Opioid analgesics in the management of neuropathic pain

Neuropathic pain affects 2 to 3% of the population in developed countries and can be particularly severe and debilitating. There has been considerable controversy regarding the role of opioid analgesics in the management of this disabling condition. However, a recent systematic review of high-quality randomized controlled trials (RCTs) utilizing opioid analgesics in the treatment of chronic neuropathic pain showed clinically significant benefit. These studies demonstrate, on average a 20 to 30% reduction in pain intensity. RCTs in patients with postherpetic neuralgia given controlled-release oxycodone or controlled-release morphine showed a significant reduction in pain intensity with variable improvement in sleep and disability. Trials of controlled-release oxycodone in painful diabetic neuropathy showed more consistent improvement in pain, sleep and ability to function. Nausea and constipation are common side effects, but can usually be controlled with anti-emetics and a bowel regimen, respectively. Psychological dependence or addiction is unusual in the absence of a history of substance abuse. Methadone may be particularly useful when conventional opioid analgesics have failed due to its N-methyl-D-aspartate (NMDA) antagonist properties. When antidepressants and anticonvulsants fail to provide adequate pain control for neuropathic pain, opioid analgesics are emerging as an important treatment option - in some cases, this class of drugs can make the difference between bearable and unbearable pain.