A systematic review 1 including 14 studies with a total of 1,145 subjects was abstracted in DARE. The patients in the included studies had pain from osteoarthritis, diabetic and peripheral neuropathy, phantom limb pain, musculoskeletal pain, postherpetic neuralgia and mixed types of pain. For intravenous opioids, mean pain relief with opioids was about 30% for neuropathic and nociceptive pain. Two RCTs found that oxycodone significantly reduced steady pain, brief pain and dynamic allodynia compared with placebo in patients with allodynia. All 7 studies assessing the quality of sleep found a significant improvement with opioids. Five RCTs found no significant difference with either an opioid or placebo for various measures of physical activity. Two studies reported lower disability scores with oxycodone compared with placebo. There was no statistically significant difference in the rates of discontinuation for opioids and placebo (30% versus 26%; RR 1.0, 95% CI: 0.1 to 1.2). The most common reasons for discontinuation were adverse effects with opioids and lack of efficacy with placebo. Patients taking opioids were more likely to report at least one adverse effect than patients taking placebo (80% versus 56%; NNH 4.2, 95% CI: 3.1 to 6.4). The most common adverse effects with opioids were constipation (41% versus 11% with placebo; NNH for 3.4, 95% CI: 2.9 to 4.0), somnolence (29% versus 10% with placebo) and nausea (32% versus 12% with placebo). Opioids also significantly increased vomiting (15% versus 3%), dizziness (20% versus 7%) and itching (15% versus 7%) compared with placebo. The studies found that about 44% of patients remained on opioids after 7 months to 2 years.
A Cochrane review[Abstract] 2 included 26 studies with a total of 4 893 subjects examining long-term opioid management for chronic noncancer pain; 25 of the studies were case series or uncontrolled long-term trial continuations, the other was an RCT comparing two opioids. Opioids were administered orally (n = 3 040), transdermally (n = 1 628), or intrathecally (n = 231) for at least 6 months. Participants had moderate or severe chronic noncancer pain (CNCP) due to nociceptive or neuropathic pain, or both (back pain, osteoarthritis, myofascial pain, osteoporotic vertebral fracture, trigeminal neuralgia, neuropathic pain, or unspecified or a variety of types of CNCP). The mean duration of pain prior to study enrollment was reported in only 10 studies, most reported an average duration of pain of about 8 years.
Many participants discontinued due to adverse effects (oral 22.9%, 95% CI 15.3% to 32.8%; transdermal 12.1%, 95% CI 4.9% to 27.0%; intrathecal 8.9%, 95% CI 4.0% to 26.1%) or insufficient pain relief (oral 10.3%, 95% CI 7.6% to 13.9%; intrathecal 7.6%, 95% CI 3.7% to 14.8%; transdermal 5.8%, 95% CI 4.2% to 7.9%). Signs of opioid addiction were reported in 0.27% of participants in the studies that reported that outcome. All three modes of administration were associated with clinically significant reductions in pain, but the amount of pain relief varied among studies. Findings regarding quality of life and functional status were inconclusive.
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