Patent ID: 8636689

Claim:
A pen injection device comprising: a sterile dual transfer spike assembly comprising a dual transfer spike having a first open end and a second open end, the dual transfer spike defining a fluidic pathway extending through the dual transfer spike from the first end to the second end; a first cartridge assembly comprising a first cartridge housing, and a first cartridge containing a first substance inside the first cartridge housing; a second cartridge assembly comprising a second cartridge housing, and a second cartridge containing a second substance inside the second cartridge housing, wherein the second cartridge housing is movable relative to the first cartridge housing from a first position wherein the first and second cartridges are not in fluid communication through the dual transfer spike to a second position wherein the first and second cartridges are in fluid communication through the dual transfer spike; a plunger rod in the first cartridge, translatable in a first direction to transfer at least a portion of the first and second substances from one of the first and second cartridges to the other of the first and second cartridges via the fluidic pathway between the first cartridge and the second cartridge; and a biasing mechanism configured to bias the plunger rod in a second direction opposite the first direction upon release of the plunger rod after said plunger rod has been translated in said first direction, in order to transfer at least a portion of the first and second substances from the other of the first and second cartridges to the one of the first and second cartridges.