Drug Delivery Device with Piston Rod Coupling

A drug delivery device adapted to receive a cartridge (380) comprising a cylindrical body portion, a distal outlet portion and an axially displaceable piston, the drug delivery device comprising:

• a housing,
• a cartridge holder adapted to receive and hold a cartridge,
• an expelling assembly comprising:
• a piston rod comprising an external thread and being adapted to engage and axially displace a piston in a loaded cartridge in a distal direction to thereby expel a dose of drug from the cartridge,
• a nut portion arranged non-moveable relative to the housing and comprising a threaded bore being in rotational engagement with the external thread of the piston rod,
• a primary drive element arranged in non-rotational engagement with the piston rod, the piston rod being axially moveable relatively to the primary drive element, whereby rotation of the primary drive element provides that the piston rod is moved axially through the nut portion,
• a drive assembly adapted to rotate the primary drive element,
• a drive coupling being actuatable between:
• a resetting state in which the piston rod can be moved proximally, and
• an operational state in which the primary drive element can drive the piston rod distally,
• user operated actuation structure actuatable from a loading state to an operational state, wherein:
• the drive coupling is actuated from the resetting state to the operational state when the actuation structure is actuated from the loading state to the operational state,
• wherein the primary drive element is not moved axially relative to the housing when the drive coupling is actuated.