Pharmacological characterization in vivo of the novel opiate, β-funaltrexamine

The profile of action of β-funaltrexamine (β-FNA), the fumaramate methyl ester derivative of naltrexone, on antinociceptive tests in vivo was investigated. β-FNA demonstrated antinociceptive actions that were of short duration and that appeared to be mediated by kappa receptor interaction. In contrast, the antagonist actions of β-FNA were of remarkably long duration and were selective toward mu agonist interactions. This profile of action is consistent with the profile of action of β-FNA in vitro. The selective long-lasting antagonism of mu-mediated effects by β-FNA may be of great value in the elucidation of multiple opioid receptor function.