Abstract: A method for removing a toxic substance from a patient utilizes a filtering device defining a first fluid flow path and a second fluid flow path. The filtering device also includes a semipermeable membrane separating the first fluid flow path and the second fluid flow path from one another, the membrane being selectively permeable to the toxic substance. The filtering device additionally includes a reservoir and a pump, the reservoir being located along the second fluid flow path between the membrane and the second inlet port. The filtering device is inserted into the patient so that it is totally surrounded by the patient, the filtering device is connected to a blood vessel of the patient so that blood from the artery is shunted along the first fluid flow path. An outlet end of the second fluid flow path is connected to the urinary bladder of the patient.