Medical injection device with telescopically movable needle shield having a cleaning chamber for the needle

A pre-filled injection device for apportioning set dose of a liquid drug comprising:

• a housing distally supporting a removable protective cap rotatable mounted on the housing, and which housing proximally supports a piston rod drive system,
• a non-replaceable cartridge embedded in the housing of the pre-filled injection device and having an interior containing a liquid preservative containing drug, the cartridge having a movable plunger with a proximal surface abutting the piston rod drive system which comprises a piston rod, for moving the movable plunger in the distal direction wherein the piston rod is prevented from movement in the proximal direction by a one-way ratchet,
• a needle cannula having a distal part with a distal tip and an opposite proximal part and a lumen there between,
• a telescopically movable 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, and which telescopically movable shield carries a cleaning chamber for containing a cleaning solvent for cleaning at least the distal tip of the needle cannula between subsequent injections, wherein the cleaning chamber has a variable volume and comprises a movable piston operating inside the cleaning chamber,
• wherein the cleaning solvent inside the cleaning chamber when filled, is identical to the liquid preservative containing drug contained in the interior of the cartridge and wherein the liquid preservative containing drug is filled into the cleaning chamber through the lumen of the needle cannula by moving the movable plunger and the cartridge relatively to each other,
• and wherein a transfer assembly is provided for transferring rotation of the removable protective cap to an axial displacement of the cartridge in the proximal direction and wherein the plunger is proximally supported by the piston rod and prevented from moving in the proximal direction,
• wherein the transfer assembly comprises a transfer element engaging a hub which carries the needle cannula and wherein the transfer element and the hub are coupled by a threaded connection, wherein the transfer element moves proximally when rotated,
• such that the liquid preservative containing drug is forced from the cartridge and into the cleaning chamber as the transfer element moves the cartridge in the proximal direction and the plunger is prevented from movement in the proximal direction.