/study / lectures / Cellular & Molecular
Pseudocholinesterase Variants — Dibucaine + Fluoride Numbers
TEXTCellular & Molecular · 5 min read
Why one patient is paralyzed for 5 minutes after sux and another is paralyzed for 8 hours. The genetics, the test, and the management.
After this lesson you can
2 min read6 sections- Distinguish normal, heterozygote, and homozygote dibucaine numbers.
- Differentiate inherited variants from acquired deficiency.
- Manage prolonged paralysis after succinylcholine.
- Counsel family members about testing.
Normal pseudocholinesterase activity
Pseudocholinesterase (butyrylcholinesterase, BChE) is a hepatically-synthesized plasma enzyme that hydrolyzes succinylcholine + mivacurium + ester local anesthetics (procaine, chloroprocaine, tetracaine) + cocaine.
The normal duration of paralysis after sux 1 mg/kg is 5-10 minutes because BChE rapidly metabolizes the drug before it reaches the NMJ in sufficient quantity to sustain blockade.
Variant or deficient enzyme prolongs paralysis dramatically.
The inheritance — homozygote vs heterozygote
- atypical (dibucaine-resistant, allele Eᵃ)
- fluoride-resistant (Eᶠ)
- silent (no enzyme produced, Eˢ)
Population prevalence: ~3-4% heterozygote for atypical; ~1:2,500-3,200 homozygote.
Heterozygote: paralysis prolonged to 20-30 minutes.
Homozygote (atypical/atypical, silent/silent, or compound heterozygote): paralysis 4-8 hours — sometimes longer.
Dibucaine number — the diagnostic test
Normal homozygote (Eᵘ/Eᵘ): DN ~80.
Heterozygote (Eᵘ/Eᵃ): DN ~60.
Homozygote atypical (Eᵃ/Eᵃ): DN ~20.
Fluoride number (FN, % inhibition by fluoride) differentiates fluoride-resistant variants — normal FN ~60, fluoride-resistant homozygote ~22.
Total plasma cholinesterase activity (units/mL) is the OTHER number — distinguishes quantitative deficiency (hepatic failure, pregnancy, malnutrition, plasmapheresis) from qualitative variants.
Acquired pseudocholinesterase deficiency
- severe hepatic failure (decreased synthesis)
- pregnancy (~25% decrease — minor clinical effect)
- malnutrition
- malignancy
- burns
- plasmapheresis
- certain drugs (ecothiophate eye drops, neostigmine excess, cyclophosphamide, oral contraceptives, MAOIs)
Usually quantitative — total enzyme down, but the enzyme itself is normal.
Modest clinical effect: paralysis prolonged by 10-30%, rarely clinically significant.
Management of prolonged paralysis after sux
Do NOT give neostigmine (it doesn't reverse phase I sux blockade and can worsen phase II).
Do NOT give more sux.
Sugammadex doesn't work (sux is not a rocuronium analog).
The treatment is TIME + supportive care.
Send a sample for dibucaine + fluoride + total cholinesterase activity — document the variant + give the patient a written card so future anesthesia teams know.
Genetic testing + family counseling
Recommended after any clinically significant prolonged paralysis.
First-degree relatives should be tested before their first general anesthetic — many programs now include this in family history screening.
Document the variant in the patient's medical record + medical-alert bracelet.
Future anesthesia: avoid sux + mivacurium; rocuronium with sugammadex reversal is the safe alternative.
⚠ Common pitfalls
- Giving neostigmine to reverse prolonged sux paralysis — doesn't work; can worsen phase II block.
- Re-dosing sux 'to be sure' — extends apnea without benefit.
- Confusing quantitative deficiency (low total activity) with qualitative variants (abnormal dibucaine number).
- Sugammadex for prolonged sux paralysis — doesn't bind sux at all.
💎 Clinical pearls
- Dibucaine number ~80 normal · ~60 heterozygote · ~20 atypical homozygote.
- Homozygote atypical: paralysis 4-8 hours — keep ventilated + sedated, wait it out.
- Future anesthetics: rocuronium + sugammadex is the safe alternative.
- Always send dibucaine + fluoride numbers AND total cholinesterase activity — they distinguish different problems.
Recap
- Dibucaine number ~80 normal · ~60 heterozygote · ~20 atypical homozygote.
- Homozygote atypical: paralysis 4-8 hours — keep ventilated + sedated, wait it out.
- Future anesthetics: rocuronium + sugammadex is the safe alternative.
- Always send dibucaine + fluoride numbers AND total cholinesterase activity — they distinguish different problems.
Mark each section done to complete the module.
References
- · Stoelting & Hines Pharmacology 6e ch 11
- · Miller's Anesthesia 9e ch 23 (NMBAs)
- · Nagelhout Nurse Anesthesia 7e (Pseudocholinesterase)
- · ASA Practice Guidelines for Monitoring and Antagonism of Neuromuscular Blockade (2023)
- · Davis et al., Br J Anaesth 1997 (BChE polymorphisms)
- · Whittaker, Monogr Hum Genet 1986 (Cholinesterase genetics)