What are the recommended intravenous (IV) medications for muscle relaxation?

Recommended IV Muscle Relaxants for Clinical Use

For intravenous muscle relaxation in clinical practice, succinylcholine is recommended for rapid sequence intubation, while cisatracurium is the preferred non-depolarizing agent for most patients, especially those with renal or hepatic impairment. 1, 2

Classification of IV Muscle Relaxants

Depolarizing Agents

• Succinylcholine
  • Fastest onset (30-60 seconds)
  • Shortest duration (5-10 minutes)
  • Dosing: 1
    • Up to 1 month: 1.8 mg/kg
    • 1 month to 1 year: 2 mg/kg
    • 1-10 years: 1.2 mg/kg

    • 10 years: 1 mg/kg

  • Best choice for rapid sequence intubation and electroconvulsive therapy 1
  • Contraindicated in primary muscle damage (myopathies) or upregulation of acetylcholine receptors 2

Non-depolarizing Agents

Intermediate-acting

• Cisatracurium (first choice for most patients)

  • Onset: 2-3 minutes
  • Duration: 30-40 minutes
  • Dosing: 0.1-0.2 mg/kg IV
  • Advantages: 2, 3
    • Organ-independent elimination (Hofmann degradation)
    • No dose adjustment needed in renal/hepatic failure
    • Minimal histamine release
    • Available as 2 mg/mL in 5 mL and 10 mL vials 3

• Rocuronium

  • Onset: 1-2 minutes (faster than other non-depolarizing agents) 4
  • Duration: 30-40 minutes
  • Dosing: 0.6 mg/kg (2 × ED95) for standard intubation 5, 6
  • Can be reversed with sugammadex 1
  • Avoid in renal failure patients 2

• Vecuronium

  • Onset: 2-3 minutes
  • Duration: 30-40 minutes
  • Dosing: 0.1 mg/kg (2 × ED95) 6

Long-acting

• Pancuronium
  • Onset: 3-5 minutes
  • Duration: 60-90 minutes
  • Avoid in elderly and those with renal/hepatic impairment 7

Clinical Decision Algorithm

1. For Rapid Sequence Intubation:

• First choice: Succinylcholine 1 mg/kg IV (adult) 1
• Alternative (if succinylcholine contraindicated): Rocuronium 0.9-1.2 mg/kg IV 1

2. For Standard Intubation:

• First choice: Cisatracurium 0.15-0.2 mg/kg IV 2, 3
• Alternative: Rocuronium 0.6 mg/kg IV 5, 6

3. For Patients with Renal/Hepatic Impairment:

• Recommended: Cisatracurium (no dose adjustment needed) 1, 2
• Avoid: Rocuronium, pancuronium 2

4. For Electroconvulsive Therapy:

• Recommended: Succinylcholine (short-acting) 1
• Alternative: Rocuronium with sugammadex reversal 1

5. For Obese Patients:

• Succinylcholine: 1.0 mg/kg based on actual body weight 1
• Non-depolarizing agents: Calculate dose based on lean body weight 1

Reversal of Neuromuscular Blockade

1. For Steroidal Agents (Rocuronium, Vecuronium):

• Preferred: Sugammadex 1
  • Moderate blockade (2 TOF responses): 2 mg/kg
  • Deep blockade (PTC 1-2): 4 mg/kg
  • Immediate reversal: 8 mg/kg

2. For Benzylisoquinolines (Cisatracurium, Atracurium):

• Use: Neostigmine 0.04 mg/kg + atropine 0.02 mg/kg 1
• Only administer when TOF count = 4
• Efficacy (TOF ratio ≥ 0.9) in 10-20 minutes

Important Considerations

• Mandatory neuromuscular monitoring is required to guide dosing and detect residual blockade 2
• Initial dosing should not be modified regardless of renal/hepatic function 1
• For maintenance doses in renal/hepatic impairment, reduce subsequent doses of non-benzylisoquinoline agents by 50-75% 2
• Avoid combining muscle relaxants with opioids due to increased risk of respiratory depression 2
• Risk of anaphylaxis is higher with succinylcholine than with cisatracurium 1

Special Populations

• Elderly: Prefer cisatracurium due to predictable pharmacokinetics 2
• Renal failure: Use cisatracurium; avoid steroidal agents 1, 2
• Hepatic impairment: Use cisatracurium 1, 2
• Neuromuscular disease: Avoid succinylcholine; use reduced doses of non-depolarizing agents 1

By following these evidence-based recommendations, clinicians can optimize the use of IV muscle relaxants while minimizing adverse effects and improving patient outcomes.