Competitive Opioid Antagonists

Opioid receptors are G protein-coupled receptors for the endogenous opioid peptides; the mu receptor is the main physiological target of most clinically important opioid analgesics, and mu-mediated inhibition of voltage-gated calcium channels on central presynaptic terminals of primary afferent nociceptors is thought to be a primary mechanism of analgesia at the spinal level. This class narrows opioid antagonism by naming how the block is exerted: competitive binding is the interaction of two or more ligands with the same binding site, one displacing the other, so a competitive antagonist occupies the agonist's own site. As MED-RT populates the class it holds alvimopan, described in the NCI Thesaurus as a selective and competitive antagonist at mu-opioid receptors in the gut, and nalbuphine, whose FDA-approved label records it as an agonist at kappa opioid receptors and an antagonist at mu opioid receptors.