Medication delivery apparatus and methods for intravenous infusions

The invention provides a medication delivery system that is preconfigured to administer an infusion therapy by a mechanical pump mechanism upon user activation. The configuration of a multi-chambered flexible bag, each chamber being filled with therapeutic liquid(s), determines the sequence and amount of each liquid to be delivered when the bag is progressively compressed by a constant force spring mechanism in the pump. The spring mechanism is charged by the user manually cocking two covers of the pump housing. A mechanical timer is coupled to the constant force spring to limit the maximum rate at which the spring compresses the flexible bag. In one embodiment of the invention, the medication delivery system further includes a manifold assembly and an administration set. The manifold assembly is configured with internal conduits and valves to direct output from each chamber of the bag to an output port in the manifold, and thence into the administration set. In additional embodiments, there are provided structures in the container to alleviate pressure drop during the application of pressure to the container.