A battery-powered programmable device designed to be implanted in a patient for the storing and subarachnoid (intrathecal) administration of narcotics/drugs (e.g., morphine sulfate, baclofen) to manage intractable pain and muscle spasms of malignant or non-malignant origin. This implantable infusion pump (IIP) delivers drug doses from its implanted refillable reservoir which is controlled by drug concentration and/or by radio-frequency (RF) signals from an external programming device. The drug reservoir, usually implanted under the skin of the lower abdomen, is typically connected to a catheter placed into the spinal fluid space.