An apparatus includes a medicament container and an actuator assembly coupled to a proximal end portion of the medicament container. A distal end portion of the medicament container is configured to be coupled to a needle. A piston is movably disposed within the medicament container such that the medicament container is divided into a first internal portion and a second internal portion, the first internal portion containing a medicament. The actuator assembly has a pressurized fluid container, a regulator and a bias member. The pressurized fluid container is configured to move relative to the medicament container between a first position and a second position. The regulator is configured to fluidically couple the pressurized fluid container and the second internal portion of the medicament container when the pressurized fluid container is in the second position. The bias member is configured to bias the pressurized fluid container in the first position.