Dose fractioning autoinjector

A method for dose fractioning by an autoinjector comprising the steps of:

• retracting a needle safety shield from an unused state to actuate an autoinjector;
• an applied force moving synchronously a member with a plunger stopper disposed to translate within a syringe or cartridge;
• interrupting autoinjector operation by removing applied force on the plunger stopper translation of needle shield pin along original track of slider to its unused state removing the applied force;
• resuming autoinjector operation by reapplying force on the plunger stopper, wherein the force is actuated by retraction of the needle safety shield;
• completing autoinjector operation by removing applied force on the plunger stopper translation upon orienting a slider to guide a radial pin of the needle safety shield to a point of no return locking out the needle safety shield.

An autoinjector comprising:

• a cartridge including a barrel, a plunger stopper disposed to translate within the barrel, the plunger stopper radially disposed within the barrel, the plunger stopper separating the interior of the barrel into a drug space configured to contain the injectable drug between the plunger stopper and a cartridge crimped stopper;
• a slider co-axially disposed with the cartridge, the slider being rotatably disposed relative to the cartridge and substantially axially fixed relative to the cartridge;
• a member axially adjacent to the plunger stopper, the axial position of the member being synchronous with the axial position of the plunger stopper within the barrel;
• a needle safety shield, the needle safety shield being slidably disposed relative to the cartridge and the slider whereby an axial force exerted on the needle safety shield slides the needle safety shield relative to the cartridge from a shielded position wherein the injection needle axially keyed to the needle safety shield is not axially exposed to an injection position wherein the injection needle is axially exposed to penetrate the injection site;
• wherein the movement of the needle safety shield is at least partially guided by a pin and track arrangement, one of the pin and the track being formed with the needle safety shield and the other of the pin and the track being formed with the slider whereby movement of the pin within the track controls the position of the needle safety shield relative to the slider, the track including a point-of-no-return, the pin returning the needle safety shield to the shielded position when the axial force is removed when the pin is disposed in the track proximal to the point-of-no-return such that the needle safety shield remains axially movable to the injection position, and the pin moving to and locking the needle safety shield in the shielded position when the axial force is removed when the pin is disposed in the track distal to the point-of-no-return with rotation of the slider;
• wherein rotation of the slider is actuated by movement of the member moving synchronous with the plunger stopper, the member rotating the slider positioning the safety shield pin to be guided along the track including the point-of-no-return to axially lock the needle safety shield in the shielded position as the plunger stopper reaches the end of all dose delivery;
• wherein the force applied to the plunger stopper is counterbalanced by a component introduced in the path of the component coupled to the member when the pin travels from the injection position to the shielded position;
• and
• wherein the needle safety shield with interlocked injection needle is removable after the safety shield pin is at the point of no return.