ROCURONIUM ONSET OF ACTION - A COMPARISON WITH ATRACURIUM AND VECURONIUM

The onset, maximal neuromuscular block, and duration of rocuronium wer e compared with atracurium and vecuronium during enflurane anesthesia. Sixty patients received rocuronium (80,100,120, or 160 mug/kg). Enflu rane enhanced a rocuronium neuromuscular block in a dose-related manne r; the ED50 was 104 +/- 11 and 83 +/- 7 mug/kg (SEM) during 1% and 2% enflurane anesthesia, respectively. Patients receiving atracurium (0.1 2 mg/kg) or vecuronium (0.02 mg/kg) were studied during 1% enflurane a nesthesia until seven in each group qualified by achieving a maximal b lock between 85% and 97%. These patients were matched with each other and with patients who had received rocuronium. Seven groups of three p atients (rocuronium, vecuronium, and atracurium) were obtained. The av erage difference in maximal block was less than 2% between matched pat ients. The ratio of dose used to achieve a similar final block suggest s potency ratios of 1, 8.5, and 1.2 for rocuronium, vecuronium, and at racurium. Rocuronium's onset time (time from drug administration to 50 %, 75%, and 90% of final block) was significantly faster than either o f the other two muscle relaxants (P < 0.01). Time to 90% of final bloc k was 1.35 min for rocuronium, 3.06 min for atracurium, and 3.71 min f or vecuronium. Using these equipotent doses, atracurium also had a sho rter time to develop neuromuscular block than vecuronium (P < 0.05). F or these three intermediate duration neuromuscular blockers, speed of onset was inversely related to their potency, confirming a relationshi p that had been demonstrated for the long-acting drugs pancuronium, d- tubocurarine, and gallamine.