The duration of action of mivacurium is prolonged if preceded by atracurium or vecuronium

We studied 45 patients (ASA I-II) during propofol-alfentanil-N₂O-O₂ anaesthesia to determine if recovery from neuromuscular block induced by mivacurium is influenced differently by prior injection of atracurium or vecuronium. Neuromuscular function was monitored by adductor pollicis EMG. Patients were randomized to receive two dosesof either mivacurium (150 and 70 μg kg^-1), atracurium (350 and 75 μg kg^-1) or vecuronium (70 and 15 μg kg^-1) followed by a final dose of mivacurium 70 μg kg^-1. The second and third doses of the muscle relaxants were administered at 25–30% recovery of the E₁ (first EMG response in the train-of-four series). Following the final dose of mivacurium, the EMG response recovered to 25 and 95% in 10.4±3.9 and 19.7±5.7 min (mean±SD), respectively, if mivacurium was the only muscle relaxant. Respective times were 100% longer if mivacurium had been preceded by atracurium (23.8 ± 3.3 and 39.8±6.9 mm) or vecuronium (22.6±3.5 and 44.1 ±7.9 min) ( P =0.000l). The 25–75% recovery times in the three groups were 4.9±1.0, 8.7±2.4 and 10.5±2.5 min, respectively ( P =0.0001). Our results indicate that there is no benefit in giving mivacurium at the end of surgery after peroperative use of atracurium or vecuronium.