A drug delivery device (10) includes an interior chamber (150) and a seal structure (160). The interior chamber (150) includes a first, liquid medicament compartment (151) and a second medicament compartment (152). The seal structure (160) is conditionable to permit fluid to pass therethrough upon pressurization of the fluid. The seal structure (160) preferably includes a sealing member (166) which moves from a first sealed position into a second by-pass position upon pressurization of liquid injection solution in the wet compartment (151) of the housing assembly (150). Such by-pass movement of the sealing member (166) enables the liquid injection solution to flow through the seal structure (160) into the second ingredient compartment (152) and mix for injection.
