Injection device for delivering a predefined plurality of predetermined dose volumes

Abstract

The invention relates to a spring driven multi-use fixed dose injection device with an End-of-Content (EoC) mechanism. A housing structure contains a volume of a liquid drug which is expelled in a predefined number of substantially equally sized dose volumes. Each dose volume is expelled automatically with the assistance of a spring which is loaded with a force sufficient to expel the full number of the predefined plurality of predetermined and equally sized dose volumes. Each dose volume is prepared and released by moving a drive element a predetermined axial distance in the proximal direction away from an initial position, followed by a rotation of the drive element by the force of the spring back to the initial position during which rotation the drive element rotates the piston rod to move helically. The End-of-Content mechanism determines how many times the drive element can be moved proximally and comprises a longitudinal track structure associated with the piston rod which has a free length defined by a proximal stop associated with the piston rod which stop prevents the drive element from moving an additional predetermined axial distance in the proximal direction required to prepare a subsequent predetermined dose volume after the predefined plurality of predetermined and equally sized dose volumes have been selected.