Priming rapacuronium: a comparison with rocuronium and mivacurium.

The aim of this study is to present the pharmacodynamics of the priming principle using rapacuronium and a comparison with rocuronium and mivacurium. After induction, 120 patients were randomly allocated to six similar groups. Groups 1 and 2 received rapacuronium 1000 micrograms.Kg-1 as a bolus or primed with 100 micrograms.Kg-1. To groups 3 and 4, rocuronium 400 micrograms.Kg-1 were given as a bolus or primed with 60 micrograms.Kg-1, finally mivacurium 100 micrograms.Kg-1 was used for groups 5 and 6 by bolus or primed with 10 micrograms.Kg-1. Neuromuscular function was monitored by electromyography and it was demonstrated that time to 80% blockade, is significantly shorter after priming: 137 (bolus) vs 101 seconds (priming) for rapacuronium, 160 vs 90 for rocuronium and 196 vs 118 for mivacurium. Onset time was also statistically accelerated by priming: 229 seconds vs 183, 289 vs 203 and 298 vs 252 respectively. No significant change was noticed in maximal blockade and clinical duration due to priming. During early onset, only the mivacurium patients showed a statistical difference in train of four fade between bolus and priming. In conclusion, priming hasten early and maximal effect produced by rapacuronium, rocuronium and mivacurium without any change in maximal blockade and clinical duration. Pre-synaptic effect does not explain consistently the mode of action of priming.