Medicament delivery device

An injection device for manually penetrating a needle arranged to the device into an injection site and automatically injecting a medicament mixture, the device comprising:

• a distal housing part;
• a proximal housing part into which a multi-chamber container is disposed, wherein the proximal housing part is configured to be manually displaced into the distal housing part for mixing at least two substances in the multi-chamber container;
• a plunger rod configured to act on a distal stopper arranged inside the multi-chamber container;
• a push button that protrudes from the distal housing part and is interactively connected to the plunger rod;
• an activation member, comprising a tubular flexible locking device releasably connected to the plunger rod;
• a drive force device pre-tensionedly arranged between a distal end surface of the activation member and a proximal end wall of the plunger rod;
• a locking member coaxially arranged around the activation member and distally slidable in relation to the activation member by the proximal housing between a first position, in which the locking member completely surrounds the tubular flexible locking device holding the plunger rod and thereby the drive force device in a pre-tensioned state, and a second position, in which the locking member partially surrounds the tubular flexible locking device;
• a guide rod coaxially arranged within the drive force device between the distal end surface of the activation member and the distal stopper, wherein a proximal portion of the guide rod protrudes through the proximal end wall of the plunger rod determining a first predetermined distance between the proximal end wall and the distal stopper, such that proximal displacement of the push button forces the plunger rod, the activation member, and thereby the guide rod to be proximally displaced, whereby the tubular flexible locking device comes completely out of contact with the locking member and with the plunger rod, thereby enabling the plunger rod to be proximally displaced the first predetermined distance by the force of the pre-tensioned drive force device such that the proximal end wall of the plunger rod hits the distal stopper for providing audible and tactile information that the automatic injection has started.