Venting syringe

Abstract

A syringe propellable by a propellant that boils at a predetermined temperature, the syringe comprising a barrel having an outlet at a front end, a stopper axially moveable in the barrel, and a third chamber for containing propellant. The stopper defines and separates a first chamber and a second chamber, the first chamber being axially forwards of the stopper and being configured for containing a medicament, and the second chamber being axially rearwards of the stopper and being configured to receive propellant for acting on the stopper to move the stopper axially forwardly in the barrel to expel medicament through the outlet upon actuation of the syringe. The syringe is configured such that, in use, upon actuation of the syringe, liquid propellant is released from the third chamber and boils outside of the third chamber at or above the predetermined temperature to provide an increasing vapor pressure in the second chamber that causes the stopper to move axially forwardly and begin to expel medicament from the first chamber through the outlet. During forward axial movement of the stopper in the barrel, propellant vents away from the second chamber through a vent hole.