The involvement of the mu-opioid receptor in gastrointestinal pathophysiology: therapeutic opportunities for antagonism at this receptor.

The localization of opioid receptors and their endogenous peptide ligands within the gastrointestinal (GI) tract and their role in the coordination of propulsion and secretion underscores the importance of opioid receptors in the maintenance of GI homeostasis. The peripherally acting micro-opioid receptor antagonists alvimopan and methylnaltrexone (MNTX) are currently under investigation as therapeutic agents to treat the deleterious GI side effects associated with opioid administration. These compounds have demonstrated efficacy in numerous animal models of GI function, and clinical studies have revealed their efficacy in the treatment of postoperative ileus (POI) and opioid-induced bowel dysfunction. Preservation of opioid-mediated analgesia has been demonstrated for these compounds in both the preclinical and clinical settings. Future studies exploring the benefits of selective antagonism of the peripheral mu-opioid receptor in the treatment of other GI conditions may open new therapeutic opportunities for alvimopan and MNTX.