An injector device for injecting or transferring a pharmaceutical product from a pharmaceutical cartridge. The injector device includes a body having a side wall having a proximal end portion and a distal end portion, the side wall having an inner surface and an outer surface, the inner surface of the side wall defining a space for receiving at least a portion of a body of a pharmaceutical cartridge therein. One or more retention members are disposed on the outer surface of the body. The injector device further includes a plunger rod having a proximal end portion and a distal end portion, the distal end portion of the plunger rod having a connection member constructed for connection to a connecting member mounted on a piston associated with a cartridge. The plunger rod has one or more receiving members formed about its length. The one or more retention members and the one or more receiving members are constructed to cooperatively retain the plunger rod on the body when the plunger rod is in a first position, and are constructed to cooperatively release the plunger rod from the body when the plunger rod is moved toward the distal end of the body to a second position. The plunger rod further includes a surface for engaging a proximal end of a body of a pharmaceutical cartridge positioned within the body of said injector and for moving a proximal end of a body of a pharmaceutical cartridge distally as the plunger rod is moved from its first position to its second position. Movement of the plunger rod from the first position to the second position releases the plunger rod from the body of the injector and simultaneously activates a pharmaceutical cartridge disposed within the body of said injector.
