Characterization of the opioid receptor binding and animal pharmacology of meptazinol.

Meptazinol is a unique opioid analgesic. Binding studies suggest a relative selectivity for mu 1 sites, as opposed to the other opioid receptor binding sites. This binding selectivity is consistent with meptazinol's supraspinal site of action and its sensitivity to the mu 1-selective opiate antagonist naloxonazine. Furthermore, at equianalgesic doses, morphine depressed respiration to a greater degree than meptazinol.