Drive mechanism for an injection device and an injection device with such a drive mechanism

A drive mechanism for an injection device in which a piston is successively moved in a first axial direction in relation to a medicament cartridge containing a medicament selectively to drive a bung closing a first end of the medicament cartridge into the medicament cartridge to expel medicament through a delivery member located at a second end of the medicament cartridge, the drive mechanism comprising: a base member, a first drive member fixed relative to the base member, a second drive member axially and rotatably moveable relative to the first drive member and a piston member axially moveable relative to the first and second drive member, wherein the second drive member is drivingly connected between the first drive member and the piston member such that rotation of the second drive member in a first direction of rotation relative to the first drive member and the piston member causes the second drive member to move in the first axial direction relative to the first drive member and the piston member to move in the first axial direction relative to both the first and second drive member, and an injection device comprising such a drive mechanism.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application pursuant to 35 U.S.C. §371 of International Application No. PCT/EP2010/060127 filed Jul. 14, 2010, which claims priority to European Patent Application No. 09009214.9 filed on Jul. 15, 2009. The entire disclosure contents of these applications are herewith incorporated by reference into the present application.

FIELD OF INVENTION

The present invention relates to a drive mechanism for an injection device and an injection device with such a drive mechanism.

In particular the present invention relates to improvements in a drive mechanism for a portable injection device for dispensing controlled quantities of a medicament. The invention also relates to an injection device incorporating the improved drive mechanism.

BACKGROUND

Injection devices are known for the self administration of a medicament by patients. For example, those suffering from diabetes may require regular injections of insulin, others may require regular injections of a growth hormone. Injection devices allow the patient to select a dose and to administer that dose. It is known to automate this process so that a user need only press a button and the injection device will dispense a selected dose of medicament. This relieves the patient of the task of controlling the amount dispensed while manually expelling the medicament from the injection device. This is a particular problem for the elderly, the infirm, those suffering from vision difficulties and those suffering from diabetes related problems which impair their faculties.

The medicament is typically contained within a cartridge located within the injection device. The cartridge has a bung or piston at one end which is driven towards a second end of the cartridge to expel the medicament for the injection device. It is a problem that injection devices should be small enough to fit into a jacket pocket or a hand bag without difficulty. At the same time, the injection device must be of a size that enables a piston or the like used to drive the cartridge and to be fully withdrawn from the cartridge to allow for replacement of the cartridge.

The object of the invention is to provide a drive mechanism for an injection device and an injection device with such a drive mechanism by which these conflicting requirements are fulfilled.

SUMMARY

According to a first aspect of the present invention, there is provided a drive mechanism for an injection device in which a piston is successively moved in a first axial direction in relation to a medicament cartridge containing a medicament selectively to drive a bung closing a first end of the medicament cartridge into the medicament cartridge to expel medicament through a delivery member located at a second end of the medicament cartridge, the drive mechanism comprising a base member, a first drive member fixed relative to the base member, a second drive member axially and rotatably moveable relative to the first drive member and a piston member axially moveable relative to the first and second drive members, characterised in that the second drive member is drivingly connected between the first drive member and the piston member such that rotation of the second drive member in a first direction of rotation relative to the first drive member and the piston member causes the second drive member to move in the first axial direction relative to the first drive member and the piston member to move in the first axial direction relative to both the first and second drive members.

Preferably, the second drive member is in screw threaded engagement with the first drive member and the piston member. More preferably, the second drive member comprises a generally annular sleeve member, the sleeve member having a first internal thread for engagement with a corresponding thread on the first drive member, and a second internal thread for engagement with a corresponding thread on the piston member. Advantageously, the first drive member comprises a first axially extending elongate spigot portion having a thread formed about an external surface for engagement with the corresponding first internal thread of the second drive member, and the piston member comprises a piston head and an axially extending piston rod having a thread formed about an external surface for engagement with the corresponding second internal thread of the second drive member.

In a particularly preferred embodiment, the first drive member and the piston member each have an axially extending bore, the mechanism further comprising a support member having a first portion adapted to slidingly engage with the bore of the first drive member and a second portion adapted to slidingly engage with the bore of the piston member, the arrangement being such that the support member prevents the piston member from rotating relative to the first drive member. More preferably, the arrangement is adapted such that when the drive mechanism is fully retracted, the spigot portion of the first drive member is substantially entirely received within the second drive member, and the piston rod is substantially entirely received within the internal bore of the first drive member.

Preferably, the first drive member can be formed as an integral component with the base member.

Preferably, the drive mechanism further comprises drive means for selectively rotating the second drive member in at least the first direction of rotation.

More preferably, the drive means for selectively rotating second drive member comprises an electric motor arranged to drive the second drive member in at least the first direction of rotation.

A plurality of elongate splines may be provided on a surface on the second drive member and the electric motor may be adapted to drive the second drive member through the splines.

Preferably, the electric motor drives the second drive member through one or more gears. In one preferred embodiment, the electric motor drives the second drive member by means of a worm gear which engages with the splines. Alternatively, the electric motor drives the second drive member by means of a spur gear which engages with the splines.

Preferably, the drive mechanism further comprises an electronic control device for controlling the operation of the drive mechanism so as to regulate delivery of the medicament in use.

In accordance with a second aspect of the invention, there is provided an injection device comprising a drive mechanism in accordance with the first aspect of the invention.

DETAILED DESCRIPTION

Like reference numerals will be used to refer to like parts of the injection device.

Referring first toFIGS. 1 to 2, there may be seen part of an injection device comprising a drive mechanism in accordance with a first embodiment of the present invention, indicated generally at10, and a medicament cartridge12.

For the sake of clarity, the medicament cartridge is shown as being transparent in all the drawings so that details of the drive mechanism can be seen within the cartridge. It will be understood that in practice the medicament cartridge may not be transparent.

Although not shown, those skilled in the art will appreciate that the injection device will comprise a main housing and a needle unit including a delivery member in the form of a hollow needle which can be secured to a first end of the main housing. A medicament cartridge12having a first end14and a second end15may be stored in the main housing. When the needle unit is in place, the needle unit pierces a flexible membrane16at the second end15of the medicament cartridge12. A displaceable bung18is located at the first end of the medicament cartridge12when the cartridge is full as shown inFIG. 1. A cover (also not shown) may be provided over the first end of the main housing to protect the needle unit from damage and a user from inadvertent pricking by the needle. The cover also provides a discrete appearance for the injection device.

The drive mechanism comprises a base member20, a first drive member22, a second drive member24, a piston member26, a control device (indicated schematically at28inFIG. 2), and a drive means, indicated generally at30. The base member20may form part of the main housing of the injection device and has a planar portion32, a mounting tab34projecting from the planar portion32for supporting one end of the first drive member22and an annular guide35for slidingly supporting the second drive member24.

The first drive member22has a mounting portion33at one end which can be attached to the mounting tab34of the base member such that the first drive member is fixed both axially and rotationally relative to the base member. The first drive member also has a spigot portion36that extends axially from the mounting portion33towards the medicament cartridge. A screw thread38is formed on the outer surface of the spigot portion36over most of its length.

The second drive member24is in the form of a generally annular sleeve and has a first bore portion40that extends over the majority of its length. A first internal screw thread (not shown) is formed on the surface of the first bore portion for engagement with the thread38on the outer surface of the spigot portion36of the first drive member22. The arrangement is such that rotation of the second drive member24results in the second drive member advancing axially relative to the first drive member towards the second end15of the medicament cartridge12along the thread38.

The end of the second drive member24closest to the medicament cartridge12is partially closed off by means of a wall42in which is formed a second bore portion44of smaller diameter than the first bore portion40. A second internal thread (also not shown) is formed on the surface of the second bore portion44for engagement with a corresponding thread46formed on a piston rod48of the piston member26. The screw thread46on the piston rod48and the second internal thread in the second bore portion44of the second drive member are arranged such that rotation of the second drive member relative to the piston member results in the piston member26advancing axially towards the second end15of medicament cartridge relative to the second drive member24.

It should be noted that the thread38on the spigot portion36of the first drive member22and the thread46on the piston rod48are of opposite hand.

The outer surface of the second drive member24is slidingly received within the annular guide35of the base member which acts to support the second drive member24and to guide its movement in the axial direction. A plurality of axial splines are provided on the outer surface of the second drive member for engagement with a worm gear that forms part of the drive means30for rotating the second drive member as will be described in more detail below.

The piston member26comprises a piston head54which can be received within the medicament cartridge12for contact with the bung18. The piston rod48extends axially away from the piston head54towards the first drive member22and is in screw threaded engagement with the second bore portion44of the second drive member24as has been described above.

An elongate support member56interconnects the first drive member and the piston member and has a first, relatively short portion58and a second, relatively long portion60. The first portion58is dimensioned so as to be slidingly received within a bore62formed in the spigot portion36of the first drive member22. The second portion60of the support member56is dimensioned so as to be slidingly received within a bore64formed in the piston rod48. The profiles of the first portion58of the support member and the bore62in the first drive member are selected so that the support member56cannot rotate relative to the first drive member22. Similarly, the outer profile of the second portion60of the support member56and the bore64in the piston rod are selected so that the piston member26cannot rotate relative to the support member56. Thus the support member56acts as an internal key for preventing the piston member26from rotating relative to the first drive member22when the second drive member24is rotated.

The bore62in the first drive member and the piston rod48are sized so that the piston rod48can be received within the bore62when the drive mechanism is fully retracted.

Rotation of the second drive member24is carried out by the drive means30. The drive means30comprises an electric motor66, a gear train indicated generally at68, a control device (not shown in the figures), and a power source in the form of a battery which provides power for the motor66and the control device by means of cables (not shown).

The electric motor66is mounted to the base member20adjacent to the second drive member24and with the axis of its output shaft arranged generally perpendicular to the axis of rotation of the second drive member24. Drive is transmitted from the electric motor66to the second drive member by means of the gear train68which includes a first, relatively small gearwheel mounted to the output shaft of the electric motor66, a second, relatively large gear wheel in mesh with the first gearwheel, and the worm: gear which is mounted for rotation with the second gear wheel. The worm gear is supported for rotation about an axis that is generally parallel to the axis of rotation of the output shaft of the electric motor66by means of a pair of flanges projecting from the annular guide35of the base member20. To this end the worm gear has a spigot portion at either end, each spigot portion being received in a hole in a respective one of the flanges. The worm gear engages with the splines on the second drive member24through an opening in the wall of he annular guide35.

Part of the second gear wheel is accommodated in a recess provided in the base of the annular guide35, to enable the worm gear to be positioned adjacent the second drive member24. It will also be noted that the second drive member24effectively forms the final gear in the gear train.

It can be seen that rotation of tile output shaft of the motor66in a first direction will be transmitted via the first gear wheel, the second gearwheel, the worm gear and the splines to cause the second drive member24to rotate relative to the first drive member22in the direction of arrow A inFIG. 3. Rotation of the second drive member24results in the second drive member24advancing axially or linearly towards the second end15of the medicament cartridge along the thread38on spigot portion36of the first drive member22and will simultaneously cause the piston member26to advance axially towards the second end15of medicament cartridge relative to both the second drive member24and the first drive member22.

As the piston member26is advanced axially towards the second end15of the medicament cartridge, the piston head54contacts the bung18to move the bung towards the second end of the medicament cartridge to expel medicament. By appropriate control of the electric motor66, the piston member26can be caused to advance towards the second end15of the medicament cartridge by a predetermined amount in order to expel a predetermined dose of medicament in a controlled manner.

Rotation of the output shaft of the motor66in a second direction opposite to the first will result in the second drive member24being rotated relative to the first drive member22in an opposite direction. This will cause the piston member26and the second drive member24to be moved axially away from the second end15of the medicament cartridge, thus retracting the drive mechanism. Operation of the electric motor, and hence movement of the second drive member24and the piston member26is controlled by the control device28. The device28may include a microprocessor (not shown) and a user interface having a display through which information can be displayed to the user and input means by which a user can input instructions, for example to set a required dose of the medicament (also not shown).

Operation of the injection device will now be described.

InFIG. 1the injection device is shown with a medicament cartridge12in position. The medicament cartridge12is full, so that the bung18is positioned close to the first end14of the cartridge and the drive mechanism is fully retracted. In this position, the spigot portion36of the first drive member is almost fully received within the second drive member24and the piston rod48is almost fully received within the bore62of the first drive member and the support member56is accommodated within the bores62,64of the first drive member and the piston rod48, respectively.

When a user wishes to administer a dose of medicament, he prepares the injection device as required and activates the control device which will display various information on the user display, such as the amount of medicament available in the cartridge, for example. The user can then use the input means to set a required dose of medicament. In accordance with a preset algorithm, the control device determines the length of time the motor66must be operated in the first direction in order to move the piston member axially towards the second end15of the cartridge by an amount that will deliver the required dose. Once the user has indicated that he is ready for the dose to be administered, the control device effects delivery by activating the electric motor for the required amount of time.

The above sequence can be repeated a number of times to administer medicament to a user until the medicament cartridge is empty or until it has insufficient medicament to deliver a predetermined minimum dose. At this stage, the drive mechanism will be fully extended in the maximum dispense position as shown inFIG. 2. In order to reset the drive mechanism10and to enable replacement of tile medicament cartridge, the electric motor66is operated in the reverse direction to move the piston member26and the second drive member24axially in a direction away from the second end15of the medicament cartridge12until the drive mechanism is fully retracted as shown inFIG. 1. This can be done in response to an input from a user or automatically by the control device when it detects that the medicament cartridge12is empty or has insufficient medicament to deliver the predetermined minimum dose. The empty medicament cartridge12can then be removed and replaced by a new cartridge.

An alternative embodiment of a drive mechanism10in accordance with invention is now described with reference toFIGS. 1 and 2. The same reference numerals will be used to denote parts which have similar functions in the drive mechanism10.

The main differences are:

the spigot portion36of the first drive member22is formed as an integral part of the base member20;

the annular guide35is also formed as an integral part with the spigot portion36of the first drive member;

an alternative drive means30is used to rotate the second drive member.

In the drive mechanism10the spigot portion36of the first drive member is formed integrally with the mounting tab34on the base member20. Also formed integrally with the tab34and surrounding the spigot portion36is the annular guide35. The annular guide35is spaced from the spigot portion36so that the second drive member24can be slidingly received in a gap formed between the annular guide35and the spigot portion36.

The drive means30comprises an electric motor66which is mounted to the base member20such that the axis of rotation of an output shaft of the motor is substantially parallel with the axis of rotation of the second drive member24. Drive is transmitted from the electric motor to the second drive member24via a series of spur gears. Whilst most of the spur gears in the series have their axes of rotation aligned substantially parallel with the axis of rotation of the second drive member24, it will be noted that the axis of rotation of the final spur gear90in the series is arranged at an angle to the axis of rotation of the second drive member24. The final spur gear also has a spigot that is rotatably supported in a hole in a flange projecting from one side of the annular guide35.

Apart from the differences discussed above, the drive mechanism10is constructed and operates in the same manner as the guide mechanism10described above in relation toFIGS. 1 to 2.

It will be seen that the inventive drive arrangement is very compact when fully retracted but is capable of being extended so as to move the bung18to the maximum dispense position. Furthermore, in accordance with the preferred embodiments, an internal key or support member56can be used to prevent the piston member26from rotating. This arrangement is simpler than that used in known telescopic, threaded drive mechanisms for injection devices in which additional external sleeves are used to prevent the piston member or other components from rotating.

The term “medicament”, as used herein, means a pharmaceutical formulation containing at least one pharmaceutically active compound,

wherein in a further embodiment the pharmaceutically active compound comprises at least one human insulin or a human insulin analogue or derivative, glucagon-like peptide (GLP-1) or an analogue or derivative thereof, or exedin-3 or exedin-4 or an analogue or derivative of exedin-3 or exedin-4.

Exendin-4 for example means Exendin-4(1-39), a peptide of the sequence H His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp-Leu-Ser-Lys-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Lys-Asn-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2.

or an Exendin-4 derivative of the sequence

or a pharmaceutically acceptable salt or solvate of any one of the afore-mentioned Exedin-4 derivative.