. The drive spring 60 is configured for being torsionally strained, i.e. it changes torsional load during the dose setting operation. Spring base member 40 is rotated by dose dial member 50 so that by rotating spring base member 40 relative to main housing 10 during the dialling up of a dose additional torsional load is accumulated in drive spring 60. The drive spring 60 is configured to release torsional load during dose expelling as the piston rod drive member 30 rotates relative to the spring base member 40.

In alternative not shown embodiments, the drive spring may be configured to become fully pre-strained during manufacture with a load sufficient for expelling the entire usable contents of a held cartridge, i.e. the drive spring will not become strained during patient use of the device such as during dose setting. In such embodiments, the drive spring 60 may be fixedly grounded relative to the housing at one end whereas the other end of the drive spring is configured for rotating the piston rod 20 or the piston rod drive member 30 by releasing stored load of the drive spring 60.

For the shown embodiment, the assembled state of the injection device 1 is shown in fig. 5A and 5B which depict the state of the device as released by the manufacturer, i.e. with a full cartridge and with the dose dial member 50 arranged at the "0" dose setting. The above mentioned cap has been removed and an injection needle assembly may be attached relative to the needle mount 16. In the following, although not shown in the drawings, the operation of the injection device 1 will be described assuming an injection needle has been mounted onto needle mount 16.

Referring to figs. 5A and 5B, the dose dial member 50 assumes the extreme proximal position relative to main housing 10. This is the default relaxed axial position where the dose dial member 50 is urged proximally by return spring 70. Due to the engagement between the thread 57 of dose dial member 50 and the helical track 37 the piston rod drive member 30 is urged proximally by return spring 70 so that the piston rod drive member assumes its most proximal end position. In this position, which is best viewed on fig. 9, the dog teeth 32 of the piston rod drive member 30 engages the teeth 12 of the main housing 12 thereby rotationally retaining the piston rod drive member 30 against the torsional load exerted by drive spring 60. The piston rod 20 is thus also prevented from rotating and the axial position of the piston rod 20 may be so that the piston rod engages the piston washer 25 which is in abutting engagement with the piston 6. As already mentioned, the dose dial member 50 assumes its "0" dose setting. As best viewed on fig. 5B and 8 the end of thread segments 57 engages the proximal end of helical track 37, i.e. engages the first stop geometry 37.1, cf. fig. 11.

The end-of-content limiter 80 is viewable in fig. 5A. End-of-content limiter 80 is positioned within an axially extending channel 18 of the main housing and is adapted to travel axially from an initial start position towards an end-of-content stop position (non- referenced). The end-of-content stop position is determined by the manufacturer and represents the total amount of expellable doses from a single cartridge. The end-of- content limiter 80 is prevented from performing rotational movements around the axis. End-of-content limiter 80 includes a thread segment 87 that engages an external thread 47 provided on spring base member 40 (cf. fig. 10). For each dose increment that the user adjusts by dialling up the dose dial member 50, due to the thread connection 47/ 87, the end-of-content limiter 80 climbs the thread 47 and thus travels a pre-defined distance towards the end-of-content stop position. Likewise, during a dose cancellation movement, the end-of-content limiter 80 travels back towards the initial start position. As the doses that are being dialled up accumulates during use of the device, e.g. typically during several separate dose preparations, an end-of-content stop geometry (non- referenced) of the end-of-content limiter 80 will enter into engagement with a corresponding blocking geometry formed by the main housing 10, or alternatively the spring base member 40, to prevent the user from dialling up a dose larger than the amount remaining in the cartridge. This will prevent expelling of incomplete doses. Turning now to figs. 6A and 6B, these drawings represent the state of injection device 1 wherein a dose of a specific magnitude has been dialled up by turning the dose dial member 50. The position of the track follower, i.e. thread 57 relative to the stop geometries 37.1 and 37.2 of helical track 37 reveals that a dose of magnitude about half the size of a maximum dose has been dialled up, corresponding to about two complete turns of dose dial member 50. The spring base member 40 has been rotated a similar amount, causing the drive spring 60 to become additionally torsionally loaded. As the piston rod driver 30 is prevented from moving axially as well as rotationally during dose setting, the dose dial member 50 has been moved in accordance with the threaded connection 37/57 and thus slightly in the distal direction relative to the main housing 10. As a result, the return spring 70 is additionally compressed which helps in the maintenance of the rotational position of the spring base member 40 by means of indexing protrusions 49 and indexing depressions 19. Hence, the spring base member 40 is prevented from unwinding despite the torsional bias exerted by the spring member 60. Due to the rotation of the spring base member 40 the end-of-content limiter 80 has been moved proximally away from the initial start position and to an extent in accordance with the amount of turning of dose dial member 50.

In case the user wishes to set a dose corresponding to the maximum settable dose, the dose dial member 50 may be rotated even further until the thread 57 meets the second stop geometry 37.2. In case the user wishes to lower an initially set dose, this can be done by dialling down the dose dial member 50 until the rotational position of the dose dial member corresponds to the desired dose amount.

Fig. 7A and 7B show a subsequent state of injection device 1 after the dose dial member 50 having been pressed in in order to trigger the expelling operation, i.e. after expelling of the desired dose. In the shown state the dose dial member 50 is still pressed-in by maintaining an externally applied force on the dose dial member. To initiate the dose expelling process, the triggering has been initially enabled by the dose dial member 50 transferring the externally applied force via the threaded connection 57/37 to the piston rod drive member 30. This causes the piston rod drive member 30 to be moved axially in the distal direction whereby the dog teeth 32 disengage the teeth 12 of main housing 10. This in turn releases the piston rod drive member 30 allowing the piston rod drive member to rotate, this being rotationally driven by the torsional load of drive spring 60. As the piston rod 20 is forced to rotate with the piston rod drive member 30, the piston rod is spun forward through the threaded central opening 17 of the nut member. The rotation of the piston rod drive member 30 and the piston rod 20 continues while the thread 57 travels in the helical track 37 back towards the end-of-dose stop provided by stop geometry 37.1. During dose expelling, when the dose dial member 50 is fully pressed-in, the piston rod drive member 30 is moved slightly forward, as the set dose is expelled, and in accordance with the threaded connection 37/57. However, in the shown embodiment, as there is an axial guide or axially extending spline connection between the piston rod drive member 30 and the piston rod 20 the axial movement of the piston rod drive member 30 during dose expelling has no influence on the axial movement of the piston rod 20. The dose expelling movement stops when the thread 57 meets the first stop geometry 37.1 whereby the piston rod drive member 30 is prevented from rotating further, i.e. the piston rod drive member assumes the end-of-dose position. By comparing figs. 6A/6B with figs. 7A/7B it becomes apparent that the piston rod 20 has driven the piston 6 of the cartridge in the distal direction by a distance in accordance with the size of the set dose. Upon release of the externally applied force on dose dial member 50, the return spring 70 acts to push the dose dial member into the default relaxed axial position and the piston rod drive member 30 accompanies the motion until the dog teeth 32 engages and locks the piston rod drive member 30 relative to the teeth 12 of main housing 10. The dose dial member 50 again assumes the 20" dose position and a renewed dose adjusting procedure may be carried out.

During the dose expelling process the spring base member 40 is prevented from rotating relative to the main housing 10. In accordance herewith the end-of-content limiter 80 maintains its axial position relative to the housing. As noted above, repeated use of the device may be carried out. Dose setting may be carried out by dialling up a dose until the end-of-content limiter 80 is being blocked by the end-of-content stop and the last dose may hereafter be expelled. Hereafter the cartridge 5 is empty and the injection device 1 is ready to become discarded.

In the above description of the exemplary embodiment, the different structures providing the desired relations between the different components just as the means providing the described functionality for the different components have been described to a degree to which the concept of the present invention will be apparent to the skilled reader. The detailed construction and specification for the different structures are considered the object of a normal design procedure performed by the skilled person along the lines set out in the present specification.

Claims

1. A drug delivery device (1) comprising :

a housing (10) extending along an axis,

- a piston rod (20) axially movable in an expelling direction relative to the housing, a piston rod drive member (30) coupled to the piston rod (20) for driving the piston rod in the expelling direction as the piston rod drive member (30) is rotated in a rotational expelling direction, the piston rod drive member (30) being :

o capable of rotating in the rotational expelling direction in a dose expelling state,

a torsion spring (60) operatively coupled with the piston rod drive member (30) and arranged to provide a force for urging the piston rod drive member (30) in the rotational expelling direction,

a trigger release arrangement (12, 32) configured to:

o in the dose setting state, prevent the piston rod (20) from moving in the expelling direction,

o in the dose expelling state, enable movement of the piston rod (20) in the expelling direction,

a dose dial member (50) for defining a travel distance of the piston rod (20), the dose dial member being :

o capable of rotation relative to the housing in the dose setting state, and o rotationally locked with respect to the housing in the dose expelling state, wherein one of the piston rod drive member (30) and the dose dial member (50) comprises a helical track (37) and the other of the piston rod drive member (30) and the dose dial member (50) comprises a track follower (57) that engages the helical track (37), and

wherein, in the dose setting state, the track follower (57) is adapted to travel the helical track (37) between a first stop (37.1) corresponding to a minimum dose limiting position and a second stop (37.2) corresponding to a maximum dose limiting position, and wherein, in the dose expelling state, the track follower (57) travels towards the minimum dose limiting position as a set dose is being expelled.

2. The drug delivery device (1) as defined in claim 1, wherein the track follower (57) defines a first blocking geometry configured for engaging a first stop geometry (37.1) at the minimum dose limiting position and wherein the first stop geometry (37.1) is fixedly arranged relative to the helical track (37).

3. The drug delivery device (1) as defined in any of claims 1-2, wherein the track follower (57) defines a second blocking geometry configured for engaging a second stop geometry (37.2) at the maximum dose limiting position and wherein the second stop geometry (37.2) is fixedly arranged relative to the helical track (37).

4. The drug delivery device (1) as defined in any of claims 1-3, wherein, in the dose setting state, the trigger release arrangement (12, 32) prevents the piston rod drive member (30) from rotating in the rotational expelling direction and wherein in the dose expelling state, the trigger release arrangement (12, 32) allows rotation of the piston rod drive member (30) in the rotational expelling direction.

5. The drug delivery device (1) as defined in any of claims 1-4, wherein the piston rod drive member (30) is axially movable from a first axial position to a second axial position, wherein the piston rod drive member (30) is rotationally locked relative to the housing (10) when the piston rod drive member (30) assumes the first axial position, and wherein the piston rod drive member (30) is free to rotate in the rotational expelling direction when the piston rod drive member (30) assumes the second axial position.

6. The drug delivery device (1) as defined in any of claims 1-5, wherein the trigger release arrangement (12, 32) further comprises an trigger activator (50) that is coupled to the piston rod drive member (30) so that operation of the trigger activator (50) by moving it axially moves the piston rod drive member (30) axially from the first axial position to the second axial position.

7. The drug delivery device (1) as defined in claims 6, wherein the trigger activator forms an injection button (50), the injection button (50) being arranged at the proximal end of the housing (10).

8. The drug delivery device (1) as defined in claims 6-7, wherein said dose dial member and said injection button form a combined dose dial and injection button (50), and wherein the combined dose dial and injection button is mounted relative to the housing (10) so as to be rotationally movable for setting a dose and axially movable for moving the piston rod drive member (30) axially from the first axial position to the second axial position.

9. The drug delivery device (1) as defined in any of the claims 1-8, wherein the piston rod (20) comprises a thread (27) and wherein a threaded nut member (13) is either fixedly mounted or fixedly mountable relative to the housing (10), and wherein the thread (27) of the piston rod (20) engages the threaded nut member (13).

10. The drug delivery device (1) as defined in claim 9, wherein the piston rod drive member (30) comprises a rotational guide (31) that connects to a longitudinal extending geometry (21) of the piston rod (20) so that, in the dose expelling state, the piston rod (20) is forced to rotate through the threaded nut member (13) as the piston rod drive member (30) rotates.

11. The drug delivery device (1) as defined in claim 10, wherein the rotational guide (31) of the piston rod drive member (30) is formed as an axially extending guide formed so that relative rotation between the piston rod (20) and the piston rod drive member (30) is prevented while axial relative movement is enabled.

12. The drug delivery device (1) as defined in any of the claims 1-11, wherein, in the dose setting state, the piston rod drive member (30) maintains its axial position during dialling up a dose and/or dialling down a dose and wherein, in the dose expelling state, as the piston rod drive member (30) rotates, the piston rod drive member (30) is moved axially relative to the housing (10).

13. The drug delivery device (1) as defined in claim 12, wherein the helical track (37) is so configured that, in the dose expelling state, as the piston rod drive member (30) rotates, the piston rod drive member (30) is moved distally relative to the housing (10).

14. The drug delivery device (1) as defined in claim 12, wherein the helical track (37) is so configured that, in the dose expelling state, as the piston rod drive member (30) rotates, the piston rod drive member (30) is moved proximally relative to the housing (10).

15. The drug delivery device (1) as defined in any of the claims 1-14, wherein the drug delivery device (1) does not comprise a mechanically operated dose dial scale component.