Synergism between atracurium and vecuronium in children.

In 30 children under balanced anaesthesia, we have determined dose-response curves and maintenance requirement of three dose ratio combinations of atracurium and vecuronium (10:1, 4:1 or 1.6:1 on a microgram:microgram basis). Neuromuscular block was monitored by adductor pollicis EMG. An equipotent dose ratio (4:1) was most potent, with a mean (SEM) ED95 of atracurium 95 (6) micrograms kg-1 with vecuronium 24 (1) micrograms kg-1. The sum of these doses is only 58% of an ED95 value of one agent (P = 0.0001). The hourly requirement to maintain a 90-95% neuromuscular block was 2.0 (0.1) times an individual ED95 dose of any combination. Recovery index was 8.9 (0.5) min. These results indicate that a combination of atracurium and vecuronium is supra-additive compared with the effects of each drug alone. However, all combinations maintained an intermediate character of neuromuscular block. Combining atracurium with vecuronium may reduce drug requirement by 40%.