Auto-injector

Method for operating an auto-injector, the auto-injector comprising:

• a tubular chassis,
• a carrier subassembly comprising a tubular carrier slidably arranged relative to the chassis and partially arranged in the chassis, the carrier containing a syringe with a hollow injection needle, a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe, wherein the syringe is locked for joint axial translation with the carrier,
• a wrap-over trigger sleeve arranged over the distal end (D) of the auto-injector, the trigger sleeve extending at least almost over the whole length of the auto-injector, wherein translation of the trigger sleeve relative to the chassis triggers needle insertion when an end face of the trigger sleeve contacts an end face of the carrier,
• a control spring arranged around the carrier, wherein the control spring is configured to insert the needle and to retract the needle after administering a dose of a liquid medicament (M),
• a first interlock configured to couple a proximal end of the control spring to either the carrier or to the chassis,
• a second interlock configured to lock the drive spring,
• a third interlock configured to couple the chassis to the carrier,
• a fourth interlock configured to couple a distal end of the control spring to either the carrier or to the trigger sleeve,
• the method comprising the steps of:
• coupling the proximal end of the control spring to the carrier by the first interlock, preventing release of the drive spring by the second interlock, preventing decoupling of the chassis from the carrier by the third interlock and coupling the distal end of the control spring to the trigger sleeve in an initial state,
• translating the trigger sleeve in proximal direction (P) relative to the chassis against the force of the control spring when the proximal end (P) of the auto-injector is being pushed against an injection site,
• disengaging the third interlock when the trigger sleeve is at least almost fully translated thereby releasing the control spring for advancing the carrier subassembly for needle insertion,
• releasing the drive spring by the second interlock when the needle reaches an injection depth during needle insertion, thereby allowing the drive spring to advance the plunger and the stopper for at least partially delivering the medicament (M),
• translating the trigger sleeve in distal direction (D) under load of the control spring relative to the carrier subassembly on removal of the auto-injector from the injection site,
• decoupling the proximal end of the control spring from the carrier and coupling it to the chassis by the first interlock and decoupling the distal end of the control spring from the trigger sleeve and coupling it to the carrier by the fourth interlock when the trigger sleeve reaches a defined position relative to the carrier,
• retracting the carrier subassembly into the chassis into a needle safe position under load of the control spring.

Auto-injector for administering a dose of a liquid medicament (M), comprising:

• a tubular chassis,
• a carrier subassembly comprising a tubular carrier slidably arranged relative to the chassis and partially arranged in the chassis, the carrier containing a syringe with a hollow injection needle, a drive spring and a plunger for forwarding load of the drive spring to a stopper of the syringe, wherein the syringe is locked for joint axial translation with the carrier,
• a wrap-over trigger sleeve arranged over the distal end (D) of the auto-injector, the trigger sleeve extending at least almost over the whole length of the auto-injector, wherein translation of the trigger sleeve relative to the chassis triggers needle insertion when an end face of the trigger sleeve contacts with an end face of the carrier,
• a control spring arranged around the carrier, wherein the control spring is configured to insert the needle and to retract the needle after administering the dose of the liquid medicament (M),
• a first interlock configured to couple a proximal end of the control spring to either the carrier for advancing it for needle insertion or to the chassis for needle retraction depending on the relative axial position of the carrier and the trigger sleeve,
• wherein the first interlock comprises a proximal collar for transmitting load of the proximal end of the control spring, the proximal collar arranged to be engaged on a thread on the carrier in an initial state, the proximal collar having a pin arranged to be splined to a first longitudinal groove in the trigger sleeve in the initial state so as to prevent rotation of the proximal collar and couple it to the carrier, wherein the first longitudinal groove is arranged to release the pin upon translation of the chassis and carrier in proximal direction (P) under load of the control spring when the auto- injector is removed from the injection site thereby allowing rotation and translation of the proximal collar relative to the carrier under load of the control spring and subsequent abutting of the proximal collar against the chassis,
• a second interlock configured to release the drive spring for injection when the carrier reaches an injection depth during needle insertion,
• a third interlock configured to couple the chassis to the carrier for joint axial translation relative to the trigger sleeve, wherein the third interlock is arranged to decouple the chassis from the carrier upon translation of the trigger sleeve in proximal direction (P) relative to the chassis thus releasing the control spring for needle insertion,
• a fourth interlock configured to couple a distal end of the control spring to either the carrier for needle retraction or to the trigger sleeve otherwise.