Interaction of halothane with non-depolarizing neuromuscular blocking drugs in man.

1 Tetanic and single twitch contractions of the adductor pollicis muscles, in response to indirect stimulation of each ulnar nerve, were recorded in patients anaesthetized with thiopentone and nitrous oxide in oxygen. 2 Concentrations of 1 and 2% halothane were administered for 10 min during recovery from neuromuscular paralysis by tubocurarine, dimethyl tubocurarine and gallamine. 3 During exposure to halothane, the peak contraction of the tetanic response was reduced and tetanic fade was increased whereas the single twitch was unaffected. 4 The effects of halothane on the tetanic responses were readily antagonized by intravenous neostigmine preceded by atropine. 5 Halothane could act post-synaptically by a non-depolarizing block or by desensitizing the post-synaptic receptors, but a pre-synaptic action seems more likely since neuromuscular block was only evident when tetanic stimulation was applied. Such an effect could be caused by impairment of the release of acetylcholine.