Twitch Depression and Train-of???Four Ratio after Antagonism of Pancuronium with Edrophonium, Neostigmine, or Pyridostigmine

During N2O--O2--halothane anesthesia pancuronium (3 mg/70 kg) was antagonized with neostigmine (2.5 or 5 mg/70 kg), pyridostigmine (10 or 20 mg/70 kg), or edrophonium (50 or 100 mg/70 kg) in 36 human subjects (6 in each group). Reversal was attempted at 10% spontaneous recovery of muscle twitch, which was measured using train-of-four stimulation. When first twitch tension was less than 70% of the control it was found that for the same tension, the train-of-four ratio was greater with edrophonium than with neostigmine, and greater with neostigmine than with pyridostigmine. It was concluded that the three antagonists have different mechanisms of action. In comparison with neostigmine, edrophonium is more and pyridostigmine is less effective at presynaptic (or fade) receptors.