Bremazocine: an opiate that induces sedation and analgesia without respiratory depression

The benzomorphan analogue bremazocine has been shown to be a potent analgesic with a low dependence liability and with no respiratory depressant effects in preliminary pharmacologic screening. As this compound may prove to be of potential interest to anesthesiologists, it was tested in the conscious dog in increasing doses (1, 5, 10, 20, and 40 micrograms/kg) while blood pressure, heart rate, respiratory rate, arterial blood-gas tensions, electrical cortical activity, and somatosensory-evoked potentials (SS-EVP) were recorded. Bremazocine had no significant cardiovascular or respiratory effects. Power spectral analysis of the EEG showed a dose-related increase of power in the theta to delta band. SS-EVP was characterized by a decrease in amplitude of the P45 and P70 waves and an increase in the latency of the P 100 peak. EEG and peak latency changes could be reversed by the kappa-specific antagonist Mr 2266 (20 micrograms/kg), but not by the classic opiate antagonist naloxone (20 micrograms/kg). It is suggested that kappa receptor sites distinct from those interacting with common opioids (mu) are responsible for the observed changes associated with bremazocine.