A medical injection device

A pre-filled injection device for ejection of individually set dose of a liquid drug,

• comprising:
• a housing structure which externally supports a removable protective cap and internally supports a piston rod drive system,
• a non-replaceable cartridge permanently embedded in the housing structure and having an interior containing a preservative containing liquid drug, the interior being defined by a distal pierceable septum and proximal movable plunger movable by the piston rod drive system which comprises a piston rod for moving the movable plunger in the distal direction,
• the removable protective cap being coupled to the housing structure such that relative rotation between the removable protective cap and the housing structure is required in order to remove the removable protective cap,
• a needle hub securing a needle cannula having a distal end with a distal tip and a proximal end and a lumen there between, which needle hub together with the needle cannula is movable from a first position to a second position,
• the first position being a position wherein the proximal end of the needle cannula is positioned distally spaced from the septum of the cartridge and,
• the second position being a position wherein the proximal end of the needle cannula has penetrated through the septum of the cartridge thereby establishing a liquid flow through the lumen of the needle cannula,
• a needle shield covering at least the distal tip of the needle cannula between injections and which needle shield carries a cleaning chamber containing a cleaning solvent, the distal tip of the needle cannula being stored inside the cleaning chamber between subsequent injections, and
• wherein the cleaning solvent inside the cleaning chamber is identical to the preservative containing liquid drug contained in the interior of the cartridge and which preservative containing liquid drug is fillable from the interior of the cartridge and into the cleaning chamber through the lumen of the needle cannula by moving the cartridge and the movable plunger inside the cartridge relatively to each other with the needle hub and the needle cannula in the second position, and
• wherein the removable protective cap at least rotationally engages the needle shield such that the required rotation of the removable protective cap forces the needle shield to rotate and
• which needle shield is helically guided relatively to the housing structure and engages the needle hub such that the helical movement of the needle shield is transferred into an axial movement of the needle hub, and
• which needle hub is guided purely axially relatively to the housing structure by a guiding arrangement provided between the needle hub and the housing structure comprising guiding structure guided by axial tracks such that the needle hub is guided purely axially from the first position to the second position upon helical movement of the needle shield whereby the proximal end of the needle cannula penetrates through the septum of the cartridge and the purely axial movement of the needle hub is transferred to the cartridge.