WO2015091819A1

WO2015091819A1 - Drug delivery device with mechanical feed-forward interface

Info

Publication number: WO2015091819A1
Application number: PCT/EP2014/078496
Authority: WO
Inventors: Mads Grønlund Andersen
Original assignee: Novo Nordisk A/S
Priority date: 2013-12-20
Filing date: 2014-12-18
Publication date: 2015-06-25

Abstract

The present invention concerns a drug delivery device comprising a housing (102) extending along a longitudinal axis between a proximal housing end and a distal housing end, a dose expelling mechanism for delivering a dose of a substance from a variable volume reservoir when the variable volume reservoir is coupled with the housing (102), a user input button (130; 157) being axially movable relative to the housing (102) between an exposed position in which a user operable portion thereof extends from the proximal housing end, and a covered position in which a majority of the user operable portion is accommodated in the housing (102), the user input button (130; 157) being biased towards the exposed position, and an interface element (175) being arranged at least partially within the housing (102) and comprising an abutment surface (177) being accessible from an exterior of the housing (102). The user input button (130; 157) and the interface element (175) are operatively coupled such that an axial movement of the user input button (130; 157) causes an opposite axial movement of the interface element (175), and vice versa.

Description

DRUG DELIVERY DEVICE WITH MECHANICAL FEED-FORWARD INTERFACE

FIELD OF THE INVENTION

The present invention relates to dose setting and delivery devices for administration of medicinal substances. BACKGROUND OF THE INVENTION

Injection devices, such as injection pens, are widely used for self-administration of liquid drugs by people in need of therapeutic treatment. Many injection devices are capable of repeated setting and injection of either a fixed or a variable volume of drug upon operation of respective dose setting and injection mechanisms in the device. Some injection devices are adapted to be loaded with a prefilled drug reservoir containing a volume of drug which is sufficient to provide for a number of injectable doses. When the reservoir is empty, the user replaces it with a new one and the injection device can thus be used again and again. Other injection devices are prefilled when delivered to the user and can only be used until the drug reservoir has been emptied. The various injection devices typically expel the drug by ad- vancing a piston in the reservoir using a motion controlled piston rod.

Within some therapy areas the tendency of a patient to adhere to the prescribed therapy is dependent on the simplicity of the specific treatment regimen. For example, many people with type 2 diabetes are diagnosed with the disease at a relatively high age where they are less prone to accept a treatment that intervenes too much with their normal way of living. Most of these people do not like constantly being reminded of their disease and, as a consequence, they do not want to be entangled in complex treatment patterns or waste time on learning how to operate cumbersome delivery systems.

WO 2009/092807 (Novo Nordisk A/S) discloses an automatic injection device with a housing and a protective cap, where the rim of the cap interacts with a dose setting mechanism with- in the housing during mounting of the cap onto a cap receiving portion to thereby set a dose. The interaction between the cap and the dose setting mechanism is also adapted to lift an injection button from a depressed and inoperable position to an active and operable position, indicating to the user that the injection device is prepared for a new dose administration.

While this device offers a number of advantages in respect of simplicity and safety, it does for example require a blocking of the injection mechanism when the cap is mounted on the cap receiving portion to prevent the user from unintended triggering of the device and a resulting expelling of a considerable volume of drug into the cap.

It is desirable to provide an injection device having an even higher level of simplicity and safety while avoiding the need for implementation of additional features to prevent potential drug wastage from unintended operation of the injection mechanism.

SUMMARY OF THE INVENTION

It is an object of the invention to eliminate or reduce at least one drawback of the prior art, or to provide a useful alternative to prior art solutions.

In particular, it is an object of the invention to provide an injection device which meets users' desires regarding a simple-to-understand and easy-to-use product.

It is a further object of the invention to enable the provision of an injection device which clearly indicates the possibilities of operation to the user and which offers a form of feedforward to the next step in the use sequence.

It is an even further object of the invention to enable the provision of an injection device which is safe and reliable, e.g. in the sense that it prevents manipulation of a set dose during dose delivery and prevents ejection of drug when in a capped, non-use state.

In the disclosure of the present invention, aspects and embodiments will be described which will address one or more of the above objects and/or which will address objects apparent from the following text. In a drug delivery device embodying the principles of the invention dismounting of a cap from a cap receiving portion causes displacement of a user manipulable button from an inoperable position to an operable position, and mounting of the cap on the cap receiving portion when the user operable button is in an operable position causes displacement of the user operable button from the operable position to the inoperable position. Thereby, the drug delivery device is perceivable as inactive or 'closed' when the cap is mounted thereon and as active or 'open' when the cap is removed therefrom.

In one aspect of the invention a drug delivery device as defined by claim 1 is provided. A drug delivery device is thus provided comprising: a housing extending along a longitudinal axis between a proximal housing end and a distal housing end, a dose expelling mechanism, a user input button for receiving input to change a state of the drug delivery device, the user input button being capable of movement relative to the housing along the longitudinal axis, and an interface element capable of movement relative to the housing along the longitudinal axis, wherein the user input button and the interface element are coupled such that a movement of one of the user input button and the interface element in a first axial direction relative to the housing results in a movement of the other of the user input button and the interface element in a second axial direction relative to the housing, which second axial di- rection is opposite to the first axial direction.

The user input button is movable between an exposed, or enabled, position in which a user operable portion of the user input button extends proximally from the proximal housing end and is physically accessible to a user, and a covered, or disabled, position in which at least one function of the user input button is disabled due to a reduced user accessibility of the user operable portion. For example, the majority (such as e.g. at least 51 %, 60%, 75%, 80% or 90%) of the user operable portion may be accommodated in the housing when the user input button is in the covered position. The user input button is biased towards the exposed position, e.g. by a spring device such as a compression spring.

The interface element is arranged at least partially within the housing and comprises an abutment surface, e.g. a distally facing abutment surface, which is accessible from an exterior of the housing, i.e. which is accessible to an external operator of the drug delivery device. The interface element is movable between a first position in which the user input button is in the exposed position and a second position in which the user input button is in the covered position. The first position can be termed a distal position, and the second position can be termed a proximal position. Hence, as the user input button is biased proximally towards the exposed position the interface element is consequently biased distally towards the first position.

The fact that the interface element and the user input button are coupled to undergo opposite axial displacements to one another and the fact that a portion of the interface element is accessible from an exterior of the housing makes it possible for a user to change the position of the user input button by manipulating the interface element. The abutment surface may be accessible from the distal housing end, or from a position distally of the distal housing end, and the interface element may be adapted to be moved towards the second position by the user, e.g. using a dedicated device. The dedicated device may be configured for detachable attachment to the housing so as to support the inter- face element in the second position against the aforementioned directional bias. A retention of the interface element in the second position naturally results in a retention of the user input button in the covered position. Thus, when the dedicated device is attached to the housing the drug delivery device is perceived as a 'closed' device, and when the dedicated device is detached from the housing the user input button will be moved automatically to the exposed position by the biasing force, whereby the drug delivery device will be perceived as an 'open' device.

The dedicated device may be a cap adapted to be mounted onto the distal housing end portion by at least a relative axial motion between the cap and the housing, e.g. to cover and protect the variable volume reservoir, and the cap may comprise a rim portion adapted for abutment with the abutment surface. The interface element may then be supported in the second position by the rim portion when the cap is mounted on the distal housing end. Thereby, it is ensured that so long as the cap is on the drug delivery device the user input button is in the covered position, which signals to the user that it is not available for operation, and when the cap is off the drug delivery device the user input button is in the exposed position, which invites the user to manipulate the user operable portion. As it is customary in the use of e.g. injection devices to mount an accompanying cap onto the housing between injections no additional handling step is introduced with this feature.

The user input button may be operable to set a dose to be delivered from the variable volume reservoir. Alternatively, or additionally, the user input button may be operable to cause a set dose to be expelled from the variable volume reservoir. In case the user input button is a dose setting button when in the exposed position it may be adapted to be rotated about the longitudinal axis to set the dose, and when in the covered position it may be impossible, or at least very difficult, to rotate relative to the housing. In case the user input button is a dose delivery button it may be axially depressed against the housing in order to execute the dose expelling from the variable volume reservoir.

The covered position thus indicates an inactive state of the drug delivery device, where e.g. no dose can be set. Notably, it is not possible to accidentally set a dose, or change a set dose, when a capped drug delivery device is e.g. being carried around in a pocket or a handbag during the day.

In another aspect of the invention a drug delivery device is provided comprising:

• a housing defining a longitudinal axis,

· a removably mountable cap, and

• a button assembly comprising:

o a user input button axially displaceable relative to the housing between an enabled position and a disabled position, the user input button being biased towards the enabled position, and

o an interface element axially displaceable relative to the housing between a first position and a second position, the interface element being adapted to receive and follow the cap axially during mounting of the cap onto the housing, when the user input button is in the enabled position,

wherein the interface element and the user input button are coupled so as to undergo oppo- site axial displacements to one another (e.g. such that a proximal displacement of the interface element causes a distal displacement of the user input button), and

wherein the button assembly is configured to bring the user input button to the enabled position in response to the cap being dismounted from the housing and to, when the user input button is in the enabled position, bring the user input button to the disabled position in re- sponse to the cap being mounted onto the housing.

Thereby, a drug delivery device is provided which signals to the user in response to a dismounting of the cap that it is ready for operation and which reverses this signal in response to the user re-mounting the cap on the drug delivery device, if the user input button remains enabled while the cap is off. In the enabled position the user input button may be operable to cause a change of state of the drug delivery device, and in the disabled position the user input button may be inoperable, or at least an operation thereof has no effect on the state of the drug delivery device. The enabled position may be a position in which the user input button protrudes from the housing and the disabled position may be a position in which a significant portion of the user input button, or the entire user input button, is depressed into the housing, thereby precluding any operationally relevant manipulation thereof. The user input button may e.g. be a dose setting button, e.g. rotatable about the longitudinal axis to set a dose of drug to be delivered from the drug delivery device, and/or a dose delivery button, e.g. axially displaceable to activate a dose expelling mechanism and cause a set dose of drug to be expelled from a drug reservoir. Thereby, a user will be automatically in- formed of when it is possible to set a dose to be delivered from the device and/or when it is possible to perform a dose administration. When the cap is mounted on the housing the user input button will be in the disabled position, regardless of whether a dose administration was just performed, thereby rendering any dose setting and/or dose delivery action impossible and giving the drug delivery device the appearance of a closed or inactive system. In particular embodiments of the invention the interface element and the user input button are coupled via a double rack and pinion drive. This enables a reliable correlation of their displacements. Alternatively, the interface element and the user input button could e.g. be coupled via a rocker arm assembly, or by means of a pulley arrangement.

The dose expelling mechanism may comprise a piston rod and a drive member for actuating the piston rod, which drive member is axially displaceable relative to the housing between a dose prepared position and a dose delivered position. The drive member may be adapted to receive and follow the cap axially during mounting of the cap onto the housing, when the user input button is in the disabled position. Further, the user input button may be biased towards the enabled position by a spring member acting between the user input button and the drive member, the spring member thus further biasing the drive member towards the dose delivered position.

This enables the drug delivery device to be automatically prepared for dose delivery by the cap during the conventional cap mounting step. The spring is thereby being strained further and is thus readied for providing energy for automatic dose delivery. The drug delivery device may further comprise a switch lock switchable between a first state and a second state, where in the first state a displacement of the drive member towards the dose delivered position is prevented while axial displacement of the interface element is allowed, and where in the second state displacement of the interface element towards the first position is prevented while axial displacement of the drive member is allowed. Thereby it is ensured that when the drive member is able to move towards the dose delivered position no axial movement of the interface element, and thereby of the user input button, can take place. An initiated dose administration may thus be completed while the dose delivery button stays depressed in the housing, and the dose delivery button will remain motionless until the switch lock switches back at some point. Further, it is ensured that when the interface element is movable towards the first position, i.e. when the user input button is movable towards, or in, the enabled position, no axial movement of the drive member can take place. No dose administration is thus possible while dose setting is enabled.

A switch between the first state and the second state may be determined by a relative axial position of the interface element and the drive member. For example, the switch lock may be arranged to switch from the first state to the second state in response to the interface element reaching a third position proximally of the second position (i.e. closer to the proximal housing end, e.g. corresponding to a fully depressed position of the user input button), and to switch from the second state to the first state in response to the drive member reaching the dose prepared position.

The switching between states may thus happen automatically in response to certain user actions, such as e.g. a depression of the user input button against the housing to active the dose expelling mechanism.

The attachment interface between the cap and the distal housing end may e.g. be a threaded interface or a bayonet interface, whereby the cap is prevented from being dismounted from the housing by pure axial motion. This will allow the cap, when mounted, to prevent distal movement of the drive member relative to the housing, and thereby ensure that even if the user input button is fully depressed, and the interface element thereby is moved from the second position to the third position, which moves the abutment surface out of abutment with the rim portion, no dose expelling is initiated. When the depressing force on the user input button is discontinued the bias on the user input button will restore the steady state condition in which the interface element abuts the cap and the switch lock is in the first state. It is thus not possible to accidentally activate the dose expelling mechanism when a capped drug delivery device is e.g. being carried around in a pocket or a handbag during the day.

In particular embodiments of the invention the drive member reaches the dose prepared position in response to the cap becoming mounted on the housing. An automatic switching thus happens in response to the user capping the drug delivery device for storage or transport.

The drug delivery device may further comprise a piston rod threadedly engaged with a nut member being fixedly arranged in the housing, wherein the drive member is coupled with the piston rod such that displacement of the drive member towards the dose delivered position causes advancement (i.e. distal movement) of the piston rod through the nut member, and further such that displacement of the drive member towards the dose prepared position leaves the piston rod unaffected. This allows simple reciprocating movements of the drive member to successively expel doses of drug from the variable volume reservoir.

In a further aspect of the invention a drug delivery device is provided comprising:

• a housing defining a longitudinal axis,

• a removably mountable cap, and

• a dose preparation assembly comprising:

o a user input button axially displaceable relative to the housing, and o a cap receiving portion adapted to abut or engage with the cap when the cap is mounted on the injection device, the cap receiving portion being operatively coupled with the user input button,

wherein the dose preparation assembly is switchable at least between a first state in which the user input button takes up a first axial position relative to the housing and a second state in which the user input button takes up a second axial position relative to the housing, and wherein the dose preparation assembly is configured to switch to the first state in response to the cap being dismounted from the injection device and to, when being in the first state, switch to the second state in response to the cap being mounted on the injection device. In a further aspect of the invention a drug delivery device is provided comprising:

• a dose setting mechanism for setting of a dose to be expelled from a reservoir,

• a dose expelling mechanism for expelling the set dose from the reservoir, and

• a switch lock switchable between a first state in which the dose setting mechanism is enabled and the dose expelling mechanism is disabled and a second state in which the dose setting mechanism is disabled and the dose expelling mechanism is enabled.

The drug delivery device may further comprise a housing defining a longitudinal axis, and the dose setting mechanism may comprise a dose setting button and an interface element, the dose setting button and the interface element being operatively coupled to perform opposite axial movements. The dose expelling mechanism may comprise an axially displacea- ble activation element, and a distal displacement of the activation element relative to the housing may cause a volume of drug to be expelled from the reservoir.

In the first state the switch lock may prevent distal displacement of the activation element relative to the housing, and in the second state the switch lock may prevent distal displace- ment of the interface element relative to the housing. A switch between the first state and the second state may be determined by a relative axial position of the interface element and the activation element.

The dose setting button may be axially displaceable relative to the housing between a first position in which the dose setting mechanism is operable to set a dose and a second posi- tion in which the dose expelling mechanism is activated.

• a housing defining a longitudinal axis,

• a dose setting mechanism for setting of a dose to be expelled from a reservoir, the dose setting mechanism comprising a dose setting button and dose indication means operatively coupled with the dose setting button and adapted to visibly indicate the size of the set dose,

• a dose expelling mechanism for expelling the set dose from the reservoir, the dose expelling mechanism comprising an axially displaceable activation element,

• a switch lock switchable between a first state in which the dose setting mechanism is enabled and the dose expelling mechanism is disabled and a second state in which the dose setting mechanism is disabled and the dose expelling mechanism is enabled, and

• an interface element coupled with the dose setting button and arranged to undergo opposite displacements to axial displacements of the dose setting button,

wherein the dose setting button is axially displaceable relative to the housing between a first position in which the dose setting mechanism is operable to set a dose and a second position in which the dose expelling mechanism has been activated,

wherein when in the first state the switch lock prevents distal axial displacement of the activation element relative to the housing and when in the second state the switch lock prevents distal axial displacement of the interface element relative to the housing, and wherein the switch lock is configured to switch between the first state and the second state in response to the activation element and the interface element taking up a specific relative axial position.

The drug delivery device may be of the prefilled type, i.e. where a variable volume reservoir, such as a cartridge, is permanently coupled with the housing, or of the loadable type, i.e. where a variable volume reservoir, such as a cartridge, can be coupled to the housing by the user in a repeatable manner, e.g. via a displaceable reservoir holder adapted to receive and releasably retain the variable volume reservoir.

In the present context, any statement related to the cap being mounted on or onto the hous- ing should be interpreted to cover both the cap being mounted on or onto the housing and the cap being mounted on or onto a part coupled with the housing, such as e.g. a reservoir holder. Further, when the cap is "mounted on" the distal housing end it is firmly attached to the housing, i.a. withstanding the axial force from the interface element originating from the biasing force on the user input button. In the present specification, reference to a certain aspect or a certain embodiment (e.g. "an aspect", "a first aspect", "one embodiment", "an exemplary embodiment", or the like) signifies that a particular feature, structure, or characteristic described in connection with the respective aspect or embodiment is included in, or inherent of, at least that one aspect or embodiment of the invention, but not necessarily in/of all aspects or embodiments of the inven- tion. It is emphasized, however, that any combination of the various features, structures and/or characteristics described in relation to the invention is encompassed by the invention unless expressly stated herein or clearly contradicted by context.

The use of any and all examples, or exemplary language (e.g., such as, etc.), in the text is intended to merely illuminate the invention and does not pose a limitation on the scope of the same, unless otherwise claimed. Further, no language or wording in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with references to the drawings, wherein Fig. 1 is a perspective view of a portion of an injection device according to an embodiment of the invention,

Fig. 2 is a perspective view detailing elements of a drive mechanism in the injection device, and Figs. 3-7 are perspective views of the portion of the injection device in different states during use.

In the figures like structures are mainly identified by like reference numerals. DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following relative expressions, such as e.g. "upwards" and "downwards" 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.

Fig. 1 is a perspective view of a portion of an injection device 100 according to an embodi- ment of the invention, specifically of a proximal portion of the injection device 100, carrying a dose engine. The injection device 100 is in a pre-use state and portions of some elements thereof have been removed from the figure to provide a detailed overview of the construction.

The injection device 100 is of the so-called pen injector type and has a tubular housing 102 extending along a longitudinal general axis and accommodating a number of functional components. The housing 102 is coupled with a drug containing cartridge (not shown) in a manner conventionally known in the art, i.a. meaning that the cartridge during use of the injection device 100 is at least axially fixed with respect to the housing 102. Central to the function of the injection device 100 is an axially extending piston rod 160 which is in thread- ed engagement with a nut 162 that is both axially and rotationally fixed in the housing 102. The distal end portion of the piston rod 160 is coupled to a piston (not shown) in the cartridge such that any advancing axial motion of the piston rod 160 is transferred to the piston, essentially for pressurisation of the cartridge, as is also conventionally known in the art. It is noted that all rotational movements described in the below and referred to as clockwise or counter-clockwise are described as seen from the distal end of the piston rod 160 (i.e. from left to right in Fig. 1 ).

The housing 102 is provided with an interior thread 128 which cooperates with an exterior helical track segment 142 on a scale drum 140, allowing the scale drum 140 to undergo a well-defined helical motion in the housing 102. The scale drum 140 carries a plurality of dose indicia 141 for indicating to a user the particular size of a set dose. The dose indicia 141 are successively viewable through a window 199 in the housing 102 when the scale drum 140 travels along the interior thread 128 e.g. from a proximal "zero dose" position to a distal "maximum dose set" position. The proximal "zero dose" position is defined by a proximal stop surface (not visible) providing a rotational stop for proximal motion of the scale drum 140 at the proximal end of the interior thread 128, whereas the "maximum dose set" position is defined by a distal stop surface (not visible) providing a rotational stop for distal motion of the scale drum 140 at the distal end of the interior thread 128. The scale drum 140 is rotationally locked to a dial 130 via a longitudinal interior projection 144 (see Fig. 4) and an axially extending spline 135 on the exterior surface of the dial 130. While rotationally interlocking the scale drum 140 and the dial 130 this splined connection allows relative axial motion between the two. The dial 130 is at its distal end portion axially locked to a coupling piece 173 which comprises an axially aligned leg 171 with a radially inwardly facing toothed surface 172. At the proximal end portion of the dial 130 a push button 157 is arranged, which is axially locked to but rotationally decoupled from the dial 130, and the two together serve as an injection button. Further, a sleeve 131 extends axially from an inner end face 103 of the dial 130. The sleeve 131 has a toothed inner surface and is configured to be brought into and out of rotational interlocking engagement with a toothed end portion 122 of a dose preparation tube 120 which extends axially within the housing 102.

The dose preparation tube 120 has a threaded end portion 123 opposite the toothed end portion 122. The threaded end portion 123 interfaces with a drive nut 195 in a non-self- locking thread engagement. The drive nut 195 forms part of an actuation rod 109, the func- tion of which will be described in detail below. The actuation rod 109, which is axially dis- placeable but rotationally fixed with respect to the housing 102, has a longitudinal extension 196 which ends in an abutment face 197. The longitudinal extension 196 is transversally offset from a main portion of the actuation rod 109 and is adapted to slide along a cartridge holder (not shown in Fig. 1 ) both during dose delivery and dose preparation. The cartridge holder is attached to a distal portion of the housing 102 and serves to hold and protect the cartridge in a manner conventionally known in the art.

A pre-tensioned compression spring 150 is arranged to act between the inner end face 103 and the actuation rod 109, constantly biasing the dial 130 and the push button 157 proximal- ly, out of the housing 102, and the actuation rod 109 distally. In the shown pre-use state of the injection device 100 distal motion of the actuation rod 109 is prevented by a lock member 180 abutting a transversal surface 198 of the actuation rod 109. The lock member 180 is pivotally arranged on the nut 162 but is in Fig. 1 prevented from pivoting by an edge portion of a button coupling rod 175 which is axially displaceable but rotationally fixed with respect to the housing 102. The button coupling rod 175 has a toothed straight edge 178, which is in engagement with a transmission wheel 170, and a longitudinal extension 176, which is transversally offset from the toothed straight edge 178 and which ends in an abutment face 177. The transmission wheel 170 is further in engagement with the toothed surface 172, such that the coupling piece 173, the button coupling rod 175, and the transmission wheel 170 together provide a double rack and pinion drive.

In the present situation, given that the actuation rod 109 is prevented from undergoing distal motion in the housing 102 due to the lock member 180, the bias of the spring 150 on the dial 130 causes the dial 130 to exert a pulling force on the coupling piece 173 which then via the double rack and pinion structure is converted to a distal movement of the button coupling rod 175, unless a counter-acting force is applied to the abutment face 177. Although not shown in Fig. 1 , in the depicted pre-use state of the injection device 100 a removable protective cap is securely mounted onto a cap receiving portion at the distal end portion of the housing 102 such that a portion of the cap abuts the abutment face 177 and resists the bias conveyed to the longitudinal extension 176, thereby maintaining the button coupling rod 175 in position. The injection device 100 is thus in fact stably locked in a tensioned state. As will be explained in more detail below once the retaining force on the abutment face 177 is removed the relaxation of the spring 150 will cause the dial 130 and the push button 157 to translate proximally. A stop surface 136 on the dial 130 limits the proximal motion of the dial 130 and the push button 157 relative to the housing 102.

Fig. 2 is a detailed view of the piston rod advancement mechanism as employed in the injection device 100. A rotatable piston rod guide 163 couples the nut 162 and the dose preparation tube 120 via an inner groove 167 for axial interlocking connection with the nut 162 and an inner groove 168 for axial interlocking connection with the threaded end portion 123. The piston rod guide 163 has a distal pawl 164, which in combination with a plurality of circum- ferentially spaced apart indentations 187 on the nut 162 provide a distal ratchet mechanism, and a proximal pawl 166 which in combination with a plurality of circumferentially spaced apart indentations 126 on the dose preparation tube 120 provide a proximal ratchet mechanism. The distal ratchet mechanism allows clockwise rotation of the piston rod guide 163 relative to the nut 162 but prevents counter-clockwise rotation of the piston rod guide 163. The proximal ratchet mechanism allows relative rotation between the dose preparation tube 120 and the piston rod guide 163 when the dose preparation tube 120 is rotated counter- clockwise, but prevents relative rotation between the dose preparation tube 120 and the piston rod guide 163 when the dose preparation tube 120 is rotated clockwise. The double ratchet comprised of the distal ratchet mechanism and the proximal ratchet mechanism thus allows the dose preparation tube 120 to drag the piston rod guide 163 along in the clockwise direction and to rotate freely in the counter-clockwise direction while the piston rod guide 163 remains stationary.

The piston rod guide 163 further has a radially inwardly directed protrusion (not visible) for engagement with an axial groove 169 on the piston rod 160. The piston rod 160 and the piston rod guide 163 are thus rotationally interlocked but capable of relative axial motion.

The functionality of the dose setting and delivery mechanisms will now be described with reference to Figs. 3-7. When taking the injection device 100 into use the protective cap is firstly removed. This removes the retaining force on the abutment face 177 and allows the spring 150 to expand. The spring 150 thus urges the dial 130 with the push button 157 prox- imally until the stop surface 136 abuts the interior end wall of the housing 102, and the double rack and pinion drive accordingly forces the button coupling rod 175 a distance distally. The end result of this is illustrated by Fig. 3.

The proximal motion of the dial 130 also causes the sleeve 131 to disengage from the toothed end portion 122. The dial 130 is thus now capable of being rotated without affecting the dose preparation tube 120. A dose is set by rotation of the dial 130 relative to the housing 102. Due to the spline connection between the dial 130 and the scale drum 140 and the threaded interface between the scale drum 140 and the housing 102 when the dial 130 is dialled counter-clockwise the scale drum 140 displaces helically downwards in the housing 102 in response, and when the dial 130 is dialled clockwise the scale drum 140 displaces helically upwards in the housing 102. In Fig. 4 the dial 130 has been dialled to set a dose of "72" units.

Dose delivery is executed by depression of the push button 157, as illustrated in Fig. 5. The push button 157 may actually be depressed a certain distance without causing more than a reversed motion of the double rack and pinion drive and a compression of the spring 150. A discontinuation of the depression force in this instance will simply cause the spring 150 to return the push button 157 to its proximal most position. However, once the button coupling rod 175, during its proximal displacement, reaches a specific axial position in the housing 102 an end surface 179 passes the fulcrum of the lock member 180 and the lock member 180 will be free to pivot, whereby the pre-tensioned spring 150 will be released and as a result force the actuation rod 109 distally. As the lock member 180 pivots to allow passage of the actuation rod 109 the button coupling rod 175 becomes prevented from distal motion in the housing 102 due to the lock member 180 being prevented from returning to the original position by the actuation rod 109. At this point if the user releases the pressure on the push button 157 the dial 130 will consequently be prevented from proximal motion and will thus stay inside the housing 102.

The depression of the push button 157 also leads to a rotational re-engagement of the sleeve 131 and the toothed end portion 122. This happens before the flipping over of the lock member 180, such that when the spring 150 is released and the actuation rod 109 is suddenly propelled distally the dial 130 and the dose preparation tube 120 are rotationally interlocked. Due to the threaded engagement between the drive nut 195 and the threaded end portion 123 the distal movement of the actuation rod 109 causes the dose preparation tube 120 to spin clockwise.

The clockwise rotation of the dose preparation tube 120 causes a clockwise rotation of the piston rod guide 163, due to the above described double ratchet mechanism, and thereby also of the piston rod 160. The threaded engagement between the piston rod 160 and the nut 162 thus results in a helical advancement of the piston rod 160, whereby the piston (not shown) is advanced axially in the cartridge (not shown) to expel a volume of drug through an attached injection needle (not shown). The volume expelled is determined by the position of the scale drum 140 in the housing 102 at the time of release of the spring 150 because the clockwise rotation of the dose preparation tube 120 also causes a clockwise rotation of the dial 130 and thereby of the scale drum 140, and the rotation of the three continues until the scale drum 140 meets the proximal stop surface which defines the "zero dose" position. This end-of-dose state of the injection device 100 is illustrated in Fig. 6.

It is noted that as the injection progresses the actuation rod 109 is moved further distally and the axial end position of the abutment face 197 corresponding to the "zero dose" position of the scale drum 140 is uniquely correlated with the distance travelled by the scale drum 140 from its position at release of the spring 150 to the proximal stop surface.

In the end-of-dose state of the injection device 100 the push button 157 is prevented from proximal motion and therefore has to stay depressed in the housing 102. Hence, it is not possible to set a dose at this point. It is common practice when handling injection devices to re-mount the protective cap following an injection. In the course of re-mounting the protective cap onto the cap receiving portion of the injection device 100 a portion of the cap, such as e.g. a segment of the cap rim or a protrusion, abuts the abutment face 197 and pushes the actuation rod 109 proximally with respect to the housing 102.

The resulting proximal movement of the drive nut 195 causes the dose preparation tube 120 to spin counter-clockwise, relative to the housing 102 but also relative to the piston rod guide 163 due to the double ratchet mechanism, so the piston rod 160 is left unaffected. The counter-clockwise rotation of the dose preparation tube 120 causes a corresponding counterclockwise rotation of the dial 130 which leads to a downward helical displacement of the scale drum 140. The proximal movement of the drive nut 195 also causes a compression of the spring 150 which is progressive until the actuation rod 109 reaches the axial position where the transversal surface 198 passes the fulcrum of the lock member 180. At this position of the actuation rod 109 the lock member 180 is free to pivot and thus no longer functions as a block for distal motion of the button coupling rod 175. So, as the spring 150 seeks to relax and con- stantly biases the inner end face 103 in the proximal direction, the dial 130 is urged proximally, pulling the coupling piece 173, and the double rack and pinion drive consequently urges the button coupling rod 175 distally, causing the lock member 180 to flip over and abut the transversal surface 198. The spring 150 will displace the dial 130 proximally a small distance until the abutment face 177 abuts the protective cap and further distal motion of the button coupling rod 175 thereby is prevented. This corresponds to the state of the injection device 100 shown in Fig. 7. In this state the lock member 180 stably prevents distal motion of the actuation rod 109, as it is prevented from pivoting by the button coupling rod 175. As long as the protective cap remains mounted on the cap receiving portion a depression of the push button 157 only leads to an additional compression of the spring 150 which has no effect on the secured injection mechanism. At termination of the push force the spring 150 will return to the slightly less compressed state shown in Fig. 7. Notably, when the protective cap is re-mounted on the cap receiving portion the actuation rod 109 is returned to the exact same axial position within the housing 102 that it initially assumed before the dose ejection was commenced. Due to the threaded interface between the drive nut 195 and the threaded end portion 123 this means that the dose preparation tube 120 is consequently returned rotationally to the exact same angular position relative to the housing 102 that it initially assumed before the dose ejection was commenced. The dose preparation tube 120 has thus during re-mounting of the protective cap undergone the exact opposite rotation to the one it underwent during the dose delivery, and since the dose preparation tube 120 and the dial 130 are rotationally interlocked so has the dial 130. Consequently, due to the splined connection between the dial 130 and the scale drum 140 and the threaded connection between the scale drum 140 and the housing 102, the scale drum 140 has been returned to the position it assumed immediately before the push button 157 was depressed and the spring 150 was released. In other words, by the re-mounting of the protective cap onto the cap receiving portion a setting of the last ejected dose has automatically been performed. In fact, every time the protective cap is mounted onto the cap receiving portion the dose preparation tube 120 will be returned, in the above described manner, to the initial angular position, which can be defined as a dose prepared position within the housing 102, thereby bringing the injection device 100 in a "DOSE PREPARED" state.

When the user dismounts the protective cap before the next injection the dial 130 and the push button 157 will re-protrude from the housing 102 and the sleeve 131 will disengage from the toothed end portion 122, as described above in connection with Fig. 3. The user can now either choose to simply position the injection device 100 at the desired skin site and press the push button 157 to deliver the same dose as was last delivered, or adjust the dose size by turning the dial 130 in the appropriate direction before performing the injection pro- cedure.

In case the user chooses to adjust the dose, and thereby set a new dose, the scale drum 140 will change position within the housing 102 and assume a new position corresponding to the desired dose viewed through the window 199. Because the dial 130 is decoupled from the toothed end portion 122 the repositioning of the scale drum 140 will not affect the dose preparation tube 120. Only when the push button 157 is subsequently depressed and the sleeve 131 reengages with the toothed end portion 122 the scale drum 140 and the dose preparation tube 120 become coupled to undergo correlated movements relative to the housing 102, provoked by the spring 150, as previously described. During these correlated movements the scale drum 140 will again reach the "zero dose" position and abruptly stop further expansion of the spring 150 and distal motion of the actuation rod 109. When this happens the axial end-of-dose position of the abutment face 197 relative to the housing 102 will be different from its previous end-of-dose position and, consequently, the dose preparation tube 120 will have undergone a different angular displacement than the one it underwent during the previous dose delivery. Nevertheless, when the cap is re-mounted on the cap receiving portion the actuation rod 109 will once again be returned to the same axial position as before, since that axial position is defined by the position of the cap portion abut- ting the abutment face 197 relative to the housing 102 when the cap is securely mounted. Due to the engagement between the drive nut 195 and the threaded end portion 123 the reversed motion of the actuation rod 109 will lead to a reversed motion of the dose preparation tube 120, which will again lead to a reversed motion of the scale drum 140. Thereby, the dose preparation tube 120 is returned to the exact same angular position relative to the housing 102 that it assumed before the dose ejection (the dose prepared position), and the scale drum 140 is returned to the position in which the new dose is viewed through the window 199.

The injection device 100 thus possesses a user interface which clearly indicates to its surroundings the possibilities of operation as well as a feed-forward to the next step in the use sequence. When the protective cap is on the injection device 100 the push button 157 is depressed which signals to the user that the system is "closed" or "passive" or "not to be operated", simply because no operation of a dose setting button or an injection button is possible. When the protective cap is removed and the dial 130 emerges automatically from the housing 102, carrying the push button 157, this signals to the user that a following step is to either set or inject a dose of the medical substance (depending on whether an injection needle 1 17 is already in position on the cartridge holder 1 14). Both operators are ready for manipulation. When the push button 157 is eventually depressed to deliver a set dose the dial 130 is locked within the housing 102 due to the double rack and pinion drive and the arrangement of the lock member 180, signalling to the user that no further operation is re- quired in connection with the current dose delivery procedure. When the protective cap is re- mounted the dial 130 and the push button 157 remains substantially depressed, and the injection device 100 is again "passive".

Notably, in case the protective cap is off and the dial 130 protrudes from the housing 102 if the cap is re-mounted without the push button 157 having been depressed to release the spring 150 then the double rack and pinion drive will simply cause the dial 130 to move back into the housing 102 and thus re-establish the "closed" appearance of the injection device 100.

As is clear from the above the lock member 180 functions as a binary switch lock between the dose setting mechanism and the dose delivery mechanism in the sense that when the piston rod 160 is advanced during dose delivery no dose setting or adjustment is possible because the dial 130 is inoperably and inescapably contained within the housing 102, and when the dial 130 protrudes from the housing 102 and is manipulate by the user the spring 150 is securely retained by the immovable actuation rod 109, preventing any advancement of the piston rod 160. The particular arrangement of the lock member 180, the button coupling rod 175, the actuation rod 109, and the spring 150 guarantees that there are only two stable positions for the lock member 180; a position in which axial motion of the actuation rod 109 is allowed while proximal motion of the dial 130 is prevented, and a position in which axial (and rotational) motion of the dial 130 is allowed while distal motion of the actuation rod 109 is prevented. In the former position the lock member 180 is retained by the actuation rod 109 until the actuation rod 109 during proximal movement relative to the housing 102 reaches the position where the transversal surface 198 passes the fulcrum of the lock member 180, at which point the lock member 180 pivots into locking abutment with the transversal surface 198 due to the distally directed force on the button coupling rod 175 provided by the spring 150 via the dial 130 and the double rack and pinion structure. In the latter position the lock member 180 is retained by the button coupling rod 175 until the button coupling rod 175 during proximal movement relative to the housing 102 reaches the position where the end surface 179 passes the fulcrum of the lock member 180, at which point the lock member 180 pivots into locking abutment with the end surface 179 due to the distally directed force on the actuation rod 109 provided by the spring 150.

Claims

1. A drug delivery device comprising:

- a housing (102) extending along a longitudinal axis between a proximal housing end and a distal housing end, - a dose expelling mechanism for delivering a dose of a substance from a variable volume reservoir when the variable volume reservoir is coupled with the housing (102),

- a user input button (130; 157) being axially movable relative to the housing (102) between an exposed position in which a user operable portion thereof extends from the proximal housing end, and a covered position in which a majority of the user opera- ble portion is accommodated in the housing (102), the user input button (130; 157) being biased towards the exposed position, and

- an interface element (175) being arranged at least partially within the housing (102) and comprising an abutment surface (177) being accessible from an exterior of the housing (102), wherein the user input button (130; 157) and the interface element (175) are operatively coupled such that an axial movement of the user input button (130; 157) causes an opposite axial movement of the interface element (175), and vice versa.

2. A drug delivery device according to claim 1 , wherein the user input button (130; 157) and the interface element (175) are operatively coupled via a double rack and pinion drive (170; 173; 175).

3. A drug delivery device according to claim 1 or 2, wherein the user input button (130; 157) comprises a dose delivery button (157) adapted to activate the dose expelling mechanism.

4. A drug delivery device according to any of claims 1 - 3, further comprising a dose setting mechanism for defining a dose to be delivered by the dose expelling mechanism, wherein the user input button (130; 157) comprises a dose dial (130) forming part of the dose setting mechanism.

5. A drug delivery device according to any of the preceding claims, further comprising a cap configured for dismountable mounting onto the distal housing end by at least relative axial motion between the cap and the housing (102), the cap comprising a rim portion adapted for abutment with the abutment surface (177), wherein the interface element (175) is axially movable relative to the housing (102) between a first position, corresponding to the user input button (130; 157) being in the exposed position, and a second position, corresponding to the user input button (130; 157) being in the covered position, and wherein when the cap is mounted on the distal housing end the rim portion abuts the abut- ment surface (177) and supports the interface element (175) in the second position.

6. A drug delivery device according to claim 5, wherein the dose expelling mechanism comprises a piston rod (160), and a drive member (109) for actuating the piston rod (160), the drive member (109) being axially displaceable relative to the housing (102) between a dose prepared position in which the dose expelling mechanism is ready to expel a dose and a dose delivered position, the drive member (109) being adapted to receive the cap in the dose delivered position and to follow the cap axially during mounting of the cap onto the distal housing end, and wherein the user input button (130; 157) is biased towards the exposed position by a spring member (150) acting between the user input button (130; 157) and the drive member (109), the spring member (150) thus further biasing the drive member (109) towards the dose delivered position.

7. A drug delivery device according to claim 6, further comprising a switch lock (180) switch- able between a dose setting state in which displacement of the drive member (109) towards the dose delivered position is prevented while axial displacement of the interface element (175) is allowed and a dose delivery state in which displacement of the interface element (175) towards the distal end position is prevented while axial displacement of the drive member (109) is allowed, wherein a switch between the dose setting state and the dose delivery state is determined by a relative axial position of the interface element (175) and the drive member (109).

8. A drug delivery device according to claim 7, wherein the switch lock (180) is arranged to switch from the dose setting state to the dose delivery state in response to the interface element (175) reaching a third position proximally of the second position, and to switch from the dose delivery state to the dose setting state in response to the drive member (109) reaching the dose prepared position.

9. A drug delivery device according to claim 8, wherein the drive member (109) reaches the dose prepared position in response to the cap becoming mounted on the distal housing end.

10. A drug delivery device according to any of claims 6 - 9, wherein the piston rod is (160) threadedly engaged with a nut member (162) being fixedly arranged in the housing (102), and wherein the drive member (109) is coupled with the piston rod (160) such that displacement of the drive member (109) towards the dose delivered position causes advancement of the piston rod (160) through the nut member (162), and further such that displacement of the drive member (109) towards the dose prepared position leaves the piston rod (160) unaf- fected.