Dose—Response Relationships for Edrophonium and Neostigmine as Antagonists of Atracurium and Vecuronium Neuromuscular Blockade

To determine the potencies of edrophonium and neostigmine as antagonists of nondepolarizing neuromuscular blockade produced by atracurium and vecuronium, dose-response curves were constructed for both antagonists when given at 10% spontaneous recovery of first twitch height. Ninety ASA physical status 1 and 2 adults were given either 0.4 mg/kg atracurium or 0.08 mg/kg vecuronium during thiopental-nitrous oxide-enflurane anesthesia. Train-of-four stimulation was applied to the ulnar nerve every 12 s, and the force of contraction of the adductor pollicis muscle was recorded. When spontaneous recovery of first twitch height reached 10% of its initial control value, edrophonium (0.1, 0.2, 0.4, or 1 mg/kg) or neostigmine (0.005, 0.01, 0.02, or 0.05 mg/kg) was administered by random allocation. Neuromuscular function in another ten subjects was allowed to recover spontaneously. Assisted recovery was defined as actual recovery minus mean spontaneous recovery observed in patients who were not given antagonists. First twitch recovery was initially more rapid when vecuronium was antagonized compared with atracurium, but no difference was detected after 10 min. At 10 min the neostigmine ED80 was 0.022 +/- 0.003 (SEM) mg/kg after atracurium and 0.024 +/- 0.003 mg/kg after vecuronium. The edrophonium ED80 was 0.44 +/- 0.11 mg/kg with atracurium and 0.46 +/- 0.12 mg/kg with vecuronium, giving a neostigmine:edrophonium potency ratio of 20. Atracurium train-of-four fade could be antagonized more easily with edrophonium, whereas that of vecuronium was more easily antagonized by neostigmine. It is concluded that edrophonium and neostigmine are not equally effective against atracurium and vecuronium.