Auto-injector

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

• an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the elongate housing having a distal end and a proximal end with an orifice intended to be applied against an injection site, wherein the syringe is slidably arranged with respect to the housing,
• a single torsion spring capable of, upon activation, pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end, operating the syringe to supply the dose, and covering the needle on removal of the auto-injector from the injection site,
• an activating member arranged to lock the torsion spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the torsion spring for injection,
• a first gear arrangement arranged for converting torque from a proximal end of the torsion spring into a translative force, and
• a second gear arrangement arranged for converting torque from a distal end of the torsion spring into a translative force, the proximal end of the torsional spring being different than the distal end of the torsional spring,
• wherein the proximal end of the torsion spring is arranged to be grounded in the housing while the distal end of the torsion spring is configured to act on a plunger through the second gear arrangement for advancing the needle and supplying the dose,
• wherein the activating member is arranged to block or release the second gear arrangement, and
• 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 releasable from its ground in the housing to act on the first gear arrangement for causing a translation through the first gear arrangement resulting in the needle getting covered.