Drug delivery device for delivering a predefined fixed dose

A drug delivery device for delivering a plurality of doses of a medicament, wherein the drug delivery device comprises:

• a housing,
• a drug reservoir comprising the plurality of doses of the medicament and a pierceable septum,
• a plurality of needle assemblies, wherein each needle assembly comprises a needle cannula fixed in a needle hub,
• a needle drum axially locked to the shield, wherein the drum comprises a plurality of axial tracks, each axial track being adapted for movable receiving a needle assembly of the plurality of needle assemblies,
• a needle shield movably arranged between an initial distal position, wherein the needle shield is adapted to cover the plurality of needle assemblies, and a proximal position, wherein the needle shield is adapted to allow an active needle assembly of the plurality of needle assemblies to extend from a distal end of the needle shield,
• a drive mechanism adapted for sequentially delivering the plurality doses,
• an activation mechanism for activating the drive mechanism to deliver a dose of the plurality of doses, wherein the activation mechanism comprises the needle shield, the needle shield being adapted to allow activation of the drive mechanism, when the needle shield is in the proximal position,
• wherein the needle drum is operably arranged to position one of the needle assemblies of the plurality of needle assemblies in an active position in axial alignment with the reservoir, wherein the needle assembly arranged in alignment with the reservoir is the active needle assembly, and
• wherein the active needle assembly can be arranged in a distal position relative to the housing, wherein the needle cannula does not pierce the septum, and a proximal position relative to the housing, wherein the needle cannula pierces the septum and is in fluid communication with the reservoir,
• wherein the needle shield is adapted to be operated from the initial distal position to the proximal position, defining a first movement of the needle shield, and from the proximal position to the initial distal position, defining a second movement of the needle shield,
• wherein the drug delivery device further comprises a hub driving structure comprising a hub driving portion movably arranged relative to the housing for driving the active needle assembly to the proximal position, in response to the first movement of the needle shield,
• wherein the drug delivery device further comprises a pulling structure axially locked to the needle shield, the pulling structure comprises a hub engaging portion for engaging and pulling the active needle assembly to the distal position, in response to the second movement of the needle shield,
• wherein the housing further comprises a support structure adapted to support the hub of the active needle assembly, when the active needle assembly is arranged in the proximal position, and wherein the support structure is further adapted to block axial movement of the active needle assembly, in response to the first movement of the needle shield, and to allow distal movement of the active needle assembly, in response to the second movement of the needle shield,
• wherein the needle shield is operationally coupled to the hub driving structure, the active needle assembly, the pulling structure and the support structure such that the operation of the needle shield is adapted to drive the active needle assembly to the proximal position of the active needle assembly, before the needle shield can reach the proximal position of the needle shield, whereby fluid connection can be establish before the drive mechanism can be activated.