A comparison in mice of naloxone and nalorphine as antagonists to neuroleptanalgesic drugs.

The effectiveness of naloxone and nalorphine in antagonizing the effects of fentanyl and droperidol on the hot plate reaction time and the respiratory rate of the mouse has been compared. Naloxone was superior to nalorphine, being a more effective antagonist, and was also free from significant agonist effects. However, neither antagonist was completely effective against the respiratory rate depression produced by combinations of fentanyl and droperidol. It is suggested that the duration of the antagonist effects of naloxone are shorter against respiratory depression than against analgesia.