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

FIELD OF THE INVENTION

0001The present invention relates to a syringe device comprising a mechanism for preventing ejection of a dose exceeding a set dose. In particular the present invention relates to a syringe device comprising two independent mechanisms for preventing ejection of a dose exceeding a set dose.

BACKGROUND OF THE INVENTION

0002When drugs are to be Injected into the human body, It may have serious or even lethal consequences if the injected dose exceeds the set dose. Accordingly, it is important that the syringe devices comprises means for limiting ejection to the set dose.

0003It is an object of the present invention to provide a syringe device comprising means for prevention ejection of a dose exceeding the set dose. Furthermore, as such means may fall, it is an object of the present invention to provide a syringe device comprising a safety mechanism adapted to prevent ejection of a dose exceeding the set dose if the means for preventing fails.

SUMMARY OF THE INVENTION

0004The present invention relates to a syringe device for ejecting a dose of a medicament according to claim 1 or claim 4.

0005An advantage of the present invention is that if a dose limiting mechanism fails to limit the ejected dose, the security mechanism is activated, and, thus, provides an extra safety for the patient.

0006In one embodiment the dose limiting mechanism and the safety mechanism are two independent mechanisms working Independently from each other.

0007In one embodiment the two mechanisms are adapted to simultaneously prevent ejection of a dose exceeding the set dose. In another embodiment the safety mechanism is only activated if the dose limiting mechanism fails to prevent ejection of a dose exceeding the set dose. In one embodiment the two mechanisms are arranged such that even if the dose limiting mechanism fails, the safety mechanism is activated instantaneously such that the ejected dose does not exceed the set dose. In another embodiment the ejected dose is insignificantly larger than the set dose, if the dose limiting mechanism fails and the safety mechanism is activated. By insignificantly larger is meant that the change in dose is too small to have serious or fatal consequences.

0008The housing may define a passage for the piston rod, the passage may have a threaded inner surface for engagement with a threaded outer surface of the piston rod, the piston rod may be arranged with respect to the housing such that rotation of the piston rod relative to the housing causes the piston rod to be displaced translationally relative to the housing.

0009In one embodiment at least one of the dose limiting mechanism and the safety mechanism is adapted to limit relative rotational movement between the piston rod and the housing, to a rotation corresponding to ejection of the set dose. This may be the case, when the piston rod comprises a threaded outer surface adapted to engage a threaded inner surface of the housing. Accordingly, rotational locking of the piston rod (relative to the housing) results in a translational locking of the piston rod relative to the housing.

0010The dose limiting mechanism may comprise at least one first stopping surface adapted to engage at least one corresponding second stopping surface of the housing. Furthermore, rotation of the dose setting member during dose setting causes the first stopping surface to move away from the second stopping surface and rotation during dose ejection may cause the first and the second surface(s) to move towards each other. Furthermore, ejection of a dose is prevented when the first stopping surface abut the second stopping surface. The dose setting member may comprise the at least one first stopping surface. Alternatively, or as a supplement, the dose setting member may be coupled to a cylinder comprising a first stopping surface, and said cylinder may be adapted to indicate the set dose. The first and second stopping surfaces may be substantially plane surfaces which may extend in a direction parallel with the axial direction of the syringe device. Alternatively, the stopping surfaces may extend in a plane transverse to the axial direction, such as a plane orthogonal to the axial direction.

0011In one embodiment the safety mechanism comprises: a limiter defining a passage for the piston rod, the passage of the limiter defining a threaded inner surface for engagement with the threaded outer surface of the piston rod, and a driver defining a passage for the limiter, the driver being rotationally retained in relation to the limiter, the driver being coupled to the dose setting member such that rotation of the dose setting member during dose setting causes the driver to rotate, wherein relative rotation between the drive and the piston rod during dose setting causes the limiter to move away from a stopping position wherein the limiter prevents ejection of a dose.

0012In one embodiment the syringe device is adapted to prevent setting of a dose which exceeds the amount of a medicament in a reservoir of the syringe device. In such embodiments, the piston rod may comprise an end-of-dose stopping surface adapted engage a corresponding surface of the limiter, when the set dose corresponds to the amount of the medicament in the reservoir of the device. Accordingly, in such embodiments the limiter serves two functions, a first function being prevention of setting of a dose exceeding the amount of the medicament left in the reservoir and a second function being a security function adapted to prevent ejection of a dose exceeding the set dose.

0013Moreover, the syringe device may comprise an ejection assisting system for providing an ejection force for assisting an operator of the device in forcing the piston in said distal direction so as to eject the set dose. The ejection assisting system may be adapted to force the piston in the distal direction so as to eject the dose, without the aid of the user, when the user has initiated the ejection.

0014The ejection assisting system may comprise a spring, such as a torsional spring which is arranged to rotate the driver relative to the housing. The spring may be pre-strained when limiter is in the stopping position, Especially when the spring is pre-strained, the redundant security system of the present invention is advantageous, as accidental un-straining of the pre-strained spring, may cause the piston rod to rotate (and thus move translationally) corresponding to a lethal dose, such as 100 IU of insulin.

DESCRIPTION OF THE DRAWINGS

0015The invention will now be described in further detail with reference to <figref idref="f0001">Fig. 1</figref>, which discloses a syringe device according to the present invention.

0016<figref idref="f0001">Fig. 1</figref> shows a syringe device 2 comprising a housing 4 and a piston rod 6. The syringe device 2 also comprises a dose setting member 8 and a driver 10, which in the figure are combined into one single unit. The syringe device further comprises a scale drum 12 for indicating a set dose through a window 14. The scale drum 12 has a threaded outer surface 15 adapted to engage a corresponding threaded inner surface 16 of the housing. The scale drum 12 is rotationally retained relative to the driver 10 through a grove-tongue engagement 18. The drum scale 12 comprises a first stopping surface 17 adapted to engage a second stopping surface 19 of the housing. The first stopping surface 17 and the second stopping surface 19 constitutes the dose limiting mechanism 21. The first stopping surface is moved away from the second stopping surface 19 during dose setting and towards each other during dose ejecting. When the two surfaces abut each other, the device is prevented from ejecting the medicament.

0017The syringe device comprises an ejection assisting system in the form of a pre-strained torsional spring 23 extending between the driver 10 and a proximal part 20 of the housing. Accordingly, when the dose setting member 8 is rotated to set a dose, the spring is strained even further.

0018The piston rod 6 comprises a threaded outer surface 22 adapted to engage a corresponding threaded inner surface of the housing 24 and accordingly rotation of the piston rod relative to the housing causes the piston rod to move translationally in relation to the housing. The threaded outer surface 22 of the piston rod also engages a threaded inner surface 26 of a limiter 28, which in <figref idref="f0001">Fig. 1</figref> is positioned in a stopping position wherein a bottom surface 30 of the limiter engages an upper surface 32 of a piston rod guide 34. The bottom surface 30 and the upper surface 32 constitute the safety mechanism 31. An air gap may be provided between the bottom surface 30 and the upper surface 32 which allows the limiter and the piston rod to rotate an angel corresponding an insignificant increase in the injected dose e.g. 3 IU of insulin, if the dose limiting mechanism 21 fails during dose injection.

0019Moreover, an upper end-of-content surface 36 of the limiter 28 is adapted to engage a lower end-of-content surface 38 of a T-shaped end part 40 of the piston rod. The end-of-content surfaces are adapted to engage, when the set dose corresponds to the amount of a medicament remaining in a reservoir (not shown) of the device. Accordingly, the engagement of the end-of-content surfaces prevents setting of a dose exceeding the amount of a medicament remaining in the reservoir. It will be appreciated that the distance between the end-of-content surfaces thus corresponds to the amount of the medicament remaining in the reservoir.

0020Moreover, an upper surface 11 of the drum 12 may be adapted to engage a lower surface 13 of the housing, when the maximum dose is set. The maximum dose is the largest dose which may be set for each ejection (provided that the syringe device comprises the required amount of medicament). The maximum dose does not correspond to the end-of-content dose which relates the remaining amount of a medicament in the device. Accordingly, as long as the remaining amount of medicament in the device is larger than the maximum dose, the end-of-content surfaces will not abut each other during dose setting, whereas when the remaining amount of medicament in the device is lower than the maximum dose, the maximum dose surfaces will not abut each other during dose setting, as the end-of-content surfaces prevents further rotation.

0021The limiter 28 and the driven 10 are locked for relative rotation by means of grove-tongue engagement 42. Thus, when the piston rod is locked for rotation relative to the housing, a relative rotation between the driver 8 and the piston rod 6 causes the limiter to move away from the stopping position and towards the t-shaped end part 40 (i.e. upwards in the figure). The piston rod is locked for rotation relative to the housing when the piston rod guide 34 is locked for rotation relative to the housing (not shown), as the piston rod guide 34 and the piston rod are locked for relative rotation due to the grove-tongue engagement 44.

0022The driver 12 and the piston rod guide 34 are interconnected by a two-way ratchet mechanism 46 comprising at least one first retaining member 48 defined by the driver 12 and at least one second retaining member 50 defined by the piston rod guide 34. The two-way ratchet mechanism is adapted to allow relative rotational movement between the driver 12 and the piston rod guide 34 during dose setting and to ensure that rotational movement of the driver during dose ejection is transferred to the piston rod guide 34.

0023The use of the device is as follows. Initially the piston rod guide is locked for rotation relative to the housing. Then the dose setting member is rotated, which causes the driver and the drum scale to rotate and the pre-strained spring to be strained even further. At the same time the limiter moves towards the T-shaped end part. If the user tries to set a dose exceeding the amount of medicament in the device, the limiter abuts the T-shaped end part whereby an even larger dose cannot be set. The dose is ejected by removing the rotational lock between the piston rod guide 34 and the housing whereby the strained spring forces the driver to rotate. The rotating driver forces the piston rod guide to rotate which again forces the piston rod to rotate. Due to the grove-tongue engagement 44 and the threaded Interconnection between the piston rod and the housing, the rotating piston rod is forced to move forward and thus the medicament is expelled from the device.