Medicament delivery device

1. A medicament delivery device having a proximal end and a distal end, the medicament delivery device comprising:

a front housing and a rear housing interconnected and axially displaceable relative to each other between an extended position and a retracted position, wherein an axial displacement of the front housing relative to the rear housing sets a dose to be delivered;

a plunger rod configured to act on a plunger of a medicament container;

a drive mechanism configured to drive the plunger rod;

an actuator operably connected to each of the front and rear housings and axially movable in the front and rear housings between a proximal end position and a distal end position, wherein the actuator is biassed by a first biassing element toward the distal end position;

a drive sleeve releasably connected to the actuator and configured to act on the drive mechanism to drive the plunger rod;

a locking ring rotatably arranged at a distal end of the rear housing and in threaded connection with an outer surface of the actuator, wherein the locking ring is prevented from axial movement relative to the rear housing; and

a release button movably disposed on the rear housing between an active state and an inactive state, wherein the release button in the active state allows unidirectional rotational movement of the locking ring relative to the rear housing such that the actuator is axially movable toward the proximal end position by rotational movement of the locking ring, and the release button in the inactive state allows bidirectional rotational movement of the locking ring relative to the rear housing such that the actuator is axially movable toward the proximal end position or the distal end position by rotational movement of the locking ring.

2. The medicament delivery device of claim 1 , wherein the front and rear housings are interconnected and axially displaceable relative to each other through an outer thread on the front housing and an inner thread on the rear housing.

3. The medicament delivery device of claim 1 , wherein the drive sleeve is biassed toward the distal end of the medicament delivery device by a second biassing element.

4. The medicament delivery device of claim 3 , wherein the first and second biassing elements include compression springs.

5. The medicament delivery device of claim 3 , wherein the first biassing element comprises a compression spring, and the second biassing element comprises a torsion spring.

6. The medicament delivery device of claim 1 , wherein the outer surface of the actuator includes dose indicators, and the locking ring has a dose window through which the dose indicators are visible.

7. The medicament delivery device of claim 1 , further comprising a transparent locking ring cover configured to hold the locking ring axially immovable relative to the rear housing.

8. The medicament delivery device of claim 1 , wherein the drive mechanism comprises:

a drive nut fixedly arranged near a proximal end of the front housing, the drive nut comprising a through bore, and a part of the bore having an inner thread; and

a hollow drive rod having an outer thread, wherein a proximal end of the hollow drive rod is unidirectionally rotatably mounted to the drive nut;

wherein the plunger rod is arranged within the hollow drive rod and in threaded connection with the inner thread of the bore, the plunger rod and the hollow drive rod are configured to mate with each other such that axial movement of the plunger rod relative to the hollow drive rod is allowed and rotation of the plunger rod relative to the hollow drive rod is prevented, and the drive sleeve is arranged in threaded connection with the outer thread of the hollow drive rod.

9. The medicament delivery device of claim 8 , wherein the drive sleeve is arranged within and axially movable relative to the actuator, and the device further comprises a coupler configured to prevent the drive sleeve and actuator from rotational movement relative to each other when the drive sleeve is in a distal axial end position relative to the actuator.

10. The medicament delivery device of claim 9 , wherein the coupler comprises a tooth coupling provided on an inside surface of a distal end of the actuator.

11. The medicament delivery device of claim 10 , wherein a pitch of the tooth coupling is the same or less than a pitch of the threaded connection between the drive sleeve and the hollow drive rod.

12. The medicament delivery device of claim 1 , wherein the proximal end position of the actuator is defined by an axial position of the rear housing such that by adjusting a relative axial position of the front housing relative to the rear housing, a length of stroke between the distal and proximal end positions of the actuator is determined, thereby enabling setting of a medicament dose.

13. The medicament delivery device of claim 1 , further comprising a container holder arranged at the front housing and configured to receive and hold the medicament container.

14. The medicament delivery device of claim 1 , wherein the release button comprises a snap catch element; the release button in the active state interacts with the locking ring, thereby providing the unidirectional rotational movement of the locking ring relative to the rear housing; and the snap catch element generates a click sound during the rotational movement.

15. The medicament delivery device of claim 1 , wherein the actuator is connected to the front housing by a guide and to the rear housing by the locking ring such that the actuator is rotatably locked but axially movable relative to the front and rear housings when the release button is in the active state.

16. The medicament delivery device of claim 1 , wherein the medicament delivery device is a pen-injector.