Provided is a manual drive unit for use with a cassette unit comprising a cassette unit housing containing there within a syringe comprising a barrel for containing a volume of a liquid drug formulation; a hollow needle at a front end of the barrel, the hollow needle defining a needle tip for dispensing of the liquid drug formulation; and a plunger that is axially movable within the barrel. The manual drive unit comprises a manual drive unit housing defining a docking cavity and a needle delivery aperture, wherein said docking cavity is arranged for docking receipt of the cassette unit at a docking position; and received by the manual drive unit housing and axially movable relative thereto, a manually operable drive transfer element for transferring axial drive to the plunger of the syringe for moving the plunger into the barrel of the syringe to eject at least part of the volume of liquid drug formulation.