Suxamethonium-neostigmine interaction in patients with normal or atypical cholinesterase.

The effect of neostigmine 0.05 mg/kg on the neuromuscular block produced by suxamethonium was investigated in 10 normal patients and in five patients with atypical plasma cholinesterase activity, by recording the twitch response to ulnar nerve stimulation. In the normal patients, neostigmine potentiated the block produced by suxamethonium whether it was of the depolarizing or desensitizing type. On the other hand, in patients with atypical plasma cholinesterase activity, neostigmine potentiated the depolarizing phase of suxamethonium block, while antagonizing the desensitizing phase. The degree of antagonism was not related to the magnitude of neuromuscular block, but was proportional to the degree of desensitization at the time of antagonism.