Influence of small doses of vecuronium and pancuronium on succinylcholine-induced neuromuscular blockade

The effects of pretreatments with vecuronium (VB) and pancuronium (PB) on succinylcholine (SCC)-induced neuromuscular blockade were evaluated in 266 patients using electromyographic responses to train-of-four (TOF) ulnar nerve stimulation repeated every 20 seconds. Seventy-five patients served as the control group and received 1 mg.kg-1 SCC without pretreatment with VB or PB. Other 191 patients were divided into three groups according to the type and dosage of pretreatment as follows: VB 20 micrograms.kg-1, VB 14 micrograms.kg-1 and PB 20 micrograms.kg-1. Five minutes after each pretreatment. SCC 1 mg.kg-1 was administered intravenously. All patients were intubated after SCC injection and then anesthesia was maintained with nitrous oxide and enflurane. Among pretreatment groups, the maximal amplitude response to TOF stimuli and TOF ratio were depressed most by 20 micrograms.kg-1 VB and least by 20 micrograms.kg-1 PB at the time of SCC administration. All pretreatments delayed the onset time from SCC injection to maximal blockade compared with that of control group. Maximal blockade induced by SCC was significantly less in VB 20 micrograms.kg-1 group than that in other pretreatment and control groups. The duration of action of SCC was shortened by pretreatments with two dosages of VB but prolonged by PB pretreatment. TOF ratio during the recovery phase was depressed in all pretreatment groups than that in control group. It is demonstrated that a non-depolarizing muscle relaxant, VB has relatively potent antagonistic action on SCC-induced effects, although another potent agent, PB exerts antagonistic action only slightly.