A medical device pump with a housing with a compartment for removably receiving a cartridge containing a therapeutic agent, a conduit configured to operatively provide a fluid flow path for therapeutic agent to exit from the cartridge, a user activated delivery button, a trigger mechanism, and a mechanical pump mechanism. The trigger mechanism, user activated delivery button and mechanical pump mechanism of the medical device pump are configured such that the trigger mechanism is activated by a user fully activating the user activated delivery button. Moreover, such full activation generates mechanical power employed by, and sufficient for, the mechanical pump mechanism to pump a predetermined volume of therapeutic agent from the cartridge and through the fluid flow path.