Case Presentation: We present the case of a 58 -year-old opioid naïve man admitted for elective knee arthroplasty received parenteral hydromorphone and enteral oxycodone for analgesia. On post-operative day one, he developed abdominal pain. Abdominal X-ray showed stool burden suggesting constipation (OIC) prompting management with laxatives; he was given 12 mg parenteral methylnaltrexone. Overnight he developed worsening diffuse abdominal pain, distension and dyspnea. He became tachycardic and hypotensive. Abdominal exam revealed acute surgical abdomen (hypoactive bowel sounds with involuntary guarding). Abdominal CT showed free air suggestive of visceral perforation and diverticulitis. He was started on broad spectrum antibiotics and underwent emergent Exploratory Laparotomy resulting in a sigmoid colectomy and diverting colostomy. Patient tolerated the procedure well and was discharged on antibiotics with outpatient surgery follow-up.
Discussion: Following approval in 2008 for use in OIC, there have been a handful of reported cases of Methylnaltrexone induced intestinal perforation. The proposed mechanism is an increased propulsive activity of the gut smooth muscles resulting in prokinetic effect.1 Most cases have been associated in patients with an underlying gut pathology.2,3 We suspect that the presence of diverticulitis in our patient predisposed him to develop a perforation. Recently the FDA issued a warning about the drug’s risk for causing intestinal perforation.4 Presence of intestinal inflammation, tumor or ileus predisposes patients to risk of perforation with Methylnaltrexone. Abdominal pain is the most common side effect of methylnaltrexone. Physicians must be aware of the warning signs like hemodynamic instability, worsening abdominal pain and distention while using this medication. Once diagnosed, stopping the medication and immediate surgical consultation is the mainstay of treatment. It is advised to prevent OIC with proactive use of laxatives (psyllium) and cathartics (polyethylene glycol, lactulose). Once diagnosed, the dosages of laxatives should be increased, and other options such as Senna, surfactants (docusate), Lubiprostone, Naloxone, Naloxegol, methylnaltrexone etc. are some options for management.
Conclusions: Opioid medications are commonly used for post-operative pain management, but have a propensity to cause many adverse effects, one of the most common being opioid induced constipation (OIC). “Narcotic Bowel Syndrome” is a severe painful form of OIC. Prophylactic laxatives, dietary fiber and fluid intake are the initial steps of management. In refractory OIC, opioid receptor (µ) antagonists like Methylnaltrexone have been approved for management. However, one must be cautious while using such agents especially in patients with abnormalities of the GI tract and be aware of certain life-threatening complications associated with it.