[Treatment of constipation in chronic pain patients].

The treatment of chronic pain, whether of cancer or noncancer origin, frequently involves the use of opioids. Delay in GI transit and constipation are the most common and often disabling side effects of opioid analgesics. Many treatments involving laxatives and prokinetic drugs have been explored to circumvent opioid-induced bowel dysfunction, but the outcome has in general been unsatisfactory. Specific antagonism of peripheral opioid receptors offers a more rational approach to the management of the adverse actions of opioid analgesics in the gut. This goal is currently addressed by the use of opioid receptor antagonists with limited absorption such as oral naloxone and by the development of peripheral opioid receptor antagonists such as methylnaltrexone and alvimopan. These drugs hold considerable promise in preventing constipation due to treatments with opioids, whereas the analgesic action of opioids remains unabated.