How effective are opioids in alleviating cancer pain?
TYPE OF REVIEW
An overview of nine systematic reviews.
RELEVANCE FOR NURSING
Pain is one of the most common symptoms associated with cancer, and between 30% to 50% of people diagnosed with cancer will experience moderate-to-severe pain at some time during their illness.
While pain can occur at any stage of the disease, it typically increases in frequency and intensity as the cancer progresses. It has been reported that approximately 40% of cancer patients suffer pain after curative treatment, 55% during cancer treatment, and 66% in advanced disease—with one-third of patients describing pain levels as distressing or intolerable.
Pain management in patients with cancer typically involves the use of opioid analgesics, with morphine considered the gold standard in the treatment of moderate-to-severe pain.
CHARACTERISTICS OF THE EVIDENCE
The primary objectives of this review were to provide an overview of the analgesic efficacy of opioids in cancer pain, and to report on the adverse events associated with their use. Nine Cochrane reviews were included, for a total of 152 studies and 13,254 participants.
The three primary outcome measures were 1) the proportion of participants reporting no worse than mild pain by 14 days after the start of treatment; 2) a Patient Global Impression of Change (PGIC) status of “much improved” or “very much improved”; and 3) withdrawals due to adverse events. The secondary outcome measures included participants experiencing any adverse event or any serious adverse event.
For the first outcome measure, positive results were reported in studies that included oral morphine and transdermal fentanyl. Ninety-six percent of 856 patients reported mild or no pain within 14 days of the start of treatment. A review of oxycodone reported low average pain scores indicative of mild pain at worst.
Five reviews included PGIC status as an outcome, however none were able to determine this outcome from any of the included studies.
There were inconsistent results reported for the number of adverse event withdrawals, however the authors noted these were always less than 20%. The number of participants experiencing any adverse event was inconsistently reported, and when it was reported there was a wide range of results, with event rates between 11% and 77%.
BEST PRACTICE RECOMMENDATIONS
The quantity and quality of evidence regarding the use of opioids in cancer pain was low, therefore no recommendations can be made. The key finding was that most patients with moderate-to-severe pain who are treated with opioids and can tolerate them should have their pain levels reduced to mild or no pain within 14 days of treatment. Most patients will experience adverse effects as a result of opioid treatment, and a portion of these will experience these effects to such a degree to necessitate alternative treatment options.
Since few reviews obtained useful clinical data, such as the proportion of patients with cancer who had no or only mild pain within a relatively short time after starting treatment, more studies are needed. Since many studies were completed within the last 20 years, researchers should undertake retrospective analyses of clinical trial data, using outcomes of clear patient benefit (no worse than mild pain within two weeks of starting opioid titration, for example) and time taken to achieve that benefit.
Wiffen PJ, et al. Opioids for cancer pain—an overview of Cochrane reviews. Cochrane Database Syst Rev