Abstract: The present disclosure refers to a system for a drug delivery device comprising a housing and a cartridge holder which may contain a cartridge filled with a medicament. The housing and the cartridge holder comprise a coding interface for dedicating a certain cartridge to a certain housing and a bayonet type attachment interface for releasably attaching the cartridge holder to the housing by an attachment movement comprising a first stage and a second stage. The system further comprises at least one compliant spring member arranged and designed such that it is strained during the first and/or the second stage of the attachment movement at least if the housing coding element does not match the holder coding element, and wherein the compliant spring member is arranged and designed to move the cartridge holder relative to the housing in a direction contrary to the attachment movement when relaxing.

Abstract: The disclosure relates to a cartridge assembly for a drug delivery device, the cartridge assembly comprising a cartridge containing a drug; a cartridge holder, the cartridge holder defining an interior cartridge holding section, where the cartridge is arranged within the cartridge holding section, wherein the cartridge holder comprises a distal region with a needle connector arranged at a distal end of the distal region and a main body region; a fixing feature which is arranged at the distal region; and a region with reduced mechanical stiffness compared to the stiffness of the main body region, the region with reduced mechanical stiffness being integrated into the distal region and arranged between the needle connector and the fixing feature, such that when the cartridge is moved in a proximal direction, an emerging load is transferred from the cartridge to the fixing feature and to the main body region in the proximal direction.

Abstract: A drug delivery device is proposed, comprising: a housing; a drive mechanism; a cartridge containing a drug, the cartridge being retained in a defined position relative to the housing, wherein the drive mechanism is configured to dispense drug from the cartridge; a cartridge bias system, which comprises at least one resilient member and at least one rigid force transfer body, wherein the rigid force transfer body is movably retained in the housing, wherein the cartridge bias system is arranged and configured to exert a force on the cartridge to maintain the cartridge in the defined position, wherein the force is provided by the at least one resilient member, and wherein the rigid force transfer body is operatively connected to the at least one resilient member such that the force is reacted by the rigid force transfer body. Further, a method to modify a drug delivery device is disclosed.