Drug Delivery Device with Cap Induced Needle Movement

Abstract

A drug delivery device (1, 200) comprising a drug delivery unit (10, 210) comprising a housing (12, 212) extending along a general axis, a variable volume reservoir (40, 40, 140, 240), and a needle support (50, 50, 150, 250) for receiving a needle assembly (30, 30, 130, 230), the needle support (50, 50, 150, 250) and the variable volume reservoir (40, 40, 140, 240) being capable of diverging relative axial motion from a first relative position to a second relative position and converging relative axial motion from the second relative position to the first relative position, a cap (20, 120, 220) removably mountable onto the drug delivery unit (10, 210) to cover at least a portion of the needle support (50, 50, 150, 250), and a coupling mechanism configured to bring the needle support (50, 50, 150, 250) and the variable volume reservoir (40, 40, 140, 240) from the first relative position to the second relative position in response to the cap (20, 120, 220) being mounted onto the drug delivery unit (10, 210).

Claims

1. A drug delivery device comprising: a drug delivery unit comprising: a housing extending along a general axis, a variable volume reservoir, and a needle support for receiving a needle assembly, the needle support and the variable volume reservoir being capable of diverging relative axial motion from a first relative position to a second relative position and converging relative axial motion from the second relative position to the first relative position, a cap removably mountable onto the drug delivery unit to cover at least a portion of the needle support, and a coupling mechanism configured to bring the needle support and the variable volume reservoir from the first relative position to the second relative position in response to the cap being mounted onto the drug delivery unit.

2. A drug delivery device according to claim 1, wherein the coupling mechanism is further configured to bring the needle support and the variable volume reservoir from the second relative position to the first relative position in response to the cap being dismounted from the drug delivery unit.

3. A drug delivery device according to claim 1, wherein the first relative position is a predetermined relative position.

4. A drug delivery device according to claim 1, wherein the second relative position is a predetermined relative position.

5. A drug delivery device according to claim 1, wherein the variable volume reservoir is axially fixed with respect to the housing, and wherein the coupling mechanism is configured to displace the needle support distally in response to a converging relative axial motion between the cap and the housing during mounting of the cap onto the drug delivery unit.

6. A drug delivery device according to claim 5, wherein the coupling mechanism is further configured to displace the needle support proximally in response to a diverging relative axial motion between the cap and the housing during dismounting of the cap from the drug delivery unit.

7. A drug delivery device according to claim 1, wherein the needle support is configured to releasably retain the needle assembly.

8. A drug delivery device according to claim 1, further comprising the needle assembly being attached to the needle support, wherein the variable volume reservoir comprises a reservoir interior and a penetrable self-sealing septum, wherein the needle assembly comprises a hollow access structure configured to penetrate the self-sealing septum, and wherein in the first relative position the hollow access structure is fluidly connected with the reservoir interior through the self-sealing septum, and in the second relative position the hollow access structure is fluidly disconnected from the reservoir interior.

9. A drug delivery device according to claim 1, wherein the coupling mechanism comprises a first interface structure arranged in the cap, a second interface structure arranged on the needle support, and a third interface structure, each of the first interface structure, the second interface structure, and the third interface structure being configured for interaction with at least one of the other of the first interface structure, the second interface structure, and the third interface structure, during mounting of the cap onto, and dismounting of the cap from, the drug delivery unit.

10. A drug delivery device according to claim 9, wherein the needle support comprises a first needle support portion adapted to hold the needle assembly and a second needle support portion adapted to receive the first interface structure.

11. A drug delivery device according to claim 10, wherein the first needle support portion and the second needle support portion extend along the general axis and are arranged eccentrically.

12. A drug delivery device according to claim 11, wherein the second needle support portion comprises the second interface structure, and wherein the third interface structure is axially fixed with respect to the housing and comprises an exterior portion configured for threaded engagement with the second interface structure, and an interior portion configured for threaded engagement with the first interface structure, such that an axial movement of the first interface structure relative to the third interface structure causes an opposite axial movement of the second needle support portion relative to the third interface structure.

13. A drug delivery device according to claim 12, wherein the cap comprises a longitudinally extending side wall and a transversal end wall, together providing a hollow interior, and wherein the first interface structure comprises a rod being translationally and rotationally fixed to the transversal end wall and extending longitudinally in the hollow interior.

14. A drug delivery device according to claim 13, wherein the third interface structure is a nut element being rotatably accommodated in the second needle support portion, wherein one of the rod and the nut element comprises a first thread, and the other of the rod and the nut element comprises a first protruding structure configured to engage with the first thread, and wherein one of the nut element and the second interface structure comprises a second thread, and the other of the nut element and the second interface structure comprises a second protruding structure configured to engage with the second thread.

15. A drug delivery device according to claim 9, further comprising a reservoir support for axially retaining the variable volume reservoir, the reservoir support being configured for axial and rotational fixation with respect to the housing, wherein the needle support and the reservoir support are capable of undergoing relative helical motion during mounting of the cap onto the drug delivery unit, wherein the mounting of the cap onto the drug delivery unit involves a relative angular displacement between the cap and the reservoir support, and wherein the first interface structure and the second interface structure are configured to rotationally fix the needle support with respect to the cap.

16. A drug delivery device comprising: a drug delivery unit comprising: a housing extending along a general axis, a reservoir support for holding a variable volume reservoir, and a needle support for receiving a needle assembly, the needle support and the reservoir support being capable of diverging relative axial motion from a first relative position to a second relative position and converging relative axial motion from the second relative position to the first relative position, a cap removably mountable onto the drug delivery unit to cover at least a portion of the needle support, and a coupling mechanism configured to bring the needle support and the reservoir support from the first relative position to the second relative position in response to the cap being mounted onto the drug delivery unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In the following the invention will be further described with references to the drawings, wherein

[0051] FIGS. 1 and 2 illustrate a relative motion between a reservoir, or a reservoir support, and a needle support carrying an injection needle, according to the present invention,

[0052] FIG. 3 is a perspective view of a drug delivery device according to a first embodiment of the invention,

[0053] FIG. 4 is a perspective view showing the interior of the cap,

[0054] FIG. 5a is a perspective view of the drug delivery device in an initial cap mounting stage,

[0055] FIG. 5b is a close up view of a section of FIG. 5a, detailing elements of the coupling mechanism,

[0056] FIG. 6 is a perspective partial section view of the coupling mechanism,

[0057] FIGS. 7-9 are perspective views of the drug delivery device during different stages of cap mounting, showing the gradual withdrawal of the drug delivery needle from the reservoir interior,

[0058] FIG. 10 is an exploded perspective view of a distal portion of a drug delivery device according to a second embodiment of the invention,

[0059] FIG. 11 is a perspective view of the needle support,

[0060] FIG. 12a is a perspective view of the reservoir support in connection with the needle support,

[0061] FIG. 12b is an enlargement of the area Q2 in FIG. 12a,

[0062] FIGS. 13-16 are perspective views of the reservoir support and the needle support during different stages of cap mounting,

[0063] FIG. 17 is a side view of the reservoir support and the needle support corresponding to FIG. 15,

[0064] FIG. 18 is a side view of the reservoir support and the needle support corresponding to FIG. 16,

[0065] FIG. 19 is a perspective view of a drug delivery device according to a third embodiment of the invention,

[0066] FIG. 20 is a partly exploded perspective view of the drug delivery device of FIG. 19,

[0067] FIG. 21 is a close up perspective view of an element of the coupling mechanism, and

[0068] FIGS. 22 and 23 are perspective views of the drug delivery device during different stages of cap mounting.

[0069] In the figures like structures are mainly identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0070] When in the following relative expressions, such as upwards and downwards, upper and lower, and clockwise and counter-clockwise, are used these 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.

[0071] In the below three different manifestations of the present invention are described with reference to the figures, of which FIGS. 3-9 illustrate a first embodiment of the invention in the context of a dual axis dose setting and injection device, FIGS. 10-18 illustrate a second embodiment of the invention in the context of a conventional type single axis tubular injection pen, and FIGS. 19-23 illustrate a third embodiment of the invention in the context of a dual axis fixed dose delivery device.

[0072] The inventive concept underlying each of these different embodiments is an automatic induction of a diverging relative motion between a support structure for a drug delivery pathway, such as e.g. an injection needle, and a reservoir in response to a mounting of a removable cap onto a drug delivery unit to thereby interrupt a fluid connection between a supported drug delivery pathway and an interior of the reservoir. This will ensure that even if a user chooses to leave the drug delivery pathway on the support structure after a completed drug delivery procedure then when the cap is mounted on the drug delivery unit, e.g. for storage of the drug delivery device, the drug delivery pathway will be disconnected from the reservoir, whereby undesired effects such as drug leakage, clogging of the drug delivery pathway, and air entry into the reservoir interior are avoided.

[0073] FIGS. 1 and 2 together sketch the basic movement pattern realised in every embodiment of the present invention. FIG. 1 shows a needle assembly 30 removably mounted on a needle holder 50 which is associated with a drug delivery unit of e.g. an injection device or an infusion pump. The needle assembly 30 comprises a needle hub 31 to which a needle cannula 32 is fixedly attached, e.g. by gluing. A generally cylindrical collar 35 extends from the needle hub 31 towards a drug containing cartridge 40, also being associated with the drug delivery unit. An inner surface portion of the collar 35 is provided with a thread 36 which is configured for secure engagement with a thread 51 on an outer surface portion of the needle holder 50.

[0074] The needle cannula 32 extends through the needle hub 31 such that a back needle 34 projects from the needle hub 31 in a proximal direction and a front needle 33 projects from the needle hub 33 in a distal direction. The front needle 33 is adapted for insertion into a subcutaneous tissue of a person, and the back needle 34 is adapted for establishing fluid communication to a cartridge interior 48 holding the drug (not shown). In a pre-use state the front needle 33 is covered by a needle cap 37 to avoid premature exposure of the sharpened needle end.

[0075] The cartridge 40 extends upwards along a longitudinal axis and is retained in the axial and radial directions by a cartridge holder 14. At its distal end portion the cartridge 40 is sealed by a penetrable septum comprising a primary septum layer 43, made of a material which is compatible with the drug in the cartridge interior 48, and a self-sealing secondary septum layer 44, e.g. made of isoprene. The septum is press-fitted to a flange section 41 of the cartridge 40 by a crimped metal seal cap 46.

[0076] In FIG. 1 the back needle 34 is axially spaced apart from the distal end portion of the cartridge 40, and the needle cannula 32 and the cartridge interior 48 are thus fluidly unconnected.

[0077] FIG. 2 shows the needle assembly 30 in a position in which the back needle 34 has penetrated both the primary septum layer 43 and the secondary septum layer 44 and established fluid communication with the cartridge interior 48. The drug is at this point able to flow through a lumen 39 in the needle cannula 32 and exit the sharpened end portion of the front needle 33.

[0078] In accordance with the invention the needle holder 50 and the cartridge holder 14 are capable of undergoing relative axial motion between the relative position depicted in FIG. 1 and the relative position depicted in FIG. 2, and as will be explained in greater detail below such relative axial motion can be induced by the mounting, respectively dismounting, of a cap onto/from the drug delivery unit. From the fluidly unconnected state (FIG. 1) to the fluidly connected state (FIG. 2) the needle holder 50, carrying the needle assembly 30, and the cartridge holder 14, carrying the cartridge 40, undergo a converging relative axial motion, whereas from the fluidly connected state to the fluidly unconnected state the needle holder 50/needle assembly 30 and the cartridge holder 14/cartridge 40 undergo a diverging relative axial motion.

[0079] FIG. 3 is a perspective view of an injection device 1 according to a first embodiment of the invention. The injection device 1 comprises a drug delivery unit 10 and a protective cap 20. The drug delivery unit 10 comprises a housing 12 which extends along a general longitudinal axis and accommodates a drug expelling mechanism, a cartridge holder 14 which is axially fixed to the housing 12 and which carries a cartridge 40, and a needle holder 50 to which a needle assembly 30 is removably attached. The needle holder 50 has a bore 55 adapted for reception of a portion of the cap 20, as will be explained in greater detail below. An injection button 15 is provided at the proximal end portion of the housing 12 for activation of the drug expelling mechanism. The injection device 1 is capable of selective dose setting, and the housing 12 thus further accommodates a dose setting mechanism which comprises a scale drum having dose indicia applied to its exterior surface. A window 99 is provided in the housing 12 for inspection of the dose indicia, as conventionally known in the art of injection devices. The dose setting mechanism is user operable, but as the dose setting procedure is irrelevant to the invention further description thereof is omitted from the present text. The cap 20 comprises an axially extending circumferential side wall 22, and an end wall 21, and is adapted to be removably mounted onto the drug delivery unit 10 so as to cover and protect the needle holder 50, the cartridge holder 14, and the cartridge 40.

[0080] FIG. 4 shows the cap 20 from a proximal viewpoint. The end wall 21 and the side wall 22 together provide a hollow 29 in which a rod 25 extends in the proximal direction from a retainer 24 fixed to the end wall 21. The retainer 24 serves to axially and rotationally fix the rod 25 with respect to the end wall 21.

[0081] FIG. 5a shows the injection device 1 at the initiation of a mounting of the cap 20 onto the drug delivery unit 10. A portion of the side wall 22 has been cut out of the figure to show how the rod 25 is designed to align with the needle holder 50.

[0082] FIG. 5b is a close up view of the area Q1 in FIG. 5a, showing details of a coupling mechanism that serves to induce a relative axial motion between the needle holder 50 and the cartridge 40 in response to a relative axial motion between the cap 20 and the drug delivery unit 10 during mounting of the cap 20 onto, or dismounting of the cap 20 from, the drug delivery unit 10. A tube 16 is fixedly connected with the housing and extends axially parallel to the cartridge 40. A nut 60 is axially fixed to the tube 16 but freely rotatable in both directions about its centre axis. The nut 60 comprises an exterior thread 61 for engagement with the needle holder 50 and an interior protrusion 62 for engagement with a non-self-locking thread 26 on the rod 25. During the continued mounting of the cap 20 onto the drug delivery unit 10 the protrusion 62 will enter the thread 26 and travel at least a portion of it.

[0083] The needle assembly 30 comprises a needle cannula 32 fixedly retained in a needle hub 31 such that a front needle 33 extends in a distal direction from the needle hub 31 and a back needle 34 extends in a proximal direction from the needle hub 31. A collar 35 having an interior thread 36 extends from the needle hub 31 in the proximal direction. The thread 36 is in releasable engagement with a needle mount 51 and is thereby axially fixed on the needle holder 50. The back needle 34 extends through a secondary septum layer 44 and a primary septum layer 43, together constituting a self-sealing septum for the cartridge 40, and resides in a cartridge interior 48.

[0084] FIG. 6 is a perspective partial section view of the coupling mechanism during mounting of the cap 20 onto the drug delivery unit 10 (the cap 20 is omitted from the figure and portions of the nut 60 and the tube 16 have been removed for the sake of clarity). The cap 20 and the housing 12 have undergone a relative converging axial motion, whereby the rod 25 has entered through the bore 55 and the nut 60 to reach into the tube 16. The relative motion between the cap 20 and the housing 12 has been purely axial, and since the rod 25 is axially and rotationally fixed with respect to the cap 20 the interaction between the non-self-locking thread 26 and the protrusion 62 has caused the nut 60 to rotate clockwise about a catch portion 13 of the tube 16.

[0085] The needle holder 50 comprises a lower portion 52 configured to contain the nut 60, a middle portion 54 carrying a thread segment 53, and an upper portion 56 comprising the needle mount 51. The thread segment 53 mates with the exterior thread 61 such that a clockwise rotation of the nut 60 causes a distal movement of the needle holder 50 relative to the cartridge holder 14. Such distal movement of the needle holder 50 is accompanied by a like distal movement of the needle assembly 30 due to the threaded engagement between the two.

[0086] A relative diverging axial motion between the cap 20 and the housing 12 introduced during dismounting of the cap 20 from the drug delivery unit 10 will cause a retraction of the rod 25 through the nut 60 and the bore 55 and thereby a counter-clockwise rotation of the nut 60 relative to the tube 16 as the protrusion 62 travels backward in the thread 26. The engagement between the exterior thread 61 and the thread segment 53 causes a resulting proximal movement of the needle holder 50 relative to the cartridge holder 14.

[0087] FIGS. 7-9 show the injection device 1 at different stages during a mounting of the cap 20 onto the drug delivery unit 10. In FIG. 7 the free end portion of the rod 25 is situated within the nut 60, and the protrusion 62 is about to travel the thread 26. The back needle 34 still resides in the cartridge interior 48, i.e. fluid communication between the front needle 33 and the cartridge interior 48 is maintained. In FIG. 8 the cap 20 has been pushed further towards the housing 12, whereby the rod 25 has entered into the tube 16 and the protrusion 62 has travelled a portion of the thread 26. In accordance with what is explained in the above this has led to a clockwise rotation of the nut 60 and a distal displacement of the needle holder 50 and the needle hub 31 relative to the cartridge holder 14 and the cartridge 40. Only a small portion of the back needle 34 is still positioned in the cartridge interior 48. In FIG. 9 the cap 20 is fully mounted on the drug delivery unit 10 and the relative axial motion between the rod 25 and the nut 60 from the state of the injection device 1 shown in FIG. 8 to that of FIG. 9 has caused a further distal movement of the needle holder 50 relative to the cartridge holder 14, whereby the back needle 34 has been pulled out of the cartridge 40. The self-sealing secondary septum layer 44 has subsequently sealed the cartridge 40 and so the needle assembly is fluidly disconnected from the cartridge interior 48.

[0088] A cap mounting procedure is conventionally executed following each dose delivery, so, notably, no additional operating steps are introduced by the invention in order to achieve the automatic separation of the needle cannula 32 from the cartridge 40. Thereby, if a user decides to use the needle assembly 30 for more than one injection (s)he does not have to worry about whether the needle cannula 32 has become clogged or air has entered the cartridge interior 48 between the injections.

[0089] At the time of the following injection the user dismounts the cap 20 from the drug delivery unit 10, also a conventional action for users of an injection device, whereby the rod 25 moves distally relative to the nut 60, and the protrusion 62 is forced to travel the thread 26 in the opposite direction, causing the nut 60 to rotate counter-clockwise and the needle holder 50 to move proximally towards the cartridge holder 14. During this movement of the needle holder 50 the back needle 34 penetrates both the secondary septum layer 44 and the primary septum layer 43, and so when the cap 20 is completely dismounted from the drug delivery unit 10 the back needle 34 again resides in the cartridge interior 48, and the injection device 1 is ready for dose setting and injection.

[0090] FIG. 10 is an exploded perspective view of a distal portion of an injection device according to a second embodiment of the invention. The distal portion is composed of a protective cap 120 comprising a cap wall 122, which is closed at one end and open at an opposite end, a needle assembly 130, a needle holder 150 adapted to releasably retain the needle assembly 130, a cartridge holder 114, and a cartridge 140. The cartridge holder 114 is adapted for axial fixation to a tubular housing (not shown), e.g. in a manner conventionally known in the art of injection pens which comprises a proximal end portion of the cartridge holder 114 being retained by a distal end portion of the housing. The housing accommodates a drug expelling mechanism and constitutes together with the cartridge holder 114, the cartridge 140, and the needle holder 150 a drug delivery unit. The cartridge 140 is adapted for axial fixation in the cartridge holder 114 when the cartridge holder 114 is fixed to the housing.

[0091] The cartridge 140 comprises a cylindrical wall 142 which is sealed proximally by a displaceable piston 145. At its distal end the cartridge 140 has a flange section 141 which is closed by a self-sealing penetrable septum (not visible). When the cartridge 140 is fixed to the housing via the cartridge holder 114 the drug expelling mechanism is capable of exerting a driving force on the piston 145 via a piston rod (not shown).

[0092] The cartridge holder 114 comprises a radially expanded rear section 160 and a front section 111 for interaction with the needle holder 150. In particular, the front section 111 is formed with two carve outs (only one is visible) having respective opposing skewed faces 117, 118 for sliding reception of a proximal portion of the needle holder 150, as will be explained in the below.

[0093] Interior portions of the cap wall 22 are provided with grooves for reception and guiding of various protruding structures, the purpose of which grooves will be clear from the below. In FIG. 10 an axial groove section 126a and a helical groove section 126h at the open end portion of the cap wall 122 are visible. Diametrically opposite these groove sections a similar pair of groove sections is provided.

[0094] FIG. 11 is a perspective view detailing the needle holder 150. The needle holder 150 comprises a cylindrical distal portion 156, having thread sections 151 interrupted by bayonet tracks 157, providing means for reception of the needle assembly 130 in either a screw-on or a slide-and-twist fashion, and two proximally extending legs 152, each leg 152 having a skewed face 155 for sliding interaction with one of the skewed faces 117, and another skewed face 153 for sliding interaction with one of the skewed faces 118. Each leg 152 also has a radial protrusion 159.

[0095] FIG. 12a is a perspective view of the needle assembly 130, the needle holder 150, the cartridge holder 114, and the cartridge 140 in an assembled state. The needle assembly 130 comprises a collar 135 configured for releasable attachment to the distal portion 156 of the needle holder 150 by engagement with the bayonet tracks 157, and a needle hub 131 carrying a needle cannula in such a way that a front needle 133 extends distally therefrom and a back needle (not visible) extends proximally therefrom. In the assembled state shown in FIG. 12a a portion of the back needle resides in the interior of the cartridge 140. The rear section 160 of the cartridge holder 114 comprises two diametrically opposite radial protrusions 162 (only one is visible).

[0096] FIG. 12b is an enlarged view of the area Q2 of FIG. 12a, detailing a rotational lock between one of the legs 152 of the needle holder 150 and the front section 111 of the cartridge holder 114. The front section 111 includes an axially flexible finger 119 which is structured to interact with an edge 158 on the leg 152 to prevent relative rotation in one direction between the needle holder 150 and the cartridge holder 114 when the needle holder 150 and the cartridge holder 114 are in the depicted relative axial position. This rotational lock prevents separation of the needle holder 150 from the cartridge holder 114 when the cap 120 is not mounted on the drug delivery unit and enables easy attachment of a needle assembly to the needle holder 150 by a motion which involves rotation of the needle assembly.

[0097] FIGS. 13-16 show the needle holder 150 and the cartridge holder 114 in different states during mounting of the cap 120 onto the drug delivery unit. Different portions of the cap wall 22 have been removed to allow inspection of a coupling mechanism which serves to induce a relative axial motion between the needle holder 150 and the cartridge holder 114 in response to an axially converging motion between the cap 120 and the housing.

[0098] The cap 120 is mounted in a two-step procedure which involves firstly a pure linear axial relative motion and secondly a helical relative motion with respect to the housing and the cartridge holder 114. FIGS. 13-15 illustrate internal movements and interactions during the linear part of the mounting, while FIG. 16 illustrates internal movements during the helical part of the mounting.

[0099] As can be seen from these figures the cap 120 has, apart from the axial groove section 126a and the helical groove section 126h, an additional axial groove 127 in an interior portion of the cap wall 122, which axial groove 127 is closer to the closed end of the cap wall 122 than the axial groove section 126a and is further of narrower width than the axial groove section 126a. A similar axial groove (not visible) is provided in the diametrically opposite portion of the cap wall 122.

[0100] In the following the internal interactions are described based on the single entities seen in the figures, instead of on the pair of entities actually present. It is, however, understood that these interactions are mirrored by the corresponding non-visible entities. When the cap 120 is slid linearly over the cartridge holder 114 the protrusion 162 is received in the axial groove section 126a and travels the axial groove section 126a gradually to the end thereof. Further, the protrusion 159 is received in the axial groove 127 and begins to travel the axial groove 127 towards the closed end of the cap wall 122.

[0101] As the protrusion 162 approaches the end of the axial groove section 126a a free surface 128 contacts the flexible finger 119 and causes the flexible finger 119 to deflect (FIG. 14). When the protrusion 162 reaches the end of the axial groove section 126a the free surface 128 has deflected the flexible finger 119 to such a degree that the needle holder 150 is no longer prevented from undergoing relative rotation with respect to the cartridge holder 114 (FIG. 15).

[0102] When the cap 120 and the cartridge holder 114 subsequently undergo relative rotation (FIG. 16) the protrusion 162 travels the helical groove section 126h, the flexible finger 119 slides along the free surface 128, and the protrusion 159 travels further distally in the axial groove 127, leading to an axial displacement of the needle holder 150 relative to the cartridge holder 114. FIGS. 17 and 18 show the relative positions of the cartridge holder 114 and the needle holder 150 corresponding to the states shown in FIGS. 15 and 16, respectively. In FIG. 17 the flexible finger 119 is deflected and has been forced out of engagement with the edge 158, enabling relative rotation between the front section 111 and the leg 152. As the cartridge holder 114 undergoes relative rotation with respect to the cap 120, and the protrusion 162 travels the helical groove section 126h the axial groove 127 prevents rotation of the needle holder 150 relative to the cap 120 due to the interaction with the protrusion 159. This causes the skewed faces 155, 153 to slide along the respective skewed faces 117, 118, whereby the needle holder 150 is urged away from the cartridge holder 114, and the back needle is retracted from the interior of the cartridge 140. FIG. 18 thus shows the position of the needle holder 150 relative to the cartridge holder 114 when the cap 120 is completely mounted on the drug delivery unit.

[0103] When the cap 120 is dismounted from the drug delivery unit before the next injection it firstly undergoes relative rotation with respect to the cartridge holder 114 for alignment of the protrusion 162 with the axial groove section 126a. This relative rotational motion causes the skewed faces 155, 153 to slide back along the respective skewed faces 117, 118, whereby the needle holder 150 is urged towards the cartridge holder 114, as the protrusion 159 slides proximally in the axial groove 127, and the back needle is re-inserted into the interior of the cartridge 140 through the self-sealing penetrable septum. Hence, when the cap 120 is subsequently completely removed from the drug delivery unit, by a linear relative motion that causes the protrusion 162 to slide out of the axial groove section 126a, fluid communication is already established between the needle cannula and the interior of the cartridge 140, and the drug delivery unit is ready for insertion of the front needle 133 into the skin of the user.

[0104] FIG. 19 is a perspective view of an injection device 200 according to a third embodiment of the invention. The design of the injection device 200 resembles the design of the injection device 1 according to the first embodiment of the invention. However, whereas the injection device 1 offers variable dose setting the injection device 200 is a fixed dose delivery device which expels the same dose at each activation of its injection mechanism (not visible). The injection device 200 comprises a drug delivery unit 210 and a protective cap 220 removably mountable there onto. The drug delivery unit 210 carries a drug containing cartridge 240 and an exchangeable needle assembly 230.

[0105] FIG. 20 shows a partly exploded view of the injection device 200. The drug delivery unit 210 comprises a casing or housing 212 and a cartridge holder 214 axially and rotationally fixed to the housing 212. The cartridge holder 214 supports a drug containing cartridge 240 having a cylindrical side wall 242, of e.g. glass or plastic, and being closed at its distal end by a self-sealing septum 44. An axially displaceable needle holder 250 has a needle mount 251 for reception of a collar 235 of a needle assembly 230, and an axially extending rack 253 on the underside of a semi-cylindrical structure. The needle assembly 230 is of the type shown in FIGS. 1 and 2, i.e. it comprises a needle cannula (not visible) fixedly attached to a needle hub (also not visible). The needle cannula comprises a front needle (not visible) adapted for providing subcutaneous entry, and a back needle (also not visible) adapted for establishing fluid communication with an interior of the cartridge 240 through the septum 44. A needle cap 237 is provided for protection of the front needle. In the cartridge holder 214 below the cartridge 240 a converter 260 is arranged. The converter 260 has a generally cylindrical base 266 on the top of which two axially extending circumferentially spaced apart rails 264 are provided, each of the rails 264 having a carve out for supporting a twin gear wheel 261. The cap 220 comprises a longitudinally extending circumferential side wall 222 which is closed at one end by a transversal end wall 221.

[0106] FIG. 21 is a perspective view detailing the converter 260. It is seen that the twin gear wheel 261 comprises a pair of gear wheels 262i, 262j connected by a shaft 263 which is rotatably retained in the carve outs of the rails 264. The base 266 is hollow and has a front opening 265 for reception of an interior portion of the cap 220, as explained in the below. The gear wheels 262i, 262j are configured for engagement with the rack 253 on the needle holder 250.

[0107] FIGS. 22 and 23 show the injection device 200 at two different stages during mounting of the cap 220 onto the drug delivery unit 210. In both figures a portion of the side wall 222 has been removed to provide an overview of a coupling mechanism serving to displace the needle holder 250 relative to the cartridge holder 214 when the cap 220 moves relative to the housing 212.

[0108] An axial shelf 225 is provided in the interior of the cap 220. The shelf 225 holds a pair of racks 226i, 226j adapted for engagement with the respective gear wheels 262i, 262j. In FIG. 22 the cap 220 is only partly mounted on the drug delivery unit 210, and the gear wheels 262i, 262j are just about to enter into engagement with the racks 226i, 226j. The needle holder 250 and the cartridge holder 214 are next to one another such that a portion of the back needle of the attached needle assembly 230 resides in the interior of the cartridge 240.

[0109] In FIG. 23 the cap 220 is completely mounted onto the drug delivery unit 210. The open end of the cap 220 is received by a cap receiving portion 209 and releasably retained thereon via a snap-fitting engagement with a couple of protrusions 208 (only one is visible) on the cartridge holder 214. During the axially converging relative motion between the cap 220 and the housing 212 from the state of the injection device 200 shown in FIG. 22 to that shown in FIG. 23 the racks 226i, 226j have forced the gear wheels 262i, 262j to rotate counter-clockwise, whereby the rack 253 has been forced distally and, accordingly, the needle holder 250 and the cartridge holder 214 have undergone a diverging relative axial motion. The racks 226i, 226j, the gear wheels 262i, 262j, and the rack 253 thus together act as a double rack-and-pinion drive during mounting of the cap 220 onto, and dismounting of the cap 220 from, the drug delivery unit 210. Hence, when the cap 220 is completely mounted on the drug delivery unit 210 a space 290 is provided between the needle holder 250 and the cartridge holder 214, and the back needle is pulled out of the septum 244, preventing any air from entering into the interior of the cartridge 240 and any drug from leaking out of the cartridge 240 through the attached needle cannula.

[0110] When the cap 220 is subsequently dismounted from the drug delivery unit 210 in order to perform the next injection the relative motions are reversed, and the double rack-and-pinion drive converts the diverging motion between the cap 220 and the housing 212 to a converging motion between the needle holder 250 and the cartridge holder 214, whereby the back needle again penetrates the septum 244 and fluid connection to the interior of the cartridge 240 is automatically established.