Drug mixing system

A drug mixing system (10) for dissolving or diluting a drug formulation (110a) stored in a vial (110) prior to use, the drug mixing system (10) comprising an adapter (100) adapted to hold the vial (110) housing the drug formulation (110a), and a reservoir (120) for housing a liquid (120a) for dissolution or dilution of the drug formulation (110a), the reservoir (120) comprising a housing (124) and a piston (125) sealingly movable within the housing (124),

• wherein the adapter (100) comprises:
• a vial mounting opening (111) adapted to hold the vial (110),
• a reservoir mounting opening (121) adapted to hold the reservoir (120),
• an outlet port (130),
• an internal adapter channel (140) fluidly connecting the vial-and reservoir mounting openings (111, 121), and the outlet port (130), and
• a liquid-retaining means (145) adapted to block at least a flow of dissolved or diluted drug formulation (110b) through the outlet port (130),
• characterized in that:
• the adapter (100) is equipped with a piston locking means (126) adapted to lock the position of the piston (125) once a predetermined volume of the liquid has been transferred from the reservoir (120) into the vial (110) by means of pressing the piston (125) into the housing (124), thereby creating and storing an overpressure,
• the drug mixing system (10) is adapted to expel, or transfer, the dissolved or diluted drug formulation (110b) from the vial (110) through the outlet port (130) upon actuation of a liquid-releasing means (155, 255) using the overpressure generated by pressing the piston (125) into the housing (124).