Drug delivery device

A drug delivery device comprising:

• a syringe from which a needle extends;
• an inner sheath adapted to be movable between a retracted position in which the needle projects beyond a distal end of the inner sheath and an extended position in which the needle is covered by the inner sheath;
• a support sheath adapted to hold the syringe and to hold the inner sheath in the retracted position as well as in the extended position;
• a piston rod that is movable from a first position in which the piston rod is retracted, to a second position in which a drug delivery process is finished, and
• an actuation head that is coupled on a proximal end of the piston rod;
• a first locking element formed by a circumferential end portion of the actuation head, the first locking element extending in a distal direction, the first locking element having one or more latching elements;
• and
• a second locking element formed by a proximal section of the support sheath, the second locking element extending in a proximal direction,
• wherein the second locking element has a plurality of latching recesses designed on a plurality of curved portions formed on an outer wall of the second locking element, each latching recess being spaced apart from other latching recesses of the plurality of latching recesses and being formed on a respective curved portion of the plurality of curved portions,
• wherein the first locking element has a double wall comprising a first inner wall and a first outer wall, the first inner wall having an outer circumference smaller than an inner circumference of the outer wall of the second locking element, and the first outer wall having an inner circumference larger than an outer circumference of the outer wall of the second locking element, and
• wherein, when the piston rod is in the second position, a recess arranged between the first outer wall and the first inner wall of the first locking element is configured to receive the outer wall of the second locking element so that each of the latching recesses of the second locking element receives a respective latching element of the first locking element.

A method of delivering drug, the method comprising:

• moving a piston rod of a drug delivery device from a first position with respect to a syringe to a second position with respect to the syringe to dispense a drug from the syringe through a needle connected to the syringe;
• and
• locking an actuation head coupled on a proximal end of the piston rod when the piston rod reaches the second position, by engaging one or more latching elements arranged on an inner surface of an outer wall of the actuation head with a plurality of latching recesses formed on an outer surface of a support sheath that holds the syringe, and
• wherein moving the piston rod from the first position to the second position causes an inner sheath of the drug delivery device to move from a retracted position in which the needle projects beyond a distal end of the inner sheath to an extended position in which the needle is covered by the inner sheath.