Neostigmine in the antagonism of the action of atracurium.

Antagonism of atracurium-induced neuromuscular blockade with neostigmine (one or two doses of 2.5 mg) was compared, using electromyography, with spontaneous recovery. Two levels of blockade were studied, one in which the initial response of the train-of-four has reached 10% of control and the other 50% of control. Adequate recovery was considered to be present when the ratio of the fourth response to the first (train-of-four ratio) had reached 70%. Neostigmine always accelerated recovery and "neostigmine block" was not detected. This acceleration of recovery after neostigmine was most marked with the greater degree of blockade, but two doses of neostigmine were no more effective than one. Spontaneous recovery to the train-of-four ratio of 70% was slow, in the order of 1 h after an initial dose of 0.5 mg kg-1 and 45 min after incremental doses of 0.2 mg kg-1. It is concluded that antagonism of atracurium with one dose of neostigmine is usually desirable, that two doses are unnecessary, and that spontaneous recovery is slower than is generally realized.