Phase 2 RCT of Alvimopan vs. Placebo After CRS/HIPEC

Inclusion Criteria: * Ability to understand and the willingness to sign a written informed consent. * Scheduled to undergo open (non-minimally invasive) CRS/HIPEC. * Scheduled to receive postoperative pain management with intravenous opioids. * Age \> 18 years. * Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 2. * Women of child-bearing potential with negative pregnancy test prior to initiating study drug dosing. Exclusion Criteria: * Greater than 7 days of consecutive opioid use immediately prior to scheduled surgery. * Child-Pugh Class C hepatic impairment. * End-stage renal disease (GFR \< 15 mL/min/1.73 m2 and/or on peritoneal dialysis or hemodialysis). * Complete mechanical bowel obstruction. * Contraindication or inability to tolerate oral medication postoperatively. * Presence of gastrointestinal ostomy after CRS/HIPEC. * Pancreatic or gastric anastomosis performed during CRS/HIPEC. * History of allergic reactions or hypersensitivity attributed to compounds of similar chemical or biologic composition as alvimopan at the treating investigators discretion. * Severe or uncontrolled medical disorder that would, in the investigator's opinion, impair ability to receive study treatment (i.e. uncontrolled diabetes, chronic renal disease, chronic pulmonary disease or active, uncontrolled infection, psychiatric illness/social situations that would limit compliance with study requirements). * History of myocardial infarction in the 12 months prior to scheduled surgery. * Pregnant or nursing.