Auto-injector

1. An auto-injector for administering a dose of a liquid medicament, the auto-injector comprising:

an elongate housing configured to contain a syringe that contains the medicament and comprises a hollow needle and a stopper for displacing the medicament, the housing having a distal end and a proximal end, and the proximal end of the housing defining an orifice and being configured to be applied against an injection site;

a torsion spring having a distal end and a proximal end, the torsion spring being configured to, upon activation, operate the syringe to supply the dose of the medicament, wherein the torsion spring is configured to cause the needle to be covered at the end of an injection;

an activation member configured to lock the torsion spring in a pressurized state prior to manual operation of the activation member and configured to, upon the manual operation of the activation member, release the torsion spring for the injection; and

a gear arrangement configured to convert torque from the proximal end of the torsion spring into a translative force,

wherein the distal end of the torsion spring is configured to be grounded in the housing while the proximal end of the torsion spring is configured to act on a plunger through the gear arrangement for advancing the plunger and the stopper to administer the dose of the medicament, and the activation member is arranged to block or release the gear arrangement.

2. The auto-injector according to claim 1 , wherein the gear arrangement comprises a first gear member coupled to the proximal end of the torsion spring, and the first gear member is engaged through a screw thread to a second gear member such that the second gear member translates on rotation of the first gear member.

3. The auto-injector according to claim 2 , wherein the screw thread has a variable pitch.

4. The auto-injector according to claim 2 , wherein the activation member is configured to be in a splined engagement with the first gear member or the second gear member of the gear arrangement in an initial state so as to rotationally fix the first gear member or the second gear member of the gear arrangement to the housing, and the activation member is configured to remove the splined engagement on the manual operation of the activation member.

5. The auto-injector according to claim 1 , wherein the activation member comprises a needle shroud arranged in the housing surrounding the syringe and translatable in a longitudinal direction, and wherein the needle shroud is coupled to the gear arrangement in a manner to, when translated in a distal direction, release the gear arrangement.

6. The auto-injector according to claim 5 , further comprising a clip arrangement comprising at least one resilient chassis clip attached to the housing, the chassis clip engageable proximally behind a shoulder of the plunger in a manner to prevent translation of the plunger in a proximal direction, wherein the chassis clip is arranged to be flexed out of engagement with the shoulder when a distal force is applied to the needle shroud.

7. The auto-injector according to claim 6 , wherein the activation member comprises an end trigger button arranged at the distal end of the housing, the end trigger button being translatable between a distal position and a proximal position, at least one trigger beam is arranged on the trigger button in a manner to outwardly support the chassis clip to prevent the chassis clip from being outwardly deflected when the end trigger button is in the distal position, and the trigger beam is configured to be repositioned on translation of the end trigger button into the proximal position in a manner to allow outward deflection of the chassis clip.

8. The auto-injector according to claim 7 , wherein the needle shroud is configured to inwardly support the trigger beam of the end trigger button when the needle shroud is in an initial position so as to prevent deflection of the trigger beam of the end trigger button, the needle shroud is configured such that an inward support of the trigger beam of the end trigger button is removed on translation of the needle shroud into the distal position, and the end trigger button is proximally biased against the housing by a trigger spring.

9. The auto-injector according to claim 7 , wherein the end trigger button comprises at least one latch feature configured to abut against a respective stop in the housing so as to prevent depression of the end trigger button, at least one latch actuation boss on a sleeve trigger that is arranged over the distal end of the housing is configured to inwardly deflect the latch feature of the end trigger button disengaging the latch feature of the end trigger button from the stop, and the end trigger button is proximally biased against the housing by a trigger spring.

10. The auto-injector according to claim 5 , wherein the needle shroud is configured to be in an initial position protruding from the proximal end of the housing in an initial state for preventing release of the gear arrangement, the needle shroud is arranged to be translated distally into the housing into a distal position against a load of a shroud spring when pushed against the injection site, the needle shroud is rotationally fixed to the housing, and, in the distal position, the needle shroud is configured to release the gear arrangement.

11. The auto-injector according to claim 1 , wherein the plunger is rotationally fixed to the housing.

12. The auto-injector according to claim 1 , further comprising an audible ratchet for detecting movement of the plunger.

13. The auto-injector according to claim 1 , wherein the syringe is slidably arranged with respect to the housing.

14. The auto-injector according to claim 1 , wherein the torsion spring is configured to, upon the activation, push the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end of the housing.

15. The auto-injector according to claim 14 , wherein the gear arrangement comprises a first gear member coupled to the proximal end of the torsion spring, and the first gear member is engaged through a screw thread to a second gear member such that the second gear member translates on rotation of the first gear member, and the proximal end of the torsion spring is configured to act on the plunger through the gear arrangement for advancing the needle.

16. The auto-injector according to claim 15 , wherein the plunger is rotationally fixed to the housing.

17. The auto-injector according to claim 1 , wherein translation through the gear arrangement results in needle retraction.