Single use injection device

Single-use injection device comprising an injection cylinder for receiving a liquid medium, an inner chamber located inside the injection cylinder, an injection needle attached to the injection cylinder, an inlet area located adjacent to the injection needle, the injection device having a longitudinal axis which extends in the direction of the injection needle, a piston that can slide inside the injection cylinder and a piston rod, the piston being movably linked to the piston rod which extends in a direction opposite to the injection needle, and an anti-reuse device that is actuated by the medium moved by the piston and that is arranged in the inlet area of the injection cylinder, a ring-shaped retaining member having an opening, the ring-shaped retainer being located in the injection cylinder between the injection needle and the piston, the anti-reuse device including a switching member having a sealing section with a larger cross-sectional area than a passage cross-section of the opening in the ring-shaped retaining member, the sealing section being retained in a rest position by means of the ring-shaped retaining member which is elastically deformable in at least one of a radial direction and in a direction of the injection needle on the side of the ring-shaped retaining member that faces the piston, and the switching member can be moved from the rest position into a locking position wherein the sealing section is located on the side of the ring-shaped retaining member that faces the injection needle, the ring-shaped retaining member providing a sealing stop for the switching member in the direction of the piston, and that a reception area for at least the sealing section of the switching member is arranged between the ring-shaped retaining member and the injection needle, the ring-shaped retaining member (21) being made of an elastically restorable material and is held in position on a housing (18) of the anti-reuse device (7) that is set inside the inner chamber (3) of the injection cylinder (2) and is made of a harder material than the ring-shaped retaining member (21), the switching member (22) includes a guiding element (23) that is adjacent to the sealing section (48) that is moveable in a guiding path (49) located in the injection cylinder (2), a guiding length between the guiding element (23) and the guiding path (49) being longer than at least the distance between the rest and locking positions of the switching member (22).