RELISTOR's Effects on Opioid-Induced Constipation

Inclusion Criteria: Experimental Group (initial screen): * Age 18 years or older * Inpatient who will undergo a 1-2 level ALIF procedure with Dr. Richard Meyrat * Are not pregnant or lactating * Does not have a history of drug abuse within the past 2 years * Does not have a gastrointestinal ostomy Experimental Group (post-operative OIC screen/rescreen) * Actively constipated (i.e., no BM in last 48 hours, difficult having a spontaneous BM, or inability to have a spontaneous BM) * Receiving mu-agonist opioids * Expected to require daily opioid analgesics for at least 7 days following enrollment * Have not received or discontinued use of any laxatives, enemas and/or promotility agents within 48 hours of enrollment and the first dose of RELISTOR. Stool softeners are permitted. * Does not have a known hypersensitivity to methylnaltrexone, naltrexone, or naloxone Observational Group (initial screen): * Age 18 years or older * Inpatient who will undergo 1-2 level ALIF procedure with Dr. Graham * Are not pregnant or lactating * Does not have a history of drug abuse within the past 2 years * Does not have a gastrointestinal ostomy Observational Group (post-operative OIC screen/rescreen): * Actively constipated (i.e. no BM in last 48 hours, difficulty having a spontaneous BM, or inability to have a spontaneous BM) * Receiving mu-agonist opioids * Expected to require daily opioid analgesics for at least 7 days following enrollment Exclusion Criteria: Experimental Group (post-…