Constipation et traitements par les opioïdes. Physiopathologie et prise en charge

Constipation is the major digestive side effect during analgesic treatment by opioids, leading to a significant impairment of the patient's quality of life and suboptimal analgesia. Constipation is due to the opioid action on μ receptors at the enteric nervous system level which promotes both motor and antisecretory effects. Opioids increase colonic segmental contractile activity, decrease propagated contractions and colonic tone, alter rectal sensitivity and increase anal sphincter pressure. Besides these motor effects, opioids enhance the incidence of hard stools via an increased water absorption in the small and large intestine. Stimulant laxatives (sennosides, bisacodyl) are often useful to obtain a symptomatic relief while rectal laxatives (enemas, suppositories) are necessary in case of distal constipation with fecal impaction. Oral naloxone is a therapeutic option to prevent opoid-induced constipation but may contribute even at a low dose (2 mg) to a poor control of pain. A significant therapeutic progress comes from the development of new peripheral opioid antagonists (methylnaltrexone, almivopan) leading to an effective analgesia with a reduced incidence of significant transit disturbances.