A COMPARISON OF THE RESPIRATORY EFFECTS OF MEPTAZINAOL PENTAZOCINE AND MORPHINE

The respiratory effects of a new strong analgesic, meptazinol,were compared with a placebo and with equianalgesic doses ofmorphine and pentazocine in a double-blind crossover trial inseven healthy volunteers. No significant change in the ventilatoryresponse to rebreathing carbon dioxide was observed after meptazinol100 mg/70 kg or placebo. However, both morphine 10 mg/70 kgand pentazocine 60 mg/70 kg depressed the slope of the ventilatoryresponse ( — 30.0% and —31.6% respectively, P>0.02,averaged over the first 3.5-h period). End-tidal carbon dioxidetension (Pe‘co) while breathing room air increased significantlyfollowing all three drugs. However, the increase in Pe’qo,after meptazinol (0.22 kPa averaged over 3.5 h) was significantlyless than that following morphine (0.40 kPa, P>0.05) andpentazocine (0.59 kPa, P>0.01). While breathing room airwith a resistive inspiratory load of 8 kPa litre₁ s, Pe‘co,again increased significantly (P>0.05) following all threedrugs. The increase in Pe’co after meptazinol was thenthe same as that after morphine (0.51 kPa averaged over 3.5h). The increase following pentazocine (0.80 kPa) was significantlygreater than that after both morphine and meptazional(P>0.02).