Drive mechanism of a drug delivery device

A drug delivery device for dispensing a dose of a medicament, the drug delivery device comprising:

• a housing comprising a radial stop;
• a cartridge at least partially filled with the medicament and being arranged in the housing or in a cartridge holder fixed to the housing;
• and
• a drive mechanism comprising
• a piston rod to operably engage with a piston of the cartridge to displace the piston in a distal direction along a longitudinal axis of the housing,
• a last dose sleeve rotatably supported in the housing and being selectively engageable with a user operable dose setting member for setting the dose, wherein the last dose sleeve is configured to be coupled to the dose setting member during dose setting and to be decoupled from the dose setting member during dose dispensing, wherein the last dose sleeve is axially fixed relative to the housing, and
• a last dose member threadedly engaged and rotatable relative to the housing, rotationally locked to the last dose sleeve, and axially displaceable relative to the last dose sleeve, wherein the last dose member comprises a radial counter stop configured to engage with the radial stop to prevent rotation of the last dose member;
• wherein the last dose sleeve is hollow, and at least one axially extending clutch member extending through the last dose sleeve is axially displaceable relative to the last dose sleeve for selectively engaging the dose setting member with the last dose sleeve exclusively during the dose setting.

A method of operating a drug delivery device, the method comprising:

• setting a dose of medicament to be dispensed by the drug delivery device by operating a dose setting member, thereby causing a last dose sleeve axially fixed relative to a housing of the drug delivery device to rotate through the housing of the drug delivery device while a last dose member threadedly engaged to the housing of the drug delivery device, rotatable relative to the housing of the drug delivery device, and rotatably locked to the last dose sleeve advances axially through the housing of the drug delivery device, the last dose member being configured to inhibit rotation of the last dose sleeve to inhibit the dose from exceeding an amount of medicament remaining in the drug delivery device, a radial counter stop of the last dose member being configured to abut a radial stop on the housing of the drug delivery device, thereby inhibiting rotation of the last dose sleeve relative to the housing of the drug delivery device, wherein the last dose sleeve is hollow, and at least one axially extending clutch member extending through the last dose sleeve is axially displaceable relative to the last dose sleeve for selectively engaging the dose setting member with the last dose sleeve exclusively during dose setting;
• and
• dispensing the dose without causing the last dose member to advance axially through the housing while the last dose member is decoupled from the dose setting member.