A system and method for intravenous, intramuscular, or subcutaneous delivery of a reconstituted medication fluid with simultaneous, uninterrupted delivery of a primary fluid. A medication fluid is prepared by reconstituting a medication with a primary fluid as diluent. A container adapted to receive a medication is retro-primed with primary fluid from a primary bag. The primary fluid mixes with the medication to reconstitute the medication and form a medication fluid. A medication delivery system and method according to the present invention allows for the continuous infusion of primary fluid both during and after the administration of a reconstituted medication, using a closed system with reduced opportunities for contamination and infection.