Dual-chamber cylinder-piston unit for the lyophilisation, storage, reconstitution and application of injection solutions for an injector, and method for filling the cylinder-piston unit

A method for filling a cylinder-piston unit (1) for a needle-free disposable injector, the cylinder-piston unit (1) comprising a piston-cylinder unit (1) for a needle-free injector, for example for providing a sterile injection solution, with a chamber (3) which is arranged in a cylinder (2) and is intended for receiving an injection solution (4), an end wall (5) with at least one nozzle bore or an outlet element (6), and a second piston (7) arranged movably in the chamber (3), chamber (3) of two-part design with a first chamber (8) and a concentric second chamber (9), the cross section of the first chamber (8) being larger than the cross section of the second chamber (9), the first chamber (8) formed such that it is closed by a first piston (10) and the second chamber (9) formed such that it is closed by the second piston (7), the first chamber (8) being separated from the second chamber (9), and the second piston (7) formed with at least one transfer passage (16), or the first chamber (8) formed with at least one closable, axially aligned freeze-drying passage (34) and the second chamber (9) formed with at least one axially aligned transfer passage (36), at the rear ends in each case of the chambers (8, 9), the method comprising at least the following steps:

• filling the second chamber (9) with a first drug component (14) of an injection solution (4), wherein the volume of the first drug component (14) is smaller than the volume of the second chamber (9);
• inserting the second piston (7), which is compressed and allows the air to escape, into the first chamber (8) until it makes contact with an annular surface (18) in order to close the second chamber (9), the second chamber (9) containing a gas cushion (31);
• filling the first chamber (8) above the second piston (7) with a solvent (19), for example water, or with the second drug component (15),
• inserting a first compressed piston (10) into the first chamber (8) and closing the first chamber (8),
• pushing in the first piston (10), with nozzle(s) (6) pointing upward in order to produce the injection solution (4) from the lyophilizate or the first drug component (14), and the solvent (19) or the second drug component (15) by means of a piston slide (20), wherein, by positive pressure in the first chamber (8), a second inner piston body (7.1) is pushed in a second outer piston ring (7.2) in the direction of a second chamber (9) until a previously closed transfer passage (16, 36) connects the second chamber (9) to the first chamber (8) and the solvent (19) or the second drug component (15) entirely enters the second chamber (9) and is dissolved or mixed with the lyophilizate or the first drug component (14) to provide the finished injection solution (4);
• subsequently pushing in a first inner piston body (10.1) together with the second inner piston body (7.1) with the aid of the piston slide (20), by screwing the piston slide (20) into a thread, partial thread or latching element, and squeezing a gas bubble (31) out of the cylinder—piston unit (1), wherein the gas bubble (31) is displaced out of the second chamber (9) through (an) upwardly pointing nozzle bore(s) or outlet element(s) (6) and a membrane (26) which is fastened to the outer cylinder (13) or to the closure cap (11) and lifts off from the nozzle bore(s) or outlet element(s) (6) when the gas cushion (31) emerges, and
• closes the nozzle bore(s) or the outlet element(s) (6) again in a sterile manner (pressure control valve) after the gas cushion emerges.