Studies show that lubiprostone can increase the overall frequency of bowel movements each week in patients with opioid-induced constipation. These actions result in increased tone, enhanced peristalsis, and increased acceleration of the small bowel and colonic transit times. Lubiprostone (Amitiza) is a type-2 chloride channel activator that increases secretion of fluid in the GI tract. Relistor should not be used in patients with peptic ulcer disease, diverticulosis, colon cancer, or obstruction. Subcutaneous methylnaltrexone was found to be significantly better at reversing OIC than lubiprostone, naloxegol, and oral methylnaltrexone. Methylnaltrexone (Relistor) does not cross the blood-brain barrier which doesn't induce symptoms of opioid withdrawal. Methylnaltrexone bromide is the first available peripherally acting opiate antagonist which is used to treat OIC. For refractory cases of OIC, newer agents may be used with methylnaltrexone being the most superior. Another laxative included saline laxative such as magnesium citrate which has an onset of action from 30 to 180 minutes. Stool softeners are ideal for preventing constipation they do not work well for established cases of constipation. The most common regime for OIC is a stimulant (senna/bisacodyl) with or without a stool softener (docusate), or daily administration of an osmotic laxative (polyethylene glycol). These laxatives increase the bulk of the stools, distend the colon, and augment peristalsis. Opioids prevent peristalsis of the increased bulk which worsens abdominal pain and can contribute to bowel obstruction. The only laxatives that should be avoided are the bulk-forming laxatives, like psyllium. The annual estimated expenditure for laxatives in the United States is over 800 million dollars. All types of laxatives can be used as initial therapy except for the bulk-forming laxatives. All healthcare workers who prescribe opioids need to also consider prophylactic treatment for constipation. Increasing dietary fiber, fluid intake, and physical exercise are the backbone to prevention therapy.
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