Dibucaine number

Dibucaine Number

The Dibucaine number is a measure used in anesthesiology to assess the activity of the enzyme butyrylcholinesterase (also known as pseudocholinesterase). This enzyme is responsible for the hydrolysis of succinylcholine, a muscle relaxant used during general anesthesia. The dibucaine number is an important diagnostic tool for identifying individuals with atypical butyrylcholinesterase, which can lead to prolonged paralysis following the administration of succinylcholine.

Background

Butyrylcholinesterase is an enzyme that hydrolyzes choline-based esters, including succinylcholine and mivacurium. Variations in the BCHE gene can lead to different enzyme activities, affecting the metabolism of these drugs. The dibucaine number is determined by measuring the inhibition of butyrylcholinesterase activity by the local anesthetic dibucaine.

Clinical Significance

Normal and Atypical Enzyme Activity

A normal dibucaine number is typically around 80, indicating that dibucaine inhibits 80% of the enzyme activity. Individuals with atypical butyrylcholinesterase have a lower dibucaine number, often below 30, which suggests reduced enzyme activity and a potential risk for prolonged neuromuscular blockade after succinylcholine administration.

Genetic Variants

The genetic variants of butyrylcholinesterase that lead to atypical enzyme activity are inherited in an autosomal recessive manner. Individuals who are homozygous for the atypical allele will have a significantly reduced enzyme activity, while heterozygous individuals may have intermediate dibucaine numbers.

Testing and Interpretation

The dibucaine number is determined by adding dibucaine to a sample of the patient's serum and measuring the remaining butyrylcholinesterase activity. The percentage of inhibition is calculated to determine the dibucaine number. This test is particularly useful in preoperative assessments to identify patients at risk for prolonged paralysis.

Management

Patients identified with a low dibucaine number should be managed carefully during procedures requiring muscle relaxants. Alternative drugs that do not rely on butyrylcholinesterase for metabolism, such as rocuronium or cisatracurium, may be used to avoid complications.

See Also

• Butyrylcholinesterase deficiency
• Succinylcholine
• Neuromuscular blockade