An administration assembly for a medicament delivery device, comprising: - an elongated tubular delivery member cover, - a cartridge holder designed to accommodate a medicament cartridge, the cartridge holder having a radially flexible and radially inwards extending cartridge blocking protrusion configured to prevent the medicament cartridge from moving proximally until being subjected to a proximally directed force larger than a threshold value, - a needle assembly comprising a double-edged needle having a proximally extending needle portion and a distally extending needle portion, wherein the needle assembly is configured to be assembled with the cartridge holder so that the distally extending needle portion extends into the cartridge holder, characterised in: - an administration mechanism including an actuator sleeve, and an actuator received by the actuator sleeve and configured to be axially displaceable relative to each other, and a plunger holder, and a plunger rod configured to be proximally biased, the plunger holder being configured to receive the plunger rod, wherein a distal end of the delivery member cover is configured to face the actuator sleeve so that distal movement of the delivery member cover causes the actuator sleeve to move in the distal direction, wherein the actuator has a second flexible radially inwards extending portion prevented from flexing radially outwards by the inner surface of the actuator sleeve when the actuator sleeve is in its initial position, such that the flexible radially inwards extending portion bears against a radial surface of the plunger holder in an initial extended position of the delivery member cover, the radial surface preventing the plunger holder from proximal displacement due to biasing as long as the actuator sleeve prevents the second flexible radially inwards extending portion from flexing radially outwards, wherein the delivery member cover is configured to be linearly displaced in the distal direction relative to the cartridge holder, and wherein the delivery member cover is configured to activate the administration mechanism when moved in the distal direction, causing the administration mechanism to move the cartridge holder and the double-edged needle in the proximal direction to provide auto-penetration, and to subsequently move the plunger rod in the proximal direction inside the cartridge holder with a force larger than the threshold value to disengage the cartridge blocking protrusion from the medicament cartridge. - an elongated tubular delivery member cover, - a cartridge holder designed to accommodate a medicament cartridge, the cartridge holder having a radially flexible and radially inwards extending cartridge blocking protrusion configured to prevent the medicament cartridge from moving proximally until being subjected to a proximally directed force larger than a threshold value, - a needle assembly comprising a double-edged needle having a proximally extending needle portion and a distally extending needle portion, wherein the needle assembly is configured to be assembled with the cartridge holder so that the distally extending needle portion extends into the cartridge holder, characterised in: - an administration mechanism including an actuator sleeve, and an actuator received by the actuator sleeve and configured to be axially displaceable relative to each other, and a plunger holder, and a plunger rod configured to be proximally biased, the plunger holder being configured to receive the plunger rod,