Syringe device with a dose limiting mechanism and an additional safety mechanism

[0001] The present invention relates to an injection device comprising a mechanism to prevent injection of a dose exceeding the set dose. In particular, the present invention relates to an injection device comprising two independent mechanisms to prevent injection of a dose exceeding the set dose.

BACKGROUND OF THE INVENTION [0002] When medications are to be injected into the human body, when the injected dose exceeds the set dose, it can have serious or even fatal consequences. Thus, it is important that the injection device contains means for limiting the injection to the set dose.

[0003] It is an object of the present invention to provide an injection device comprising means for preventing injection of a dose exceeding the set dose. Furthermore, since such means may fail, it is an object of the present invention to provide an injection device comprising a safety mechanism adapted to prevent injection of a dose exceeding the set dose if the preventive means fail.

SUMMARY OF THE INVENTION [0004] The present invention relates to an injection device for injecting a dose of a medicament, which injection device comprises:

• a housing • a dose injection mechanism, comprising:

• a dose setting member rotatable relative to the housing so as to set a dose to be injected, • a piston rod positioned relative to the housing so that the translational movement of the piston rod in the distal direction results in injection of the dose,

• a dose limiting mechanism adapted to interact with the dose injection mechanism to prevent injection of a dose exceeding the set dose; and • a safety mechanism that is so positioned relative to the dose injection mechanism that if the dose limiting mechanism fails, the safety mechanism prevents injection of a dose exceeding the set dose.

[0005] An advantage of the present invention is that if the dose limiting mechanism does not limit the injected dose, the safety mechanism is activated and thus provides additional patient protection. [0006] In one embodiment, the dose limiting mechanism and the safety mechanism are two independent mechanisms working independently of each other.

[0007] In one embodiment, the two mechanisms are adapted to simultaneously prevent injection of a dose exceeding the set dose. In another embodiment, the safety mechanism is activated only if the dose limiting mechanism fails to prevent injection of a dose exceeding the set dose. In one embodiment, the two mechanisms are set up so that even if the dose limiting mechanism fails, the safety mechanism will be injected immediately the dose will not exceed. In another embodiment, the injected dose is slightly higher than the set dose when the dose limiting mechanism fails and the safety mechanism is activated . A slightly higher dose means that the dose change is too small to have serious or fatal consequences.

activated so that the set dose.

[0008] The housing may form a passage for the piston rod, and the passage may have a threaded inner surface engaging the threaded outer surface of the piston rod, the piston rod may be positioned relative to the housing such that rotation of the piston rod relative to the housing causes the piston rod to be displaced with respect to the housing .

[0009] In one embodiment, at least one of the dose limiting mechanism and the safety mechanism is adapted to limit the relative rotational movement between the piston rod and the housing for rotation corresponding to injection of a set dose. This could be the case if the piston rod comprises a threaded outer surface adapted to be connected to the threaded inner surface of the housing. Accordingly, the rotatable locking of the piston rod (relative to the housing) blocks the translational movement of the piston rod relative to the housing.

[0010] The dose limiting mechanism may include at least one first retaining surface adapted to be connected to at least one respective second retaining surface of the housing. Furthermore, rotation of the dose setting member during dose setting may cause the first retaining surface to move away from the second retaining surface, and rotation during injection of the dose may cause the first and second surfaces to move toward each other. In addition, dose injection can be prevented when the first retaining surface rests against the second retaining surface. The dose setting member may include at least one first retaining surface. Alternatively or in addition, the dose setting member may be connected to a cylinder comprising a first retaining surface, said cylinder may be adapted to indicate a set dose. The first and second retaining surfaces may be substantially flat surfaces that may extend in a direction parallel to the axial direction of the device. Alternatively, the retaining surfaces may extend in a plane not transverse to the axial direction, such as a plane perpendicular to the axial direction.

[0011] In one embodiment, the safety mechanism comprises: a stop forming a passage for a piston rod, the stop passage comprising a threaded inner surface for connection with the threaded outer surface of the piston rod; and a driving member forming a passage for the stop, the driving member being rotatably maintained relative to the stop, and further the driving member is connected to the dose setting member such that rotation of the dose setting member during dose setting causes the driver to rotate; wherein the relative rotation between the drive member and the piston rod during dose setting causes the stop to move away from the stop position and the stop to prevent injection of the dose.

[0012] In one embodiment, the injection device is adapted to prevent the setting of a dose that exceeds the amount of medicine present in the container of the injection device. In such embodiments, the piston rod may include a dose retaining surface adapted to be connected to the respective surface of the stop when the set dose corresponds to the amount of medicine in the container of the injection device. Therefore, in such embodiments, the limiter performs two functions, the first function is to prevent the dose setting exceeding the amount of medicine remaining in the container, and the second function is the safety function adapted to prevent injection of a dose exceeding the set dose.

[0013] Furthermore, the injection device may comprise an injection aid system providing an injection force to assist the device operator in pushing the piston in said distal direction to inject a set dose. The injection support system may be adapted to push the plunger distally to inject the dose without user assistance when the user has started the injection.

[0014] The injection support system may include a spring, such as a torsion spring, which is adapted to rotate the drive member relative to the housing. The spring can be preloaded when the stop is in the stopped position. Especially when the spring is pre-stressed, the redundant safety system of the present invention is advantageous because inadvertently relaxing the pre-stressed spring can cause the piston rod to rotate (and therefore move progressively) which corresponds to a lethal dose such as 100 IU (international units) of insulin.

[0015] The invention will now be described in more detail with reference to Fig. 1, which discloses an injection device according to the present invention.

[0016] Fig. 1 shows an injection device 2 comprising a housing 4 and a piston rod 6. The injection device 2 also includes a dose setting member 8 and a drive member 10, which in the figure are combined into a single unit. The injection device further includes a scaled drum 12 showing the set dose through a window 14. The scaled drum 12 has a threaded outer surface 15 adapted to be connected to the corresponding threaded inner surface 16 of the housing. The scaled drum 12 is kept rotatable relative to the drive member 10 through the groove-projection 18. The scaled drum 12 includes a first retaining surface 17 adapted to be connected to the second retaining surface 19 of the housing. The first retaining surface 17 and the second retaining surface 19 constitute the dose limiting mechanism 21. The first retaining surface is moved away from the second retaining surface 19 during dose setting and they are brought together during injection of the dose. When two surfaces lean against each other, the device is protected against injection of medicine.

[0017] The injection device comprises an injection aid system in the form of a pre-tensioned torsion spring 23 extending between the drive member 10 and the proximal part 20 of the housing. Accordingly, when the dose setting member 8 is rotated to set the dose, the spring is tensioned even more.

[0018] The piston rod 6 comprises a threaded outer surface 22 adapted to be connected to the corresponding threaded inner surface of the housing 24 and, accordingly, rotation of the piston rod relative to the housing causes the piston rod to translate in a translational motion relative to the housing. The threaded outer surface 22 of the piston rod also engages with the threaded inner surface 26 of the stop 28, which in Fig. 1 is located in the stop position where the lower surface 30 of the stopper engages with the upper surface 32 of the piston rod guide 34. The lower surface 30 and upper surface 32 constitute a safety mechanism 31. There may be an air gap between the lower surface 30 and the upper surface 32, which allows the limiter and piston rod to rotate by an angle corresponding to a slight increase in the injected dose, e.g. 3 IU (international units) of insulin if the dose limiting mechanism 21 fails when injecting the dose.

[0019] Furthermore, the upper surface 36 of the "end of content" of the stop 28 is adapted to contact the lower surface 38 of the "end of content" of the end portion 40 of the T-shaped piston rod. The surfaces of the "end of content" are adapted to contact when the set dose corresponds to the amount of medicine remaining in the tank (not shown) of the instrument. Therefore, the contact of the "end of content" surface prevents setting a dose that exceeds the amount of medicine remaining in the reservoir. It is understood that the distance between the "end of content" surfaces thus corresponds to the amount of medicine remaining in the reservoir.

[0020] Furthermore, the upper surface 11 of the drum 12 may be adapted to engage the lower surface 13 of the housing when the maximum dose is set. The maximum dose is the highest dose that can be adjusted for each injection (assuming that the injection device contains the required amount of medicine). The maximum dose does not correspond to the "end of content" dose that relates to the remaining amount of medicine in the instrument. Therefore, as long as the remaining amount of medicine in the device is greater than the maximum dose, the "end of content" surfaces will not touch each other during dose setting, while when the remaining amount of medicine in the device is less than the maximum dose, the maximum dose surfaces will not touch. with each other during dose setting, because the "end of content" surfaces prevent further rotation.

[0021] The stop 28 and the drive member 10 are locked against mutual rotation by means of a groove-projection connection 42. Thus, when the piston rod is locked against rotation relative to the housing, mutual rotation between the drive member 8 and the piston rod 6 causes the stop to slide away from the stop position and towards the T-shaped end portion 40 (i.e., top of the drawing). The piston rod is locked against rotation relative to the housing when the piston rod guide 34 is locked against rotation against the housing (not shown) when the piston rod guide 34 and the piston rod are blocked against relative rotation due to the groove-projection connection 44.

[0022] The driving member 12 and the piston rod guide 34 are interconnected by a two-way ratchet mechanism 46 comprising at least one first retaining element 48 formed by the driving member 12 and at least one second retaining element 50 formed by the piston rod guide 34. The bi-directional ratchet mechanism is adapted to allow relative obstructive movement between the drive member 12 and the piston rod guide 34 during dose setting and to ensure that the rotational movement of the drive member during injection of the dose is transmitted to the piston guide guide 34.

[0023] The use of the device is as follows. Initially, the piston rod guide is locked against rotation relative to the housing. The dose setting member is then rotated, which causes the drive member and scaled drum to rotate and the pre-tensioned spring tensions even more. At the same time, the stop moves towards the T-shaped end portion. If the user attempts to set a dose that exceeds the amount of medicine in the instrument, the limiter rests against the T-shaped end portion, and therefore a larger dose cannot be set. The dose is injected by removing the rotation lock between the piston rod guide 34 and the housing, where the tensioned spring forces the drive member to rotate. The rotating drive member forces the piston rod guide to rotate, which again forces the piston rod to rotate. Due to the 44 groove-projection connection, and the threaded connection between the piston rod and the housing, the rotating piston rod is forced to move forward and in this way the medicine is ejected from the device.

NOVO NORDISK A / S

Proxy:

77P25379PL00

EP 1 909 871 B1