Improved method for sterilizing a prefilled syringe (pfs)

A sterilization method for sterilizing a syringe of the prefilled syringe (PFS) type, having

• a syringe barrel internally comprising an interior chamber filled with a liquid pharmaceutical product to be injected, the interior chamber comprising a proximal end in the vicinity of which there is at least one mechanical blocking means
• a closure cap closing the chamber at its distal end;
• a seal arranged in the interior chamber of the barrel forming a head of the plunger piston;
• the method comprising:
• a sterilization cycle involving a sterilization plateau, and the following steps of:
• i) prior to the sterilization cycle, generation within the interior chamber of the barrel of at least a bubble of gas, of sufficient volume so as to cause the seal to move back from its initial position that it occupies after filling of the interior chamber with the liquid pharmaceutical product as far as an intermediate sterilization position in which it is in abutment against the mechanical blocking means;
• and/or
• ii) after the sterilization plateau, the application to the seal of a back-pressure that is great enough to allow the seal to move forward from its intermediate sterilization position more or less as far as its initial position.