Response to succinylcholine in patients carrying the K-variant of the butyrylcholinesterase gene.

Succinylcholine is usually metabolized quickly by the butyrylcholinesterase enzyme (BChE) but genetic variants of BChE may prolong the duration of action. The Kalow (K) variant is the most common mutation in the butyrylcholinesterase gene (BCHE), being present in 25% of Caucasians. The significance of the K-variant for the duration of action of succinylcholine has not been well studied. Our hypothesis was that the duration of action of succinylcholine would be prolonged in patients heterozygous for the K-variant genotype compared with the normal genotype (wild-type). We included 70 adult surgical patients who received succinylcholine 1 mg/kg for rapid sequence induction. Neuromuscular monitoring was performed using ulnar nerve stimulation and acceleromyography. Duration of action of succinylcholine was defined as the time to 90% recovery of first twitch in train-of-four (T(1) 90%), BChE activity was determined, and the presence of BCHE K and A (atypical) variants were determined using DNA analysis. The wild-type BCHE was present in 38 patients, and 21 were heterozygous for the K-variant. Mean (SD) T(1) 90% in patients heterozygous for the K-variant, 11.6 (3.5) minutes, was longer than in patients with the wild-type genotype, 9.5 (2.7) minutes (P = 0.023), with a mean (95% confidence interval) difference of 2.1 (0.3-4.0) minutes. Patients heterozygous for the K-variant had a BChE activity of 5978 U/L compared with 7703 U/L in the wild-type group (P = 0.0045). We conclude that the mean duration of action of succinylcholine is prolonged for the patient heterozygous for the K-variant allele by at most 4 minutes relative to the wild-type, but this difference is small relative to the wide variability and overlap in recovery times among all patients.