[0001] This disclosure relates to the field of a dose delivery mechanism for an injection device, preferably a reusable pen-injector injection device for injecting a selected dose of medicament.

BACKGROUND

[0002] Pen-injector injection devices are well known and an example is shown in WO2015/032780. At the centre of the injection device is a longitudinally-extending lead screw, around which the other components are concentrically arranged about a longitudinal axis extending through the lead screw, the medicament cartridge and out to the injection site. This concentric arrangement, about a single longitudinal axis, is highly desirable in order that maximum use is made of the limited space for the internal components of the injection device. As can be seen from the cross-sectional views in WO2015/032780, the available internal space for any additional components in a pen- injector injection device is very limited indeed. Another example of an injection device with all of its components concentrically arranged about a longitudinal axis is shown

schematically in Figure 1 .

[0003] A further advantage of the concentric arrangement of the internal components is to ensure that the injection device is well-balanced, during use, when its internal components are subjected to substantial mechanical forces. The handling properties and user-experience of injection devices are critical factors in their design.

[0004] US7828779 describes an injection device having a reservoir module 10 connected to a dosing and activating module 20. The reservoir module 10 is arranged about a longitudinal axis L, which is also the translational axis of the piston which displaces medicament from the reservoir.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] In accordance with an aspect of the present invention there is provided an injection device comprising:

a a housing having a first longitudinal axis;

b a medicament cartridge holder;

c a plunger element for ejecting a dose of medicament from the injection device, and

d a drive assembly, including a drive shaft arranged concentrically about said first longitudinal axis, the drive assembly capable of providing an axial force to said plunger element for ejecting a dose of medicament from the injection device;

wherein said medicament cartridge holder and said plunger element are arranged around a second longitudinal axis which is substantially parallel to but offset from the first longitudinal axis.

[0006] By having some of the components located about a second longitudinal axis which is offset from the longitudinal axis of the housing, additional internal space is created within the device. Additional components, for example components for e-health telematics could be incorporated into the injection device.

[0007] In certain embodiments, the drive assembly comprises a rotational to axial coupling, where the drive assembly is rotationally drivable by a torsion spring and is arranged to provide an axial force for ejecting the dose from the injection device.

[0008] In certain embodiments, the drive assembly further comprises a worm gear engaged in a rack wherein rotation of said worm gear causes the rack to advance axially forward or backward with respect to said worm gear. The forward advancing rack provides the axial force for ejecting medicament from the injection device. The worm gear may be arranged around said first longitudinal axis and said rack may be arranged around said second longitudinal axis.

[0009] In certain embodiments, the drive assembly further comprises a worm gear rotational lock engageable with the worm gear, preferably in a forward end thereof, so as to substantially prevent rotation of the worm gear. The worm gear rotational lock may be disengageable from the forward end of the worm gear by being pushed axially forward by the drive shaft.

[0010] In certain embodiments, the drive assembly further comprises means engageable between the drive shaft and the worm gear and which, when engaged, rotationally lock the drive shaft and worm gear together. Preferably, the means is a clutch which may comprise splines. In an embodiment, said means is engageable before said worm gear rotatational lock is disengaged.

[0011] The injection device may further comprise a medicament cartridge. Medicament may be contained in the medicament cartridge. In certain embodiments, the medicament may be selected from the group comprising: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain,

immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying antirheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, or in the expression of protective immunity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 (PRIOR ART) is a schematic view of a pen-injector injection device having a longitudinal axis L;

Figure 2 is a schematic view of an injection device according to an embodiment of the invention;

Figure 3 is a schematic cross sectional view of selected components of the injection device of Figure 2;

Figure 4 is a perspective view of another embodiment of the injection device;

Figure 5 is an exploded view of the injection device of Figure 4;

Figure 5A is a perspective view showing further detail of the dose limit nut;

Figure 5B is a perspective view showing further detail of part of the plunger rack;

Figure 6 is a cross-sectional view of the injection device of Figure 4;

Figures 7 and 7A - 7C illustrate incrementing the dose;

Figures 8, 8A and 8B illustrate decrementing the dose;

Figures 9, and 9A - 9D illustrate maximum/minimum dose limiting;

Figures 10 and 10A illustrate over-torque protection;

Figures 1 1 ,1 1 A— 1 1 C, 12 and 12A - 12B illustrate dose delivery;

Figures 13, 13A and 13B illustrate a haptic feedback feature;

Figures 14 and 14A - 14E illustrate last dose protection;

Figure 15 is a diagrammatic summary of the key engagement points of the components of the injection device of Figure 4, at four stages of dose delivery; Figure 16 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose setting

(incrementing the dose);

Figure 17 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose delivery;

Figures 18, 18A and 18B show how the units wheel is incremented; and

Figures 19, 19A and 19B show how the tens wheel is incremented;

DETAILED DESCRIPTION

[0013] In the present disclosure, the following terms may be understood in view of the below explanations:

[0014] The term "injection device" may refer to a device intended for the injection of a medicament to the body and includes devices configured for various delivery methods, such as intradermal, subcutaneous, intramuscular, intravenous, intraosseous,

intraperitoneal, intrathecal, epidural, intracardiac, intraarticular, intracavernous, and intravitreal, which may include via a cannula, catheter or similar device. Injection device includes syringes of all types, devices that contain said syringes such as auto-injectors, pen-injectors, patch injectors and other similar devices.

[0015] The term "pen -injector" may include any device configured to deliver a dose of a medicament from a cartridge.

[0016] The term "user" may refer to a medical practitioner, end user or other user associated therewith.

[0017] The term "coupling" may refer to a connection between components (not necessarily a direct connection; there may be intermediate components therebetween) that enables a force to be transmitted between the components.

[0018] The term "a rotational coupling" may refer to a coupling which enables a rotational force to be transmitted between the components.

[0019] The term "operatively connectable" may refer to at least two individual components which are releasably connectable together in such a way that the individual components can work together, for example wherein rotation of one of the individual components effects rotation of all of the operatively connected components.

[0020] The term "dose selector" may refer to a component or components which, when actuated by a user, enable a dose of medicament to be selected. [0021] The term "dose indicator" may refer to a component or components which provide a display or indication to the user of the selected dose of medicament.

[0022] The term "splines" may refer to one or more ridges, ribs or other protrusions on one component which engage in corresponding grooves or the like on a second component to connect the two components together.

[0023] The term "a splined connection" may refer to a connection effected by one or more splines.

[0024] The term "forward" or "forwards" may refer to a direction towards the end of the injection device from which medicament is expelled.

[0025] The term "backward", "backwards", "rearwards" or "rearwardly" may refer to a direction away from the end of the injection device from which medicament is expelled.

[0026] The term "drive assembly" may refer to an assembly of components capable of using a driving force from, for example, a spring, to eject medicament from an injection device.

[0027] The term "backlash" may refer to a clearance caused by a gap between mechanical components.

[0028] The term "medicament" may include a substance in liquid or gas form. The medicament may be selected from the group comprising of: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain,

immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying antirheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, or in the expression of protective immunity.

[0029] When referring to the injection device, the term "containing the medicament" may refer to the medicament being contained within a suitable medicament container, such as a pre-filled syringe or cartridge, within the injection device.

[0030] The term "a force path" may refer to a path between two or more coupled components via which a force can be transmitted between the components. A force path may be "interrupted" if there is a gap between the two or more components, i.e. if they are no longer coupled. Transmission of force between coupled components may be "held back" for example by a ratchet arrangement, but in such a case the force path is not

"interrupted".

[0031] The term "a clutch" may refer to a component or feature suitable for operatively connecting two component parts either by a positive fit e.g. with teeth, splines, grooves or the like suitable for engaging and disengaging each other, or by a non-positive (e.g.

frictional) connection or a combination thereof. Disengaging the clutch may interrupt a force path between two or more coupled components.

[0032] The term "plunger element" may refer to a piston, plunger, plunger rack or other component which moves axially forward during dose delivery causing medicament to be expelled from the injection device, for example by pushing a stopper into a cartridge of medicament. The term "plunger element" does not include the components which provide axial force to the plunger element.

[0033] Description of a First Example Embodiment

[0034] A prior art injection device 10 is shown in Figure 1. The injection device 10 is configured to deliver a dose of medicament and extends along a longitudinal axis L between a front end 10a and a rear end 10b of the injection device 10. All of the components of the injection device 10 are arranged about the longitudinal axis L. The injection device 10 has a housing 12 and a needle (not shown) can be attached to the front end 10a. A dose selector 16 is provided at the rear end 10b and is arranged to permit the selection of a desired dose of medicament for delivery through the needle into an injection site. A medicament cartridge holder 25 for holding a cartridge from which medicament can be dispensed is located at the front end 10a of the injection device 10.

[0035] Figure 2 shows an injection device 10' according to an embodiment of the invention. The injection device 10' is configured to deliver a dose of medicament and has a front end 10a' and a rear end 10b'. A needle (not shown) can be attached to the front end 10a'. A dose selector 16' is provided at the rear end 10b' and is arranged to permit the selection of a desired dose of medicament for delivery through the needle into an injection site.

[0036] The injection device 10' comprises a housing 12' which extends along a longitudinal axis L. A medicament cartridge holder 25' for holding a cartridge from which medicament can be dispensed is located at the front end 10a' of the injection device 10'. The medicament cartridge holder 25' is arranged around a second longitudinal axis Lc wherein the two longitudinal axes L and Lc are substantially parallel but offset from one another. The medicament cartridge holder 25' may be generally symmetrical around axis Lc. The housing 12' may be generally symmetrical around axis L.

[0037] Referring to Figure 3, a dose indicator 18 is disposed within the housing 12' and displays reference indicia, such as numbers or symbols, to indicate the level of dose selected by the dose selector 16'. The dose indicator 18 is preferably arranged about the longitudinal axis L.

[0038] A drive spring 20 is provided which can be charged by the application of force to elastically deform the spring 20, and the resulting elastic energy is stored by the spring 20 (i.e. it is prevented from elastically relaxing during a storage phase). Therefore, charging the spring 20 involves increasing the energy stored by the spring 20. The spring is preferably arranged about the longitudinal axis L.

[0039] The spring 20 is coupled to a drive assembly 22 and is arranged to provide a driving force thereto when energy stored by the spring 20 is released. The drive assembly 22 acts on a plunger element 22a to expel medicament from a medicament cartridge 24 having a barrel and a stopper 26 moveable in the barrel. In such embodiments, the plunger element 22a may act to move the stopper 26 so as to expel medicament through an opening in the barrel. In certain embodiments, the medicament cartridge 24 is connected to a needle.

[0040] At least part of the drive assembly 22 is arranged about longitudinal axis L.

However, plunger element 22a which acts on the stopper 26, is arranged about longitudinal axis Lc.

[0041] Therefore, as can be seen in Figure 3, the medicament cartridge holder 25', any medicament cartridge 24 held therein and the plunger element 22a is arranged about longitudinal axis Lc which is offset from the longitudinal axis L of the housing 12'.

[0042] Description of Second Example Embodiment

[0043] A further, non-limiting, embodiment of an injection device according to the present invention is illustrated in Figures 4-19B.

[0044] Referring to Figures 4 - 6, the injection device 100 includes a housing 112, a dose selector 116, a dose button 130 and dose button spring 131 , a units wheel 118, a tens wheel 119, a dose indicator spring 117, a drive shaft 140, a drive spring 120, a dose limit nut 141 , a worm gear 142, a worm gear support 143 and a worm gear rotational lock 144, all located concentrically about a common longitudinal axis L. The axis L extends between a front end 100a and a rear end 100b of the injection device 100. [0045] The injection device 100 has a medicament cartridge 124 supported in a cartridge holder 125 at the front end 100a of the injection device 100. The cartridge 124 is sealed by an axially-moveable cartridge stopper 126 at its rear end. The cartridge and cartridge holder are located concentrically about a second longitudinal axis Lc, such that the cartridge is offset from the main housing 112, with L and Lc offset from one another as shown in Figure 6.

[0046] The dose button 130 is biased rearwardly by the dose button spring 131. The dose selector 116 is provided at the rear end 100b of the injection device 100 and is arranged to permit the selection of a desired dose of medicament for delivery from the medicament cartridge 124 into an injection site. The dose selector 116 is axially constrained with respect to the housing 112 but is rotatable with respect thereto, about axis L. The dose selector 116 is rotationally coupled to the drive shaft 140 via pawl features 115, visible in Figure 7A, which engage splines 149 on the drive shaft 140. The housing 112 is provided with teeth 113 (visible in Figure 7B) on an inside surface thereof for engaging ratchet arms 146 on the drive shaft 140. Tabs 114 on the dose selector 116 are capable of depressing the drive shaft ratchet arms 146 when required, as shown in Figure 8B. The housing 112 is also provided with ramp features 111 (visible in Figure 12A) which facilitate disengagement of the ratchet arms 146 from the inside surface of the housing 112 when required.

[0047] A dose indicator is disposed within the housing 112 and displays reference indicia, such as numbers or symbols, to indicate the level of dose selected by the dose selector 116. The housing 112 includes an aperture 112a through which the dose indicator is visible. The dose indicator comprises the units wheel 118 for displaying units and the tens wheel 119 for displaying tens. The units wheel 118 is selectively engageable with the tens wheel to increment the tens wheel each time the units wheel moves through units 0 to 9. The units wheel 118 is rotationally coupled to the drive shaft 140.

[0048] As with the first embodiment, described with reference to Figures 1 -3, biasing means in the form of dose indicator spring 117 biases the units wheel 118 and tens wheel 119 axially rearwardly in the housing.

[0049] The housing 112 has features on an inside surface thereof for engaging with the units wheel 118 and the tens wheel 119.

[0050] An internal surface of the housing 112 is provided with a tens housing feature 108 selectively engageable with the tens wheel 119 to prevent rotation thereof. The tens housing feature comprises one or more axially forwardly extending formations 108 which may be equally spaced around the internal circumference of the housing 112. The formations 108 engage with corresponding axially rearwardly extending formations 119b at the rear of the tens wheel 119. The tens housing feature formations 108 and the tens wheel formations 119b may be teeth, notches, castellations or any other shaped formations that, when engaged together, prevent relative rotation between the tens wheel 119 and the housing 112.

[0051] An internal surface of the housing 112 is provided with a units housing feature 107 capable of moving the units wheel axially-forward against said biasing means 117. The units housing feature is an axially forwardly extending formation 107 having a cam surface which can engage with an axially rearwardly extending formation 118b on the units wheel 118 in order to push the units wheel 118 axially forwards.

[0052] Teeth 118a on the front end of the units wheel 118 are engageable with correspondingly shaped teeth 119a at the rear end of the tens wheel 119. On the tens wheel 119, the teeth 119a (for engaging the units wheel) and the tens wheel formations 119b (for engaging the housing) may be concentrically arranged around the longitudinal axis of the injection device, with the teeth 119a radially inward of the formations 119b.

[0053] The drive spring 120 is a torsion spring which is fixed at one end with respect to the housing 112 and rotationally coupled at its other end to the drive shaft 140 via the units wheel 118.

[0054] A worm gear arrangement is provided which comprises a worm gear 142 meshed with a toothed plunger rack 145 located within the housing 112. During dose delivery, the worm gear 142 drives the plunger rack 145 forward which, in turn, pushes against the cartridge stopper 126 to deliver a dose of medicament. A splined clutch 150 at the forward end of the drive shaft 140 enables the worm gear 142 and drive shaft 140 to be splined together during dose delivery but not during dose setting and this will be described in more detail later. In Figure 6, the worm gear rotational lock 144 is engaged in the forward end of the worm gear 142, preventing rotation thereof. The worm gear rotational lock 144 is capable of being pushed axially forward by the drive shaft 140 in order to disengage the lock from the worm gear 142.

[0055] The dose limit nut 141 is keyed to the drive shaft 140 so that they are rotationally coupled but not axially coupled. The dose limit nut 141 is engaged with the teeth of the plunger rack 145 and can travel axially forward and backward along the plunger rack 145 as the dose is incremented or decremented respectively. The axial range within which the dose limit nut 141 can travel along the plunger rack 145 is determined by dose limit nut endstop features 141 a, 141 b which can engage features 147, 148 on the plunger rack thread to serve as endstops for the travel of the dose limit nut 141. Figure 5A shows the maximum dose limit nut endstop feature 141a and the minimum dose limit nut endstop feature 141 b in more detail. Endstops 141 a, 141 b are able to engage features 147, 148 respectively on the plunger rack 145 (Figure 5B). These features 147, 148 are preferably changes in the depth of or formations on the plunger rack thread, past which the dose limit nut 141 cannot travel. During dose delivery, the dose limit nut 141 rotates about axis L with the drive shaft 140 to which it is keyed, but it does not move axially with respect to the plunger rack 145 with which it is engaged, thus always keeping the dose limit nut 141 within the range defined by the max/min dose endstops 141 a, 141 b.

[0056] The operation of the respective features of the injection device 100 will now be described in more detail below.

[0057] Dose setting - incrementing the dose

[0058] With the injection device 100 in the configuration shown in Figure 7, the user grips the dose selector 116 and rotates it clockwise about axis L, with respect to the housing 112, in order to increment the dose and charge the drive spring 120. As the dose selector 116 is turned clockwise, the pawl features 115 engaging the splines 149 on the drive shaft 140 cause the drive shaft 140 to also be driven clockwise, as shown in Figure 7A.

[0059] While the dose is being incremented, the ratchet arms 146 on the drive shaft 140 engage with the teeth 113 on the inside surface of the housing 112 to prevent un-winding by the drive spring 120, as shown in Figure 7B.

[0060] As shown in figure 7C, the drive shaft 140 is splined to the units wheel 118 which charges or torques up the drive spring 120. In other words, torque is transferred from the dose selector 116 to the drive spring 120 directly through the dose indicator, i.e. the units wheel 118.

[0061] Dose setting - decrementing the dose

[0062] When it is desired to decrement the selected dose, the dose selector 116 is turned anti-clockwise. As shown in Figure 8A, as the dose selector 116 is turned anti- clockwise, there is a small amount of backlash at point A such that the dose selector 116 can rotate slightly with respect to the drive shaft 140. This small relative movement is sufficient to allow the tabs 114 on the dose selector 116 to depress the drive shaft ratchet arms 146 so that they can click past the housing teeth 113, allowing the drive spring to unwind slightly before the ratchet arms 146 catch again on the next housing tooth 113. This is represented in Figure 8B. Each decrement preferably equates to 11 U ("international unit") of medicament.

[0063] Dose setting - maximum/minimum dose

[0064] As the drive shaft 140 is rotated during dose setting, the dose limit nut 141 , which is keyed to the drive shaft 140, is also rotated (Figure 9A). The dose limit nut 141 travels forwards when incrementing the dose and rearwards when decrementing the dose (Figure 9B). The dose limit nut 141 is engaged in the thread of the plunger rack 145. Endstop features 147, 148 are located on the plunger rack 145, past which the dose limit nut 141 cannot travel (Figure 9C). These endstop features 147, 148 may be changes in the depth of the thread. As shown in Figure 9D, when the dose limit nut 141 rotates into a position wherein the dose limit nut endstop feature 141a engages feature 147 on the plunger rack 145, further rotation of the dose limit nut 141 is prevented so that a dose of medicament greater than the desired maximum dose of medicament cannot be set. Limiting the travel of the dose limit nut 141 sets the maximum and minimum doses of medicament that can be set during dose setting, preferably 100IU and OIU respectively.

[0065] Dose setting - over torque

[0066] As shown in Figure 10A, in the event the user applies too much force (over- torque) to the dose selector 116 in either rotational direction, the dose selector pawl features 115 will flex radially outwardly to allow them to skip past splines 149 on the drive shaft 140. Preferably the interfacing surface areas of the pawl features 115 and/or splines 149 act as a cam lever, preferably having a matching angle and/or a defined static and dynamic surface friction at the interface surface. The over-torque for flexing out the dose pawl features 115 to skip past spline 149 is preferably at least 10% higher than the torque required for dialling up (incrementing) or dialling down (decrementing) the dose indicator 18, 118. The dialling up torque can be 30 to 80 Nmm, preferably less than 60 Nmm, more preferably 30 to 50 Nmm. The dialling down torque can be 20 to 60 Nmm, preferably less than 50 Nmm, more preferably 30 to 40 Nmm. The over-torque in the dialling up direction may be different to the over-torque in dialling down direction. The outward flexing force and/or strength of one flexible pawl arm 115 could be lower compared to a second flexible pawl arm.

[0067] Figure 16 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose setting

(incrementing the dose). The drive shaft 140 rotates clockwise. The dose limit nut 141 rotates clockwise and advances forwards with respect to the plunger rack 145.

[0068] Dose delivery

[0069] To initiate dose delivery, the user presses the dose button 130 against the bias of the dose button spring 131 as shown in Figure 1 1A. This pushes the drive shaft 140 axially forwards. Although the drive shaft 140 is splined to the units wheel 118, it is free to slide axially with respect thereto (Figure 1 1 B).

[0070] As the drive shaft 140 advances, at its forward end, the splined clutch 150 between the drive shaft and the worm gear 142 engages (Figure 1 1 C, Figure 15 - Worm Gear Clutch 150). Preferably the drive element, in particular the worm gear 142 and the drive shaft 140 engage after 0.5 mm to 1.5 mm advancement of the dose button 130, more preferably after 0.8 mm to 1.2 mm advancement of the dose button 130. Once the clutch 150 has started to engage, the ratchet arms 146 on the drive shaft 140 begin to disengage from the inside surface of the housing 112 aided by ramp features 111 (Figure 12A, Figure 15 - Hold Ratchet). Preferably the hold ratchet, in particular the ratchet arms 146 on the drive shaft 140 start to disengage from the structured, in particular toothed surface of the housing 112 after 1 .5 mm to 2.5 mm advancement of the dose button 130, more preferably after 1 .6 mm to 1 .9 mm advancement of the dose button 130. Also, as the drive shaft 140 moves forward, the splines 149 coupling the drive shaft 140 to the dose selector 116 disengage (Figure 12B, Figure 15 - Over torque ratchet). Preferably the over torque ratchet, in particular the drive shaft splines 149 on the drive shaft 140 start to disengage from the dose selector pawls 115 after 1 .5 mm to 3.5 mm of advancement of the dose button 130, more preferably after 2 mm to 3 mm advancement of the dose button 130. The dose indicator and drive shaft 140 are now free to rotate about longitudinal axis L.

[0071] The drive spring 120 drives the units wheel 118 to rotate about longitudinal axis L. The units wheel 118 drives the drive shaft 140 which drives the worm gear 142.

[0072] Figure 17 summarises schematically the mechanical motion of the drive shaft 140, dose limit nut 141 , worm gear 142 and plunger rack 145 during dose delivery. The drive shaft 140, dose limit nut 141 and worm gear 142 all rotate anti-clockwise. Only the plunger rack 145 advances forwards. During dose delivery, the dose limit nut 141 rotates with the drive shaft 140 but does not move axially with the plunger rack 145. The dose limit nut 141 and the drive worm gear 142 preferably have the same thread pitch.

[0073] The worm gear 142 actuates the plunger rack 145 to move axially forwards causing the cartridge stopper 126 to be driven into the cartridge in order to expel medicament thus delivering the selected dose.

[0074] When the dose button 130 is released, the dose button spring 131 returns the dose button 130 and drive shaft 140 to their original starting positions. This axially rearward movement disengages the worm gear clutch 150 and re-engages the drive shaft ratchet arms 146 with the housing 112 thereby stopping dose delivery.

[0075] Dose delivery - haptic feedback

[0076] During dose delivery, the drive shaft ratchet arms 146 run (rotationally) on a relatively smooth track 110 on the inside surface of the housing 112 (Figure 13A).

Optionally, this track could be modified to include ridges 109 which would provide audible/haptic feedback to the user during dose delivery (Figure 13B). The ridges 109 are conveniently placed relatively close to the user's fingers.

[0077] Last dose protection

[0078] When the medicament cartridge 124 is relatively empty, after several doses have already been delivered therefrom, it is undesirable for the user to be able to select a dose that is larger than the available quantity of medicament remaining. Last dose protection is provided to deal with this situation. Conveniently, the last dose protection is provided by the same feature as the max/min dose limiting i.e. the dose limit nut 141.

[0079] As shown in Figure 14, after several doses have been delivered, the plunger rack 145 and dose limit nut 141 have advanced axially forwards such that the dose limit nut 141 is approaching the worm gear 142. When there is less than a predetermined amount (e.g. 100IU) of medicament available, the worm gear 142 serves as an endstop, stopping the dose limit nut 141 from moving further forwards and before the maximum dose limit feature 147 on the plunger rack 145 is reached (Figure 14A). Preferably, it is the dose limit nut endstop feature for maximum dose limiting 141a which engages the worm gear 142. If the user tries to increment the dose further, torque is transmitted through the dose limit nut 141 into the worm gear 142, the torque being reacted to by the worm gear rotational lock 144 (Figure 14B). As such, the worm gear 142 is unable to rotate due to rotational engagement with the rotational lock 144.

[0080] During dose delivery, when the drive shaft 140 is moved axially forwards, the worm gear clutch 150 is engaged before the worm gear rotational lock 144 is disengaged (Figure 14C). The axially-forward movement of the drive shaft 140 causes its forward end to push the worm gear rotational lock 144 out of the front of the worm gear 142. With the worm gear rotational lock 144 disengaged, the worm gear 142 is free to rotate, driven by the drive shaft 140 (Figure 14D). Once dose delivery is finished, the drive shaft 140 moves rearwardly. The worm gear rotational lock 144 re-engages, before the worm gear clutch 150 is disengaged (Figure 14E).

[0081] Figure 15 is a diagrammatic summary of the key engagement points of the injection device components, at four stages of dose delivery.

[0082] Dose display

[0083] As already described above, during dose selection the user rotates the dose selector 116 which also drives the drive shaft 140 around. Ratchet arms 146 interact with teeth 113 in the housing 112 to prevent unwinding (Figure 18A). The drive shaft 140 is splined to the units wheel 118 which, as it turns, increments the displayed unit (Figure 18B). [0084] The units wheel 118 and tens wheel 119 are biased rearwardly by dose indicator spring 117. Twice per revolution of the units wheel 118, the units wheel 118 is moved axially forwards by the cam surface of the units housing feature 107 engaging with the formation 118b on the units wheel 118. This axially forward movement causes the teeth 118a of the units wheel 118 to engage with the teeth 119a of the tens wheel 119 (Figure 19A). Continued forward axial movement of the units wheel 118 pushes the formations 119b of the tens wheel 119 away from the tens housing feature 108, so that the tens wheel 119 is free to rotate with respect to the housing 112, allowing the tens wheel 119 to be driven around by the units wheel 118 by one increment (Figure 19B).

[0085] In a preferred embodiment, the selectable and settable dose range is 1 to 100 IU, with a minimum dose setting of 1 IU, wherein per 360 degree rotation of the dose selector 116, 20 to 30 I U may be set. As the units wheel 118 and tens wheel 119 arrangement permits indication of the set IU dose by two digits, a much larger font size for the indicated dose number is usable, thus the arrangement affords better readability of the set dose and usability of the injection device 10, 100.

[0086] As with the first embodiment, described with reference to Figures 1 -3, the medicament cartridge holder 125, any medicament cartridge 124 held therein and at least part of the drive assembly, namely the plunger rack 145, is arranged about longitudinal axis Lc which is substantially parallel to but offset from the longitudinal axis L of the housing 112.

[0087] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0088] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0089] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0090] Reference numerals

10, 10' injection device

L longitudinal axis

Lc second longitudinal axis (cartridge holder)

10a, 10a' front end of the device

10b, 10b' rear end of the device

12, 12' housing

16, 16' dose selector

18 dose indicator

20 spring

22 drive assembly

22a drive assembly component

24 medicament cartridge

25, 25' medicament cartridge holder

26 cartridge stopper

100 injection device

L longitudinal axis (housing)

Lc second longitudinal axis (cartridge)

100a front end of the device

100b rear end of the device

107 units housing feature

108 tens housing feature

109 housing ridge features

1 10 housing smooth inside surface track

1 1 1 housing ramps for drive shaft ratchet arms

1 12 housing

1 12a aperture in the housing

1 13 housing teeth

1 14 tabs

1 15 dose selector pawl

1 16 dose selector

1 17 dose indicator spring

1 18 units wheel

1 18a teeth on units wheel (for engaging tens wheel)

1 18b formation on units wheel (for engaging units housing feature)

1 19 tens wheel

1 19a teeth on tens wheel (for engaging units wheel)

1 19b formations on tens wheel (for engaging tens housing feature) 120 drive spring

124 medicament cartridge

125 cartridge holder

126 cartridge stopper

130 dose button

131 dose button spring

140 drive shaft

141 dose limit nut

141 a dose limit nut endstop feature for max dose limiting and last dose limiting

141 b dose limit nut endstop feature for min dose limiting

142 worm gear

143 worm gear support

144 worm gear rotational lock

145 plunger rack

146 drive shaft ratchet arms

147 max dose endstop on plunger rack for dose limit nut

148 min dose endstop on plunger rack for dose limit nut

149 drive shaft splines

150 worm gear clutch

A backlash point for over-torque protection