Reaction to succinylcholine in two patients segregating for the plasma cholinesterase allele Ek

Recently, several new alleles have been identified at plasma cholinesterase locus E1. We have had the opportunity for the first time to monitor the response to succinylcholine in two patients with the newly discovered genotype Ea1Ek1. The duration of action and type of neuromuscular block following succinylcholine 1.0 and 1.5 mg kg-1 i.v., respectively, were evaluated using train-of-four nerve stimulation and a Myograph 2000. One patient was anaesthetized with halothane, and the other was given a modified neurolept anaesthesia. Time to first response to nerve stimulation was 15 and 16 min, and time to 50% twitch height recovery was 19 and 20 min, respectively in the two patients. Both showed a depolarizing block. One of the patients received three bolus doses of succinylcholine 1 mg kg-1. This patient gradually developed a phase II block, which was easily reversed by edrophonium. The results indicate that patients with genotype Ea1Ek1 are slightly more sensitive to succinylcholine than are genotypically normal patients (Eu1Eu1) and patients heterozygous for the normal and the atypical gene (Eu1Ea1).