A drug delivery device (1) is provided comprising a housing (4) comprising a distal end and a proximal end and a cartridge (3) adapted and arranged to contain at least one dose of a drug (16), a bung (5) being movably arranged within the cartridge (3). In an initial state of the device (1), the bung (5) is arranged in a proximal end position with respect to the cartridge (3). The device (1) further comprises a piston rod (9) adapted and arranged to move the bung (5) in the distal direction with respect to the cartridge (3) for delivering a dose of the drug (16). The device (1) further comprises a mechanism operable such that, after a dose delivery operation was completed, the piston rod (9) is moved into the proximal direction with respect to the bung (5) by a back off distance (D), wherein in the initial state, a distance between a distal end of the piston rod (9) and a proximal end of the bung (5) is greater than zero, with the distance between the piston rod (9) and the bung (5) in the initial state being defined by the back off distance (D).Furthermore, a method for assembling a drug delivery device (1) is provided.本發明係提供一藥物傳送裝置(1),藥物傳送裝置(1)係包含一包含一遠端及一近端之殼體(4)以及一被調適且配置以含有至少一劑量的一藥物(16)之匣(3),一塞件(5)被可移動地配置於匣(3)內。在裝置(1)的一初始狀態中,塞件(5)相對於匣(3)配置於一近端位置。裝置(1)進一步包含一活塞桿(9),活塞桿(9)被調適且配置以相對於匣(3)在遠末方向移動塞件(5)以供傳送一劑量的藥物(16)。裝置(1)進一步包含一機構,該機構可操作以在一劑量傳送操作完成後使得活塞桿(9)相對於塞件(5)移動達一後退距離(D)進入近鄰方向,其中在初始狀態中,活塞桿(9)的一遠端與塞件(5)的一近端之間的一距離係大於零,其中在初始狀態中之活塞桿(9)與塞件(5)之間的距離係由後退距離(D)所界定。尚且,本發明提供一用於組裝一藥物傳送裝置(1)之方法。1‧‧‧藥物傳送裝置2‧‧‧匣固持件3‧‧‧匣4‧‧‧殼體5‧‧‧塞件7A‧‧‧插入件7B‧‧‧驅動機構9‧‧‧活塞桿10‧‧‧調整構件11‧‧‧支承表面13‧‧‧驅動機構14‧‧‧致動構件15‧‧‧彈簧構件16‧‧‧藥物17‧‧‧遠端18‧‧‧近端
