Cocaine and succinylcholine sensitivity: a new caution.

Cocaine was stable (93.6 +/- 5.0 (SD)% remaining after 120 minutes) when incubated in plasma from six patients with histories of succinylcholine sensitivity and low dibucaine numbers (phenotype A), but was rapidly hydrolyzed (40.6 +/- 6.6% remaining after 120 minutes) when incubated in plasma obtained from normal subjects (phenotype U). Intermediate decay (69.4 +/- 9.0% remaining) occurred in three heterozygous offspring of the succinylcholine-sensitive patients. Since serum cholinesterase has recently been implicated in the human metabolism of cocaine, patients who are homozygous for the atypical enzyme may be at greater risk for a toxic reaction when administered this drug. We recommend caution in using cocaine for topical anesthesia in patients with histories of succinylcholine sensitivity or low dibucaine numbers.