Auto-injector

An auto-injector (A) for administering a dose of a liquid medicament, comprising:

• a substantially tubular and reusable front-end device comprising:
• a support sleeve with a first screw thread adapted to engage a housing of a back-end device of the auto-injector (A) to attach the front-end device to the back-end device and
• an outer sleeve mounted onto a support sleeve of the front-end device by a second screw thread,
• wherein the front-end device is adapted to receive a syringe with an injection needle and a barrel containing the dose of the medicament and wherein the direction of rotation of the first screw thread is opposite to the direction of rotation of the second screw thread, and
• wherein a support collar separates the first screw thread from the second screw thread and a latch formed to the outer sleeve is arranged to latch to the support collar of the support sleeve to initially prevent a relative rotation between the outer sleeve and the support sleeve;
• and
• a reusable back-end device comprising:
• a housing,
• a plunger connected to or adapted to engage a stopper providing a fluid tight seal for a distal end of the barrel,
• a motor for displacing the plunger,
• wherein the front-end device is attached to the housing via the first screw thread and the outer sleeve is mounted onto the support sleeve of the front-end device by a second screw thread, wherein the direction of rotation of the first screw thread is opposite to the direction of rotation of the second screw thread.