An administration mechanism for a medicament delivery device is disclosed having a linearly displaceable medicament delivery member cover, an actuator sleeve, an actuator, wherein the medicament delivery member cover is configured to axially displace the actuator sleeve from an initial position to a distally displaced position thereby displacing the actuator sleeve relative to the actuator, a rotator having a guide structure, a plunger holder, and a plunger rod that is proximally biased. The actuator can engage with the plunger holder in the initial position of the actuator sleeve to prevent the plunger holder from proximal displacement relative to the actuator. The actuator can be released from engagement with the plunger holder by displacement of the actuator sleeve towards the distally displaced position to enable proximal displacement of the plunger holder, the plunger rod and the rotator relative to the actuator. The actuator can rotate the rotator relative to the plunger holder, releasing the plunger rod from the plunger holder.