Auto-injector

An auto-injector for administering a dose of a liquid medicament, comprising:

• an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice intended to be applied against an injection site, wherein the syringe is slidably arranged with respect to the housing,
• a spring capable of, upon activation:
• pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end,
• operating the syringe to supply the dose of the medicament, and
• retracting the syringe with the needle into the covered position after delivering the medicament,
• an activating means arranged to lock the spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring for injection,
• wherein the spring comprises a single drive spring in a shape of a compression spring arranged to be grounded in the housing at a distal end of the drive spring for advancing the needle and for injecting the dose of the medicament via a plunger,
• wherein a proximal end of the drive spring is grounded in the housing and the distal end of the drive spring is released from its ground in the housing for retracting the syringe,
• wherein a retraction sleeve is axially movable arranged in the housing, wherein the drive spring is arranged inside the retraction sleeve with the distal end of the drive spring bearing against a distal end face of the retraction sleeve and with the proximal end of the drive spring bearing against a thrust face of a decoupling member,
• wherein at least one resilient decoupling arm is arranged at the decoupling member, the decoupling arm arranged for bearing against a first shoulder of the plunger in a proximal direction,
• wherein the resilient decoupling arm is supportable by an inner wall of the retraction sleeve in order to prevent the decoupling arm from being flexed outward and slip past the first shoulder,
• wherein at least one aperture is arranged in the retraction sleeve allowing the decoupling arms to be flexed outward by the first shoulder thus allowing the first shoulder to slip past the decoupling arm in the proximal direction,
• wherein the aperture extends at least almost to a position of the decoupling arms in an as delivered state,
• wherein the aperture is arranged to be angularly misaligned with respect to the decoupling arm when the retraction sleeve is in a proximal position, and
• wherein the aperture is arranged to rotate so as to align with the decoupling arms upon translation of the retraction sleeve out of the proximal position in a distal direction.