The respiratory effects of meptazinol

The respiratory effects of the new analgesic, meptazinol, were compared with a placebo and with equianalgesic doses of morphine and pentazocine and with diazepam in a double-blind crossover trial in seven healthy volunteers. No significant change in the ventilatory response to rebreathing carbon dioxide was observed after meptazinol or placebo but morphine, pentazocine and diazepam depressed the slope of the ventilatory response (-30.0%, -31.6% and -50.0% respectively, P less than 0.02). End-tidal carbon dioxide tension (PE',CO2) breathing air increased significantly following all three analgesic drugs but not after diazepam. However, the increase in PE',CO2 after meptazinol (0.22 kPa averaged over 3.5 hr) was significantly less than that following morphine (0.40 kPa, P less than 0.05) and pentazocine (0.59 kPa, P less than 0.01). While breathing with a resistive inspiratory load of 8 kPa/l/sec, PE',CO2 increased significantly (P less than 0.05) following all three analgesics but not diazepam. The increase in PE', CO2 after meptazinol was then the same as that after morphine (0.51 kPa averaged over 3.5 hr). The increase following pentazocine (0.80 kPa) was significantly greater than that after both morphine and meptazinol (P less than 0.02). In a preliminary study of pain relief following cholecystectomy there was no significant difference in the analgesic effect of meptazinol compared to morphine, both drugs being given by continuous infusion. More of the patients given morphine had apnoeic periods, although the difference between the groups was not significant.