Naloxazone

Naloxazone is an irreversible μ-opioid receptor antagonist which is selective for the μ₁ receptor subtype. Naloxazone produces very long lasting antagonist effects as it forms a covalent bond to the active site of the mu-opioid receptor, thus making it impossible for the molecule to unbind and blocking the receptor permanently until the receptor is recycled by endocytosis.

It has been reported that naloxazone is unstable in acidic solution, dimerizing into the more stable and much more potent antagonist naloxonazine. Under conditions in which no naloxonazine formation could be detected, naloxazone did not display irreversible μ opioid receptor binding.