March 26, 2003 -- There are few effective treatment options for the roughly 3 million Americans who live with debilitating, chronic pain caused by nerve damage. It is widely believed that opium-based drugs, though often prescribed for chronic pain management, are not very effective for so-called neuropathic pain. But new research suggests opioids are a useful treatment option for managing chronic pain caused by nerve damage.
The study shows the morphine-like drug levorphanol to be as effective as other widely used treatments for relieving chronic pain due to nervous system damage, although pain management came at a price. Patients who took the highest and most effective doses of the opioid also had the most treatment-related side effects, such as restlessness, depression, confusion, and personality changes. These side effects often led them to stop taking the drug.
"This study provides strong evidence that opioids are valid and effective drugs for relieving chronic neuropathic pain," lead researcher Michael C. Rowbotham, MD, tells WebMD. "But there are still a lot of unanswered questions."
Chronic pain caused by nerve damage can result from injury, stroke, or diseases like diabetes, shingles, and multiple sclerosis. Such pain usually does not respond to anti-inflammatory medications used to treat other types of chronic pain. But tricyclic antidepressants and certain anti-epileptic drugs have been shown to be effective for some patients.
In this National Institutes of Health-funded study, Rowbotham and colleagues at the University of California, San Francisco, compared two eight-week treatment regimens of levorphanol in patients with a wide range of neuropathic pain conditions. Their findings are published in the March 27 issue of TheNew England Journal of Medicine.
The researchers found that high-dose treatment with opioids provided much greater chronic pain relief than lower doses of the drug. Pain was reduced by 36% among patients in the high-dose group, compared with 21% in those taking lower doses. There was no evidence that any of the study participants built up a tolerance to the medication, requiring escalating doses, and no addictive behavior was observed.
Patients with chronic pain caused by stroke or brain lesions were least likely to report benefits from opioids, while those with chronic pain from spinal cord injury or multiple sclerosis had good pain relief. Patients with chronic pain resulting from shingles, diabetes, and localized nerve injury also responded well to the drug.
Although the opioid was not compared directly with antidepressant and anti-convulsive therapies used to treat neuropathic pain, the responses achieved with the higher doses of levorphanol are similar to those seen in trials evaluating these medications.
"We now know that the opioids work, but we still don't understand the risks and benefits in this population," neurologist and pain expert Kathleen M. Foley, MD, tells WebMD. "In the cancer population it has been shown that these drugs are effective for long periods, that escalating dosages are not needed, and that abuse and addiction are not a problem. We now need large clinical trials to find out if this is also true for these patients."
But pain researcher Gary Bennett, PhD, says even though opioids may have a place in the armamentarium of existing neuropathic pain drugs, there is an urgent need for better treatments.
"When you have pain you aren't looking for a 20% or 30% drop in that pain," the McGill University professor tells WebMD. "The objective is to have no pain, and very few patients experience complete pain relief with the available treatments."