The invention relates to a pre-filled injection device for apportioning set dose of a liquid drug. The housing of the pre-filled injection device internally supports a non-replaceable cartridge (160) having an hollow interior containing a liquid preservative containing drug and externally supporting a removable protective cap (150). The piston rod drive system of the injection device comprises a piston rod abutting a plunger provided inside the cartridge. A needle cannula (130) having a distal part with a distal tip and an opposite proximal part and a lumen there between is insertable into the cartridge. A telescopically movable (110) shield movable from an extended position covering at least the distal tip of the needle cannula to a retracted position exposing at least the distal tip of the needle cannula is further provided. The telescopically movable shield carries a cleaning chamber (120) able to contain a quantum of the liquid preservative containing drug for cleaning at least the distal tip of the needle cannula between subsequent injections. The quantum of the liquid preservative containing drug contained in the hollow interior of the cartridge is transferred to the cleaning chamber through the lumen of the needle cannula by moving the cartridge axially in relation to the plunger by use of a transfer assembly.
