Injection device for delivering a plurality of pre-defined fixed doses

Abstract

The invention relates to a multiuse fixed dose injection device for ejecting multiple pre-defined fixed doses of a liquid drug. The injection device comprises a housing structure, a dose selection button and a piston rod assembly. The housing structure is configured for holding a loaded cartridge containing the liquid drug. The dose selection button is functionally coupled to the housing structure for selecting one of the pre-defined fixed dose and the piston rod assembly is distally adapted to move a piston inside the loaded cartridge and adapted to carry a gear wheel, which is rotatably coupled with a piston rod. The injection device further comprises a first toothed rack associated with the housing structure and a second toothed rack associated with the dose button. The gear wheel and the first toothed rack are permanently engaged both during dose selection and during dose ejection, and the gear wheel and the second toothed rack are disengaged during dose selection and engaged during dose ejection.

Description

[0001] INJECTION DEVICE FOR DELIVERING A PLURALITY OF PRE-DEFINED FIXED DOSES

[0002] THE TECHNICAL FIELD OF THE INVENTION:

[0003] The invention relates to an injection device for ejecting a plurality of pre-defined fixed doses of a liquid drug from a drug container. The invention preferably relates to the dose selection and dose ejection of the pre-defined fixed doses using a rotatable dose selection button and more preferably to the gearing mechanism of such injection device. The drug container used is preferably an exchangeable medical cartridge thus making the injection device a reusable injection device.

[0004] The invention further relates to an End-of-Content mechanism for such injection device and to a cartridge change system for changing the exchangeable cartridge in such an injection device.

[0005] DESCRIPTION OF RELATED ART:

[0006] Traditional injection devices for 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.

[0007] An example of such insulin injection devices is disclosed in US 5,304,152. In one example disclosed, the piston rod is proximally provided with a gear wheel whereby the piston rod can be moved distally by translating a threaded element axially inside the injection device.

[0008] Over the last 10 to 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 do not need to be injected in a very precise and individual volume but can easily be injected as a pre-defined fixed dose 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. Hence, the requirement to these injection devices is somewhat different from what is required from a traditional injection device used for insulin.

[0009] As a result of this a large number of so-called fixed dose injection devices has emerged over the last decade. Some of these fixed dose injection devices inject one fixed dose whereafter the whole injection device is discarded. Such injection devices are often referred to as single shot fixed dose injection devices as they only contain one single dose of the liquid drug to be delivered in one single shot. However, in order to reduce the amount a plastic waist and also the production cost, fixed dose injection devices which are able to inject a plurality of predefined fixed doses has been developed. Such injection devices are often referred to as multiuse fixed dose injection devices. Usually, these injection devices are pre-filled by the manufacturer with the amount of drug needed for a specific number of injections and once the predetermined number of injections has been delivered the entire injection device is discarded.

[0010] An example of such pre-filled multiuse fixed dose injection device for ejecting fixed doses of a liquid drug is disclosed in WO 2020 / 089167. With such injection device, the user can expel a pre-defined fixed dose a predetermined number of times before the injection device is discarded. The particular injection device disclosed is a torsion spring driven injection device wherein each of the fixed doses are automatically ejected by the use of a torsion spring which is strained by the user during selection of the fixed dose.

[0011] An example of a manual pre-filled injection device suitable for expelling a predetermined number of pre-defined fixed doses is also disclosed in WO 2003 / 080160. This injection device, as disclosed in the embodiments on the figures 10 -19 has a dose selection button which is manually rotated out from the housing during dose selection and which rotates back into the housing during dose expelling. The disclosed injection device further has a gearing mechanism to gear the axial distance the dose selection button is moved relatively to the axial distance the piston rod is moved. The gearing mechanism is highly complicated and comprises a gear wheel having two different rolling diameters and two different toothed racks all rotationally mounted and engaging the gear wheel both during dose selection and during dose expelling.

[0012] DESCRIPTION OF THE INVENTION:

[0013] It is an object of the present invention to eliminate or reduce one or more drawbacks of the prior art, or to provide a useful alternative to prior art solutions.

[0014] In particular, it is an object of the invention to provide a manually operational injection device with a gearing for manually injecting a plurality of pre-defined fixed doses which comprises a limited number of parts and which is simple in its structure and at the same time robust and reliable. Thus, making scalability to high volume production possible.

[0015] It is further an object of the present invention to provide a manually operational multiple fixed dose injection device having a comparable low environmental impact.

[0016] The invention is defined in claim 1. Advantageous embodiments are further defined in the dependent claims.

[0017] Accordingly in one aspect the present invention relates to an injection device for ejecting a number of pre-defined fixed doses of a liquid drug which comprises:

[0018] - A housing structure configured for holding a loaded cartridge containing the liquid drug,

[0019] - A dose selection button which is functionally coupled to the housing structure for selecting a fixed dose,

[0020] - A piston rod assembly which is adapted to move a plunger inside the loaded cartridge and comprising a piston rod and a gear wheel, which gearwheel is rotatably coupled with the piston rod.

[0021] The fixed dose injection device further comprises a first toothed rack which is associated with the housing structure and a second toothed rack which is associated with the dose selection button and wherein, the gear wheel and the first toothed rack are engaged with each other both during dose selection and during dose ejection, and the gear wheel and the second toothed rack are disengaged during dose selection and engaged during dose ejection.

[0022] Further, according to the invention, the gear wheel and the second toothed rack are disengaged during dose selection allowing the dose selection button to rotate helically out from the housing structure preferably independently of the piston rod assembly, to thereby select the pre-defined fixed dose and the gear wheel and the second toothed rack are engaged during dose ejection and the dose selection button is adapted to translate axially back into the housing structure to thereby eject the selected pre-defined fixed dose. The gearing mechanism thus comprises two toothed racks and a gear wheel operationally connected to the piston rod. The first toothed rack is permanently engaged with the gear wheel such that the gear wheel will always roll on the first toothed rack. The first toothed rack is preferably operationally related to the housing structure e.g. via another element. The second toothed rack and the gear wheel can however be brought into and out of engagement with each other. The second toothed rack is preferably linked to the dose selection button.

[0023] The term “associated with” is to be construed broadly. Hence, the first toothed rack being associated with the housing is preferably meant to imply that the first toothed rack is carried by a constructional element which is somehow linked to the housing structure, and the second toothed rack being associated with the dose selection button is preferably meant to imply that the second toothed rack is somehow linked to the injection button.

[0024] Both when selecting the pre-defined fixed dose and when ejecting the selected pre-defined fixed dose is the gear wheel engaged with first toothed rack. In respect of the second toothed rack, the gear wheel is in engaged with the second toothed rack during dose ejection but is moved out of engagement with the gear wheel during dose selection allowing the second toothed rack to move helically without engaging the gear wheel. Hence, the dose selection button can move helically out from the housing structure following a different pitch than the one defined by the toothed racks.

[0025] Hence in a first mode wherein the user selects the fixed dose to be ejected, the dose selection button associated with the second toothed rack is rotated helically out from the housing structure, which decouples the second toothed rack from the gear wheel thereby allowing the dose selection button to be moved any distance out from the housing structure. The pitch on the threaded engagement between the dose selection button and the housing structure are preferably different from the pitch of the threaded connection between the second tooted rack and the gear wheel.

[0026] In a second mode wherein the user ejects the selected fixed dose, the dose selection button is translated axially back into the housing structure without rotation. In the second mode, the gear wheel is in contact with both the toothed racks and thus rolls on both toothed racks. The rolling diameter of the gear wheel thus defines the gearing ratio which in the present example of the invention is set to 1:2 such that the piston rod travels half the translational distance of the distance the dose selection button travels in the second mode. However, any gearing ratio can be used.

[0027] The herein described fixed dose device is thus suitable for ejecting a pre-determined number of pre-defined fixed doses from an exchangeable loaded cartridge. The volume of these predefined fixed doses are preferably the same for all doses and determined by the manufacturer of the injection device such that the specific volume of the doses are inherent in the injection device and unchangeable for the user of the injection device.

[0028] The user is required to simply rotate the dose selection button to thereby select one of the pre-defined fixed doses available in the loaded cartridge and to press the dose selection button back into the housing structure to thereby manually eject the selected pre-defined fixed dose. This operation can only be done the number of times pre-determined by the manufacturer of the injection device. Once the pre-determined number of pre-defined fixed doses has been expelled, the user can replace the loaded cartridge with a new and fresh cartridge and expel the number of pre-defined fixed doses available in the next cartridge loaded into the injection device.

[0029] In one example, the cartridge can be irreversible embedded in a cartridge unit preferably made from a suitable polymer such that the user can replace the entire cartridge unit once the pre-determined number of pre-defined fixed doses has been expelled.

[0030] To guide the dose selection button during selection of the fixed dose, the housing structure or the dose selection button is provided with one or more thread segments and the other of the dose selection button or the housing structure is provided with at least one helical track. Due to this helical interface between the dose selection button and the housing structure, the dose selection button is always rotated helically out from the housing structure when the user selects the pre-defined fixed dose to be injected.

[0031] To guide the dose selection button during expelling of the fixed dose, the housing structure or the dose selection button are provided with one or more thread segments and the other is provided with at least one translational track. Due to this translational interface between the dose selection button and the housing structure, the dose selection button is always translated axially back into the housing structure when the user ejects the selected predefined fixed dose.

[0032] In a preferred example, the dose selection button is thus able to move helically out from the housing structure during dose selection and to translate axially back into the housing during expelling of the selected pre-define fixed dose by being guided in the housing structure.

[0033] In order to notify the user that the injection device is ready to eject the selected fixed dose a clicker arrangement is provided which provide the user with an audible and / or tactile signal once the one or more thread segments enters into the at least one translational track from the at least one helical track. This clicker arrangement is preferably located in the intersection between the at least one helical track and the at least one translational track and activated by the one and more thread segments. In a further example, similar clicker arrangement can be provided in other positions as well. It can e.g. be advantages if the user is also provided with a signal when starting to select a dose.

[0034] In one example, the clicker arrangement comprises a segment or protrusion having one or more lowered portions which lowered portions engages a raised knob provided in the dedicated position in the track configuration. The segment or protrusion having lowered portions could in a further example be the thread segment carried by the housing structure and the raised knobs could be provided in specific positions along the route the thread segments travel in the helical and / or translational track. An audible and / or tactile signal could then be delivered when the raised knob engages or disengages with one of the lowered portions of the thread segment. By using raised knobs in the track and lowered portions in the thread segment the thread segment is also fixated in the different positions once the raised knob has entered into the lowered portion. Hence both a non-permanently positioning of the dose selection button and a signal is provided by this solution.

[0035] In the first mode wherein the user selects the fixed dose to be expelled, the second toothed rack and the gear wheel are rotated out of engagement with each other. This is preferably done by rotating the second toothed rack radially around the longitudinal axis of the injection device to thereby disengage the second toothed rack and the gear wheel. In order to rotate the second toothed rack around the longitudinal axis of the injection device, the second toothed rack is preferable linked to the dose selection button to rotate together with the dose selection button during dose selection.

[0036] The dose selection button is preferably rotated one full revolution to select the dose to be ejected. The full revolution secures that the second toothed rack of the dose selection button always ends up in a position in which the second toothed rack is re-engaged with the gear wheel carried by the piston rod. Once the dose selection button has been rotated a full rotation, the second toothed rack and the gear wheel are radially engaged. However, the rotational span can easy be selected by the manufacturer to be less than one full revolution simply by changing the intersection between the helical track used during dose selection and the position of the translational track used during expelling of the selected pre-defined fixed dose.

[0037] Although the term used is one full revolution, such revolution could be slightly less than 360 degrees in order to have sufficient space for the various tracks utilized.

[0038] The housing structure preferably comprises a housing part and a cartridge holder releasable coupled together along the centre axis. In one example, the cartridge holder carries a replaceable cartridge and, in another example, the cartridge is embedded in the cartridge holder to form a drug unit or cartridge unit which is replaceable as a whole. Whether, the cartridge holder has a replaceable cartridge or a permanently and irreversible embedded cartridge, the cartridge holder, which could also be referred to as the cartridge unit, is preferably connected to the housing part by a bayonet coupling.

[0039] In one example a cradle supporting the piston rod and carrying the first toothed rack is rotatable connected to the housing structure such that the cradle can be rotated via its engagement with the cartridge holder. The gear wheel which is rotatable connected to the piston rod, preferably at a proximal end thereof also follows the rotation of the cradle to be rotated out of engagement with the second toothed rack during rotation of the cradle by the cartridge holder. The cradle is in one example operational considered a part of the housing structure as the cradle at any time is longitudinal fixated in the housing structure. However, the cradle is thus only axially fixated in the housing structure and hence able to rotate relatively to the housing structure. In the disclosed example, the cradle is able to pivot in relation to the housing structure preferably between two different positions. The cradle thus being considered a pivotable element associated with the housing structure. As the cradle supports and guides the piston rod assembly and the cradle carries the first toothed rack, the gear wheel of the piston rod assembly and the first toothed rack are permanently engaged.

[0040] In a second aspect of the invention an End-of-Content mechanism is provided. An End-of- Content mechanism is generally a mechanism which prevents the user from selecting a further dose once the initial quantum of liquid drug in the cartridge has been used. In the area of injection devices expelling a pre-determined number of pre-defined fixed doses, an end-of-content mechanism secures that once the last of the pre-determined number of doses has been expelled the user cannot select a full dose anymore.

[0041] According to the invention such End-of-Content mechanism for the multiple fixed dose device herein described comprises a flexible element such as a small arm or the like connected to, or being part of, the dose selection button which flexible element is bended radially outwardly to engage with the housing structure when a predetermined number of fixed doses has been set and ejected.

[0042] In one example, the flexible element is bended radially outwardly by the gear wheel when the gear wheel has been moved to its preferred end position. Once bended outwardly, the flexible element preferably engages with the housing structure e.g. via a stop protrusion provided on an inner surface of the housing structure. Hence, the position of this stop protrusion, the position of the flexible element and the position of the gear wheel in its end position defines when the dose selection button is being blocked for further rotation.

[0043] In one example, the multiple fixed dose device is designed to expel four equally sized doses, hence the piston rod is moved forward in the distal direction four times wherein each movement has the same translational distance such that the same volume is expelled in each of the four movements. The pre-defined fixed doses thus refer to the volume ejected. Although the same volume is ejected each time the injection device is operated, the liquid drug contained in different cartridges or cartridge units can have different strengths. Following the fourth and last movement, the gear wheel is brought to its end position and is radially positioned adjacent to the flexible element. If the user tries to rotate the dose selection button once more in an attempt to select a fifth dose, the gear wheel will abut and force the flexible element outwardly to engage with the housing structure thus hindering the user in selecting a fifth dose. The engagement between the flexible element and the inner surface of the housing structure can be refined by providing a protrusion of the inner surface of the housing structure and / or provided the flexible element with an engagement feature.

[0044] In a third aspect of the invention, the multiple fixed dose injection device described herein is provided with a cartridge change system wherein rotation of the cartridge holder disengages the engagement between the second toothed rack and the gear wheel thereby allowing the piston rod in being moved to its initial position.

[0045] In one example, the cartridge holder is forced to rotate when connected to or disconnected from the housing part containing the drive mechanism due to a bayonet interface, this rotation of the cartridge holder is then utilized to rotate the gear wheel out of engagement with the second toothed rack. Once there is no engagement between the gear wheel and the second toothed rack, the piston rod carrying the gear wheel can be pushed translationally back to its initial position.

[0046] The cartridge holder being either a regular cartridge holder holding an exchangeable cartridge or a cartridge holder formed as a cartridge unit having a cartridge permanently and irreversible embedded therein.

[0047] In a preferred example, the cartridge holder, or cartridge unit if the cartridge is irreversible fixed in the cartridge unit, engages and rotates the cradle. The cradle can thus be in a position in which gear wheel is in contact with the second toothed rack of the dose selection button or the cradle can be pivoted (i.e. rotated) by the cartridge holder to a position wherein the gear wheel is disconnected from the second toothed rack such that the gear wheel and the piston rod can be pressed axially back to its initial position before a new cartridge or cartridge unit is attached. The cradle is preferably able to pivot (rotate) around the longitudinal axis (X) of the housing structure. Without the cartridge change system herein described it would not be possible to move the piston rod assembly back to its initial start position, hence, the injection device would not be reuseable. Hence, the multi-use fixed dose injection device herein described and claimed can be either a pre-filled injection device or a re-usable injection device.

[0048] The multiuse fixed dose injection device described herein consist of only eight simple parts or components which are all preferably moulded from a suitable plastic. In order to facilitate take-back followed by re-use or re-cycling, the eight components are preferably made from the same polymer or at least from polymers which can be re-cycled together. In one example, components which are physically linked together can be made from the same polymer or type of polymers thus being recyclable together without disassemble the linked components. Further, to facilitate re-use or re-cycling of the polymer parts, the eight parts are preferably coupled together by using techniques which makes its relatively easy to dissemble the injection device such as threads or simple click fasteners. In one example, one or more of the polymers parts can however be moulded from an already re-cycled polymer. The polymer parts being made from re-cycled polymers are preferably the parts not requiring very strict tolerances such as the protective cap and / or the cartridge holder.

[0049] The polymer parts could also be moulded from other 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.

[0050] DEFINITIONS:

[0051] 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.

[0052] 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”. 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.

[0053] 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.

[0054] 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. In the GLP-1 class of liquid drugs based on Liraglutide and Semaglutide trademarks like Victoza,®, Saxenda®, Ozempic® and Wegovy® all by Novo Nordisk A / S are well known products.

[0055] “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 durable 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.

[0056] 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 filled by the manufacture of the injection device at a factory facility 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 volume 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 or durable 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 or durable injection devices are usually sold one at a time. When using pre-filled injection devices an average user on an insulin treatment 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 durable or reusable 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 “Cartridge unit”. After use, when the cartridge in the cartridge unit is empty, or at least when the pre-determined number of doses has been expelled, the user discards the whole cartridge unit and replaces it with a new and fresh cartridge unit containing a cartridge (or similar container) with liquid drug sufficient for a new plurality of injections.

[0060] By the term “Pre-defined fixed dose” is meant a dose of the liquid drug having a predefined fixed volume which is determined by the manufacturer of the injection device and are inherent in the injection device such that the user can only select and expel one or more of the pre-defined fixed doses without any possibility for the user to change the volume of the fixed dose. In a preferred example 2 to 8 pre-defined fixed doses, and preferably 4 to 6 predefined doses, are available in one injection device.

[0061] 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.

[0062] All headings and sub-headings are used herein for convenience only and should not be constructed as limiting the invention in any way.

[0063] 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.

[0064] 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.

[0065] This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.

[0066] BRIEF DESCRIPTION OF THE DRAWINGS:

[0067] The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

[0068] Figure 1 A show a side view of the injection device with the protective cap mounted.

[0069] Figure 1 B show a side-view of the injection device without the protective cap.

[0070] Figure 2 show an exploded view of the injection device according to the invention.

[0071] Figure 3A show a cross-sectional view of the injection device in the initial start position. Figure 3B show a cross-sectional view similar to that of figure 3A, however, the injection device has been rotated 90° around the longitudinal axis (X).

[0072] Figure 4 show a cross-sectional view of the injection device wherein the first predefined fixed dose has been selected.

[0073] Figure 5 show a perspective view of the gear wheel.

[0074] Figure 6A-B show different perspective views of the piston rod.

[0075] Figure 7A-B show different perspective views of the housing part.

[0076] Figure 8A-B show different perspective views of the cartridge holder.

[0077] Figure 9 show a perspective view of the protective cap.

[0078] Figure 10 show a perspective view of the cradle.

[0079] Figure 11 show a perspective view of the bearing.

[0080] Figure 12 show a perspective view of the dose selection button.

[0081] Figure 13A-B show different side views of the dose selection button.

[0082] Figure 13C show a view of the first thread segment inside the housing part.

[0083] Figure 14A show a cross-sectional view of the injection device with the piston rod in the end position.

[0084] Figure 14B show a side view of the injection device with the housing structure visually removed.

[0085] Figure 14C show a cross-sectional view along the line AA in figure 14B.

[0086] Figure 15 show an example of a cartridge unit and a different housing structure.

[0087] 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.

[0088] DETAILED DESCRIPTION OF EMBODIMENT: 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.

[0089] 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 1. 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 1A-B and in figure 3A-B.

[0090] When referring to clock-wise and anti or counter clock-wise in the following examples it is understood that the injection device is viewed from a position distal to the injection device. Clock-wise 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 counter clock-wise is a rotation in the opposite direction.

[0091] 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.

[0092] “Translational movement” is meant to be a strictly linear movement without any rotation.

[0093] “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.

[0094] “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. “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.

[0095] Figure 1A-B discloses the multiuse fixed dose device as it is delivered to a user. The outer shell of the injection device, herein referred to as the housing structure, comprises a housing part 10 and a cartridge holder 30 which are releasable coupled together. Prior to use, the cartridge holder 30 or part thereof is covered by a protective cap 5 which is to be removed before using the injection device. A cartridge 40 containing the liquid drug to be injected is secured by the cartridge holder 30. The cartridge 40 is preferably a so-called PenFill® wherein a plastic adapter top 41 carrying the needle mounted is secured at the distal end of the cartridge 40. Alternatively, the needle mount can be a part of the cartridge holder 30. Proximally, the injection device is provided with a dose selection button 20 which the user rotates out from the housing part 10 to select the fixed dose to be injected. The dose selection button 20 is in the disclosed example a longitudinal tube shape component which at the proximal end has a finger grip 22.

[0096] Figure 2 and figure 3A-B discloses different views of the injection device with the dose selection button 20 in the initial position. The shell of the injection device comprises the housing structure made up from the housing part 10 and the cartridge holder 30. The housing part 10 guides the dose selection button 20 which has both a helical interface and a translational interface with the housing part 10. The dose selection button 20 is helically interfaced with the housing part 10 such that the dose selection button 20 rotates helically out from the proximal end of the housing part 10 during dose selection. During dose expelling, the dose selection button 20 is to be pushed translationally and axially back into the housing part 10 by the user as will be explained.

[0097] Distally the housing part 10 carries the cartridge holder 30 which secures an exchangeable cartridge 40. The cartridge 40 is preferably made from glass and is distally provided with a membrane 42 to be pierced by a double pointed injection needle. Proximally, the cartridge 40 is provided with a movable piston or plunger 43 which can be moved in the distal direction by a piston rod 50.

[0098] The cartridge holder 30 is preferably connected to the housing part 10 by a bayonet interface. In one example, the cartridge 40 can be removed from the cartridge holder 30 in order to insert a new and fresh cartridge 40 whereafter the cartridge holder 30 is attached to the housing part 10. However, the cartridge 40 could also be permanently embedded or incapsulated in the injection device to form a so-called pre-filled injection device. In a further example, the cartridge 40 could be permanently retained in the cartridge holder 30, such that the cartridge 40 and the cartridge holder 30 together form a disposable drug containing unit which can be removed and replaced by a new and fresh drug containing unit. A new and fresh drug containing unit i.e. a cartridge and a cartridge holder permanently locked together would thus be required for each exchange.

[0099] The cartridge holder 30 and the cartridge 40 could hence be permanently coupled together by the cartridge holder 30 having a protrusion, a knob, or the like which the cartridge 40 has to pass during assembly and which hinders the cartridge 40 from being removed from the cartridge holder 30 once it is inserted into the cartridge holder 30. Alternatively, the cartridge holder 30 can be formed from one or more parts which are irreversible click-fitted together to permanently secure the cartridge 40.

[0100] In figure 3A-B, the injection device is disclosed in the initial start position before any dose is selected and ejected. The plunger 43 is located proximally inside the cartridge 40 and the dose selection button 20 is in abutment with the housing part 10. Further, the piston rod 50 is in its most proximal position. In this position, the piston rod 50 preferably abuts the plunger 43 such that any movement of the piston rod 50 in the distal direction is directly transferred to a similar movement of the plunger 43. Preferably, the plunger 43 and the piston rod 50 are mounted such that a small pressure is applied onto the plunger 43 to thereby eliminate tolerances and avoiding an air-gap between the piston rod 50 and the piston 53.

[0101] Figure 4 disclose the injection device with the first dose selected. The dose selection button 20 has hence been rotated one full revolution out from the housing part 10. As seen, the housing part 10 secures a tube-like cradle 60 thus being associated with the housing structure. This cradle 60 is distally attached to the housing part 10 such that the cradle 60 can rotate relatively to the housing part 10 but is at the same time axially fixated inside the housing part 10, hence the cradle 60 cannot move axially in relation to the housing part 10 when the dose selection button 20 is moved out from the housing part 10. The cradle is only able to rotate relatively to the housing part 10. A tube-like bearing 70 is further provided inside the dose selection button 20. This bearing 70 is in the same way attached to dose selection button 20 at the proximal end in a way allowing relative rotation of the bearing 70 relatively to the dose selection button 20, but at the same time locking the dose selection button 20 and the bearing 70 together in the axial direction, hence, the bearing 70 is associated with the dose selection button 20 and follows the axial movement of the dose selection button 20 but not necessarily the rotation of the dose selection button 20.

[0102] The tube-like bearing 70 and the cradle 60 are able to move telescope axially in relation to each other but are rotationally locked to each other as will be explained.

[0103] The piston rod 50 is guided in the cradle 60. The shapes of the piston rod 50 and the cradle 60 are such that the piston rod 50 is able to translate relatively to the cradle 60 but prevented form rotating relatively to the cradle 60.

[0104] At the distal end of the piston rod 50, the piston rod 50 abuts the movable plunger 43 inside the cartridge 40 such that a further forward movement in the distal direction will build up pressure inside the cartridge 40 and thus force the liquid drug to flow out through a double pointed injection needle attachable to the needle mount on the adapter top 41 at the distal end of the cartridge 40.

[0105] The piston rod 50 is further provided with a gear wheel 80 such that the piston rod 50 and the gear wheel 80 makes up a piston rod assembly. 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 50. A flexible arm 52 provided on the piston rod 50 obstructs the free rotation of the gear wheel 80 as will be explained.

[0106] In sum, the injection device consists of 8 components as best seen in figure 2 together with an exchangeable cartridge 40 containing the liquid drug. These parts (except the cartridge) are preferably all made from a polymer material and to increase the possibility of recycling the plastics, the 8 components are preferably made from the same polymer. However, some of the components not requiring very precise tolerances like e.g. the protective cap, can be produced from 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 such that the different components can be individually handled and recycled if needed.

[0107] The Gear Wheel (80)

[0108] The gear wheel 80 as disclosed in figure 5 is in its centre provided with a radial axis 81 which is secured to the piston rod 50 and which allows the gear wheel 80 to rotate relatively to the piston rod 50. The radial axis 81 is preferably moulded as an integrated part of the gear wheel 80 such that the whole gear wheel 80 is one unit rotationally mounted on the piston rod 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.

[0109] The Piston Rod (50)

[0110] The piston rod 50 is disclosed in figure 6A-B and comprises a distal end which is able to abut the movable plunger 43 inside the cartridge 40 during dose expelling. For this purpose, the distal end of the piston rod 50 is provided with a piston rod foot 51 to better distribute the forces onto the plunger 43. As disclosed, this foot 51 can be moulded as an integral part of the piston rod 50 or alternatively configured as a separate part which is attached to the piston rod 50.

[0111] Proximally, the piston rod 50 is provided with an axial opening 55. The surrounding walls 56 of the axial opening 55 are each provided with a circular opening 57 into which the radial axis 81 of the gear wheel 80 fits. The walls 56 are further provided with a radial track 58 allowing the radial axis 81 of the gear wheel 80 to be clicked onto the piston rod 50 and be secured rotationally on the piston rod 50.

[0112] Inside the axial opening 55, one or more flexible arms 52 (also seen in figure 3A) are provided which engages the peripheral teeth 82 on the gearwheel 80 thereby securing that the gearwheel 80 is somewhat restricted in its rotational movement relatively to the piston rod 50. Hence, the gear wheel 80 cannot rotate freely but requires an external force in order to rotate. The one or more flexible arms 52 are preferably moulded as an integral part of the piston rod 50.

[0113] Housing Part (10) The housing part 10 disclosed in detail in figure 7A-B has an elongated tubular shape and is distally provided with a peripheral bayonet track 11 on the outer surface for engaging with a cartridge holder 30 as will be explained. All though the housing part 10 is disclosed with a bayonet track 11 , the bayonet track 11 could alternatively be provided on the cartridge holder 30.

[0114] On the inner distal surface, the housing part 10 is provided with a number of longitudinal recesses 12 to be engaged by first protrusions 61 provided proximally on the cradle 60 to guide the rotation of the cradle 60.

[0115] The distal end of the housing part 10 is further provided with through-going radial openings 13 through which second protrusions 62 provided on the cradle 60 extend thereby locking the cradle 60 axially to the housing part 10. This is also seen in figure 3B.

[0116] The cradle 60 is thus locked to the housing part 10 in the axial direction but allowed to rotate the angular distance determined by the angular extension of the through-going radial openings 13. The cradle 60 is preferably rotated by the cartridge holder 30 as will be explained.

[0117] Internally, in the housing part 10 an inner thread is provided. The inner thread is preferably shaped as an inwardly pointing first thread segment 15a which could further be accompanied by a second thread segment 15b as disclosed in figure 7B wherein the tubular housing part 10 has been cut over to better view the various protrusions on the inner surface. The purpose of these thread segments 15a,b are to guide the dose selection button 20 helically during dose selection and translational during dose expelling as will be explained.

[0118] The housing part 10 is also provided with an inner stop protrusion 16 on the inner surface which is part of the End-of-Content mechanism.

[0119] On the outside surface, the housing part 10 can be provided with an anti-roll protrusion 14 preventing the injection device from rolling when placed on a surface such as a table of the like.

[0120] Cartridge Holder (30) The cartridge holder 30 disclosed in figure 8A-B is distally provided with a ring of teeth 35 which is able to engage and rotationally secure the adapter top 41 of a cartridge 40 as it is generally known in the art.

[0121] Longitudinally, one or more windows 31 are provided through which a user can inspect the liquid drug stored in the cartridge 40. Preferably, two such windows 31 are provided aligned with each other. The cartridge holder 30 can in one example be provided with printed or engraved indicia or symbols indicating the amount of liquid drug in the cartridge 40 such that a user can easily read out the remaining content of the cartridge 40. The indications can also be provided in the moulding or as individual windows wherein each window e.g. indicates one fixed dose size.

[0122] In a further example, the position of the piston rod relative to the cartridge holder 30, are preferably scanned or photographed by a camera e.g. a camera in a smartphone. The scanned or photographed image can thereafter be processed in an app or the like stored in the smartphone to provide the user with information regarding the selected doses. This information could e.g. refer to the consumption of the fixed doses e.g. which number of dose are being used and how many doses are left in the cartridge which further can support the user in ordering new cartridges for the injection device, e.g. in an automated process.

[0123] Proximally, the cartridge holder 30 is provided with a plurality of bayonet protrusions 32 engaging the bayonet track 11 on the housing part 10 such that the cartridge holder 30 can be attached to the housing part 10 by a relative rotation of the two components. The bayonet protrusions 32 are in one example supplemented by openings 33 through which the user can inspect that the cartridge holder 30 is correctly attached e.g. by having a colour indication on the housing part 10 viewable through the opening 33. The visual part preferably being the side walls of the bayonet track 11.

[0124] As previously described, the cartridge 40 and the cartridge holder 30 can be permanently connected to form one drug containing unit which can easily be replaced by a new and fresh drug containing unit using the bayonet interface 11, 32. In the bayonet interface 11 , 32, the bayonet protrusions 32 and the bayonet track 11 can be placed on either of the cartridge holder 30 or on the housing part 10 respectively. The cartridge holder 30 is further provided with a number of inwardly pointing knobs 36 for engaging and rotating the cradle 60 as will be explained. In the disclosed example, two such knobs 36 are provided each having a longitudinal slot 37.

[0125] When the cartridge holder 30 is connected to the housing structure 10 using the bayonet interface 11, 32 between the cartridge holder 20 and the housing part 10, the longitudinal slot 37 will engage with a second protrusion 62 provided on the cradle 60, the effect of which will be explained.

[0126] Protective Cap (5)

[0127] To cover the housing structure and in particular the cartridge holder 30 e.g. including the cartridge 40 when the injection device is not in use, a protective cap 5 as disclosed in figure 9 is provided. This protective cap 5 is an elongated tube-shaped structure distally closed by a radial end wall 6 which is preferably moulded as an integral part of the protective cap 5. However, in one example the end wall 6 can be a separate part attached to the tube-like structure.

[0128] The protective cap 5 is further provided with a recessed portion 7 which can e.g. accommodate a label or the like. Internally, the protective cap 5 can be provided with a click mechanism for removable securing the protective cap 5 on the cartridge holder 30.

[0129] Internally, the protective cap 5 can in one example be provided with non-shown ribs or the like such that the protective cap 5 can only be mounted on the housing structure 10, 30 once the injection needle has been removed.

[0130] Cradle (60)

[0131] The cradle disclosed in figure 10 is moulded as a tube-shaped elongated 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.

[0132] The circumferential closed tube is internally, at least on a part thereof, shaped in the same shape as the piston rod 50 such that the piston rod 50 is able to slide inside the circumferential closed tube but unable to rotate relatively to the cradle 60. Hence, the piston rod 50 and the cradle 60 can only move axially in relation to each other.

[0133] The distal end of the cradle 60 is provided with second protrusions 62 which engage the opening 13 in the housing part 10 such that the cradle 60 is axially secured to the housing part 10 but able to rotate relatively.

[0134] The outer distal end of the cradle 60 is further provided with a number of outwardly pointing first protrusions 61 which engages longitudinal recesses 12 in the housing part 10 to guide the rotation of the cradle 60. The rotation of the cradle 60 is further transferred to a similar rotation of the piston rod 50. The first protrusions 61 can in one example be provided on a flexible beam to make the first protrusions 61 resilient thus providing the user with a tactile and / or audible information when the first protrusion 61 shifts into and out from the longitudinal recesses 12.

[0135] Longitudinally, the cradle 60 is provided with a first toothed rack 65 on which the gear wheel 80 mounted on the piston rod 50 can roll in the axial direction. Since the piston rod 50 is rotationally locked to the cradle 60 as explained above, the gear wheel 80 is also locked to the cradle 60 and is hence always engaged with the first tooted rack 65, both during dose selection and during dose expelling. Whenever the gear wheel 80 rolls on the first toothed rack 65, the piston rod 50 moves translational since the gear wheel 80 is rotationally coupled to the piston rod 50.

[0136] The cradle 60 also has an inner end flange 66 which defines the initial position of the piston rod 50 understood such that the proximal end of the piston rod 50 abuts this end flange 66 when the piston rod 50 is in the initial start position as disclosed in figure 3. Following use of the injection device, the users manually push the piston rod 50 back into its initial position as will be explained.

[0137] Bearing (70)

[0138] To support the cradle 60, a bearing 70 associated with the dose selection button 20 is disclosed in detail in figure 11. The bearing 70 is shaped as a tube-like elongated element having a longitudinal opening 71 and a plurality of radial flanges 72 further supporting the dose selection button 20. Proximally, the bearing 70 is provided with an outwardly pointing flange 73 (also seen in figure 3A-B) which is secured in a recess provided on the inner surface of the dose selection button 20 making the dose selection button 20 rotational in relation to the bearing 70. Due to this engagement, the bearing 70 follows the axial movement of the dose selection button 50 both when the dose selection button 50 is rotated out from the housing part 10 to select the fixed dose to be injected and when the dose selection button 50 is pushed translationally back into the housing part 10 during dose expelling.

[0139] The bearing 70 is further provided with an inner recess 74 guided by the longitudinal sides 63 of the cradle 60 such that the bearing 70 cannot rotate relatively to the cradle 60 but is able to rotate together with the cradle 60.

[0140] Hence, when a user selects a dose by rotating the dose selection button 20 helically in the proximal direction, the bearing 70 follows the axial movement without rotating as it is rotationally locked by the cradle 60 which again is rotationally locked to the housing part 10.

[0141] As best seen in figure 2 and in figure 3A, the gear wheel 80 protrudes out though the longitudinal opening 71 of the bearing 70 to engage a second toothed rack 21 provided on the inner surface of the dose selection button 20 as will be explained.

[0142] Dose Selection Button (20)

[0143] The dose selection button 20 is disclosed in figure 12. As seen in figure 12, the inner side is provided with the second toothed rack 21 for moving the gear wheel 80. Also, on the inner surface a flexible EoC arm 45 is provided which is able to be bended outwardly to engage with the housing part 10 following the ejection of the last dose as will be explained.

[0144] Most proximally, the dose selection button 20 has a grip 22 which a user would grip between the fingers to rotate the dose selection button 20. The grip 22 can in one example be made from a softer polymeric material than the remaining part of the dose selection button 20, either in a 2K moulding or by making the grip 22 as a separate band or separate part connected to the dose selection button 20. On the outer surface the dose selection button (20) is provided with different tracks wherein at least one is a helical track 23.

[0145] Selection of a Dose

[0146] When selecting the dose to be ejected, the user rotates the dose selection button 20 helically out from the housing part 10 following the helical track 23 on the dose selection button 20. During rotation of the dose selection button 20, the toothed rack 21 on the inner surface of the dose selection button 20 is rotated radially out of engagement with the gear wheel 80 which allows the dose selection button 20 to follow the pitch of the helical track 23 on the dose selection button 20.

[0147] Figure 4 discloses the situation in which the user has selected the first dose. The dose selection button 20 has been rotated one full revolution and the first toothed rack 21 has reengaged the gear wheel 80. As seen in figure 3A-B and in figure 4 the toothing inside the dose selection button 20 do not need to engage with the gear wheel 80 in the initial position, however the second toothed rack 21 needs to engage with the gear wheel 80 when a dose is selected.

[0148] The dose selection button 20 is further disclosed in figure 13A-B. Visually, figure 13B is rotated 90° clockwise when compared with figure 13A. On the distal half of the outer surface of the dose selection button 20, a helical track 23 for guiding the dose selection button 20 during dose selection is provided. As best seen on figure 13B, this helical track 23 connects to a translational track 24 which guides the dose selection button 20 during dose expelling.

[0149] In figure 13A, the first thread segment 15a (indicated by punctured lines in figure 13A-B) on the inner surface of the housing part 10 is located in the start of the helical track 23 as indicated with broken lines. When a user rotates the dose selection button 20 counterclockwise (as seen from a position distal to the injection device) to select one of the fixed doses, the first thread segment 15a is moved along the arrow “S” in the helical track 23 (the rotational part is though the dose selection button). Following a rotation of one full revolution, the first thread segment 15a enters into the translational track 24 as indicated in figure 13B. To secure that the first thread segments 15a remain inside the boundaries of the tracks 23, 24, a second guiding system can be provided. This system takes form in a second thread segment 15b, also indicated by punctured lines in figure 13A. During dose selection this second thread segment 15b is guided in a similar helical track 28 and after one full revolution, the second thread segments 15b is guided translationally in a parallel translational track 29 during dose expelling.

[0150] The first thread segment 15a is preferably shaped with two lowered portions 17a,b as shown in figure 13C wherein the housing part 10 is cut open. In the start position, a first raised knob 25 in the helical track 23 is positioned in the first lowered portion 17a. When the user rotates the dose selection button 20 to select the fixed dose, the first raised knob 25 snaps out of the first lowered portion 17a which provides the user with a tactile signal that dose selection has been initiated.

[0151] A second raised knob 26 is provided in the translational track 24. Once the first thread segment 15a enters into the translation track 24, the second lowered portion 17b is caught by this second raised knob 26 providing the user with a further tactile signal informing that the fixed dose has now been selected and can now be released.

[0152] The two lowered portions 17 a,b in combination with the two knobs 25, 26 being rotationally dislocated in the track 24 provides a very attractive feel to the user when selecting the fixed dose.

[0153] The dose selection button 20 is proximally in the translational track 24 provided with a flexible wing 27 which can only be passed by the first thread segment 15a in the direction used when expelling the fixed dose. i. e pushing the dose selection button 20 translational in the distal direction. Once the fixed dose has been expelled it is thus not possible to pull the dose selection button 20 away from the housing part 10 as this is hindered by the flexible wing 27 engaging the first thread segment 15a as seen in figure 13A.

[0154] During dose selection, when the user rotates the dose selection button 20 as explained above, the second toothed rack 21 provided on the inner surface of the dose selection button 20 is rotated radially out of engagement with the gear wheel 80 which is rotationally locked in the radial direction by the engagement of the piston rod 50 with the cradle 60. When the second toothed rack 21 and the gear wheel 80 are rotated out of engagement, the dose selection button 20 is free to rotate independently of the gear wheel 80 following the engagement between the thread segments 15a, 15b and the helical tracks 23, 28.

[0155] In the herein described example, the dose selection button 20 is to be rotated one full revolution the set a dose. The rotational distance from disengagement between the gear wheel 80 and the second toothed rack 21 to a new engagement is thus preferably around 360°. However, in another example, the helical interface to the dose selection button 20 can be such that the dose selection button 20 can be rotated less than one full revolution

[0156] Ejecting a Dose

[0157] Once the fixed dose has been selected by rotating the dose selection button 20 one full revolutions and the first thread segment 15a is clicked onto the second raised knob 26 as indicated in figure 13B, which is also the position depicted in figure 4, the fixed dose is ready to be released.

[0158] In this position, the second toothed rack 21 has again radially engaged with the gear wheel 80 in a position dictated by the pitch of the helical track 23 on the dose selection button.

[0159] The pitch of the helical track 23 thus determines the distance the dose selection button 20 is moved out from the housing part 10 and thus determined the length the dose selection button 20 is translated during dose expelling.

[0160] The gearing between the gear wheel 80 and the toothed racks 21 , 65 are preferably 1:2 such that the piston rod 50 is moved half the distance of the dose selection button 20 during dose expelling however any suitable gearing ratio can be used.

[0161] The distance that the piston rod 50 is moved during dose expelling and the diameter of the cartridge 40 determines the volume of the fixed dose to be delivered. It is thus possible to alter the delivered volume simply by using a different pitch of the helical track 23 and dose selection buttons 20 with different pitches can thus accommodate different dose volumes.

[0162] Multiple fixed dose injection devices with different volumes of the fixed dose can thus be made by only changing the pitch of the helical thread 23 on the dose selection button 20. Different volumes can hence be obtained only by changing only one of the components of the injection device.

[0163] During dose expelling the first thread segment 15a slides proximally inside the translational track 24 following the arrow “E” as indicated in figure 13B and once the fixed dose has been expelled, the first thread segment 15a is captured by the first raised knob 25 and the flexible wing 27.

[0164] In the second guiding system, the second thread segment 15b moves translational in the parallel translational track 29 as disclosed in figure 13A.

[0165] End-of-Content

[0166] After the last dose has been selected and injected, the piston rod 50 and hence the gear wheel 80 has been moved to a distal position as disclosed in figure 14A and in figure 14B. In this position, the plunger 43 inside the cartridge 40 has reached its most distal position inside the cartridge 40.

[0167] If the user hereafter tries to select a new dose, the flexible EoC arm 45 provided in the structure of the dose selection button 20 will be bended outwardly and engage with the inner stop protrusion 16 inside the housing part 10 as disclosed on figure 14C. This inner stop protrusion 16 is also shown on figure 7B. The engagement between the outwardly bended EoC arm 45 and the inner stop protrusion 16 will prevent the dose selection button 20 from being rotated further and the user can therefore not select a new dose.

[0168] In figure 14B, the housing structure 10, 30 has been visually removed allowing a view to the flexible EoC arm 45 being bended outwardly by the gear wheel 80. All though figure 14C is a view along the line AA in figure 14B, the housing part 10 is disclosed in figure 14C

[0169] Rewinding the Piston Rod

[0170] Once a cartridge 40 has been emptied, the user can remove the used cartridge 40 and insert a new and fresh cartridge 40 containing liquid drug for a number of ejections. The cartridge 40 is secured by the cartridge holder 30 either permanently or removable as previously explained. The cartridge holder 30 is removed by rotating the cartridge holder 30 in the bayonet interface 11 , 32 between the housing part 10 and the cartridge holder 30. This rotation is transferred to a similar rotation of the cradle 60 due to the engagement of the longitudinal slots 37 in the cartridge holder 30 with the second protrusions 62 provided distally on the cradle 60.

[0171] These second protrusions 62 where two is preferably provided extend radially out through the openings 13 in the housing part 10 as also disclosed in figure 3B such that they can engage with the longitudinal slots 37 in the cartridge holder 30.

[0172] Since both the piston rod 50 and the gear wheel 80 are rotational locked to the cradle 60, a rotation of the cradle 60 is transferred to a similar rotation of the piston rod 50 and the gear wheel 80 i.e the piston rod assembly. As a result, the gear wheel 80 is rotated out of engagement with the second toothed rack 21 provided on the inner surface of the dose selection button 20.

[0173] During rotation of the cradle 60 the engagement between the first protrusions 61 and the longitudinal recesses 12 inside the housing part 10 both guides the rotation and provides the user with a tactile signal. Preferably, two such longitudinal recesses 12 are provided for each first protrusion 61, hence in the disclose example; four recesses 12 and two first protrusions 61 are provided. The cradle 60, the bearing 70, the piston rod 50 and the gear wheel 80 are thus rotatable between two different positions, a first position wherein the gear wheel 80 is engaged with the second toothed rack 21 associated with the dose selection button 20 and a second position wherein the gear wheel 80 is rotated out of engagement with the second toothed rack 21. In the latter position, the piston rod 50 with the gear wheel 80 can be moved translational backwards to the initial position as the gear wheel 80 rolls on the first toothed rack 65 associated with the cradle 60 and thus the housing part 10.

[0174] In order to rotate the gear wheel 80 out of engagement with the second toothed rack 21 in the dose selection button 20, a rotation of around 50° is preferred, however the design of the interface can be made to accommodate a different angle if required.

[0175] Once the gear wheel 80 and the second toothed rack 21 is disengaged, the user can hence push the piston rod 50 back into the housing part 10 and into the cradle 60. The abutment between the proximal end of the piston rod 50 and the end flanges 66 proximally on the cradle 60 indicates that the piston rod 50 has been pushed back to its initial position.

[0176] Following this, the user can mount the cartridge holder 30 (with a new cartridge 40) onto the housing part 10 again using the bayonet interface 11, 32 between the cartridge holder 30 and the housing part 10. During the rotation of the bayonet interface 11, 32, the longitudinal slots 37 engages with the second protrusions 62 on the cradle 60 and thus rotates the cradle 60 back to its initial position wherein the gear wheel 80 engages with the second toothed rack 21.

[0177] Figure 15 discloses a further example of the invention wherein the cartridge is permanently and irreversible embedded in a polymer housing referred to as a cartridge unit 130. This cartridge unit 130 is on an inner surface provided with a not-shown protrusions which engage a bayonet track 111 provided in the housing structure 110. This bayonet track 111 can further be provided with an axial coding entrance 118 for receiving a further coding protrusion also provided on the inner surface of the cartridge unit 130 to only allow specific cartridge units 130 to be connected to specific housing structures 110.

[0178] Further, the housing structure 110 is extended with an axial sleeve 119 which protects the piston rod by covering the piston rod when extended whereby the user is hindered in obtaining physical contact with the extended piston rod.

[0179] When connecting the cartridge unit 130 to the housing structure 110, this axial sleeve 119 enters into the radial space between the cartridge itself and the polymer housing of the cartridge unit 130.

[0180] The proximal part of the cartridge unit 130 partly covering the housing structure proximal to the axial sleeve 119 when the cartridge unit 130 is mounted preferably carries a label which can be inspected by a user at any time, even after a protective cap has been connected to the distal part of the cartridge unit 130.

[0181] 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:

Claims

CLAIMS:

1. An injection device for ejecting a number of pre-defined fixed doses of a liquid drug, comprising:- A housing structure (10, 30) configured for holding a loaded cartridge (40) containing the liquid drug,- A dose selection button (20) functionally coupled to the housing structure for selecting one of the pre-defined fixed doses,- A piston rod assembly (50, 80) adapted to move a plunger (43) inside the loaded cartridge (40) comprising a piston rod (50) and a gear wheel (80), which is rotatably coupled with the piston rod (50),Wherein the injection device further comprises a first toothed rack (65) associated with the housing structure and a second toothed rack (21) associated with the dose selection button (20),Wherein the gear wheel (80) and the first toothed rack (65) are engaged both during dose selection and during dose ejection, and wherein the gear wheel (80) and the second toothed rack (21) are disengaged during dose selection allowing the dose selection button (20) to rotate helically out from the housing structure (10, 30) independently of the piston rod assembly (50, 80) to thereby select the predefined fixed dose and wherein the gear wheel (80) and the second toothed rack (21) are engaged during dose ejection and the dose selection button (20) is adapted to translate axially back into the housing structure (10, 30) to thereby eject the selected pre-defined fixed dose.

2. An injection device according to claim 1 , wherein one of the housing structure (10, 30) or the dose selection button (20) is provided with one or more thread segments (15a, 15b) and the other of the housing structure (10, 30) or the dose selection button (20) is provided with at least one helical track (23, 28) guiding the one or more thread protrusions (15a, 15b) during dose selection.

3. An injection device according to claim 1 or 2, wherein one of the housing structure (10, 30) or the dose selection button (20) is provided with one or more thread segments (15a, 15b) and the other of the housing structure (10, 30) or the dose selection button (20) is provided with at least one translational track (24, 29) guiding the one or more thread protrusion (15a, 15b) during dose ejection.

4. An injection device according to claim 3, wherein the inter-section between the at least one helical track (23, 28) and the at least one translational track (24, 29) is provided with a clicker arrangement providing the user with an audible and / or tactile signal once the one or more thread segments (15a, 15b) enters into the at least one translational track (24, 29) from the at least one helical track (23, 28).

5. An injection device according to any of the previous claims, wherein the second toothed rack (21) and the gear wheel (80) are adapted to be rotated out of engagement during dose selection.

6. An injection device according to claim 5, wherein the gear wheel (80) disengages the second toothed (21) radially during dose selection.

7. An injection device according to claim 5 or 6, wherein the dose selection button 20 is rotated one full revolution to select the pre-defined fixed dose to be ejected.

8. An injection device according to claim 6 or 7, wherein the second toothed rack (21) and the gear wheel (80) are radially engaged when the dose selection button (20) has been rotated to select the pre-defined fixed dose.

9. An injection device according to any of the previous claims, wherein the housing structure (10, 30) comprises a housing part (10) and a cartridge holder (30) releasable coupled together.

10. An injection device according to any of the previous claims, wherein the cartridge holder (30) engages with a cradle (60) associated with the housing structure (10, 30) to rotate the cradle (60) relatively to the housing structure (10, 30) during rotation of the cartridge holder (30).

11. An injection device according to claim 10, wherein the gear wheel (80) of the piston rod assembly (50, 80) follows the rotation of the cradle (60) to be rotated out of engagement with the second toothed rack (21) during rotation of the cradle (60) by rotation of the cartridge holder (30).

12. An end-of-content mechanism for the injection device according to any of the claims 1 to 11 , wherein the dose selection button (20) is provided with a flexible arm (45) which is provided in a specific axial position and which is adapted to bend radially outwardly to engage with the housing structure (10, 30) when a predetermined number of pre-defined fixed doses has been set and ejected.

13. An end-of-content mechanism for the injection device according to claim 12, wherein the flexible arm (45) is adapted to bend radially outwardly by engagement with the gear wheel (80).

14. A cartridge change system for the injection device according to any of the claims 1 to 11, wherein rotation of the cartridge holder (30) disengages the engagement between the second toothed rack (21) and the gear wheel (80) thereby allowing the piston rod assembly (50, 80) being moved to its initial position.

15. A cartridge change system for the injection device according to claim 14, wherein the cartridge holder (30) rotationally engages the cradle (60) such that the cradle (60) follows rotation of the cartridge holder (30).

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