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Veterinary Specialty Hospital - North County

Methylnaltrexone (MNTX) Clinical Study


Help us improve outcomes for pets undergoing surgery!


Ethos Discovery seeks to define the rate at which methylnaltrexone (MNTX), an FDA-approved opioid-inhibiting drug for humans, is metabolized in dogs following intravenous administration. The opioid-inhibiting effects of MNTX only act in locations outside of the spinal cord, allowing it to still provide its important pain relief effects while preventing it from binding in locations like the GI tract, where it can cause complications such as regurgitation. This means your pet will receive the benefits of pain control and pain management without the risk of opioid-related complications.

Once defined, an ideal dose will be identified, and a future study will evaluate how reliable this dose of MNTX is at reducing postoperative regurgitation in dogs!


Opioids are typically given to pets and humans as pain control medications after operations. Certain properties of opioids can cause reduced motility within the GI tract and increase the risk of regurgitation, potentially leading to more severe complications like aspiration pneumonia. Methylnaltrexone is able to reduce the effect of opioids on the intestines while keeping the opioid’s pain-reducing properties. We hope to see that pets continue to receive the beneficial pain control normally achieved through opioids without as high of a risk for postoperative complications brought on by regurgitation.

Methylnaltrexone (MNTX) inhibits the peripheral effect of opioids (i.e., binding within the intestines) while preserving the opioid’s centrally-acting (i.e., within the spinal cord) pain-reducing properties. It is believed that MNTX will allow pets to still receive the beneficial pain control normally achieved through opioids but will not be at as high of a risk for postoperative complications brought on by ileus and regurgitation.


Eligible patients will initially undergo the collection of blood samples over a 12-hour period on the first day of the study after receiving an injection of MNTX.

Dogs will then have additional injections of MNTX and one-time blood samples collected every 24 hours for 4 more days.


  • Dogs weighing more than 5 kg (11 lbs).

  • Dogs with no known sensitivity to MNTX.

  • Dogs without liver or renal diseases.


  • Bulger Veterinary Hospital, Lawrence, MA

  • VSH – North County, San Marcos, CA

Benefits of Participation

Pet owners who participate receive

  • Free of charge:

    • The cost of the MNTX, physical exams, hospitalization, and diagnostics associated with the study. Costs outside of the study requirements will not be covered.

  • Additional coverage:

    • Up to $3,000 towards the cost associated with treating any side effects suspected to be related to the study protocol.


Enroll or request more information below