Patent ID: 7815598

Claim:
An injection device for use with a two-chamber ampoule, comprising: a front casing part with which the two-chamber ampoule can be associated; a rear casing part coupled to the front casing part; a retainer positioned within the rear casing part and axially slidable relative to the rear casing part; a threaded rod to which the retainer is rotatably coupled such that rotation of the threaded rod moves the retainer axially in a dispensing direction, wherein the threaded rod is not axially movable relative to the rear casing; a piston rod and an associated piston arranged proximate a distal end of the piston rod; a spring operably coupled between the retainer and a proximal end of the piston rod; wherein the threaded rod is rotated to move the retainer, spring and piston rod in the dispensing direction, whereby the piston rod moves the piston in the dispensing direction until blending is achieved, creating a blended dose; wherein dispensing of the blended dose is performed by releasing the spring to drive the piston rod and piston in the dispensing direction; wherein the spring is biased and the piston rod is released when at least one holding element is released; wherein the at least one holding element engages with a groove in the piston rod and is fixed relative to the piston rod during the blending movement; wherein the at least one holding element is pressed into the groove in the piston rod by a blocking element at a position of the piston rod which is reached at the end of the blending movement; and wherein the blocking element protrudes through a window introduced in the rear casing part.