A reusable fixed dose injection device with automatic priming

Abstract

The invention relates to a reuseable injection device (1) for ejecting a plurality of fixed doses of a liquid drug from a replaceable cartridge, wherein a piston rod arrangement (50) is divided into two separate parts, i.e., a washer part (52) and a rod part (51), the two parts being urged away axially from each other by a spring element (53). When a new cartridge assembly (20) is attached to housing structure (10), the washer part (52) of the piston rod arrangement (50) is moved proximally against the force of the spring element (53) by engagement with the plunger (42) inside the cartridge (40) thereby accumulating force in spring element (53). Upon mounting of an injection needle onto the cartridge assembly (20) the accumulated force urges the washer part (52) in the distal direction back to its initial position thus performing an automatic priming of the injection device (1).

Description

[0001] A Reusable Fixed Dose Injection Device with Automatic Priming

[0002] THE TECHNICAL FIELD OF THE INVENTION:

[0003] The invention relates to an injection device for ejecting a plurality of fixed doses of a liquid drug from an exchangeable cartridge assembly. The fixed doses in the plurality are preferably doses containing the same predetermined volume for each and all doses. Further, the number of doses to be injected from the reusable injection device before re-loading of the cartridge assembly are also pre-determined by the manufacturer of the injection device. The invention thus relates to a reusable multi-use fixed dose injection device. The invention preferably relates to the priming mechanism of such injection device and in particular to an automatic priming mechanism.

[0004] The invention further relates to a cartridge coding system for such injection device.

[0005] DESCRIPTION OF RELATED ART:

[0006] Traditional injection devices for injecting insulin require a dose selection mechanism by which the user is able to set a large number of different and very precise doses as the volume of insulin needed in one injection varies from person to person. Over the last 20 years various drugs in the GLP-1 class have become more and more used not only for the treatment of diabetes but also for the treatment of obesity and other chronical diseases. Drugs within the GLP-1 class may not need to be injected in a very precise and individual volume but can easily be injected as a fixed dose having a size which is agreeable with most people. Several of the drugs available in the GLP-1 class need not even to be injected on a daily basis but can be injected only once a week or even less frequently. Hence, the requirement to these injection devices is somewhat different from what is required from a traditional settable injection device used for insulin.

[0007] As a result of this a large number of fixed dose injection devices has emerged over the last decade of years. Some of these fixed dose injection devices inject one fixed dose volume in one single shot whereafter the entire injection device is discarded. Such injection devices are often referred to as single shot fixed dose injection devices or simply single shot devices as they only contain one single dose of the liquid drug.

[0008] However, in order to reduce the amount a plastic waste and to also lower the production costs, fixed dose injection devices which are able to inject a plurality of fixed doses have been developed. These injection devices are often referred to as multi-use fixed dose injection devices due to their ability to contain a plurality of fixed doses. Usually, these injection devices are pre-filled with the amount of drug needed for the specific number of injections and once the predetermined number of injections has been completed the entire injection device is discarded.

[0009] An example of such pre-filled multi-use fixed dose injection device for ejecting fixed doses of a liquid drug is disclosed in US 12,109,398. With this type of injection device, for a predetermined number of times, the user can expel a fixed dose before the injection device is discarded. The particular injection device disclosed in US 12,109,398 is a torsion spring driven injection device wherein each of the fixed doses are automatically ejected utilizing a torsion spring which is strained by the user during selection of each of the fixed doses.

[0010] A general issue with pre-filled injection devices is to eliminate, or at least minimize, the distance, the so-called air gap, occurring between the position of the plunger in the filled cartridge and the piston rod arrangement during manufacturing of the injection device. This is mainly due to the high tolerances in the production of the glass cartridges resulting in the plunger being positioned in different positions inside the individual cartridge once the cartridge is filled with a specific volume, which volume filling also has tolerances. A number of solutions to this problem is addressed in WO 2010 / 124961. In one of the disclosed solutions depicted on figure 20-25, a torsion spring is provided between the piston rod and the piston rod foot which torsion spring rotates the piston rod foot into contact with the plunger in the cartridge during assembly of the pre-filled injection device.

[0011] US 8,900,202 discloses a similar solution in which a compression spring is provided between the piston rod and the piston rod foot. Once the spring has urged the piston rod foot into contact with the plunger inside the cartridge, the piston rod foot is irreversible locked to the piston rod by a number of radial spikes which are secured by a fixing ring.

[0012] The solutions disclosed in WO 2010 / 124,961 and in US 8,900,202 are meant to be used in a pre-filled injection device which is discarded once the content has been used. Once the piston rod foot is irreversible locked to the piston rod it is not possible to move the piston rod foot relatively to the piston rod after assembly of the injection device as this is not required since the cartridge is not meant to be exchanged.

[0013] Many insulin devices are also made in a reusable form wherein the user can exchange the cartridge to thereby avoid having to discard the injection device once the content in the cartridge has been used. An example of such reusable injection device for use with insulin is disclosed in WO 2022 / 013155.

[0014] An overall issue with reusable injection devices is how to perform priming of the injection device when inserting a new and fresh cartridge. When the user loads a new cartridge into a reusable injection device it is costumery to eject small incremental doses with the injection needle mounted to thereby bring the piston rod arrangement into contact with the plunger inside the exchangeable cartridge prior to performing the first injection. This is known as priming the injection device. In an insulin device, the user typically expels 1-2 IU repeatedly until the user visually observes that drops of liquid drug is present at the tip of the injection needle. This indicates that the piston rod arrangement is in abutment with the plunger inside the cartridge.

[0015] The reason that priming is required when loading a new cartridge into the injection device is primarily because cartridges have rather high tolerances as they are typically produced from glass. Hence, when the manufacturer fills a specific volume of liquid drug into the cartridge, the position of the plunger inside the cartridge will vary depending on the specific tolerances on the individual cartridge together with the tolerances of the volume filled.

[0016] When a new cartridge is loaded into a reusable injection device it is thus important to move the piston rod arrangement into physical contact with the plunger to make sure that the first dose to be injected has the correct volume. However, when using relatively large fixed dose volumes it is no longer possible to move the piston rod forward in small incremental steps and to use a full fixed dose to prime the injection device would lead to a waste of liquid drug.

[0017] Hence, there is a strong need for alternative ways to prime a reusable fixed dose injection device without wasting large amounts of liquid drug by using a full fixed dose for priming.

[0018] US 6,726,661 and EP 937,477 disclose solutions wherein the priming mechanism is a separate mechanism which is disconnected from the dose setting and injection mechanism. Both solutions are based on incremental movements of the piston rod by a separate priming mechanism. However, when using such solution, control over the location of the piston rod is easily lost which makes it difficult to use such solutions for a fixed dose device as there must be sufficient travel distance left in the piston rod to expel the prescribed number of fixed doses.

[0019] Further, WO 2013 / 110769 discloses a reusable injection device wherein the cartridge is front loaded into the housing arrangement. In order to make sure the piston rod arrangement is in contact with the plunger inside the cartridge when a new cartridge is loaded, a spring is provided to urge the piston rod arrangement in the distal direction. However, since the spring is operational between the housing and the piston rod it has a limited working range and further, the control over the axial position of the piston rod is also lost.

[0020] DESCRIPTION OF THE INVENTION:

[0021] It is an object of the present invention to eliminate or reduce one or more drawbacks of the prior art and to provide a useful alternative to the prior art solutions.

[0022] In correspondence herewith, in a first aspect of the invention, an injection device is provided as defined in claim 1. Advantageous embodiments are further defined in the dependent claims.

[0023] Accordingly, in one aspect, the present invention relates to an injection device for ejecting a plurality of fixed doses of a liquid drug, which injection device comprises: a housing structure supporting a drive mechanism and comprising a piston rod arrangement, and,

[0024] an exchangeable cartridge assembly connectable to the housing structure and securing a cartridge containing the liquid drug and which cartridge proximally is provided with a movable plunger movable at least in a distal direction to expel the liquid drug through a connectable injection needle.

[0025] Further, the piston rod arrangement comprises a washer part and a rod part and the piston rod arrangement is adapted to move the plunger in the distal direction inside the cartridge during dose ejection, and with a spring element coupled, at least functionally, between the rod part and the washer part.

[0026] The washer part is adapted to be proximally movable from a first position to a second position by the movable plunger upon connecting the exchangeable cartridge assembly to the housing structure which movement from the first position to the second position accumulates a force in the spring element, and the washer part is further adapted to be movable from the second position and back to the first position by release of accumulated force from the spring element.

[0027] Once the user attaches a new and fresh cartridge assembly to the housing structure, the plunger located proximally inside the cartridge pushes the washer part in the proximal direction thereby straining the spring element. The washer part hereafter applies a force onto the plunger via the strained spring element thus urging the plunger in the distal direction. Hence, it is secured that the piston rod arrangement always abuts the plunger when a new and fresh cartridge assembly is attached and at the system secures that automatic priming is executed.

[0028] By performing automatic priming as claimed herein it is secured that the first dose selected and expelled has the correct volume as the piston rod arrangement abuts the plunger and do not travel through a free airspace during dose expelling. At the same time manual priming is avoided and the quantity of liquid drug waisted can be kept to a minimum.

[0029] By fixed doses is meant that both the first dose and the following doses i.e. the doses following the first fixed dose, all have the same volume as the first dose, and typically 3 to 6 fixed doses are provided in one single cartridge assembly. Once the user has expelled the number of doses contained in the cartridge assembly, the cartridge assembly can easily be replaced by a new and fresh cartridge assembly and automatic priming be performed again.

[0030] The washer part and the rod part which together with the spring element makes up the piston rod arrangement are in one example mounted relatively to each other such that they are slidable by translational movement relatively to each other, preferably guided by mutually engaging guiding means. By translational movement is here meantan axial movement without any rotation. Hence, the two parts can be provided with some kind of tongue and groove engagement or corresponding elements guiding the translational movement.

[0031] In a further example, the guiding means are provided with stop means determining the translational distance the washer part and the rod part are adapted to move in relation to each other. The guiding means could e.g. comprise a longitudinal track and a guiding protrusion which could be physically operational in the longitudinal track. In such example, the stop means could be a closed track however other ways of stopping the relative movement of the protrusion relatively to the longitudinal track could be foreseen.

[0032] Although any of the rod part or the washer part could carry either the longitudinal track or the protrusion it is preferred to provide the longitudinal track in the rod part and the protrusion on the washer part.

[0033] During mounting of the cartridge assembly onto the housing structure, the spring element is strained as an axial force is accumulated in the spring element. This accumulated force is then released when the user mounts the injection needle to the injection device, thereby establishing fluid flow between the cartridge and the lumen of the injection needle. The release of the accumulated force moves the washer part in the distal direction thus automatically forcing a small amount of liquid drug out through the lumen of the injection needle.

[0034] The spring element which delivers the axial force pushing the washer part and the rod part apart from each other can be any kind of spring element; mechanical, hydraulic or pneumatic. In a preferred example, the spring element is a compression spring made from a metallic material. However, a spring made from plastic material could also be used. In the latter example, the plastic spring could be moulded as an integral part of either the washer part or the rod part or both.

[0035] The first position is defined by the position into which the washer part is distally moved by the force of the spring element. Hence, the first position is the initial position of the washer part when no cartridge assembly is attached to the housing structure.

[0036] The second position is the position wherein the washer part is moved to a proximal position by the plunger inside the cartridge assembly. When the user connects the cartridge assembly to the housing structure, the plunger inside the cartridge abuts the washer part and forces the washer part proximally relatively to the rod part. The washer part can be moved proximally until it engages with the rod part. This maximum distance is defined as the length “L”. The tolerance of the plunger position inside the cartridge thus needs to be obtained within the distance “L”, such that a force will always be applied to the plunger when the cartridge assembly is attached,

[0037] In one example, the rod part is prevented from proximal movement when the piston rod arrangement is in its initial position. This is preferably done by the proximal end of the rod part abutting an element preventing further proximal movement of the rod part. The element is in one example the housing structure or a part connected to the housing structure. In a preferred example, the element is the guiding tube which is axially secured to the housing. Hence, the piston rod arrangement abuts the end flange in the guiding tube when the piston rod arrangement is in its initial position.

[0038] In one embodiment, the cartridge assembly comprises a cartridge loaded in a cartridge holder part. The user of the injection device is hence required to insert a new and fresh cartridge into the cartridge holder before attaching the cartridge holder to the housing structure.

[0039] However, in a preferred embodiment, the cartridge is pre-mounted in the cartridge holder such that the cartridge assembly comprises the cartridge irreversible and permanently secured in the cartridge holder part. In this case, the cartridge assemblies are sold as separate units which the user attaches to the housing structure. As the manufacturer has pre-mounted the cartridge in the holder arrangement, the entire unit can be coded to fit to specific housing structures.

[0040] No matter if the cartridge assembly is a cartridge loaded into the cartridge holder by the user or a finished cartridge assembly wherein the manufacturer has permanently secured the cartridge to a holder part, it is preferably connected to the housing structure by a bayonet interface, although other interfaces can also be used.

[0041] In the latter embodiment, the cartridge is preferably secured to the holder part by having click arms or the like provided on the holder part grip onto or behind the neck part of cartridge such that the cartridge is irreversible and permanently secured to the holder part. The holder part is preferably moulded from a plastic material.

[0042] It is further an object of the present invention to provide a cartridge coding system for an injection device according to the present invention. The cartridge coding system accordingly comprises:

[0043] a housing structure and a cartridge assembly arranged to be releasable coupled together, a bayonet track associated with the housing structure and having an axial opening and a peripheral track,

[0044] a bayonet protrusion associated with the cartridge assembly

[0045] wherein the cartridge coding system further comprises:

[0046] a code opening associated with the bayonet track, and

[0047] a coding protrusion associated with the cartridge assembly,

[0048] such that the cartridge assembly can only be coupled to the housing structure when the code opening and the code protrusion are aligned.

[0049] Accordingly, for a cartridge assembly in which a cartridge is irreversible and permanently secured, a standard bayonet engagement can be provided with an additional axial opening and an additional protrusion which has to be aligned in order to engage the bayonet engagement. Hence a plurality of different code openings and protrusions engagements can be provided to thereby code a specific cartridge assembly to a specific housing structure. By doing this it is ensured that only cartridge assemblies with the correct strengths for the specific housing structure can actually be fitted to the specific housing structure.

[0050] Such coding systems are very useful in injection systems wherein the manufacturer has premounted the cartridge in a cartridge holder part which are then sold as separate assemblies or units. The user is in such case supported in only connecting the correct cartridge assembly to the dedicated housing structure or dose engine part. Since different housing structures expel different volumes as explained, it is very important to use the correct cartridge assembly together with the dedicated housing structure in order to receive the correct quantity of the active pharmaceutical ingredient.

[0051] In certain embodiments of the said cartridge coding system one or more code protrusions are provided on an inner surface of the cartridge assembly and the bayonet track is provided on an outer surface of the housing structure.

[0052] Although the term “polymer” or “plastic” are used throughout this description, the polymer or plastic parts could also be moulded from biodegradable materials such as e.g. polymers produced from sugar or e-methanol i.e. methanol produced from renewable energy sources such as wind or solar energy. Other fossil replacement materials as well as other naturally biological degradable materials could also be used.

[0053] DEFINITIONS:

[0054] An “injection pen” or “pen for injection” is typically an injection apparatus having an oblong or elongated shape somewhat like a pen for writing. Although such pens usually have a tubular cross-section, they could easily have a different cross-section such as triangular, rectangular or square or any variation around these geometries.

[0055] The term “Needle Cannula” is used to describe the actual conduit performing the penetration of the skin during injection. A needle cannula is usually made from a metallic material such as e.g. stainless steel and connected to a hub to form a complete injection needle also often referred to as a “needle assembly” or simply “injection needle”. A needle cannula could however also be made from a polymeric material or a glass material. The hub also carries the connecting means for connecting the needle assembly to an injection apparatus and is usually moulded from a suitable thermoplastic material. The “connection means” could as examples be a luer coupling, a bayonet coupling, a threaded connection or any combination thereof. The term “Needle unit” is used to describe one single needle assembly carried in a container. Such container usually has a closed distal end and an open proximal end which is sealed by a removable seal. The interior of such container is usually sterile such that the needle assembly is ready to use. Needle units specially designed for pen injection systems are defined in ISO standard No. 11608, part 2, and are often referred to as “pen needles”. Pen needles are usually double pointed having a front-end for penetrating through the skin of a user and a back-end for penetrating into the cartridge containing the drug such that liquid communication is established during injection.

[0056] As used herein, the term “Liquid drug” is meant to encompass any drug-containing flowable medicine capable of being passed through a delivery means such as a hollow needle cannula in a controlled manner, such as a liquid, solution, gel or fine suspension. Representative drugs include pharmaceuticals such as peptides, proteins (e.g. insulin, insulin analogues and C-peptide), and hormones, biologically derived or active agents, hormonal and gene-based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form. “Cartridge” is the term used to describe the container or ampoule actually containing the drug which are often referred to as the primary packing as it is in direct contact with the liquid drug. Cartridges are usually made from glass but could also be moulded from a suitable polymer. A cartridge or ampoule is preferably sealed at one end by a pierceable membrane referred to as the “septum” which can be pierced e.g. by the non-patient end of a needle cannula. Such septum is usually self-sealing which means that the opening created during penetration seals automatically by the inherent resiliency of the septum material once the needle cannula is removed from the septum. The opposite end of the cartridge is typically closed by a movable “plunger” which is a piston-like element made from rubber or a suitable polymer. The plunger is during use slidable moved inside the cartridge preferably in a distal direction. The space between the pierceable membrane and the movable plunger holds the liquid drug which is pressed out as the plunger decreased the volume of the space holding the liquid drug. The cartridges used for both pre-filled injection devices and for reusable injections devices are typically factory filled by the manufacturer with a predetermined volume of a liquid drug. A large number of the cartridges currently available contains either 1 ,5 ml or 3 ml of liquid drug. Since a cartridge usually has a narrower distal neck portion into which the plunger cannot be moved not all of the liquid drug contained inside the cartridge can actually be expelled. The term “initial quantum” or “substantially used” therefore refers to the injectable content contained in the cartridge and thus not necessarily to the entire content.

[0057] By the term “Pre-filled injection device” is meant an injection device in which the cartridge containing the liquid drug is pre-filled by the manufacture of the injection device and permanently embedded in the injection device such that it cannot be removed without permanent destruction of the injection device. Once the pre-filled amount of liquid drug in the cartridge is used, the user normally discards the entire injection device. Usually, the cartridge which has been filled by the manufacturer with a specific amount of liquid drug is secured in a cartridge holder which is then permanently connected in a housing structure such that the cartridge cannot be exchanged.

[0058] This is in opposition to a “Reusable injection device” in which the user can himself change the cartridge containing the liquid drug whenever it is empty. Pre-filled injection devices are usually sold in packages containing more than one injection device whereas reusable injection devices are usually sold one at a time. When using pre-filled insulin injection devices an average user might require as many as 50 to 100 injection devices per year whereas when using reusable injection devices one single injection device could last for several years, however, the average user would require 50 to 100 new cartridges per year.

[0059] For some reusable or durable injection devices, the cartridge is permanently and irreversible embedded in a plastic shell or the like which is removable attached to the housing of the injection device. Such plastic shell comprising a cartridge permanently embedded therein is often referred to as a “Drug container unit”. After use, when the cartridge in the drug container unit is empty, the user discards the whole drug container unit and replaces it with a new and fresh drug container unit containing the irreversible secured cartridge (or similar container) with liquid drug sufficient for a plurality of injections.

[0060] All references, including publications, patent applications, and patents, cited herein are incorporated by reference in their entirety and to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0061] All headings and sub-headings are used herein for convenience only and should not be constructed as limiting the invention in any way. The use of any and all examples, or exemplary language (e.g. such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and / or enforceability of such patent documents.

[0062] This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS:

[0064] The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

[0065] Figure 1A shows a side view of the injection device with the protective cap mounted. Figure 1B shows a side view of the injection device with the protective cap removed. Figure 2 shows an exploded view of the injection device.

[0066] Figures 3A-B show cross-sectional views of the injection device.

[0067] Figure 4 shows a cross-sectional view of the injection device with the first dose selected.

[0068] Figures 5A-B show side views of the housing structure of the injection device.

[0069] Figures 6A-B show perspective views of the housing structure of the injection device. Figures 7A-B show perspective views of the cartridge assembly.

[0070] Figure 8 shows the principle of the coding system.

[0071] Figure 9 shows a perspective view of the guiding tube of the injection device Figure 10 shows a perspective view of the bearing of the injection device Figures 11A-B show side views of the dose selection button of the injection device.

[0072] Figures 12A-B show perspective views of the dose selection button of the injection device Figure 13A shows a perspective view of the piston rod arrangement of the injection device.

[0073] Figure 13B shows a cross-sectional view of the piston rod arrangement of the injection device.

[0074] Figure 14 shows a perspective view of the rod part of the piston rod arrangement of the injection device.

[0075] Figure 15 shows a perspective view of the washer part of the piston rod arrangement of the injection device.

[0076] The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

[0077] DETAILED DESCRIPTION OF EMBODIMENT:

[0078] When in the following terms as “upper” and “lower”, “right” and “left”, “horizontal” and “vertical” or similar relative expressions are used, these only refer to the appended figures and not necessarily to an actual situation of use. 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.

[0079] In that context 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 supporting the injection needle, whereas the term “proximal end” is meant to refer to the opposite end carrying the dose selection button as indicated in figure 3A-B. Distal and proximal is meant to be along an axial orientation extending along the longitudinal axis (X) of the injection device as also shown in figure 3A-B.

[0080] When referring to clockwise and anti or counterclockwise in the following examples it is understood that the injection device is viewed from a position distal to the injection device. Clockwise is thus a rotation following the arms on an ordinary clock rotating to the right when e.g. moving from 12 O'clock to 3 O'clock, and wherein counterclockwise is a rotation in the opposite direction.

[0081] To explain the various movements which take place in the injection device described in the example, the following terminology are used throughout the following detailed description.

[0082] “Translational movement” is meant to be a strictly linear movement without any rotation.

[0083] “Rotational movement” is any movement of rotation around a centre which centre can be a centre point i.e. in one planar or a centre axis i.e. having a longitudinal extension.

[0084] “Axial movement” means any movement in an axial direction. Such movement can be a strictly translational movement or include a rotational movement which thus makes it a “Helical movement” as this is meant to be an axial movement combined with a rotational movement. By “axial” is meant in a lengthwise direction but not necessarily along a straight line. “Radial” is meant to be at an angle to the axial direction. The angle is not necessarily 90° hence the radial direction is not necessarily perpendicular to the axial direction.

[0085] “Telescopic” is meant to cover the situation in which a movable element moves out from, and / or into, a base element. The telescopic movement can be either translational or include a rotation thus making the telescopic movement helical.

[0086] Figure 1A-B disclose an example of a reusable multi-use fixed dose injection device 1 according to the invention with the cartridge assembly 20 mounted. The outer shell of the injection device 1 comprises a housing structure 10 containing the dose selection- and expelling mechanism and a cartridge assembly 20 containing the liquid drug composition.

[0087] Prior to use, the distal part of the injection device 1 which is primarily the cartridge assembly 20 is covered by a protective cap 5 as seen in figure 1 A, which cap 5 the user needs to remove before an injection can be performed.

[0088] Proximally, the injection device 1 has a dose selection button 30 by which the user repeatedly can select one of the fixed doses in the plurality of fixed doses contained in the cartridge assembly 20. The reusable multi-use fixed dose injection device 1 herein described is functionally similar to the one described in WO 2025 / 196054 A1 which is hereby incorporated by reference.

[0089] Figure 2 discloses an exploded view of the injection device. The main components being:

[0090] The housing structure - 10

[0091] The exchangeable cartridge assembly - 20

[0092] The dose selection button - 30

[0093] The piston rod arrangement - 50

[0094] The guiding tube - 60

[0095] The bearing - 70.

[0096] The gearwheel - 80.

[0097] The piston rod arrangement 50 which in figure 2 is encircled comprises a rod part 51 , a washer part 52 and a compression spring 53 mounted therebetween thus urging the rod part 51 and the washer part 52 away from each other as will be explained.

[0098] The figures 3A + 3B discloses two different cross-sectional views of the injection device 1 with the dose selection button 30 in the initial position i.e. no dose has been selected. In figure 3B, the injection device has been rotated 90 degrees around the longitudinal axis (X) relatively to figure 3A.

[0099] The outer shell of the injection device 1 basically comprises the housing structure 10 and the cartridge assembly 20. The housing structure 10 guides the dose selection button 30 which has both a helical interface and a translational interface with the housing structure 10 as will be explained. The dose selection button 30 is helically interfaced with the housing structure 10 such that the dose selection button 30 rotates helically out from the proximal end of the housing part 10 during dose selection. During dose expelling, the dose selection button 30 travels translationally (i.e. without rotation) back into the housing structure 10.

[0100] Distally, the housing structure 10 carries the exchangeable cartridge assembly 20 which secures a cartridge 40. The cartridge 40 itself is preferably made from glass and is distally provided with a membrane 41 to be pierced by a double pointed injection needle. Proximally, the cartridge 40 is provided with a movable piston 42 which can be moved forward in the distal direction by a piston rod arrangement 50. The piston rod arrangement comprises a rod part 51, a washer part 52 and a compression spring 53 as e.g. seen in the encircled part on figure 2.

[0101] The cartridge assembly 20 is a pre-assembled unit comprising a cartridge holder part 25 and a cartridge 40 permanently secured to the cartridge holder part 25. Distally, the cartridge holder part 25 is provided with a needle mount 21 and proximally an opening through which the cartridge 40 is inserted during assembly of the cartridge assembly 20. The cartridge holder part 25 is preferably made from a suitable plastic material. As best seen on figure 3B, the cartridge holder part 25 has a pair (or more) of click arms 22 which snaps behind the neck portion 43 on the cartridge 40 and secures the cartridge 40 permanently to the cartridge holder part 25 thus making up the cartridge assembly 20.

[0102] The cartridge holder part 25 of the cartridge assembly 20 is further provided with a bayonet interface such that the cartridge holder part 25 and thus the cartridge assembly 20 can be easily connected to, and disconnected from, the housing structure 10.

[0103] Alternatively, the cartridge assembly 20 can be produced from two or more parts which are irreversible click-fitted together around the cartridge 40 to thereby secure the cartridge 40. An example of a cartridge assembly made from a plurality of parts which are permanently attached to each other by adhesive or by welding is given in US 5,334,162.

[0104] The functionality of the reusable multi-use fixed dose injection device 1 is the same as described in European patent application No. EP 24165122.3 and figure 4 disclose the injection device with the first dose selected and the most distal part of the cartridge assembly 20 cut away. The dose selection button 30 has hence been rotated one full revolution out from the housing part 10. As seen, the housing part 10 secures a tube-like guiding tube 60. This guiding tube 60 is distally attached to the housing part 10 such that the guiding tube 60 can rotate relatively to the housing part 10 but is at the same time axially fixated inside the housing part 10, hence the guiding tube 60 cannot move axially in relation to the housing part 10 when the dose selection button 30 is moved out from the housing part 10, the guiding tube 60 is only able to rotate relatively to the housing part 10.

[0105] A tube-like bearing 70 is further provided inside the dose selection button 30. This bearing 70 is clicked into the dose selection button via a holding flange 74 at the proximal end in a way allowing relative rotation of the bearing 70 relatively to the dose selection button 30, but at the same time locking the dose selection button 30 and the bearing 70 together in the axial direction, hence, the bearing 70 follows the axial movement of the dose selection button 30 but not necessarily the rotation of the dose selection button 30.

[0106] The tube-like bearing 70 and the guiding tube 60 are thus able to move telescopically in relation to each other but are rotationally locked to each other as will be explained.

[0107] The piston rod arrangement 50 is guided in the guiding tube 60. The shape of the piston rod arrangement 50 and the guiding tube 60 are such that the piston rod arrangement 50 is able to translate axially relatively to the guiding tube 60 but prevented form rotating relatively to the guiding tube 60.

[0108] The piston rod arrangement 50 is further provided with a gear wheel 80. This gear wheel 80 can be provide in any random position on the piston rod 50 but is preferably attached at the proximal half of the piston rod 50 and most preferably attached to the proximal end of the piston rod arrangement 50. A flexible arm 54 provided on the rod part 51 piston rod arrangement 50 obstructs the free rotation of the gear wheel 80 as will be explained.

[0109] In sum, the reusable multi-use fixed dose injection device 1 comprises a very low number of components as best seen in figure 2. These components are preferably made from suitable polymeric materials such as plastic although some parts such as springs or the like could be made from a suitable metal, and to increase the possibility of recycling the plastic parts, the components are preferably made from the same type of plastic. However, some of the components not requiring very precise tolerances like e.g. the protective cap 5, can be made form an already recycled plastic. To accommodate recycling, the components are locked together in a simple way making it easy to disassemble the parts of the injection device 1 such that the different components can be individually handled and recycled if needed.

[0110] The Gear Wheel (80)

[0111] The gearwheel is best seen in figure 3A and in figure 3B and is in the centre provided with a radial axis 81 which is secured to the piston rod arrangement 50 and which allows the gear wheel 80 to rotate relatively to the piston rod arrangement 50. The radial axis 81 is preferably moulded as an integrated part of the gearwheel 80 such that the gearwheel 80 is one single unit rotationally mounted to the piston rod arrangement 50. On the outer peripheral surface, the gear wheel 80 is shaped with a plurality of peripheral teeth 82 which are able to engage with toothed racks as will be explained. The piston rod arrangement 50 is provided with openings into which the radial axis 81 fits such that the gear wheel 80 can be rotationally mounted to the piston rod arrangement 50.

[0112] Housing Structure (10)

[0113] The housing structure 10 shown as a side view in figure 5A-B and in perspective in figure 6A-B comprises a longitudinal tube extension 11 extending in the distal direction. This longitudinal extension 11 is preferably moulded as an integral part of the housing structure 10. By having such longitudinal extension 11, the piston rod arrangement 50 is protected also when the cartridge assembly 20 is removed as it is not immediately possible for a user to physically obtain contact with the piston rod arrangement 50. Hence the longitudinal extension protects 11 the piston rod arrangement 50. The longitudinal extension 11 is further provided with a number of openings or windows 12 through which the user can inspect the content of the cartridge 40 when the cartridge assembly 20 is mounted.

[0114] The housing structure 10 is further, on the outer surface, provided with an anti-roll feature 13 and a protrusion 14 engaging and securing the protective cap 5 when mounted.

[0115] Internally, the longitudinal extension 11 of the housing structure 10 is provided with a number of longitudinal rails 15 on which the cartridge 40 is guided when the cartridge assembly 20 is mounted onto the housing structure 10 as will be explained.

[0116] As best seen in figure 5A-B, the housing structure 10 is provided with a bayonet track 16a-b made up from an axial opening 16a and a peripheral track 16b which both cooperates with bayonet protrusions 27 provided on an inner surface of the cartridge assembly 20 to thereby lock the cartridge assembly 20 to the housing structure 10. Preferably, two bayonet tracks 16a-b are provided.

[0117] In addition to the bayonet track 16a-b, an axial code opening 17 can be provided as will be explained. The housing structure 10 is further provided with an angular opening 19 in which the guiding tube 60 can be anchored as will be further explained. In this way the guiding tube 60 is axially locked to the housing structure 10 but able to rotate the angle defined by the angular opening 19.

[0118] Cartridge assembly (20)

[0119] The cartridge assembly 20 is disclosed in figure 7A-B and is basically a plastic component securing the cartridge 40. The plastic component which is referred to as the cartridge holder part 25 is distally provided with a needle interface 21 for securing a double pointed pen-needle. On the inner surface one or more click arms 22 (best seen in figure 3B) is provided which grips behind the neck portion 43 of the cartridge 40 to thereby irreversible connect the cartridge 40 to the cartridge holder part 25 thus making up the cartridge assembly 20. The cartridge 40 and its content can be viewed through the opening / window 23.

[0120] In a more simple form, the click arms 22 securing the cartridge 40 can be formed as simple dot-shaped protrusions that grips behind the neck part 43 of the cartridge 40 as e.g. disclosed in WO 1992 / 04926. In one example, these dot-shaped protrusions can be provided with a deformation zone to better obtain forces.

[0121] The cartridge assembly 20 which is provided to the user as one finished unit can further be provided with a mechanical coding system such that a specific cartridge assembly fits to a specific housing structure. In this way a separation between various types or strengths of the liquid drugs can be controlled.

[0122] The inner surface of the cartridge holder part 25 of the cartridge assembly 20 is provided with a number of bayonet protrusions 27 (best seen in figure 7B) to engage with the bayonet track 16a-b of the housing structure 10 such that the cartridge assembly 20 is forced to rotate during attachment to the housing structure 10. In addition to the bayonet protrusions 27 one or more code protrusion 28 can be provided to engage axial code openings 17 leading into the peripheral track 16b of the bayonet track 16a-b.

[0123] The coding principle is further disclosed in figure 8 wherein it can be seen that the bayonet protrusion 27 on the cartridge assembly 20 can only fully engage with axial opening 16a of the bayonet track 16a-b in the housing structure 10 if the code protrusion 28 is provided in alignment with the axial code opening 17. By having different positions of the code protrusion 28 and the aligned code opening 17 a variety of different code matches can be made. If e.g. pairs of the code protrusions 28 and the aligned code openings 17 are located 15 degrees apart on the periphery then six different matches can be established within 90 degrees. The bayonet protrusion 27 and the axial opening 16a of the bayonet track 16a-b would preferably be in the same position for all six different coding solutions and if the axial opening 16a in the bayonet track 16a-b e.g. stretches over 20 degrees all six different codes can be provided within 110 degrees. This leaves amble room for having two bayonet protrusions 27 and two bayonet tracks 16a-b on the full 360 degrees.

[0124] The coding system can further be extended by e.g. having bayonet tracks 16a-b and bayonet protrusions 27 with different angular extensions.

[0125] Towards the proximal end, the cartridge holder part 25 is, also on the inner surface, provided with a number of longitudinal slots 26 designed for engaging with second protrusions 61 provided on the guiding tube 60 such that the cartridge holder 25 is able to rotate the guiding tube 60 as will be explained.

[0126] Guiding tube (60)

[0127] The guiding tube 60 disclosed in figure 9 is moulded as a tube-shaped structure wherein the distal part is shaped as a circumferential closed tube and the proximal part is shaped as an open half-circular structure having longitudinal sides 63.

[0128] The circumferential closed tube is internally, at least on a part thereof, shaped in the same shape as the piston rod arrangement 50 such that the piston rod arrangement 50 is able to slide inside the circumferential closed tube part but unable to rotate relatively to the guiding tube 60. Hence, the piston rod arrangement 50 and the guiding tube 60 can only telescope translational in relation to each other.

[0129] The outer distal end of the guiding tube 60 is provided with a number of outwardly pointing first protrusions 61 which engages longitudinal recesses provided on an inner surface of the housing structure 10 to guide the rotation of the guiding tube 60. Any rotation of the guiding tube 60 is further transferred to a similar rotation of the piston rod arrangement 50. The first protrusions 61 can in one example be provided on a flexible beam to make the first protrusion 61 resilient thus providing the user with a tactile and / or audible signal when the first protrusion 61 shifts into and out from the longitudinal recesses inside the housing structure 10.

[0130] The distal end of the guiding tube 60 is further provided with second protrusions 62 which engages the angular openings 19 in the housing structure 10 such that the guiding tube 60 is axially locked to housing structure 10 but able to rotate relatively to the housing structure 10 the degrees allowed by the peripheral extension of the angular opening 19.

[0131] Longitudinal, the guiding tube 60 is provided with a first toothed rack 65 on which the gear wheel 80 mounted on the piston rod arrangement 50 can roll in the axial direction. Since the piston rod arrangement 50 is rotationally locked to the guiding tube 60 as explained above, the gearwheel 80 is also radially locked to the guiding tube 60 and is hence always engaged with the first toothed rack 65, both during dose selection and during dose expelling.

[0132] Whenever the gear wheel 80 rolls axially on the first toothed rack 65, the piston rod arrangement 50 moves translational relatively to the first toothed rack 65 since the gear wheel 80 is rotationally coupled to the piston rod arrangement 50.

[0133] The guiding tube 60 further has an end flange 66 which defines the initial position of the piston rod arrangement 50 understood such that the proximal end of the piston rod arrangement 50 abuts this end flange 66 when the piston rod arrangement is in its initial position as disclosed in figure 3B. Following use of the injection device, the user resets the piston rod, e.g., by manually pushing back the piston rod arrangement 50 into its initial position, thereby enabling use of the injection device for a new series of injections.

[0134] Bearing (70)

[0135] To support the guiding tube 60, a bearing 70 as disclosed in figure 10 is provided. The bearing 70 is shaped as a tube-like elongated element having a longitudinal opening 71 and a plurality of radial flanges 72 which is supported by the dose election button 30.

[0136] Proximally, the bearing 70 is provided with a push member 73 which is carried inside the dose selection button 30 as best seen in figure 4. This push member 73 is preferably moulded as an integral part of the bearing 70. Most proximally, the push member 73 is shaped to accommodate the shape of the thumb finger of a user. The bearing 70 is further provided with a holding flange 74 located adjacent the push member 73 and which secures the bearing 70 to the dose selection member 30 such that the bearing 70 and the dose selection member 30 move together axially but is able to rotate relatively. Hence, when a user rotates the dose selection button 30 to select the fixed dose and the dose selection button 30 moves helically away from the housing structure 10, the bearing 70 follows the axial movement of the dose setting button 30 both when the dose selection button 30 is rotated out from the housing structure 10 to select the fixed dose to be injected and when the dose selection button 30 is pushed translationally back into the housing structure 10.

[0137] The bearing 70 is further provided with an inner recess 75 guided by the longitudinal sides 63 of the guiding tube 60 such that the bearing 70 cannot rotate relatively to the guiding tube 60 but is able to rotate together with the guiding tube 60. The inner recess 75 and the longitudinal side 63 thus guides the telescopic movement between the bearing 70 and the guiding tube 60.

[0138] Hence, when a user selects the fixed dose by rotating the dose selection button 30 helically in the proximal direction, the bearing 70 follows the axial movement without rotating as it is rotationally locked to the guiding tube 60 which again is rotationally locked to the housing structure 10.

[0139] As best seen in figure 3A and in figure 4, the gear wheel 80 protrudes out through the longitudinal opening 71 in the bearing 70 to engage a second toothed rack 31 provided on the inner surface of the dose selection button 30 as will be explained.

[0140] Dose Selection Button (30)

[0141] The dose selection 30 shown as a side view in figure 11A-B and in perspective in figure 12A-B is used to select one of the fixed doses in the plurality of fixed doses. By fixed dose is meant that every dose has the same fixed volume which is pre-determined by the manufacturer of the reusable multi-use fixed dose injection. Should there be any variation in the volume it is not intended but due to tolerances on the mechanical components.

[0142] The dose selection button 30 is on the inner surface provided with a toothed rack 31 for moving the gear wheel 80. Further, a flexible EoC arm 32 is provided which is able to be bended outwardly to engage with the housing structure 10 following ejection of the last fixed dose. The flexible EoC arm 32 is preferably bended outwardly by engagement with the gearwheel 80 as further explained in ....

[0143] Most proximally the dose selection button 30 has a grip 33 which surrounds the push member 73 on the bearing 70 and which grip 33, the user grips between the fingers to rotate the dose selection button 30.

[0144] On the outer surface, the dose selection button 30 is provided with one helical track 34 and one translational track 35. Both the helical track 34 and the longitudinal track 35 engages the guiding protrusion 18 located on the inner surface of the housing as e.g. seen in figure 4.

[0145] Piston Rod Arrangement (50)

[0146] The piston rod arrangement 50 is disclosed in figure 13 A-B and consist of a rod part 51, a washer part 52 and a compression spring 53 located between the rod part 51 and the washer part 52.

[0147] The rod part 51 is further disclosed in figure 14 and the washer part 52 in figure 15.

[0148] Proximally, the rod part 51 is provided with a set of radial openings 55 for securing the radial axis 81 of the gearwheel 80 such that the gearwheel 80 and the rod part 51 move together axially, however allowing the gear wheel 80 to rotate relatively to the rod part 51.

[0149] As seen in figure 14, the rod part 51 has a hollow space 56 and is distally provided with an opening into this hollow space 56. When assembling the piston rod arrangement 50, the compression spring 53 is first inserted into hollow space 56 followed by the washer part 52 as best seen in figure 13B.

[0150] The washer part 52 is provided with a number of outwardly pointing keys 57 which engages longitudinal slots 58 in the rod part 51 such that, once assembled, the distal position of the washer part 52 is determined by the engagement between the outwardly pointing key 57 and the distal end of the longitudinal slots 58.

[0151] Selection of a Fixed Dose When selecting a fixed dose to be ejected, the user rotates the dose selection button 30 helically out from the housing structure 10 following the helical track 34 on the dose selection button 30. During rotation of the dose selection button 30, the second toothed rack 31 on the inner surface of the dose selection button 30 is rotated radially out of engagement with the gearwheel 80 which thus allows the dose selection button 30 to follow the pitch of the helical track 34 on the dose selection button 30.

[0152] Figure 4 discloses the situation in which the user has selected the first full dose. The dose selection button 30 has been rotated one full revolution and the second toothed rack 31 has re-engaged the gearwheel 80.

[0153] When the dose selection button 30 has been rotated one full revolution, the guiding protrusion 18 will be in the position “A” shown in figure 12A and the dose selection button 30 has been moved out from the housing structure 10 a distance determined by the pitch of the helical track 34 as shown in figure 4.

[0154] Although only one helical track 34 is disclosed in the figures, more than one identical helical track can be provided.

[0155] During the relative movement between the guiding protrusion 18 in the housing structure and the helical track 34 in the dose selection button 30, the second toothed rack 31 is out of engagement with the gear wheel 80 hence the pitch of the helical track 34 can be any pith decided by the manufacturer of the injection device. Further, the pitch of the helical track 34 determines how far out from the housing structure 10, the dose selection button 30 is moved during rotation.

[0156] The user can at any time during dose selection regret the selection and rotate the dose setting button 30 in the opposite direction thus cancelling the dose selection in progress.

[0157] Ejection of a Dose

[0158] Once the fixed has been selected by rotating the dose selection button 30 one full revolution, the guiding protrusion 18 is situated in position “A” indicated in figure 12A, and the user is ready to eject the selected fixed dose. In this position (“A”), the second toothed rack 31 has again radially engaged with the gear wheel 80 in the position dictated by the pitch of the helical track 34 on the dose selection button 30.

[0159] Dose expelling is performed by pressing back the dose selection button 30 translational into the housing structure 10 by the user applying a pressure onto the push button 73. During the translational movement of the push button 73 and the dose selection button 30, the translational track 35 slides along the guiding protrusion 18. Once the guiding protrusion 18 is in the position indicated with “B” in figure 12A, the fixed dose has been ejected.

[0160] A click arm 36 at the proximal termination of the translational track 35 secures that the dose selection button 30 cannot be pulled translationally out from the housing structure 10 in this position. Once the guiding protrusion 18 is located in this position, the next dose can be selected by rotation of the dose selection button 30 in the helical track 34 and the injection process starts over again.

[0161] The gearing between the gearwheel 80 and the toothed racks 31, 65 are preferably 1:2 such that the piston rod arrangement 50 is moved half the distance of the dose selection button 30 during dose expelling however any suitable gearing can be used.

[0162] The distance that the piston rod arrangement 50 is moved during dose expelling and the inner diameter of the cartridge 40 determines the volume of the fixed dose to be delivered by the stroke. It is thus possible to alter the delivered volume simply by using different pitches of the helical track 34 and dose selection buttons 30 with different pitches can thus accommodate different dose volumes.

[0163] A series of multiple use fixed dose injection devices with different volumes of the fixed dose can thus easily be created simply by changing the pitch of the helical track 34 on the dose selection button 30. Different volumes can hence be obtained by changing only of the components of the injection device.

[0164] Changing of the Cartridge assembly

[0165] Once the content of liguid drug inside the cartridge 40 in the cartridge assembly 20 has been used, the user can remove the cartridge assembly 20 and connect a new and fresh cartridge assembly 20 by use of the bayonet interface 16a-b, 27 between the cartridge assembly 20 and the housing structure 10.

[0166] Once the cartridge assembly 20 is rotated to be released from the housing structure 10, the cartridge assembly 20 rotates the guiding tube 60 as the second protrusion 62 on the guiding tube 60 follows the rotational movement of the longitudinal slots 26 inside the cartridge assembly 20. The rotation of the guiding tube 60 forces both the bearing 70 and the piston rod assembly 50 to follow this rotation, and as the piston rod assembly 50 rotates so does the gear wheel 80 connected to the piston rod assembly 50.

[0167] The radial rotation of the gear wheel 80 thus rotates the gear wheel 80 out of engagement with the second toothed rack 31 inside the dose selection button 30.

[0168] When the gear wheel 80 and the second toothed rack 31 are out of engagement, the piston rod assembly 50 can be pushed translational back to its initial position as the gearwheel 80 is only rolling on the first toothed rack 65 in the guiding tube 60.

[0169] When a new and fresh cartridge assembly 20 is attached to the housing structure 10, the rotation in the bayonet track 16a-b rotates the guiding tube 60 in the opposite direction such that the gear wheel 80 again engages with the second toothed rack 31 inside the dose selection button 30.

[0170] Hence, during replacement of the cartridge assembly 20, the gearwheel 80 is initially rotated out of engagement with the second toothed rack 31 and then rotated back into engagement.

[0171] Automatic Priming

[0172] When attaching a new and fresh cartridge assembly 20 to the housing structure 10 via the bayonet interface 16a-b, 27, it must be safeguarded that the piston rod assembly 50 is in physical contact with the plunger 42 inside the cartridge assembly 20 before selecting and ejecting he first fixed dose, i.e., to make sure that the full translational movement of the piston rod arrangement 50 is transferred to a similar movement of the plunger 42 inside the cartridge 40. Due to the extension 11 on the housing structure 10, it is not possible to reset the device by manually pressing back the piston rod arrangement 50 to its initial position by using a finger to press back the washer part 52. However, in a new and fresh cartridge assembly 20, the plunger 42 is always positioned at the proximal end of the cartridge assembly 50, and will, as the cartridge assembly 50 is attached, abut against the piston rod arrangement 50 and thus push back the piston rod arrangement 50 in the proximal direction.

[0173] As seen in figure 13A-B, the piston rod arrangement 50 comprises a rod part 51 wherein a washer part 52 has been inserted. The washer part 52 slides in a hollow space 56 in the rod part 51 and is urged in the distal direction by a compression spring 53. When the piston rod arrangement 50 is pushed back to its initial position, which is when the rod part 51 abut against the end flange 66 in the guiding tube 60 as seen in figure 3B, further axial proximal force exertion onto the piston rod arrangement 50 will strain the compression spring 53.

[0174] As best seen in figure 13B, the washer part 52 is configured to move the distance “L” relatively to the rod part 51. This length (indicated with “L” in figure 13B) determines the longitudinal distance the washer part 52 is able to slide relatively to the rod part 51.

[0175] Further, the rod part 51 is provided with a longitudinal opening 58 in which an outwardly pointing key 57 on the washer part 52 is guided which engagement defines the most distal position of the washer part 52 relatively to the rod part 51.

[0176] The washer part 52 is thus movable from a first position to a second position by the movable plunger 42 upon connecting the exchangeable cartridge assembly 20 to the housing structure 10. The movement from the first position to the second position hence accumulates a force in the compression spring 53.

[0177] The first position of the washer part 52 relatively to the rod part 51 is the position shown in figure 13B wherein the compression spring 53 has moved the washer part 52 to its most distal position in which the outwardly pointing keys 57 on the washer part 52 engages with the distal end of the longitudinal tracks 58 in the rod part 51.

[0178] The second position is the position into which the washer part 52 is moved by the plunger 42 inside the cartridge 40 when the cartridge assembly 20 is connected to the housing structure 10, hence the second position depend on the position of the plunger 42 inside the cartridge 40 which again varies due to tolerances. The second position can thus be any random position within the distance “L” indicated in figure 13B. The distance “L” thus has to be calculated such that it can obtain the tolerances of the position of the plunger 42 inside the cartridge 40 such that a force will always be present on the plunger 42 when a new and fresh cartridge assembly 20 is connected to the housing structure 10.

[0179] When a user attaches a cartridge assembly 20 to the housing structure 10, the plunger 42 abuts the washer part 52 of the piston rod arrangement 50 at its distal end and pushes the washer part 52 in the proximal direction, hence the force occurring from the compression spring 53 will attempt to move the plunger 42 in the distal direction. However, when no injection needle is mounted, the plunger 42 is unable to move in the distal direction due to the liquid drug inside the cartridge 40, and the force applied from the compression spring 53 will thus push against the plunger 42. When the user mounts an injection needle and the liquid drug is allowed to flow out from the cartridge 40, the force of the compression spring 53 will move the plunger 42 slightly (the distance “L” or less) in the distal direction and a small amount of the liquid drug will wash out through the injection needle. As an injection needle is usually covered by a needle cover i.e. a cup shaped plastic element surrounding the tip of the needle cannula, the drops flowing from the tip of the injection cannula will spray into the needle cover. In one example a sponge material can be provided inside the needle cover to absorb the liquid drug being expelled during priming of the injection device.

[0180] Cartridges have relative high tolerance as they are typically produced from glass, and the filling of the liquid drug into the individual cartridge 40 also has some tolerance. The result being that the position of the plunger 42 inside each cartridge 40 varies from cartridge to cartridge. The length “L” that the washer part 52 is able to move is thus set such that this movement is able to obtain the tolerances of the position of the plunger 42 inside the cartridges 40.

[0181] Automatic priming of the new and fresh cartridge assembly 20 is thus obtained by the plunger 42 always pushing slightly on the washer part 52 when the cartridge assembly 20 is mounted onto the housing structure 10 such that the force applied from the compression spring 53 works on the plunger 42 when no injection needle is attached.

[0182] Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these but may be embodied in other ways within the subject matter defined in the following claims. List of Parts:

[0183] 1 Injection Device 51 Rod Part

[0184] 2 52 Washer Part

[0185] 3 53 Compression Spring 4 54 Flexible Arm

[0186] 5 Protective Cap 55 Radial Openings 6 56 Hollow Space

[0187] 7 57 Outwardly Pointing Keys 8 58 Longitudinal Slots 9 59

[0188] 10 Housing Structure 60 Guiding tube

[0189] 11 Tube Extension 61 First Protrusion 12 Window 62 Second Protrusion 13 Anti Roll Feature 63 Longitudinal Sides 14 Protrusion 64

[0190] 15 Rails 65 First Toothed Rack 16a Axial Opening 66 End Flange

[0191] 16b Peripheral Track

[0192] 17 Axial Code Openings

[0193] 18 Guiding Protrusion

[0194] 19 Angular Opening

[0195] 20 Cartridge assembly 70 Bearing

[0196] 21 Needle Mount 71 Longitudinal Opening 22 Click Arms 72 Radial Flange

[0197] 23 Opening / Window 73 Push Member 24 74 Holding Flange 25 Cartridge Holder Part 75 Inner Recess

[0198] 26 Longitudinal Slots

[0199] 27 Bayonet Protrusions

[0200] 28 Code Protrusions

[0201] 29

[0202] 30 Dose Selection Button 80 Gearwheel

[0203] 31 Second Toothed Rack 81 Radial Axis

[0204] 32 EoC arm 82 Peripheral Teeth 33 Grip

[0205] 34 Helical Track

[0206] 35 Translational (longitudinal) Track

[0207] 36

[0208] 37

[0209] 38

[0210] 39

[0211] 40 Cartridge

[0212] 41 Membrane

[0213] 42 Movable Piston

[0214] 43 Neck Portion

[0215] 44

[0216] 45

[0217] 46

[0218] 47

[0219] 48

[0220] 49

[0221]

[0222] 50 Piston Rod Arrangement

Claims

CLAIMS:

1. A reusable injection device for ejecting a plurality of fixed doses containing the same predetermined volume of liquid drug, comprising:- a housing structure (10) supporting a drive mechanism comprising a piston rod arrangement, and- an exchangeable cartridge assembly (20) connectable to the housing structure (10), and which exchangeable cartridge assembly (20) secure a cartridge (40) containing the liquid drug and which cartridge (40) proximally is provided with a movable plunger (42) movable at least in a distal direction to expel the liquid drug through a connectable injection needle, wherein the piston rod arrangement (50) comprises a washer part (52) and a rod part (51) and which piston rod arrangement (50) is adapted to move the plunger (42) in the distal direction inside the cartridge (40) during dose ejection, and wherein a spring element (53) is coupled between the washer part (52) and the rod part (51),wherein the washer part (52) is adapted to move from a first position to a second position by the movable plunger (42) upon connecting the exchangeable cartridge assembly (20) to the housing structure (10) which movement from the first position to the second position accumulates an axial force in the spring element (53), andwherein the washer part (52) is adapted to move from the second position and back to the first position by the axial force delivered from the spring element (53).

2. An injection device according to claim 1 , wherein the washer part (52) and the rod part (51) are provided with mutually engaging guiding means (57, 58) guiding the washer part (52) and the rod part (51) translational in relation to each other.

3. An injection device according to claim 2, wherein the guiding means (57, 58) further are provided with stop means determining the translational distance the washer part (52) and the rod part (51) is adapted to move in relation to each other.

4. An injection device according to claim 2 or 3, wherein the guiding means (57, 58) comprises a longitudinal track (58) guiding a protrusion (57).

5. An injection device according to claim 4, wherein the longitudinal track is a closed track.

6. An injection device according to claim 4 or 5, wherein the longitudinal track (58) is provided on the rod part (51) and the protrusion (57) is provided on the washer part (52).

7. An injection device according to any of the previous claims, wherein the axial force accumulated in the spring element (53) is releasable upon connecting the connectable injection needle to the injection device.

8. An injection device according to any of the previous claims, wherein the connectable injection needle is connectable to the distal end of the cartridge assembly (20).

9. An injection device according to any of the previous claims, wherein the first position is the position whereto the washer part (52) is distally moved by the force of the spring element (53).

10. An injection device according to any of the previous claims, wherein the second position is the position where to the washer part (52) is proximally moved by the plunger (42) inside the cartridge assembly (20).

11. An injection device according to any of the previous claims, wherein the cartridge assembly (20) comprises a cartridge (40) loaded in a cartridge holder part (25).

12. An injection device according to claim 11, wherein the cartridge assembly (20) comprises the cartridge (40) irreversible and permanently secured in the cartridge holder part (25).

13. A cartridge coding system for an injection device according to any of claims 1 to 12, comprising:- a housing structure (10) and a cartridge assembly (20) arranged to be releasable coupled together,- a bayonet track (16a-b) associated with the housing structure (10) and having an axial opening (16a) and a peripheral track (16b),- a bayonet protrusion (27) associated with the cartridge assembly (20),wherein the cartridge coding system (16a, 27; 17, 28) further comprises- a code opening (17) associated with the bayonet track (16a-b), and- a coding protrusion (28) associated with the cartridge assembly (20),such that the cartridge assembly (20) can only be coupled to the housing structure (10) when the code opening (17) and the code protrusion (28) are aligned.

14. A cartridge coding system for an injection device according to claim 13, wherein one or more code protrusions (17) are provided on an inner surface of the cartridge assembly (20) and the bayonet track (16a-b) is provided on an outer surface of the housing structure (10).

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