Pneumatic powered autoinjector

A device for injecting a viscous medicament, comprising:

• a dispenser having a reservoir for containing a viscous medicament and a needle suitable for injecting the medicament, wherein the gauge of the needle is equal to or greater than about 21 gauge;
• a pressurized gas source;
• a driver activated by flow of pressurized gas from the pressurized gas source, wherein the driver comprises a multistage piston having at least an insertion stage characterized by a first surface area and an injection stage characterized by a second surface area larger than the first surface area, said driver being configured such that the flow of pressurized gas acts sequentially against the insertion stage and the injection stage to exert at least an insertion force and an injection force sequentially against the dispenser;
• a bias mechanism having a spring force sufficient to bias the reservoir and needle in a retracted position within the dispenser until the driver exerts the insertion force against the dispenser;
• and
• an actuator which initiates the flow of pressurized gas from the pressurized gas source to the driver.

A method for injecting a viscous medicament, the method comprising:

• providing a viscous medicament in a device having a cap comprising a pressurized gas source including a microcylinder of compressed gas, a body comprising a dispenser having a reservoir for containing the viscous medicament and a needle for injecting the viscous medicament, the needle having a needle gauge that is equal to or greater than about 21 gauge, a driver situated between the cap and the dispenser, the driver comprising a multistage piston having at least an insertion stage and an injection stage, and an actuator adjacent the pressurized gas source;
• activating the actuator to compromise the microcylinder and initiate flow of pressurized gas from the pressurized gas source;
• and
• transmitting the flow of pressurized gas to the driver to exert an insertion force and an injection force sequentially on the dispenser, the injection force being of sufficient magnitude to drive the viscous medicament through the needle.