Syringe with needle guard injection device

A method for delivering a therapeutic agent using an injection device including a guard comprising a proximal end, a distal end, and a latch member extending from the guard, and a syringe slidably received in the guard, the syringe comprising a proximal end, a distal end, a needle extending from the distal end, and a plunger extending from the proximal end, the syringe being biased to move relative to the guard from a first position wherein the needle is exposed beyond the distal end of the guard towards a second position wherein the needle is disposed within the guard, the latch member retaining the guard in the first position, wherein the guard and the syringe further comprise cooperating detents and detent pockets, and wherein the cooperating detents and detent pockets engage one another when the syringe is in the second position to prevent subsequent movement of the syringe with respect to the guard, the method comprising:

• inserting the needle into a patient;
• depressing the plunger through an injection stroke to inject the therapeutic agent into the patient until the plunger at least disengages the latch member during the injection stroke, whereupon the syringe is free to move from the first position;
• releasing the plunger, whereupon the syringe automatically withdraws proximally within the guard towards the second position, and
• retaining the guard in the second position by engaging detent pockets on the syringe with cooperating detents on the guard.