Clinical Experience with ORG NC45 (Norcuron) as the Sole Muscle Relaxant

Abstract

The neuromuscular effects of ORG NC45, used as the sole muscle relaxant, were compared with a succinylcholine-pancuronium sequence in patients during nitrous oxide-fentanyl anaesthesia. The subjects were divided into four groups with ten in each group. After induction of anaesthesia they received either succinylcholine, 1 mg-kg-1 or ORG NC45 in doses of 50, 70 or 90 μxg-kg-1 and tracheal intubation was done 90 seconds later. Neuromuscular transmission was monitored using train-of-four stimulation. Succinylcholine produced 100 per cent block with uniformly excellent intubating conditions whereas the three doses of ORG NC45 were associated with blocks of 7.5, 18.7 and 30.7 percent and acceptable conditions in only 30 per cent of subjects. Muscle relaxation was maintained in the NC45 groups with increments of 10 |xg-kg~’ and in the succinylcholine group with pancuronium, initially as a bolus of 40 μg-kg-1, followed by increments of 5 μg-kg-1 . All increments were given at 10 per cent recovery of twitch height. The overall requirement to maintain 90 per cent block with pancuronium was 1.1 μg-kg-1-min-1; compared with 1.28 μxg-kg1-min-1 with ORG NC45. No cumulative effects were seen with either drug during the first hour of neuromuscular blockade. At the end of the operation the neuromuscular block was antagonized with atropine 18 μxg-kg-1, and neostigmine 36 μxg-kg-1 and recovery was significantly more rapid with NC45 than pancuronium. We conclude that the lack of cumulation, easy reversibility and lack of cardiovascular effects suggest that NC45 has advantages over currently available non-depolarizing muscle relaxants but that its onset of action is too slow for rapid intubation.