Chronic non-cancer pain (CNCP) is a significant public health problem with negative social and economic impacts. CNCP is highly prevalent in many countries. In the United States, about 100 million adults were affected by CNCP in 2008, and it was estimated that the national cost of pain ranged from $560 to $635 billion (Gaskin 2012). Recent population-based surveys in European countries including Spain, Portugal, Ireland, Denmark, Norway and Iceland have estimated that 25-35% of adults report chronic pain (Breivik 2013). Estimates from the Canadian Chronic Pain Study II, a population-based survey, found the prevalence of CNCP in Canada to be 25% (Boulanger 2007).
Opioids are the most potent analgesics available for the short-term treatment of CNCP such as low back pain (Furlan 2011). As a type of narcotic pain medication, they can have adverse effects if they are not used properly. Some studies have reported risks of long-term opioid use, including addiction, misuse, and overdose (Dunn 2010; Von Korff 2011). Some physicians are reluctant to prescribe opioids for CNCP, mainly due to concerns regarding adverse effects, medical complications, risks of diversion, and uncertainty about their efficacy with respect to functional outcomes and quality of life (Boulanger 2007; Morley-Forster 2003). These concerns are primarily related to the chronic, non-terminal nature of the condition which requires ongoing long-term opioid therapy.
Despite these concerns, the use of opioids in many western countries has increased dramatically in the last two decades. The top opioid analgesic consumers per capita include Sweden, France, Australia, Canada, Belgium and the USA (INCB 2006; Diener 2008). Canada’s recorded prescription opioid consumption increased by about 50% between 2000 and 2004, a rate of increase substantially greater than that of the USA during the same period (INCB 2006). Sweden, Australia, and France also recorded substantial increases during this time of 40%, 86% and 91% respectively (Diener 2008). Between 2000 and 2010, Canada's prescription opioid consumption increased by 203% (INCB 2011).
Description of the condition
The population of interest for this review is individuals aged 12 years and older who are experiencing CNCP that has persisted for 3 months or longer. CNCP includes, but is not limited to, conditions such as low back pain and other musculoskeletal pain, neuropathic pain, osteoarthritis, rheumatoid arthritis, fibromyalgia, headaches and migraines, complex regional pain syndrome, reflex sympathetic dystrophy, and causalgia. We will exclude studies focused on individuals receiving end of life or palliative care, as well as studies on neonatal cases, and pregnant women. Additionally, we will exclude studies focused solely on people with cancer, acute post-operative pain, ischemic pain due to vascular disease, pancreatitis, abdominal pain, sickle cell disease, and Crohn’s disease.
Description of the intervention
For this review, long-term use of opioids will be defined as administration of prescription opioid analgesics for three months duration or longer, for the purposes of treating CNCP. Opioids administered by oral, transdermal, transmucosal or rectal route will be included and opioids administered intramuscularly, intravenously or with pumps will be excluded. Experimental studies in human volunteers or animals will also be excluded.
How the intervention might work
A better understanding of the impact of long-term use of opioids for CNCP is needed. Opioids have been shown to be effective in treating CNCP, but this evidence is based on 62 randomized controlled trials of short duration (less than 16 weeks) (Furlan 2011). There is uncertainty about what happens beyond 16 weeks and whether these patients continue to exhibit benefits or if they develop complications. Opioids can have a wide range of complications such as sexual dysfunction, bowel obstruction, cognitive effects (on concentration, attention and short-term memory), traffic accidents, delayed return to work, depression, fatigue, cardiovascular events such as myocardial infarct, exacerbation of sleep apnea, and hyperalgesia/increased pain sensitivity. For the purpose of study feasibility, we focus on the complication outcomes of misuse, abuse or addiction, overdose, falls and fractures.
Why it is important to do this review
While there is evidence of the effectiveness of opioids for treating CNCP from previous review and other studies (Furlan 2006; Chou 2009), little is known about the long-term effects and complications associated with long-term use of opioids for this condition. This knowledge can empower physicians and patients to make informed decisions about the initiation, continuation, or termination of long-term opioids.
The Cochrane review by Noble et al (Noble 2010) on long-term opioid management for chronic non-cancer pain included 1 randomized trial and 25 case series assessing the following outcomes: pain relief, health-related quality of life, function, and adverse effects (e.g., nausea, vomiting, constipation). Most of the participants in the included studies had back pain. The authors found that many patients discontinued long-term opioid therapy due to adverse events or insufficient pain relief. However, patients who were able to continue opioids experienced clinically-significant pain relief. The results for function and quality of life were inconclusive. Many minor adverse events occurred, but serious adverse events, including iatrogenic opioid addiction were rare. The Noble 2010 review did not include large observational studies, nor did they report on outcomes such as overdose, falls and fractures.