Neuromuscular blocking action of suxamethonium after antagonism of vecuronium by edrophonium, pyridostigmine or neostigmine.

The reported effects of edrophonium on a subsequent dose of suxamethonium are variable and the effects of pyridostigmine have not been evaluated extensively. We have studied this interaction in patients anaesthetized with propofol and sufentanil. After recovery from an initial bolus (1 mg kg-1) of suxamethonium, vecuronium was infused to produce 75% block. After 30 min, the infusion was discontinued and saline 5 ml, edrophonium 0.75 mg kg-1, pyridostigmine 0.24 mg kg-1 or neostigmine 0.05 mg kg-1 was given. Fifteen minutes later the mean durations of a second bolus of suxamethonium were: 10.5 (SD 3.9) min (saline), 10.9 (3.7) min (edrophonium), 18.7 (5.4) min (pyridostigmine) and 23.8 (7.4) min (neostigmine). Corresponding plasma cholinesterase activities (percentage of baseline) were: 91 (18), 87 (9), 21 (10) and 52 (26). When both treatment groups and individual patients were compared, the changes in duration of action did not correlate with changes in cholinesterase activity. These data suggest that other mechanisms in addition to cholinesterase inhibition may contribute to this drug interaction.