A cylinder ampoule (1) having a first end sealed by a closure through which an injection unit can communicate with a medicament in the ampoule and a second end closed by a piston (3) which can be forced into the ampoule (1) to press out a dose of a medicament stored in the ampoule between the closure and the piston (3) through said injection unit, which cylinder ampoule (1) has a not circular inner cross section and which piston (3) has a not circular cross section corresponding to the inner cross section of the ampoule (1). A piston rod (4) has a pressure foot (5) which has a cross section corresponding to the inner cross section of the ampoule (1) and is inrotateably connected to the piston rod (4).