Effectiveness of Long-Term Opioid Therapy for Chronic Non-Cancer Pain

Abstract

Background: Opioids have been utilized for thousands of years to treat pain and their use continues to escalate. It is estimated that 90% of the patients who present to pain centers and receive treatment in such facilities are on opioids. However, in contrast to increasing opioid use and the lack of evidence supporting long-term effectiveness in chronic non-cancer pain, is the escalating misuse of prescription opioids, including abuse and diversion. There is also uncertainty about the incidence and clinical salience of multiple, poorly characterized adverse drug events, including endocrine dysfunction, immunosuppression, infectious disease, opioidinduced hyperalgesia, overdoses, deaths, and psychosocial and economic implications. Study Design: A comprehensive review of the literature. Objective: The objective of this comprehensive review is to evaluate the clinical effectiveness and safety of chronic opioid therapy in chronic non-cancer pain. Methods: A comprehensive review of the literature relating to chronic opioid therapy in chronic non-cancer pain. The literature was collected from various electronic and other sources. The literature that was evaluated included randomized trials, observational studies, case reports, systematic reviews, and guidelines. Outcome Measures: Pain relief was the primary outcome measure. The secondary outcome measures were functional improvement and adverse effects. Short-term effectiveness was considered to be less than 6 months; long-term effectiveness was considered to be at least one year. Results: Given the complexity and widespread nature of opioid therapy, there is a paucity of qualitative and/or quantitative literature. The available evidence is weak for pain relief combined with improvement in functional status. Only one drug, tramadol, is effective for pain relief and improvement of functional status. Limitations: This is a narrative review without application of methodologic quality assessment criteria. Even so, a paucity of literature exists concerning both controlled and observational literature for multiple drugs and multiple conditions of chronic non-cancer pain. Conclusions: This comprehensive review illustrates the lack of literature on long-term opioid therapy; thus, opioid therapy should be provided with great restraint and caution, based on the weak evidence available. Key words: Chronic non-cancer pain, opioids, opioid effectiveness, adverse effects, morphine, hydrocodone, hydromorphone, fentanyl, tramadol, methadone, oxycodone