The Dibucaine Number test measures the percentage inhibition of the pseudocholinesterase enzyme by dibucaine. It is used to differentiate individuals with mutations in the butyrylcholinesterase enzyme. Normal individuals have dibucaine numbers of 80 or above, while those with atypical mutations have numbers between 40-60 for heterozygotes and 20 or less for homozygotes. Those with atypical mutations experience prolonged effects from succinylcholine and other neuromuscular blocking drugs.

1. By
Dr.SANDEEP

2. • The Dibucaine Number is a measure of the qualitative
activity of Pseudo cholinesterase and is the percentage
of inhibition of the enzyme by the local anesthetic
Dibucaine.
• It is used to differentiate individuals who have substitution
mutations of the Butryl cholinesterase enzyme

3. • Dibucaine (cinchocaine), is an amino amide L.A.
• It was commonly used for central neuraxial anesthesia.
• When administered to humans i.v , it is capable of
inhibiting the plasma Pseudocholinesterase enzyme.
• This tetrameric enzyme is responsible for the
metabolism of a number of substances including amino
ester local anaesthetics and Succinylcholine

4. • Synthesis-liver
• Converts Succinylcholine to Succinylmonocholine
and choline
• The activity of the enzyme refers to the number of
substrate molecules (micromoles) hydrolysed per
unit of time, often expressed in international units
(IU)
• Dibucaine inhibits its normal activity.

5. • Depolarizing neuromuscular blocker.
• Composed of two molecules of acetylcholine linked back
to back through the acetate methyl groups.
• Like Ach, stimulates cholinergic receptors at the NMJ,
nicotinic and muscarinic autonomic sites.
• Rapid onset of effect and ultra short duration of action
• ED95 is 0.51 to 0.63 mg/kg.

6. • Administration of 1mg/kg of Sch results in complete
suppression of neuromuscular stimulation in
approximately 60 seconds.
• In patients with normal Butrylcholinesterase, recovery of
90% muscle strength requires 9 to 13 min
• Metabolised to Succinylmonocholine and then to succinic
acid and choline.
• Elimination t ½ is 47 sec

7. • Reduced Butyrylcholinesterase activity may occur as a
result of
inherited causes
acquired causes.

8. • In the inherited type, an individual receives a gene from
each parent, one of which may be the wild type
Butyrylcholinesterase, or the mutant.
• Some mutations will slow or completely deactivate the
enzyme's ability to catalyze the breakdown of Sch
• Inherited reductions occur due to mutations at a single
autosomal location on the long arm of chromosome 3

9. • At least one substitution is capable of altering the
efficiency of enzymatic catalysis.
• A point mutation has been identified that changes Asp-70
to Gly in the atypical form of serum cholinesterase,
leading to reduced affinity of atypical cholinesterase for
choline esters.
• It can be Homozygous typical
Heterozygous atypical
Homozygous atypical

10. PEOPLE SUCH AS
• Elderly
• pregnant
• Infants
• Parturition
and certain other physiologic conditions have low
Pseudocholinesterase enzyme levels.

11. PATHOLOGIC STATES DRUGS
• Liver diseases • Oral contraceptives
• Malnutrition, • MAOI
• burns, • Anticholinesterase drugs
• malignancy • Tetrahydroaminacrine
• Uremia • Hexafluorenium
• O.P. poisoning • Metocllopramide
• Chronic infections • Bambuterol(prodrug of
• Hypothroidism terbutaline)
• Collagen vascular • Esmolol
diseases • Cytotoxic drugs
• Ecothiphate

12. • The Dibucaine Number is used to differentiate individuals
who have substitution mutations of the
butrylcholinesterase enzyme
• The extent of the catalysis can be determined by
measuring % of Sch that remains unchanged in the blood
after a standard dose of Dibucaine inhibition challenge
which has been established as the DIBUCAINE
NUMBER TEST.

13. • Typical measurement of Dibucane number yields values
of
80 and above for wild type homozygotes (normal),
40-60 for heterozygotes (atypical),
20 or less for atypical homozygotes.

14. TYPE OF GENOTYPE INCIDENCE DIBUCAINE RESPONSE
BUTRYLCHOLINE NUMBER TO SCH OR
STERASE MIVACURIUM
HOMOZYGOUS E1uE1u NORMAL NORMAL NORMAL
TYPICAL
HETEROZYGOUS E1uE1a 1/480 50-60 LENGTHENED
ATYPICAL BY 50%-100%
HOMOZYGOUS E1aE1a 1/3200 20-30 PROLONGED
ATYPICAL BY 4-8 HRS

15. • The distinctive quality of Dibucaine is that its enzyme
inhibition of the wild type Butyrylcholinesterase (Typical)
is substantially greater than that of the mutant
Butyrylcholinesterase (Atypical).
• Thus, the atypical enzyme is said to be resistant to
Dibucaine inhibition.

16. • When enzyme activity is reduced, there is an increase in
the duration of the neuromuscular blockade - which may
necessitates the unnecessary post op mechanical
ventilation due to prolonged neuromuscular blockade
• But, in most of the cases, there is only mild increase in
the duration of the apnea
Eg:- Decrease to 20% of normal activity by severe liver
disease, the duration of apnoea, increases from a
normal duration of 3 minutes to just 9 minutes