An implantable drug delivery apparatus for delivering a drug into a bodily fluid in a body cavity of a patient over a period of time includes a variable-volume vessel defining a working chamber for receiving a drug and recirculating a therapeutic fluid. The fluid can contain a bodily fluid, such as, for example, perilymph, and a drug. The device allows for the controlled delivery of the therapeutic fluid to a predetermined location in the bodily cavity of the patient, such as, for example, a cochlea of a human ear.