Succinylcholine Dosing in Myasthenia Gravis
Succinylcholine should be avoided entirely in patients with myasthenia gravis (MG), and rocuronium at doses ≥0.9 mg/kg should be used instead as the neuromuscular blocking agent of choice. 1
Why Succinylcholine is Contraindicated in MG
Myasthenia gravis represents a relative contraindication to succinylcholine due to unpredictable and potentially dangerous responses at the neuromuscular junction. Patients with MG have:
- Reduced acetylcholine receptors at the neuromuscular junction, making their response to depolarizing agents like succinylcholine highly variable and unpredictable 1, 2
- Risk of prolonged paralysis due to altered receptor dynamics, even with standard dosing 1
- Potential for inadequate blockade requiring higher doses, which paradoxically increases the risk of prolonged apnea 3
Recommended Alternative: Rocuronium
When neuromuscular blockade is required in MG patients, rocuronium is the preferred agent:
- Dose: 0.9-1.2 mg/kg IV for rapid sequence intubation, providing excellent intubating conditions within 60 seconds 4, 1
- Duration of action: 30-60 minutes (compared to succinylcholine's 4-6 minutes), but this longer duration is acceptable given the superior safety profile 4, 1
- Sugammadex should be immediately available for reversal if needed, particularly important in MG patients where prolonged paralysis is especially problematic 4, 5
Critical Management Considerations
If succinylcholine must be used despite MG (extremely rare emergency scenarios):
- Expect significantly reduced dose requirements - MG patients may require only 50% of the normal dose due to receptor downregulation 1
- Standard adult dose would normally be 0.6-1.0 mg/kg, but in MG this should be reduced to approximately 0.3-0.5 mg/kg if absolutely necessary 3
- Neuromuscular monitoring is mandatory to assess depth of blockade and guide reversal 4
Common Pitfalls to Avoid
- Do not assume normal dosing applies - MG patients have fundamentally altered neuromuscular junction physiology 1, 2
- Do not use succinylcholine for maintenance - even if used for intubation, switch to non-depolarizing agents for any additional relaxation needed 3
- Do not forget post-intubation sedation protocols when using rocuronium, as the 30-60 minute paralysis period requires adequate sedation to prevent awareness 1
- Do not proceed without reversal agents available - have sugammadex immediately accessible when using rocuronium in MG patients 4, 5
Standard Succinylcholine Dosing (For Reference in Non-MG Patients)
For context, standard succinylcholine dosing in patients WITHOUT MG:
- Adults: 1.0 mg/kg IV for rapid sequence intubation 4, 1, 3
- Pediatric dosing varies by age: 4, 1
- <1 month: 1.8 mg/kg
- 1 month to 1 year: 2.0 mg/kg
- 1-10 years: 1.2 mg/kg
10 years: 1.0 mg/kg
However, these doses should NOT be used in MG patients - rocuronium remains the preferred choice. 1