an improved injection device includes containing a pump and pump control circuitry , a handle with a needle for delivering a therapeutic agent to a patient , a cartridge holding the agent and a tube for delivering the agent from the cartridge to the handle . preferably the cartridge is disposed in a cartridge holder coupled to the tube . a quick disconnect coupling is provided between the cartridge holder and the housing so that it can be easily mounted thereon . the housing further has a receptacle for receiving and storing the tip of the handle .