Dibucaine number

Dibucaine number is an indirect measure of pseudocholinesterase functionality.

Dibucaine hydrocholoride is an amide local anesthetic, which when injected intravenously, can inhibit plasma cholinesterase or butyryl cholinesterase–the enzyme responsible for clearance of paralytics such as succinylcholine and mivacurium. This known property of Dubicaine has become standardized to measure the amount of effective plasma cholinesterase in an individual through the Dibucaine Number (DN). The DN is thus defined as the “percent of butylcholinesterase activity that is inhibited by dibucaine.” (1)

The amount of plasma cholinesterase can vary in individuals due to either genetics, or more temporal factors (1,2). Regarding genetics, deficiencies in the enzyme follow an autosomal recessive pattern of inheritance. A homozygous “normal” individual has a DN of 70-80. Individuals with a DN of 80 typically have neuromuscular blockade with succinylcholine which lasts 5-10 minutes. However, heterozygote individuals (prevalence- 1/480) have Dibucaine Number of 50-60, and a block that is prolonged by 50-100% or to about 15-20 minutes. Homozygous recessive individuals, with two copies of the abnormal gene, (prevalence- 1/ 3,200), have significant prolongation of the blockade for several hours (2,3). In several case reports, lower Dibucaine numbers have been identified temporally related to obesity, insulin resistance, coronary artery disease, hypertension, renal failure, pregnancy, burns, shock, liver failure, or after treatments like cyclophosphamide or plasmapheresis—largely attributed to failed synthesis or loss of the enzyme (1,2).