US Patent 7524304 Drug infusion device

The invention provides a drug delivery infusion device comprising an injection means (18) in fluid connection with a drug reservoir chamber (12) and pressure-generation means (10) coupled to both the drug reservoir (12) and to a liquid-filled control chamber (13), wherein the coupling is such that the liquid-filled control chamber (13) serves to constrain the motion of the pressure-generation means (10), thereby controlling the drug infusion rate, wherein the liquid-filled control chamber (13) is associated with means for controlled depletion of the liquid therein whereby depletion of the volume of liquid in the control chamber enables the pressure-generation means to drive the drug in the reservoir chamber therefrom for infusion thereof.