A Prospective, Multicentre Study of Low Dose Targeted Drug Delivery (TDD) for Chronic Back Pain Patients who have Failed Spinal Cord Stimulation

This study will involve the use of the SynchroMed II drug infusion system (Medtronic), which consists of a programmable pump and catheter, and the use of low dose targeted drug delivery (TDD) therapy in patients with chronic primary back pain who have "failed" spinal cord stimulation (SCS) therapy. "Failed" refers to the loss of efficacy of a permanently implanted SCS system over time, or failure to adequately respond to SCS therapy after implantation, or failure to adequately respond to a trial of SCS therapy. Patients must have failed at least two SCS interventions, or have failed one and are not suitable for subsequent SCS interventions. The purpose of this study is to assess the efficacy and safety of TDD therapy as an alternative treatment option for these patients. Eligible patients will receive a permanent implant of a SynchroMed II infusion system, consisting of a programmable pump (20ml or 40ml size) and a catheter. This involves a 60-90 min surgical procedure in which an incision is made in the abdomen for placement of the pump under the skin, and a second incision is made in the back for insertion of the catheter into the intrathecal space, the other end of which is then connected to the pump. The implant visit may or may not include a brief intra-hospital trial of the therapy (infusion or bolus of morphine). The trial method (or no trial) is at the discretion of the Investigator. Suitable patients who are on systemic opioid medications must undergo a 6-week opioid taper to achieve = 20mg morphine equivalent prior to trial/implantation. The Control Workflow for TDD (Medtronic) will be used as a guide to help eliminate systemic opioids and establish the lowest effective infusion drug dose and the desired refill interval for implanted patients. The main opioids that will be used intrathecally are morphine sulphate or hydromorphone. The starting intrathecal drug dose will be 0.2mg/day morphine. Following the Control Workflow for TDD, the pump will be programmed to administer drug at a steady state to achieve a 3-month refill interval. For a 20ml pump, this is achieved with a drug dose of 0.2mg/day at a concentration of 1mg/ml and a set flow rate of 0.2ml/day. For a 40ml pump, this is achieved with drug dose 0.2mg/day, concentration 0.5mg/ml, flow rate 0.4ml/day. Drug dose may be increased by 0.1-0.15mg/day every 4-weeks until a clinically effective dose is achieved (50% pain relief or greater) in the absence of significant side effects. The clinically desired target is a total morphine equivalent dose of 1.5mg/day. Patients will attend routine, standard care follow-up consultations at 1-, 4-, 6- and 12-months post-implant at their participating centres. Information/data to be collected at each visit includes: pump refill information, concomitant medications, pain scores, quality of life scores, health status score, global impression of change, work status. The study will be conducted across 4 research/pain management centres by a team of 6 highly experienced pain specialist physicians around Australia.