Alvimopan

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A peripherally acting mu-opioid receptor antagonist, wasapproved by the US FDA to accelerate thetime to gastrointestinal recovery followingbowel resection surgery. It is the firstpharmacotherapy to be approved for thisapplication.
Ileus — a temporary impairment ofgastrointestinal function — is a complicationthat affects almost all patients that undergomajor bowel surgery. It results in abdominaldiscomfort, nausea and vomiting, and is amajor reason for prolonged hospitalization.
The pathophysiology of post-operative ileus(POI) is complex. An important contributoryfactor is the activation of m-opioid receptors in the gastrointestinal tract by endogenous opioidsthat are released in response to the stress causedby surgery, as well as by opioid analgesics thatare the most common treatment for pain inpatients undergoing surgery1,2. Activation ofthese peripheral m-opioid receptors leads to anincrease in colonic muscle tone and a reductionin propulsive activity in the gastrointestinaltract. Consequently, opioid treatmentto provide pain relief following surgery isthought to prolong POI. The adverse effects of opioids on thegastrointestinal tract can be reversed bym-opioid-receptor antagonists such as naloxoneand nalmefene, but these drugs are also activein the central nervous system, and so inhibitthe analgesic effects of systemic opioids.To overcome this issue, efforts have beendirected at identifying m-opioid receptorantagonists with peripherally restrictedactivity. One such research programmeresulted in the discovery of alvimopan.
Drug properties
Alvimopan is a potent and selective antagonistof the human m-opioid receptor4 –6. It is orallyavailable, but its activity is peripherallyrestricted because its moderately large,zwitterionic form and polarity limitgastrointestinal absorption and preventpassage through the blood–brain barrier4 –6.Preclinical and small-scale clinical studiesdemonstrated that alvimopan administeredorally can selectively antagonize thegastrointestinal effects of opioid agonists suchas morphine without affecting analgesia.

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