Alvimopan is a drug which behaves as a peripherally acting μ-opioid antagonist. With limited ability to cross the blood–brain barrier, many of the undesirable side-effects of the opioid agonists such as constipation are minimized without affecting analgesia or precipitating withdrawals. Alvimopan is indicated in patients to avoid postoperative ileus following partial large or small bowel resection with primary anastomosis. Alvimopan accelerates the gastrointestinal recovery period as defined by time to first bowel movement or flatus. Alvimopan competitively binds to mu-opioid receptor in the gastrointestinal tract. Unlike methylnaltrexone (another peripherally acting mu-receptor antagonist) that bears a quaternary amine, alvimopan owes its selectivity for peripheral receptors to its kinetics. Alvimopan binds to peripheral mu-receptors with a Ki of 0.2 ng/mL and dissociates slower than most other ligands.
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