WO2005058392A2

WO2005058392A2 - Cartridge for delivery device

Info

Publication number: WO2005058392A2
Application number: PCT/DK2004/000873
Authority: WO
Inventors: Martin VON BÜLOW
Original assignee: Novo Nordisk A/S
Priority date: 2003-12-18
Filing date: 2004-12-16
Publication date: 2005-06-30
Also published as: WO2005058392A3

Abstract

The invention relates to a cartridge for a delivery device, the cartridge comprising a drug res-ervoir, a displaceable portion and a transmission liquid whereby an external expelling force can be transmitted from the displaceable portion to the reservoir via the transmission liquid. The cartridge may be used in a delivery device to improve interaction between external force-generating expelling means and the reservoir. Advantageously, the cartridge may be used in combination with an impulse generating jet injection device.

Description

CARTRIDGE FOR DELIVERY DEVICE

The invention relates to a cartridge for a delivery device, the cartridge comprising a drug reservoir and a transmission liquid whereby an external expelling force can be transmitted to the reservoir via the transmission liquid. The cartridge may be used in a delivery device to improve interaction between external force-generating expelling means and the reservoir. For example, the cartridge may be used in combination with an impulse generating jet injection device.

BACKGROUND OF THE INVENTION

Subcutaneous and intramuscular delivery of liquid drugs by injection is common in the medical arts. As some medications, such as insulin, must be given frequently by injection to an individual, it is desirable that the injections can be performed easily.

Many patients dislike needle injections due to pain or fear for needles. Further, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Also, the disposal of used needles is a growing concern. This disposal presents a problem to individuals other than healthcare workers. Children, for example, may find used needles in the trash, putting them at risk of contracting infection. Discarded needles likewise pose a risk to waste disposal workers.

In efforts to minimize the fears and risks associated with needle injections, several types of needle-free jet injectors have been developed. These devices penetrate the skin using a high velocity liquid jet, and deliver medication into the tissue of a patient. In order to accomplish this, a force is exerted on the liquid medication. Jet injectors, in general, contain a liquid drug which has been transferred into a chamber having a small orifice at one end. A drive means, e.g. a ram, is accelerated using either a coil spring or a compressed gas energy source. The ram impacts a plunger, which in turn creates a high pressure impulse within the chamber. This pressure impulse ejects the liquid medicament through the orifice at high velocity, piercing the skin. The energy source continues to apply a force to the plunger, which quickly propels the drug through the opening in the skin, emptying the syringe in a fraction of a second. The drive means may be adapted to provide a two-stage injection, i.e. a first penetrating burst of drug at a high pressure followed by a subsequent delivery of the remaining amount of drug at a lower pressure. Injectable drugs may be supplied in glass vials sealed with an inert rubber stopper. To administer the liquid drug, the user must transfer the liquid drug from the vial to a liquid drug delivery device, such as a syringe and needle, or a needleless jet injector syringe. Transfer- ring the liquid drug adds cost to administering injections in a hospital or clinic because of the labor expense. Immunizing large populations requires administering many injections per hour, hence transferring the liquid drug presents a significant time constraint. For the patient who must self-administer liquid drugs, such as a diabetic patient requiring several insulin injections a day, transferring the liquid drug can be an inconvenience. Also, with each transfer, there is an opportunity for error in the amount of liquid drug being transferred and administered.

In an effort to eliminate transferring a liquid drug from a vial, pre-filled glass cartridges have been developed. These pre-filled cartridges are similar in design to a syringe. One end is closed and includes either a needle or an inert rubber septum. If a needle is not integral, then a needle subassembly that penetrates the rubber septum is attached prior to use. A movable rubber piston closes the end opposite the needle. To administer the liquid drug, the pre-filled cartridge is placed in a device consisting of a holder and a driver that meets the movable rubber plunger. The user depresses the plunger to dispense the medication.

An example of the use of pre-filled cartridges is in the treatment of diabetes with multiple daily injections of insulin by use of an injection device, e.g. pen-shaped, in which a pre-filled cartridge containing an amount of insulin sufficient for several days can be mounted, the injection device comprising means for setting a desired dose and subsequently expelling the dose. A disadvantage of pre-filled cartridges, however, is that they still require using a needle to penetrate the skin and deliver the medication to the target tissue.

Neither glass vials containing multiple doses of a drug nor pre-filled cartridges can be used with traditional jet injectors. For example, if the force generated by the jet injector drive means was applied directly to the piston the cartridge would in most cases burst. This is because a significant amount of impulse energy is transmitted from the energy source. Although not directly impacted, the glass walls of the cartridge do not have sufficient strength to withstand the large amplitude pressure waves that result when the ram impacts the piston. Addressing this problem, US patent application 2002/0055707 discloses a jet injection device comprising a reservoir in the form of prefilled drug cartridge, an impulse chamber to which an amount of drug to be expelled by jet action is transferred through a fluid connection between the reservoir and the impulse chamber. The impulse chamber has an injection nozzle at a distal end, and a drive piston adapted to engage a ram member at the proximal end. JP- 2001-346878A discloses a similar arrangement in which the drug cartridge is in fluid communication with the impulse chamber through an inlet opening in the impulse piston, fluid communication between the opening and the cartridge being provided by a flexible hose member.

US patent 5,348,539 discloses an infusion pump for use with standard pre-filled single dose IV bags. The pump includes an inflatable chamber having a diaphragm which expands under fluid pressure to compress the sidewalls of an IV bag. A fluid is directed under pressure to the chamber for causing it to inflate under influence of a control system. In one embodiment the fluid comprises a liquid which is transferred to and from the chamber from a reservoir. In another embodiment the fluid comprises a gas.

EP 1 125 593 discloses a hypodermic needleless injection system comprising a fluid-filled transmission chamber in which a collapsible variable-volume drug reservoir containing a vol- ume of a liquid drug is arranged, the reservoir being in fluid communication with a jet nozzle. A piston is provided acting on the fluid-filled cavity to thereby reduce the volume of the cavity and there, via the fluid, the volume of the reservoir which correspondingly is collapsed driving out the drug through the nozzle. US patent 5,492,534 discloses a container with two pouches in pressure transmitting relationship.

US 2002/0111589 discloses a drug injection device comprising a variable-volume drug-filled reservoir in the form of a cylindrical container with a piston at an end thereof, a mechanism acting on the piston to drive out drug from the reservoir, the mechanism comprising a spring and a transmission fluid acting on the piston.

In view of the above, it is an object of the present invention to provide a cartridge comprising a drug reservoir, the cartridge being adapted to be used in combination with an expelling device, the cartridge providing an interface between the expelling means of the expelling device and the drug reservoir. In the alternative, it is an object to provide a cartridge which allows a reservoir to be used as an impulse chamber without the necessity to transfer an amount of drug from the reservoir to an impulse chamber.

In the alternative, it is a further object to provide a cartridge which allows a varity of reservoirs to be used in combination with expelling means for which they would normally not be suitable.

In the alternative, it is an object to provide a cartridge which can be used in combination with an impulse generating jet injection (or nebulizing) device.

In the alternative, it is an object to provide a cartridge comprising a conventional glass reservoir containing a liquid drug, the cartridge being simple and compact in design, thus allowing for cost-efficient manufacture, e.g. as a single-use disposable cartridge, the cartridge being suitable for use in combination with an impulse generating jet injection (or nebulizing) device.

In the alternative, it is an object of the invention to provide a cartridge and reservoir configuration which allows a small and handy jet injection device to be provided.

In the alternative, it is an object to provide a jet injection device that can be modeled similar in function and configuration as a conventional pen type injector, to make the patient comfortable with the jet injection device, and so that the jet injection device can easily be utilized by a non-professional user, e.g. a insulin requiring diabetic.

Further objects and advantages of the present invention will be apparent from the below disclosure as well as from the description of exemplary embodiments.

DISCLOSURE OF THE INVENTION

In the disclosure of the present invention, embodiments will be described which will address one or more of the above objects or which will address objects apparent from the below disclosure as well as from the description of exemplary embodiments.

Correspondingly, in a first aspect a cartridge for a delivery device is provided, comprising a housing defining a transmission chamber, the housing comprising a displaceable portion, a drug reservoir comprising a substantially cylindrical body with an axially displaceable piston arranged in the chamber, at least a portion of the cylindrical body being arranged within the transmission chamber, and an outlet for in a situation of use establishing fluid communication with the drug reservoir. The cartridge further comprises a transmission liquid contained in the transmission chamber, the transmission liquid providing a means for transmitting a displacement of the displaceable housing portion to the piston, wherein, in a situation of use, displacement of the displaceable housing portion towards the transmission chamber results in a corresponding displacement of the piston, thereby expelling an amount of drug through the outlet means.

The cylindrical body may e.g. be formed substantially from a polymeric material (or blends thereof) providing a certain flexibility or it may be formed from a substantially non-flexible material such as from glass or a polymeric material (or blends thereof), and it may be arranged substantially within the housing. Advantageously such a reservoir is in the form of a conven- tional glass cartridge as used in a pen-formed injection device, such a reservoir comprising a self-sealing needle-penetratable septum providing an outlet for the cartridge. The cylindrical body may have a circular or non-circular cross-section.

In a further aspect a cartridge for a delivery device is provided, comprising a housing defining a variable-volume transmission chamber or cavity, the housing comprising a displaceable portion suitable for engagement with means for displacing the displaceable housing portion. The cartridge further comprises a variable-volume drug reservoir containing a volume of a liquid drug, the drug reservoir comprising a displaceable portion, at least the displaceable portion of the drug reservoir being arranged within the transmission chamber, an outlet means for, in a situation of use, establishing a fluid communication with the drug reservoir, and a transmission liquid contained in the transmission chamber, the transmission liquid providing a means for transmitting a displacement of the displaceable housing portion to the displaceable reservoir portion. By this arrangement displacement of the displaceable housing portion towards the transmission chamber results in a corresponding volume-reducing dis- placement of the displaceable reservoir portion, whereby an amount of drug is expelled through the outlet means in a situation of use, e.g. when a fluid communication has been established with the drug reservoir.

As long as the displaceable reservoir portion is arranged within the transmission chamber the remaining portion of the reservoir may be arranged fully or partially outside the transmission chamber, however, advantageously the drug reservoir is arranged substantially or fully within the housing surrounded by the transmission liquid. By this arrangement it can be prevented that the pressure in the reservoir rises above the pressure in the surrounding transmission liquid, thereby reducing the risk that the reservoir will deform, fracture or burst.

Apart from protecting the reservoir against damage during application of an expelling force, the cartridge may also be used to provide an interface between expelling means adapted for displacing the displaceable housing portion but which would be unsuitable for displacing a portion of the reservoir.

Thus, in an exemplary embodiment the drug reservoir is in the form of a generally flexible reservoir, substantially the entire reservoir thereby being displaceable. The flexible reservoir may be comprise first and second flexible foil portions sealed together to form an enclosed cavity for containing the drug, the reservoir having a pouch-like configuration, and may ad- vantageously comprise a self-sealing needle-penetratable septum.

The displaceable housing portion may be of any convenient configuration and may represent a smaller or larger portion of the housing. For example, the housing may be in the form of a generally flexible container which can be compressed or it may be in the form of a relatively rigid housing comprising a relatively small portion displaceable relative thereto. Indeed, the housing should be adapted for a volume reduction corresponding to the desired volume reduction of the drug reservoir.

In an exemplary embodiment the displaceable housing portion is in the form of a piston slidably received in the housing. The piston may be received in a substantially cylindrical portion of the housing protruding into the transmission chamber from an opening formed in the housing, the opening allowing a plunger of a delivery device to engage a proximal (i.e. rear) surface of the piston. The plunger may also be formed integrally with the piston and thus be a portion of the housing.

In a further aspect a jet injection assembly is provided comprising a cartridge as described above, in combination with a jet expelling device and an outlet nozzle mounted relative thereto, wherein the outlet nozzle is adapted to be arranged in fluid communication with an interior of the drug reservoir, and the jet expelling device comprises impulse generating means for displacing the displaceable housing portion, thereby reducing the volume of the drug reservoir and thereby expelling an amount of drug through the outlet nozzle. In accordance with the intended the use, the nozzle may be configured to e.g. provide a well-defined jet of liquid for skin-penetration or an aerosol for inhalation.

The term "nozzle" does not imply that a singular nozzle opening is defined, i.e. the nozzle may comprise a number or a system of nozzle openings. In accordance with the intended the use, the nozzle(s) may be configured to e.g. provide a well-defined jet of liquid for skin- penetration or an aerosol for inhalation or to comprise a pointed outlet to help penetrate a skin surface. When used as a jet injection device, the fluid outlet nozzle may be provided with a pointed hollow needle adapted to penetrate a superficial layer of the skin of a user, thereby aiding the jet of drug to create an opening in the skin from the surface to the subcutaneous space. Such a needle may be relatively short, e.g. 1 mm or less.

In an exemplary embodiment the liquid outlet nozzle is adapted to be arranged against the skin of a subject, the impulse generating means being adapted to create a force for injecting the liquid drug through the outlet nozzle and into the subject through the skin. The jet expelling device may further comprise drive means for displacing the displaceable housing portion with a reduced force relative to the impulse generating means. Advantageously the jet injection device comprises means for selectable setting a dose of drug to be injected, means for actuating the impulse generating means and the drive means, and actuatable release means, whereby actuation of the release means first causes release of the impulse generating means thereby expelling a portion of the set dose at a high pressure through the outlet nozzle, followed by release of the drive means for subsequent expelling of the remaining portion of the set dose through the outlet nozzle. In this way a device providing for automatic two-stage jet injection is provided.

To provide a compact and inexpensive-to-produce cartridge, the jet expelling device may comprise a cavity adapted to receive the cartridge in a close fit, the cavity providing the housing with an increased rigidity thereby reducing deformation thereof during jet expelling of drug.

As used herein, the term "drug" is meant to encompass any drug-containing flowable medicine or medicament capable of being passed through a nozzle under high pressure in a controlled manner, such as a liquid, solution, gel or fine suspension. Representative drugs in- elude pharmaceuticals such as peptides, proteins, and hormones, biologically derived or ac- tive agents, hormonal and gene based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form. In the description of the exemplary embodiments reference will be made to the use of insulin. Correspondingly, the term "subcutaneous" infusion is meant to encompass any method of transcutaneous delivery to a subject. Further, the term needle (when not otherwise specified) defines a piercing member adapted to penetrate the skin of a subject.

BRIEF DESCRIPTION OF THE DRAWINGS

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

fig. 1 shows a sectional view of a cartridge for a jet expelling device, and

fig. 2 shows a jet expelling assembly in a sectional view.

In the figures like structures are generally identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following terms such as "upper" and "lower", "right" and "left", "horizontal" and "vertical" or similar relative expressions are used, these only refer to the appended figures and not to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as there relative dimensions are intended to serve illustrative purposes only.

Fig. 1 shows a sectional view of a cartridge 1 comprising a housing 10 and a therein arranged reservoir 50 containing a liquid drug to be expelled.

The reservoir has a general configuration corresponding to a typical standard cartridge used for e.g. insulin. More specifically, the reservoir comprises a columnar housing member 51 having a distal opening closed by a needle-penetratable and self-sealing septum 55 held in place by a metal cap 56, and a proximal opening. A piston 52 is slidably arranged within the housing member, whereby a variable-volume interior drug-filled space is defined by the housing member, the piston and the septum, the moveable piston thereby representing a displaceable portion of the reservoir. The housing member may be manufactured from glass and the septum and piston from an elastomeric material, i.e. corresponding to a standard insulin cartridge. The reservoir may have any desired volume, e.g. around 3 ml as in a standard insulin cartridge or 1.5 ml as in a more compact cartridge.

The cartridge housing comprises a main portion 11 and a lid 21 which in combination forms a transmission chamber 20 adapted to receive a reservoir and to be filled with a. transmission liquid. The housing comprises a protrusion 12 with a distal opening 13 and an inner seal member 16 adapted to sealingly engage the metal cap of the reservoir. The protrusion fur- ther comprises external connection means 14 adapted to engage a nozzle unit 70 (see below), e.g. a thread or a bayonet. The lid comprises an opening 22 from which a distally open cylindrical portion 23 protrudes, a displaceable portion drive piston 24 being slidably arranged there within. The moveable drive piston represents a displaceable portion of the housing 10, the main portion, the lid and the drive piston in combination providing a variable- volume transmission chamber. The lid further comprises a number of support members 25 adapted to engage and support the proximal end of the reservoir, the reservoir thereby being held in place by the support members and the inner seal member. The support members are configured to provide free fluid communication between the distal opening of the reservoir (and thereby the piston) and the transmission chamber.

The transmission chamber further comprises a transmission liquid fully filling the interior of the transmission chamber, e.g. filling the interior of the cylindrical portion 23 and fully supporting the outer surfaces of the reservoir and the cylindrical portion. By this arrangement displacement of the displaceable housing portion (i.e. the drive piston) towards the transmis- sion chamber will due to the incompressible transmission liquid result in a corresponding displacement of the displaceable reservoir portion (i.e. the piston), thereby expelling an amount of drug through outlet means arranged in fluid communication with the interior of the reservoir (see below). In the shown embodiment the drive piston and the reservoir piston have identical displacement-areas such that the two piston moves in tandem, however, the dis- placement-areas may differ thereby providing a "gear-ratio" different from 1 :1 between the two pistons, which may also have cross-sections different from circular.

To properly transmit displacement of the drive piston to the reservoir piston, it is important that the transmission chamber does not deform when pressurized, i.e. when the drive piston is moved inwardly. To prevent this, the housing may e.g. be provided with a number of inter- nal support members (not shown) which interconnects opposed surfaces. Further, the cartridge housing may be supported by external means engaging the outer surface thereof (not shown). Ideally the transmission chamber is free from any gas enclosures, i.e. fully filled by the transmission liquid. In order to secure this during manufacture, the housing may be pro- vided with filling inlet means and venting means for evacuating the enclosed gas (not shown).

In the shown embodiment the housing comprises a main portion and a lid, each provided with a number of functional structures, however, these structures and the associated func- tionality may be provided in any convenient way by any desired number of components.

As described above, the cartridge of the invention will be suitable for use in a jet injection device in which a high impulse force is transmitted to the drug to be expelled by means of impulse generating means, thereby introducing the drug through the skin of a subject.

In the following a situation of use will be described. First the cartridge is mounted in a jet injection device by means not shown, the jet injection device comprising a plunger 90 adapted to engage the proximal surface of the drive piston. The cartridge may e.g. contain insulin. Thereafter a new nozzle unit 70 is connected to the distal protrusion 12, the nozzle compris- ing connection means 71 for engagement with corresponding connection means on the cartridge (e.g. a thread or a bayonet), a proximally (or rearwardly) projecting pointed hollow needle 72 (often termed a back-needle) adapted to penetrate the septum of the reservoir, and a distally facing nozzle 73 in fluid communication with the needle, whereby a fluid communication can be provided between the nozzle and the interior of the reservoir. Before the device is ready for use, the plunger is forwarded a small distance to thereby expel the air in the needle and the nozzle. In the shown embodiment a single nozzle opening is shown, however, a number or a system of nozzle openings may be provided. In accordance with the intended the use, the nozzle(s) may be configured to e.g. provide a well-defined jet of liquid for skin-penetration or an aerosol for inhalation or to comprise a pointed outlet to help pene- trate a skin surface. When used as a jet injection device, the fluid outlet nozzle may be provided with a short pointed hollow needle adapted to penetrate a superficial layer of the skin of a user, thereby aiding the jet of drug to create an opening in the skin from the surface to the subcutaneous space. In many cases it will be desirable if the given dose to be expelled can be selected by the user. Accordingly, the jet injection device may be provided with means for selecting the dose to be injected, i.e. the distance the plunger will be advanced. In case the means for driving the plunger is mechanical (e.g. one or more springs) it will have to be actuated before use, however, the drive means may also be gas-driven. When the dose is selected and the drive means is actuated the user places the nozzle against a skin portion of a subject and releases the drive means whereby the plunger drives the drive piston further into the cartridge, the transmission liquid transmitting the displacement of the drive piston to the reservoir piston thereby driving the set amount of drug out through the nozzle and subsequently through the skin of the subject.

Under static conditions the pressure on the inner and outer surface of the reservoir housing will be the same, whereas under actual dynamic conditions the pressure will rise in the transmission chamber before it rises in the interior of the reservoir, whereby a pressure dif- ference is generated across the reservoir housing wall. However, as the reservoir comprises an essentially incompressible liquid drug, deformation of the reservoir housing will be minimal, this in contrast to the situation in which the impulse from the plunger was applied directly to the reservoir piston.

To initiate an injection, the impulse generator is released thereby driving forward the impulse piston whereby the liquid drug in the impulse chamber is forced from the impulse chamber through the nozzle and punctures the skin of the subject.

The drive means may be adapted to provide a two-stage injection, i.e. a first penetrating burst of drug at a high pressure followed by a subsequent delivery of the remaining amount of drug at a lower pressure. Correspondingly, a jet injection device to be used with the cartridge of the invention may further comprise drive means for displacing the plunger with a reduced force relative to the impulse generating means. For example, such a jet injection device may comprise means for selectable setting a dose of drug to be injected, means for ac- tuating the impulse generating means and the drive means, and actuatable release means, whereby actuation of the release means first causes release of the impulse generating means thereby expelling a portion of the set dose at a high pressure through the outlet nozzle, followed by release of the drive means for subsequent expelling of the remaining portion of the set dose through the outlet nozzle. The impulse and drive means may be separate means, e.g. two different springs, or common means, e.g. a gas supply, controlled to provide the desired varying force.

With reference to fig. 2 a jet expelling assembly will be described, the assembly comprising an expelling portion 101 , a cartridge 201 coupled to the expelling portion, and a nozzle member 270 adapted to be coupled to the cartridge. The expelling portion comprises a housing 110, a dose setting assembly 140 and an impulse generating assembly 150. The cartridge substantially corresponds to the cartridge described with reference to fig. 1 and thus comprises a fluid-filled housing 210 in which are arranged a columnar reservoir 250 with a piston 252, and a cylindrical portion 223 with a drive piston 224. The cartridge is housed in a distal portion 110' of the housing. The dose setting assembly comprises a user actuatable dial member 141 rotationally mounted in a proximal portion 112 of the housing, the dial member comprising a tubular extension being in engagement with a threaded impulse plunger 142, the engagement allowing the dial member to rotate the plunger, the plunger yet being allowed to slide axially relative to the dial member. This relationship may e.g. be provided by the plunger and the bore of the tubular extension having (a) corresponding non- circular cross-sections, this allowing the tubular extension to rotate the plunger, and (b) no structure on the inner surface of the tubular extension engaging the thread of the plunger, this allowing the threaded plunger to slide axially relative to the tubular extension. For exam- pie, the plunger and bore may have one or more longitudinally flattened portions preventing rotation and the surface of the bore may be smooth.

The impulse generating assembly 150 comprises a displaceable transfer member 151 , a spring 152, an actuation lever 153, and a release member 154. The transfer member com- prises a threaded bore adapted to engage the threaded plunger, this allowing the plunger to be moved longitudinally relative to the transfer member as the plunger is rotated by the dial member. For example, when the dial member is rotated clock-wise the plunger is moved in a distal direction relative to the transfer member. The dose setting assembly preferably comprises a mechanism preventing the dial member to be turned anti-clockwise during normal use. If the cartridge is replaceable the dose setting assembly will have to be resettable. The spring engages the proximal end of the transfer member and forces it distally towards the piston. The lever is pivotally connected to the housing and comprises a toothed portion 155 in engagement with a correspondingly toothed portion 156 on the transfer member. The release member is pivotally connected to the housing and comprises a hook 157 adapted to engage a corresponding hook 158 on the transfer tube. In a situation of use a new nozzle member 270 is mounted in fluid communication the reservoir. The user then actuates the impulse generating assembly by pivoting the actuation lever in the distal direction, this resulting in the transfer member being moved proximally against the force of the spring to an energized position in which it is locked by engagement with the release member. Preferably a coupling (not shown) is provided in the actuation lever allowing the lever to be returned to its initial position after actuation as well as allowing the transfer member to move distally without moving the lever. Thereafter the user set a desired dose of drug to be expelled from the reservoir by rotating the dial member a desired number of in- crements, this moving the plunger proximally as described above. The maximum amount of drug which can be selected is determined by the allowed travel of the plunger. In the filled position there should still be a distance between the impulse piston and the transfer tube as the transfer tube should be allowed to accelerate before acting upon the impulse piston to create the desired impulse. Thus a stop mechanism (not shown) may be provided limiting travel of the impulse piston. Now the user places the nozzle against a desired skin surface where after the user releases the release member, this resulting in the transfer member being accelerated distally by the spring, this bringing the distal end of the impulse plunger into engagement with the drive piston, this transmitting an impulse to the cartridge piston via the fluid in the cartridge, whereby a jet of drug is expelled from the reservoir through the nozzle and through the skin and into the subcutis of the patient. Further distal movement of the plunger by means of the spring will then result in expelling of the remaining set dose, the distal position of the plunger being reached when the transfer member engages its distal-most position.

The jet expelling assembly may be a disposable prefilled device as shown, or it may be adapted for used with replaceable cartridges mounted in the distal housing portion.

The jet expelling assembly of fig. 2 comprises a single spring providing both an initial impulse to the impulse chamber and the force to empty the impulse chamber once the skin has been penetrated by a jet of drug. Alternatively a jet expelling assembly for injecting fluid medicament into a patient in a two-stage process may be provided. During the first stage fluid is expelled from the injector under relatively high pressure, to create an opening through the skin of the patient. During the second stage, fluid is infused through the opening into the patient at a lower pressure, and for a longer period of time. For example, US patent 5,911,703, hereby incorporated by reference, discloses a jet expelling assembly with an impulse/drive mecha- nism including two springs which are positioned to urge against the impulse chamber piston as they elongate. The drive mechanism comprises a transfer rod (i.e. corresponding to the transfer member of the above-described fig. 6 embodiment) driven by two coaxially positioned separate springs, which are engaged with the rod. Specifically, the first of the two co- axial springs is an impulse spring which is characterized by a relatively high spring constant and the fact that it is dimensioned to have a relatively short action distance. In comparison with the first spring, the second spring, an injection spring, has a lower spring constant and a longer action distance. Initially, during acceleration of the transfer rod, both the impulse spring and the injection spring push on the rod. However, it is primarily the force of the im- pulse spring that accelerates the rod. The impulse spring expands until the impulse spring is restrained by a spring stop. After the impulse spring is stopped from expanding, the rod continues moving through a coast distance, until the rod collides with the impulse piston. As a result of this collision, the momentum of the transfer rod causes the piston to accelerate very rapidly. This rapid advancement of the piston is referred to as the impulse stage, and is the first of two stages of advancement of the piston. The impulse stage is very brief, e.g. less than about five milliseconds. Due to the rapid advancement of the piston during the impulse stage, the fluid is expelled through the jet nozzle under high pressure creating a hole or an opening in the skin. After the impulse stage, the injection spring continues to expand and push against the transfer rod. The result is a second stage, referred to as the injection stage. During the injection stage, the injection spring exerts a much smaller force against the rod and piston than the force which was exerted on the piston during the impulse stage. Accordingly, fluid medicament is expelled from the impulse chamber at a much lower pressure and at a much lower rate than during the impulse stage. The duration of the injection stage is much longer than the duration of the impulse stage, and can last as long as five seconds, or longer. During the injection stage, fluid medicament is allowed to slowly infiltrate into the subcutaneous tissue. As appears, such a two-spring two-stage mechanism may be used as an alternative to the one-spring mechanism disclosed in present fig. 2.

In the above description of the preferred embodiments, the different structures and means providing the described functionality for the different components have been described to a degree to which the concept of the present invention will be apparent to the skilled reader. The detailed construction and specification for the different components are considered the object of a normal design procedure performed by the skilled person along the lines set out in the present specification.

Claims

1. A cartridge (1 ) for a delivery device, comprising: a housing (10) defining a transmission chamber (20), the housing comprising a dis- placeable portion (24), a drug reservoir comprising a substantially cylindrical body (51 ) with an axially displaceable piston (52) arranged there within, at least a portion of the cylindrical body being arranged within the transmission chamber, an outlet (55) for, in a situation of use, establishing fluid communication with the drug reservoir, a transmission liquid contained in the transmission chamber, the transmission liquid providing a means for transmitting a displacement of the displaceable housing portion to the piston, wherein displacement of the displaceable housing portion towards the transmission chamber results in a corresponding displacement of the piston, thereby expelling an amount of drug through the outlet.

2. A cartridge as in claim 1 , wherein the cylindrical body is formed substantially from glass.

3. A cartridge as in claim 1 , wherein the cylindrical body is formed substantially from polymeric material.

4. A cartridge as in any of claims 1-3, wherein the drug reservoir is arranged substan- tially within the housing.

5. A cartridge as in any of claims 1-4, wherein the drug reservoir contains an insulin formulation.

6. A cartridge as in any of claims 1-5, wherein the outlet comprises a self-sealing nee- dle-penetratable septum (55, 65).

7. A cartridge as in any of claims 1-6, wherein the displaceable housing portion is in the form of a piston (24) slidably received in the housing.

8. A cartridge as in claim 7, wherein the housing comprises an opening, the piston being in the form of a plunger member slidably received in the opening.

9. A cartridge as in any of claims 1-6, wherein the housing comprises an opening (22) and a substantially cylindrical portion (23) protruding into the transmission chamber from the opening, the displaceable housing portion being in the form of a piston (24) slidably received in the cylindrical portion.

10. An assembly comprising a cartridge (201 ) as defined in any of the previous claims, a jet expelling device (101) and an outlet nozzle (270), the outlet nozzle being adapted to be arranged in fluid communication with an interior of the drug reservoir, and the jet expelling device comprising an impulse generating assembly (150) for displacing the displaceable housing portion, thereby reducing the volume of the drug reservoir and thereby expelling an amount of drug through the outlet nozzle.

11. An assembly as in claim 10, wherein the outlet nozzle is adapted to be arranged against the skin of a subject, the impulse generating assembly being adapted to create a force for injecting the liquid drug through the outlet nozzle and into the subject through the skin.

12. An assembly as in claim 10, further comprising a dose setting assembly (140) for selectable setting a dose of drug to be expelled.

13. An assembly as in claim 10, further comprising a drive assembly for reducing the volume of the drug reservoir with a reduced force relative to the impulse generating assembly when a portion of the drug has been expelled by the impulse generating assembly.

14. An assembly as in claim 13, further comprising an actuator for actuating the impulse generating assembly and the drive assembly, a dose setter for selectable setting a dose of drug to be expelled, and an actuatable release, wherein actuation of the release causes the impulse generating assembly to expel a portion of the set dose from the reservoir at a high pressure through the outlet nozzle, followed by subsequent expelling of the remaining portion of the set dose from the reservoir through the outlet nozzle by means of the drive assembly at a lower pressure.

15. An assembly as in any of claims 10-14, wherein the jet expelling device comprises a cavity (110') adapted to receive the cartridge in a close fit, the cavity providing the cartridge housing with an increased rigidity thereby reducing deformation thereof during jet expelling of drug.

16. An assembly as in any of the previous claims, wherein the fluid outlet nozzle comprises a pointed hollow needle adapted to penetrate a superficial layer of the skin of a user.