Depolarizing NMB
Succinylcholine
Anectine, Quelicin Neuromuscular blocker — fluorescent red 20 mg/mL
The fastest onset, shortest duration paralytic — with serious contraindications.
Typical adult doses
| Indication | Dose | Onset | Duration |
|---|---|---|---|
| Rapid sequence intubation | 1–1.5 mg/kg IV | 30–60 s | ≈5–10 min (label 4–6) |
| Emergency without IV | 3–4 mg/kg IM (max ≈150 mg) | — | — |
Mechanism
Depolarizing agonist at nicotinic ACh receptors → fasciculations → sustained depolarization (phase I block). Hydrolyzed by plasma (pseudo)cholinesterase.
Key effects
- Fasciculations
- K⁺ rises ≈0.5 mEq/L in normal patients
- Myalgias
Watch out for
- Dangerous hyperkalemia with receptor upregulation: burns, crush/major trauma, denervation (stroke, SCI), prolonged immobility — risk begins ≈24–72 h after injury and persists for months
- Myopathies (pediatric boxed warning: hyperkalemic cardiac arrest)
- Malignant hyperthermia trigger; masseter spasm
- Bradycardia (children, repeat doses)
- ↑ IOP/ICP/intragastric pressure
- Prolonged block with pseudocholinesterase deficiency; phase II block with large repeated doses
Pimp questions
Pimp question 1
Why avoid succinylcholine in a 2-week-old burn but not in the first hours?
Answer
Extrajunctional ACh receptor upregulation takes time to develop (≈24–72 h) and then causes exaggerated K⁺ release.
Pimp question 2
What prolongs succinylcholine?
Answer
Pseudocholinesterase deficiency — genetic variants, liver disease, pregnancy, some drugs.