A cartridge system for use with a drug delivery device (100′), comprising: —a pre-filled cartridge comprising: a) a cartridge body (210) accommodating a drug, b) a piston (250) slidably disposed in the cartridge body (210) and configured for providing a proximal seal, the piston (250) comprising: b1) a piston first member (260) comprising a first material and forming a distal end, a proximal end and a sealing periphery in contact with the cartridge body (210), wherein the distal end is in contact with the drug and wherein the proximal end of the piston first member (260) includes a proximally facing opening, and b2) a piston second member (270) comprising a material of lower compressibility compared to the first material, the piston second member (270) comprising a sleeve-formed portion arranged in the proximally facing opening of the piston first member (260), wherein the piston second member (270) comprises a proximally facing opening forming a socket； and—a plug unit (280) coupleable or coupled into the socket of the piston second member (270), wherein the plug unit (280) comprises an electronic sensor unit (290) configured to determine the axial position of the piston (250) within the cartridge body (210) and wherein the plug unit (280) is at least partially received within the proximally facing opening of the piston first member (260).Un système de cartouche destiné à être utilisé avec un dispositif d'administration de médicament (100'), comprenant : - une cartouche pré-remplie comprenant : a) un corps de cartouche (210) contenant un médicament, b) un piston (250) disposé de manière coulissante dans le corps de cartouche (210) et conçu pour fournir un joint d'étanchéité proximal, le piston (250) comprenant : b1) un premier élément de piston (260) comprenant un premier matériau et formant une extrémité distale, une extrémité proximale et une périphérie d'étanchéité en contact avec le corps de cartouche (210), l'extrémité distale étant en contact avec le médicame
