Succinylcholine, also known as suxamethonium chloride, is a skeletal muscle relaxant used as an adjunct for general anesthesia. It is administered intravenously and is used to facilitate endotracheal intubation, mechanical ventilation, and other surgical procedures.1 Introduced into clinical practice in the 1950s, succinylcholine has a rapid onset and short duration of action: it can enable optimal intubation conditions in less than a minute and can wear off in 10–15 minutes.2 These factors have made succinylcholine a popular choice in the emergency setting.
Succinylcholine induces muscle relaxation by binding to cholinergic receptors on nerve cells, which results in depolarization of the motor end plate, the junction of nerves and muscle fibers. The sodium channels become inactivated, and neurons become unresponsive to the neurotransmitter acetylcholine, which is involved in muscle control. In what is known as phase I block, muscles relax and a reduction in contractile response sets in.3 With higher doses or prolonged infusion of succinylcholine, a phase II neuromuscular blockade can occur. Neurons become repolarized but the receptors still do not respond to acetylcholine, resulting in a prolonged neuromuscular blockade.4 The effects of succinylcholine are terminated due to the degradation of the drug by the enzyme cholinesterase in the blood plasma and liver.3
It is not surprising, therefore, that a contraindication to succinylcholine is decreased plasma cholinesterase activity. In patients with this deficiency, drug metabolism and, concomitantly, muscle paralysis, are prolonged, which may lead to health complications.1 Other contraindications include muscle myopathies, renal and liver failure, and patients who are not adequately sedated. In these situations, an alternative to succinylcholine is needed during general anesthesia.
Succinylcholine is far from perfect: it has many potential side effects and is associated with several adverse events. The drug exerts a strong effect on the cardiovascular system. It is associated with dysrhythmia of the heart and has been observed to produce both bradycardia (abnormally slow heart rate) and tachycardia (abnormally fast heart rate).5 In the early 1990s, there emerged reports of cardiac arrest in in healthy children given succinylcholine. It was later revealed that many of these children had undiagnosed Duchenne muscular dystrophy or another muscular dystrophy, though elective succinylcholine use in all children would be restricted in 1995.6 Succinylcholine can be a trigger for malignant hyperthermia, a severe reaction to certain anesthetic drugs that can cause high body temperature, rigid muscles, and other potentially fatal symptoms.7 Additionally, cases of inadequate muscle relaxation from succinylcholine have been reported.5
Because of these and other disadvantages inherent to succinylcholine, alternatives have become popular. Rocuronium is a nondepolarizing neuromuscular blocking drug that has a faster onset of maximal action than succinylcholine, which can be beneficial for anesthesia, and shares few of succinylcholine’s disadvantages; rocuronium, for example, does not carry any risk for malignant hyperthermia. In a 2019 study, Guihard et al. found that the endotracheal intubation success rate in an out-of-hospital emergency setting was similar in patients that received rocuronium and those receiving succinylcholine.2 Mivacurium is another short duration neuromuscular blocking drug that appears to be less effective than succinylcholine on its own but may behave synergistically with other muscle relaxants.5 Though succinylcholine has historically been a popular muscle relaxant for intubation and anesthesia, it may be eclipsed by other neuromuscular blocking drugs.
References
1. Hager, H. H. & Burns, B. Succinylcholine Chloride. in StatPearls (StatPearls Publishing, 2022).
2. Guihard, B. et al. Effect of Rocuronium vs Succinylcholine on Endotracheal Intubation Success Rate Among Patients Undergoing Out-of-Hospital Rapid Sequence Intubation: A Randomized Clinical Trial. JAMA 322, 2303–2312 (2019), DOI: 10.1001/jama.2019.18254
3. Succinylcholine [TUSOM | Pharmwiki]. https://tmedweb.tulane.edu/pharmwiki/doku.php/succinylcholine.
4. Phase II depolarizing blockade. https://www.openanesthesia.org/aba_phase_ii_depolarizing_blockade/.
5. Cook, D. R. Can Succinylcholine Be Abandoned? Anesth. Analg. 90, S24 (2000), DOI: 10.1097/00000539-200005001-00006
6. Rosenberg, H. & Gronert, G. A. Intractable cardiac arrest in children given succinylcholine. Anesthesiology 77, 1054 (1992), DOI: 10.1097/00000542-199211000-00040
7. Dexter, F., Epstein, R. H., Wachtel, R. E. & Rosenberg, H. Estimate of the relative risk of succinylcholine for triggering malignant hyperthermia. Anesth. Analg. 116, 118–122 (2013), DOI: 10.1213/ANE.0b013e31826f5e3b
