Auto-Injector

A method comprising:

• removing a cap from a proximal end of an auto-injector to remove a protective sheath covering a needle of a syringe without causing axial movement of the syringe relative to a tubular chassis of the auto-injector;
• after removing the cap, depressing a trigger button of the auto-injector to disengage a distal portion of a plunger from a tubular carrier by an inward deflection to release the plunger from being held in a first position relative to the tubular carrier, the plunger comprising (i) a flange, and (ii) a proximal portion extending proximally from the flange to a proximal end of the plunger, wherein the distal portion extends distally from the flange to a distal end of the plunger, and an axial length of the proximal portion is greater than an axial length of the distal portion;
• upon releasing the plunger from being held in the first position relative to the tubular carrier, proximally advancing the plunger relative to the tubular chassis to insert the needle of the syringe into an injection site by a proximally-directed force of a drive spring disposed around the distal portion of the plunger, wherein a proximal end of the drive spring applies the proximally-directed force to the flange of the plunger, and a radial distance between the drive spring and the distal portion of the plunger is substantially constant along at least half of an axial length of the distal portion;
• after inserting the needle of the syringe into the injection site, proximally advancing the proximal portion of the plunger within the syringe to inject a medicament from the syringe into the injection site by the proximally-directed force of the drive spring, the proximal portion being substantially centered on a longitudinal axis of the tubular chassis;
• and
• after injecting the medicament from the syringe into the injection site, retracting the syringe distally into the tubular chassis of the auto-injector using a control spring, wherein a proximal end of the control spring is engaged to a first collar, and a distal end of the control spring is engaged to a second collar.

A method comprising:

• removing a cap from a proximal end of an auto-injector to remove a protective sheath covering a needle of a syringe without causing axial movement of the syringe relative to a tubular chassis of the auto-injector;
• after removing the cap, depressing a trigger button of the auto-injector to disengage a distal portion of a plunger from a tubular carrier by an inward deflection to release the plunger from being held in a first position relative to the tubular carrier, the plunger comprising (i) a flange, and (ii) a proximal portion extending proximally from the flange to a proximal end of the plunger, wherein the distal portion extends distally from the flange to a distal end of the plunger, an axial length of the proximal portion is greater than an axial length of the distal portion, and the proximal and distal portions of the plunger are substantially centered about a longitudinal axis of the tubular chassis;
• upon releasing the plunger from being held in the first position relative to the tubular carrier, proximally advancing the plunger relative to the tubular chassis to insert the needle of the syringe into an injection site by a proximally-directed force of a drive spring disposed around the distal portion of the plunger, wherein a proximal end of the drive spring applies the proximally-directed force to the flange of the plunger;
• and
• after inserting the needle of the syringe into the injection site, proximally advancing the proximal portion of the plunger within the syringe to inject a medicament from the syringe into the injection site by the proximally-directed force of the drive spring.

A method comprising:

• depressing a trigger button of an auto-injector to disengage a distal portion of a plunger from a tubular carrier by an inward deflection to release the plunger from being held in a first position relative to the tubular carrier, the plunger comprising a flange and a proximal portion extending proximally from the flange to a proximal end of the plunger, wherein the distal portion extends distally from the flange to a distal end of the plunger, an axial length of the proximal portion is greater than an axial length of the distal portion, and a majority of the proximal and distal portions of the plunger are substantially centered about a longitudinal axis of the tubular carrier;
• upon releasing the plunger from being held in the first position relative to the tubular carrier, proximally advancing the plunger relative to the tubular carrier to insert a needle of a syringe into an injection site by a proximally-directed force of a drive spring disposed around the distal portion of the plunger, wherein a proximal end of the drive spring applies the proximally-directed force to the flange of the plunger;
• and
• after inserting the needle of the syringe into the injection site, proximally advancing the proximal portion of the plunger within the syringe to inject a medicament from the syringe into the injection site by the proximally-directed force of the drive spring.