A syringe assembly (10) comprising: a cylinder (12) for containing one or more medications, the cylinder (12) has a front outlet (12a) to allow the expulsion of said one or more medications from said cylinder (12) through said exit (12a)； a first plug (14) disposed in the cylinder (12) and axially movable therein and defining a first volume (16) in the cylinder (12) axially forward of the first plug (14) and a second volume (18) in the cylinder (12) axially back of the first plug (14)； a second plug (20) disposed in the cylinder axially back of the first plug (14) and axially movable therein, the second plug (20) providing a fluid tight seal at a rear end of the second volume (18)； a first piston rod (22) connected to the first plug (14) and extending axially backwards through the second plug (20), engaging the second plug (20) with the first piston rod (22) but allowing the axial sliding of the first (22) piston rod therethrough； and a second piston rod (24) connected to the second plug (20), to axially move the second plug (20) when the second piston rod (24) moves axially； characterized in that the first plug (14) has a bi-directional valve that can be moved between a sealing configuration and an open configuration to selectively place the first volume (16) in fluid communication with the second volume (18), the bi-directional valve can be move from the sealing configuration to the open configuration by increasing the fluid pressure in any of the first and second volumes (16, 18)； where the first piston rod (22) is axially movable to axially move the first plug (14) and pressurize the first volume (16) and the second volume (18) causing the bidirectional valve to move to the open configuration and connect The first volume (16) and the second volume (18) form fluidly.Un montaje (10) de jeringa que comprende: un cilindro (12) para contener uno o más medicamentos, el cilindro (12) tiene una salida (12a) delantera para permitir la expulsión de dicho uno o más medicam
