Auto-injector with active agent container latching

A method for operating an auto-injector for an active agent container, the auto-injector comprising an elongated casing arranged to accommodate the active agent container, a shiftable piston in the active agent container for delivering an active agent and a piston rod operable to displace the piston, a shiftable needle protecting tube for protecting an infection needle, a spring arranged to urge the needle protecting tube, a locking sleeve positioned inside the elongated casing and positionable relative to the elongated casing, the active agent container, and the piston rod, the locking sleeve having a locking tongue protruding elastically outward from the locking sleeve such that a distal end of the locking tongue is positioned radially outward of an outer radial circumference of the locking sleeve in a rest position and arranged to lock the needle protecting tube, and a needle protecting cap arranged to enclose the infection needle and prevent the needle protecting tube from being shifted, the method comprising the steps of:

• a) removing the needle protecting cap from the auto-injector while preventing the active agent container from moving;
• b) pressing the auto-injector onto a tissue and shifting the needle protecting tube backwards into the elongated casing while compressing the spring;
• c) delivering the active agent while a force of a driving spring is acting on the piston via the piston rod;
• d) retracting the auto-injector to remove the injection needle from the tissue;
• e) shifting the needle protecting tube back to its initial state by a force of the spring to cover the injection needle;
• and
• f) positioning the locking tongue behind an end edge of the needle protecting tube formed in the needle protecting tube between a proximal and distal end of the needle protecting tube to secure the needle protecting tube from being shifted relative to the injection needle.