An autoinjector (100') for expelling a single dose of drug from a held cartridge (600) comprising a piston (630). The autoinjector comprises a base (220, 200') comprising a base thread component (204') and a plunger (310, 400) configured to be moved by a force provided by an actuator (330) and adapted for cooperation with the piston (630). A needle shield (350, 380') is axially movable from an initial extended position via a triggering position to a trigger release position. The needle shield (350, 380') is operatively coupled to a plunger release element (320') cooperating with the plunger (310, 400) to define a releasable retaining mechanism that retains the plunger release element (320') threadedly engaged with the base thread component (204') in a predefined relative rotational and axial position and against rotational bias provided by the actuator (330). The needle shield (350, 380') is configured for operating the retaining mechanism to release the retaining of the plunger release element (320', 1320) and base thread component (204', 1204) from the predefined relative rotational and axial position upon the needle shield (350, 380') being moved into its trigger release position. As the needle shield (350, 380') is moved from the initial extended position to the triggering position, a pair of cooperating means (388',328') operatively couples the needle shield (350, 380') with the plunger release element (320') to rotate the plunger release element against the rotational bias provided by the actuator (330).La présente invention concerne un injecteur automatique (100) destiné à expulser une dose unique d'un médicament à partir d'une cartouche maintenue (600) comprenant un piston (630). L'injecteur automatique comprend une base (220, 200') comprenant un composant de filetage de base (204') et un piston plongeur (310, 400) conçu pour être déplacé par une force fournie par un actionneur (330) et adaptée pour coopérer avec le piston (630). Une protection d'aiguille (3
