A self-contained portable apparatus for administration of a drug solution includes a housing having an enclosure for receiving a flexible pouch containing a drug solution, the output of which is connectable to a conduit for delivering the drug solution to a recipient. A pressurization system is arranged for providing a constant and controllable gas pressure to the housing in order to obtain a controllable delivery of the drug solution. The pressurization system includes a pressure source for delivering positive pressure gas a pressure accumulation tank connected to the source and the second chamber a one-way valve arranged between the pressure source and the pressure accumulation tank and a mechanical pressure regulator arranged between the pressure accumulation tank and the housing. Hereby, an extremely stable and well controllable output pressure and output flow is obtainable.
