The prefilled injection device (100) according to the invention includes: a tubular body (3) closed at the front by a closing element (2) and provided with a first (9) and a second (8) chambers； a first liquid substance contained in the first chamber (9)； a second solid or liquid substance, contained in the second chamber (8) and intended to mix with the first substance for the reconstruction of the injectable solution. The device is characterized by comprising a front chamber (17), defined between a front plug (27) and the closing element (2), said front plug (17) being empty so that the closing element (2) is separated by the second substance. If the contact between the active substance (or second substance) and the closing element 2 is avoided, it is not necessary to carry out any stability test of the active substance with the closing element.
