Pharmacological characterization in vivo of the novel opiate, beta-funaltrexamine.

The profile of action of beta-funaltrexamine (beta-FNA), the fumaramate methyl ester derivative of naltrexone, on antinociceptive tests in vivo was investigated. Beta-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 beta-FNA were of remarkably long duration and were selective toward nu agonist interactions. This profile of action is consistent with the profile of action of beta-FNA in vitro. The selective long-lasting antagonism of mu-mediated effects by beta-FNA may be of great value in the elucidation of multiple opioid receptor function.