What are the recommended muscle relaxers and their dosages?

Recommended Muscle Relaxants and Dosages

For musculoskeletal spasm, cyclobenzaprine 5 mg three times daily is the preferred first-line agent, offering equivalent efficacy to 10 mg with significantly less sedation. 1

Anesthetic/Procedural Muscle Relaxants

Rapid-Onset Agents for Intubation

• Succinylcholine (Suxamethonium) remains the gold standard for rapid sequence intubation and electroconvulsive therapy 2
  • Standard dosing: 1.0 mg/kg IV based on actual body weight 2, 3
  • Obese patients (BMI ≥40): 1.0 mg/kg based on actual body weight 2
  • Pediatric dosing: Age-adjusted (< 1 month: 1.8 mg/kg; 1-12 months: 2.0 mg/kg; 1-10 years: 1.2 mg/kg; >10 years: 1.0 mg/kg) 2
  • Laryngospasm: 1.0 mg/kg IV or 4.0 mg/kg IM/sublingual 2
  • Contraindications: Primary muscle damage (myopathies, myotonia), upregulation of nicotinic receptors (chronic motor deficits, extensive burns, prolonged critical illness) due to risk of rhabdomyolysis and life-threatening hyperkalemia 2

Non-Depolarizing Agents

• Rocuronium: Preferred alternative when succinylcholine is contraindicated 2, 3

  • Standard intubation: 0.6-1.2 mg/kg based on lean body weight 3
  • Rapid sequence: >0.9 mg/kg in pediatrics 2
  • Obese patients: Dose based on lean body weight (Janmahasatian formula) 2
  • Laryngospasm/airway obstruction: 0.1-0.2 mg/kg 2
  • Myasthenia patients: 50-75% dose reduction required 2

• Atracurium/Cisatracurium (Benzylisoquinolines): Preferred in renal/hepatic failure due to organ-independent elimination 2

  • Dosing: Based on lean body weight 2
  • Myasthenia patients: 50-75% dose reduction 2

• Vecuronium and Pancuronium: Dosed based on lean body weight 3

Reversal Agents

• Sugammadex: Preferred for reversal of steroidal muscle relaxants, especially in neuromuscular disease, obesity, and renal impairment 2, 3
  • Moderate blockade: 2.0 mg/kg 3
  • Deep blockade: 4.0 mg/kg 3
  • Immediate reversal: 8.0 mg/kg 3
  • Obese patients: Dose based on ideal body weight 2
  • Caution: Reduced efficacy in elderly and severe renal failure (CrCl <30 mL/min) 3

Oral Muscle Relaxants for Musculoskeletal Conditions

First-Line Agents

• Cyclobenzaprine: Most extensively studied with consistent efficacy 1, 4

  • Preferred dosing: 5 mg three times daily 5, 1
  • Alternative: 10 mg three times daily (higher sedation) 5, 1
  • Hepatic impairment: Start 5 mg and titrate slowly in mild impairment; avoid in moderate-to-severe 5
  • Avoid in elderly: Structurally similar to tricyclic antidepressants with anticholinergic effects, CNS impairment, delirium, and fall risk 6
  • Duration: Typically 7 days; not recommended beyond 2-3 weeks 5

• Baclofen: Preferred for elderly and renally impaired patients 6, 3

  • Starting dose: 5 mg three times daily 6, 3
  • Maximum tolerated dose: 30-40 mg/day 6, 3
  • Caution: Never discontinue abruptly due to withdrawal risk (CNS irritability) 3

• Tizanidine: Alternative for elderly/renally impaired 6, 3

  • Starting dose: 2 mg three times daily 6, 3, 7
  • Titration: Increase by 2-4 mg steps to maximum 36 mg/day 7
  • Dosing interval: Every 6-8 hours, maximum 3 doses per 24 hours 7
  • Monitoring required: Orthostatic hypotension and sedation 6, 3
  • Food effects: Complex pharmacokinetic changes when switching between fed/fasted states 7

Agents with Limited Evidence

• Metaxalone: Fewest side effects reported but limited comparative data 8, 4
• Methocarbamol: Very limited evidence for musculoskeletal conditions 4
• Chlorzoxazone: Inconsistent data; rare serious hepatotoxicity 4

Agents to Avoid

• Carisoprodol: Avoid entirely due to high sedation, fall risk, and significant potential for physical and psychological dependence 6, 8, 4
• Orphenadrine: Avoid due to strong anticholinergic properties causing confusion, urinary retention, and cardiovascular instability 6
• Cyclobenzaprine in elderly: Avoid due to anticholinergic effects, sedation, and increased fall risk 6

Antispasticity Agents

• Baclofen: First-line for spasticity from upper motor neuron syndromes 4

  • Evidence: Fair evidence of efficacy vs placebo in multiple sclerosis 4
  • Dosing: As above for musculoskeletal use

• Tizanidine: Roughly equivalent efficacy to baclofen 4

  • Adverse effects: More dry mouth than baclofen; baclofen causes more weakness 4

• Dantrolene: Effective for spasticity but rare serious hepatotoxicity 4

  • Insufficient evidence: Compared to baclofen or tizanidine 4

• Diazepam: Fair evidence for spasticity but not recommended as first-line 4, 9

Critical Safety Considerations

• Avoid co-prescribing with opioids or benzodiazepines: Increases mortality risk 3- to 10-fold 6
• American Geriatrics Society warning: Muscle relaxants are potentially inappropriate medications for older adults due to anticholinergic effects, sedation, and fall risk 6, 3
• Shortest duration necessary: Use lowest effective dose for shortest time, particularly in elderly 6, 3
• Neuromuscular monitoring essential: For anesthetic muscle relaxants to ensure complete reversal and prevent residual blockade 3
• Avoid combination with anticholinergics: Especially in elderly patients 3
• Monitor for: Orthostatic hypotension, sedation, fall risk 6, 3

Surgical Applications

• Abdominal laparotomy/laparoscopy: Muscle relaxants recommended to facilitate procedures 2
• ENT laser surgery: Probably recommended 2
• Neuromuscular monitoring: Corrugator supercilii muscle preferred site due to sensitivity comparable to laryngeal muscles 2