Neuromuscular Blocking Agents (Paralytics) – Study Notes

Purpose: Block muscle contraction at the neuromuscular junction.

• Classes:

  1. Depolarizing agents

  2. Non-depolarizing agents

1. Depolarizing Agent

Drug: Succinylcholine (Sux)

• Onset: ~60 sec

• Duration:

  • Breathing returns: 4–5 min

  • Complete reversal: 10–12 min

• Use:

  • Drug of choice for rapid sequence intubation (RSI)

  • Given only as IV push (not infusion)

• Effects:

  • Fasciculations (skeletal muscle twitching before paralysis)

• Side effects / Risks:

  • ↑ Serum potassium → risk of hyperkalemia

    • Dangerous in burns, spinal cord injury, trauma with muscle damage

    • Upregulation of ACh receptors → excessive K⁺ release

    • Risk of lethal arrhythmias

  • Safe in spinal cord injury if <24 hrs post-injury

  • Risk of malignant hyperthermia

2. Non-depolarizing Agents

Subclasses

• Amino-steroids

• Benzylisoquinolinium (benzyl)

Categorized by Duration

Intermediate-acting (most common in ICU)

Amino-steroids:

• Rocuronium (Zemuron)

  • Onset: 1–3 min (fastest in this group)

  • Duration: 30–90 min (dose dependent)

  • Use: Alternative to succinylcholine in RSI

  • Dosing:

    • IV push: 0.6 mg/kg

    • Infusion: 0.6–0.9 mg/kg/hr (rare)

• Vecuronium (Norcuron)

  • Onset: 3–4 min

  • Duration: 35–45 min

  • Potency: 6× stronger than rocuronium

  • Dosing:

    • IV push: 0.1 mg/kg

    • Infusion: 0.05–0.1 mg/kg/hr

Benzyls:

• Atracurium

  • Onset: 3–4 min

  • Duration: 35–45 min

  • Metabolized in plasma (good for renal/hepatic impairment)

  • Side effect: Histamine release → hypotension, tachycardia, flushing

  • Not commonly used now

• Cisatracurium (Nimbex)

  • Onset: 5–7 min (slower)

  • Duration: 35–45 min

  • Also metabolized in plasma (good for renal/hepatic failure)

  • No histamine release (safer than atracurium)

  • Commonly used for continuous infusion

  • Dosing:

    • IV push: 0.15 mg/kg

    • Infusion: 0.15–0.2 mg/kg/hr

Long-acting

• Pancuronium (Pavulon) – Amino-steroid

  • Onset: 2–4 min

  • Duration: 60–120 min (longest)

  • Side effect: Vagolytic effect → tachycardia

  • Dosing:

    • IV push: 0.04–0.1 mg/kg

    • Infusion: 0.01–0.1 mg/kg/hr

Key Clinical Notes

• Most common infusions:

  • Cisatracurium (Nimbex)

  • Pancuronium (Pavulon)

• Succinylcholine: RSI, fast-acting, short duration, but dangerous in certain populations.

• Rocuronium: Fast onset, good RSI alternative, longer action than sux.

• Vecuronium: Moderate onset, shorter than roc, more potent.

• Atracurium vs Cisatracurium: Similar metabolism, but cisatracurium safer (no histamine release).

• Pancuronium: Longest acting, risk of tachycardia.