Portable drug delivery system

An injection device for administering a formulation from a pre-filled cylindrical cartridge with attached cannula, said injection device comprising:

• a barrel having a cylindrical bore and a chamber adapted for receiving and positioning a cartridge coaxial with said bore;
• a push rod slideably disposed within and coaxial to said bore, said push rod for pushing the contents of the cartridge through the cannula;
• an ejection plate coupled to said barrel within said chamber and a spring coupled to said barrel and said ejection plate, said ejection plate moveable between a cartridge loading position wherein one end of said ejection plate is extended out of said chamber and an operating position wherein both ends of said ejection plate are positioned within said chamber, said spring biasing said ejection plate to said cartridge loading position;
• and
• an ejection release means coupled to said barrel for locking and releasing said ejection plate, said ejection release means operating between a cartridge lock position wherein a portion of said ejection release means holds said cartridge in the operating position within said chamber such that a cartridge resting on said ejection plate is positioned coaxial with the bore of said barrel, and a cartridge release position wherein said ejection release means is moved away from contact with a cartridge in said chamber, whereby said ejection plate forcibly removes a spent cartridge from said barrel in response to said spring after said cannula has been removed from said cartridge.