INJECTION SPRING FOR AGED PREFILLED SYRINGE AND AUTO INJECTOR

An auto injector apparatus includes a syringe and an auto injector. The syringe includes a barrel holding a therapeutic fluid including an anti-calcitonin gene-related peptide (anti-CGRP) antibody. The syringe also includes a stopper disposed within the barrel and the stopper moves axially within the barrel between a first position and a second position to expel at least some of the therapeutic fluid from the syringe. The auto injector includes a rod that abuts the stopper and an injection spring that drives the rod to apply a dispensing force through the rod to the stopper. The dispensing force includes a first dispensing force of between 20 N and 40 N and a second dispensing force of between 12 N and 20 N. The injection spring initially applies the first dispensing force and then applies the second dispensing force to move the stopper to the second position.