An implantable
osmotic pump system includes a rigid pump housing defining an opening adapted to receive a
catheter; one or more membrane assemblies fitted to the pump housing; an osmotic engine within the rigid pump housing and a flexible pharmaceutical agent compartment disposed within the pump housing. The flexible pharmaceutical agent compartment is adapted to enclose a volume of a pharmaceutical agent and to cause the pharmaceutical agent to be infused through the opening as water crosses the membrane
assembly or assemblies and increases the volume of the osmotic engine. The flexible pharmaceutical agent compartment may include
polyethylene teraphthalate (PET), for example, and / or may include a metallic layer such as gold, silver,
platinum and / or aluminum, for example, to inhibit the transfer of gas or liquid across the compartment. A
catheter may be bonded to the opening of the pump housing and to a corresponding opening in the flexible pharmaceutical agent compartment. The flexible pharmaceutical agent compartment may be free floating inside the pump housing, being only attached to the
catheter and / or to the opening of the pump housing. As the present implantable
osmotic pump does not include a movable
piston, the pump housing may have a cylindrical shape in which the height of the pump housing is less than the
diameter thereof, a non-cylindrical shape and / or a shape that conforms to the patient's
anatomy at the
implant site.