EP2438947A1 — Auto-injector

USPTO Abstract

The invention refers to an auto-injector (1) for administering a medicament (M), comprising: - a chassis (2), a syringe (3) with a hollow needle (4) and a stopper (6) - a drive spring (8) capable of, upon activation: advancing the needle (3), injecting the medicament (M), and retracting the syringe (3) with the needle (4) after delivering the medicament (M), - activating means (20) arranged to lock and release the drive spring (8), wherein the drive spring (8) is a compression spring arranged to be grounded at a distal end (8.1) in the chassis (2) for advancing the needle (4) and for injecting the dose of medicament (M) via a plunger (9) and wherein the drive spring (8) is arranged to have its ground in the chassis (2) switched to its proximal end (8.2) for retracting the syringe (3). A retraction sleeve (10) is axially movable arranged around the syringe (3), wherein the retraction sleeve (10) is fixable in a maximum proximal position for providing ground at the distal end of the drive spring (8), wherein the retraction sleeve (10) is arranged to take the syringe (3) with it when released and translated in distal direction (D), wherein the compression spring (8) is wrapped over the retraction sleeve (10) with its distal end bearing against a thrust face (13) on the retraction sleeve (10) and with its proximal end bearing against a thrust collar (37) arranged to be coupled to the plunger (9) for joint axial translation for advancing the needle (4) and for injecting the dose of medicament (M) and to decouple from the plunger (9) for retraction.