Pain control following major spine surgery is difficult to achieve. Opiates are often necessary in high doses, and may be associated with significant side effects including constipation. Alvimopan is a drug approved by the Food and Drug Administration (FDA) and is used to help the bowel recover more quickly in patients who are having bowel surgery, so that they can eat solid foods and have regular bowel movements. Alvimopan is in a class of medications called peripherally acting mu-opioid receptor antagonists. It works by protecting the bowel from the constipation effects of opioid (narcotic) medications that are used to treat pain after surgery.