A comparison of the respiratory effects of meptazinol, pentazocine and morphine

Abstract

The respiratory effects of a new strong analgesic, meptazinol, were compared with a placebo and with equianalgesic doses of morphine and pentazocine 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 100 mg/70 kg or placebo. However, both morphine 10 mg/70 kg and pentazocine 60 mg/70 kg depresesd the slope of the ventilatory response (-30.0% and -31.6% respectively, P less than 0.02, averaged over the first 3.5-h period). End-tidal carbon dioxide tension (PE'CO2) while breathing room air increased significantly following all three drugs. However, the increase in PE'CO2 after meptazinol (0.22 kPa averaged over 3.5 h) 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 room air with a resistive inspiratory load of 8 kPa litre-1 s, PE'CO2 again increased significantly (P less than 0.05) following all three drugs. The increase in PE'CO2 after meptazinol was then the same as that after morphine (0.51 kPa averaged over 3.5 h). The increase following pentazocine (0.80 kPa) was significantly greater than that after both morphine and meptazinol (P less than 0.02).