Succinylcholine is hydrolyzed by pseudocholinesterase (butyrylcholinesterase). A patient with dibucaine-resistant pseudocholinesterase variant (dibucaine number ~20) receives succinylcholine for intubation. What is the expected clinical consequence and its mechanism?
- A Malignant hyperthermia due to RYR1 channel activation by succinylcholine
- B Prolonged apnea (scoline apnea) because the atypical enzyme cannot hydrolyze succinylcholine, maintaining neuromuscular blockade ✓
- C Rapid drug resistance because the atypical enzyme has higher affinity and hydrolyzes succinylcholine faster
- D Hyperkalemic cardiac arrest due to excessive acetylcholine accumulation at the motor end plate
Correct answer: B. Prolonged apnea (scoline apnea) because the atypical enzyme cannot hydrolyze succinylcholine, maintaining neuromuscular blockade
Explanation
The normal pseudocholinesterase (BCHE) rapidly hydrolyzes succinylcholine to succinylmonocholine and then succinate, limiting neuromuscular blockade to 3-5 minutes. The atypical (dibucaine-resistant) BCHE variant has markedly reduced activity for succinylcholine hydrolysis (dibucaine number ~20 vs ~80 in normals). In homozygous patients, succinylcholine is not adequately hydrolyzed, resulting in prolonged apnea lasting 1-3 hours — a pharmacogenomic emergency requiring ventilatory support until the drug is eventually metabolized by other pathways.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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