Sch and MG

 Q: Succinylcholine (SCh) dose in myasthenia gravis should be? (select one) 

A) higher than calculated dose 

B) lower than calculated dose 

C) It should not be used in myasthenia gravis

Answer: A

In general, it is advisable to overestimate the dose of succinylcholine. The dose of SCh should be calculated based on total body weight, including obese and pregnant patients. Higher dose gives a better level of paralysis without much higher risk. If a dose is underestimated, it may leave the patient partially unparalysed. 

This also holds true for patients with myasthenia gravis (MG). SCh can be used safely in MG, and require about 25 percent higher dose. The usual dose of SCh is 1.5 mg/kg of total body weight. In patients with MG it should be increased to 2 mg/kg. MG patients are partially resistant to SCh and require a higher dose to appropriately stimulate the remaining acetylcholine receptors.

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References:

1. Naguib M, Samarkandi AH, El-Din ME, et al. The dose of succinylcholine required for excellent endotracheal intubating conditions. Anesth Analg 2006; 102:151. 

2. Guay J, Grenier Y, Varin F. Clinical pharmacokinetics of neuromuscular relaxants in pregnancy. Clin Pharmacokinet 1998; 34:483. 

3. Patanwala AE, Sakles JC. Effect of patient weight on first pass success and neuromuscular blocking agent dosing for rapid sequence intubation in the emergency department. Emerg Med J 2017; 34:739. 

4. Levitan R. Safety of succinylcholine in myasthenia gravis. Ann Emerg Med 2005; 45:225.