A battery-powered, sterile device designed to be implanted in a patient for the long-term or intermittent infusion of narcotics, short-acting anaesthetic agents, antineoplastic drugs, and other agents. This implantable infusion pump (IIP) delivers drug doses from its implanted reservoir which is controlled by drug concentration and/or by radio-frequency (RF) signals from an external programming device. A catheter connected to the reservoir is inserted into the epidural or subarachnoid (intrathecal) space of the spinal canal or into a blood vessel.