Opioids for Chronic Noncancer Pain

摘要

Opioids have a special place in pain medicine. They are among the most powerful analgesics in clinical use. The remarkable advances that have been made in the management of cancer-related pain are mainly due to the widely accepted use of strong opioids as advocated by the World Health Organization (1996). Why did it take so long for opioids to gain acceptance in the management of cancer pain, and why is the threshold so high for the use of opioids in chronic noncancer pain? To try to answer this question, let us compare opioids with two other major groups of analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs) and tricyclic antidepressants (TCAs). NSAIDs are widely used for nocicep-tive pain. They are effective, but can cause serious adverse effects (allergy, renal failure, gastric ulcers, and heart failure) as described by McQuay and Moore (this volume). In neuropathic pain TCAs are the standard. Their adverse effect profile resembles that of opioids-sedation, dizziness, dry mouth, and constipation. Analgesic tolerance is seen with opioids, and long-term follow-up studiea are required to find out whether tolerance limits their usefulness for chronic pain. However, all randomized and controlled studies on antidepressants and anticonvulsants are of 3-6 weeks' duration (McQuay et al. 1996). Because plasticity is a typical phenomenon in the central nervous system, one could argue that there is no reason why tolerance should not also develop to the analgesic effects of antidepressants. Respiratory depression is a serious complication related to opioids. However, if the opioid dose is titrated against pain and adjusted carefully, respiratory depression should not be a problem.