A self-contained portable apparatus for administration of a drug solution is disclosed, comprising: 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 said drug solution to a recipient. A pressurization system is arranged for providing a constant and controllable gas pressure to the housing, wherein a controllable pressure is obtained for a controllable delivery of the drug solution. The pressurization system comprises: a pressure source for delivering positive pressure gas a pressure accumulation tank connected to said source and to said second chamber, arranged to provide a positive pressure reservoir a one-way valve arranged between said pressure source and said pressure accumulation tank, enabling gas to flow solely in the direction from the pressure source to the pressure accumulation tank and a mechanical pressure regulator arranged between said pressure accumulation tank and said housing. Hereby, an extremely stable and well controllable output pressure and output flow is obtainable.
