Nondepolarizing neuromuscular blocking drugs and train-of-four fade.

The aim of this study was to examine differences in prejunctional effects of different relaxants by measuring the train-of-four (TOF) fade during the onset and recovery of neuromuscular block. The relaxants studied were atracurium (225 micrograms.kg-1), mivacurium (65 micrograms.kg-1) rocuronium (300 micrograms.kg-1) and vecuronium (40 micrograms.kg-1). The TOF ratios were measured at approximate heights of T1 (first response in the TOF) of 90, 75, 50, and 25%. The TOF fade (as shown by lower TOF ratios) increased with a decrease in the T1 during onset of neuromuscular block. Although there was a slightly greater fade with atracurium and rocuronium during the onset of block, the differences among the relaxants were insignificant. It is concluded that the relative prejunctional effects of these relaxants are similar.