Gabapentin use in the prevention of succinylcholine-induced fasciculation and myalgia

ML Rayhill, MD Perloff 
 Department of Neurology, Pain Management Group, Boston University School of Medicine, Boston University Medical Center, 72 E. Concord St, C3, Boston, MA 02118, USA

Correspondence Address:
M D Perloff
Department of Neurology, Pain Management Group, Boston University School of Medicine, Boston University Medical Center, 72 E. Concord St, C3, Boston, MA 02118
USA

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Prophylactic use of gabapentin for prevention of succinylcholine-induced fasciculation and myalgia: a randomized, double-blinded, placebo controlled study by Pandey CK et al.,[1] suggests gabapentin as a possible preventative therapeutic option for postoperative succinylcholine adverse reactions. Gabapentin has an ideal safety profile and is very well tolerated-especially given a single dose of 600 mg used in the study. We present some points of consideration that may affect the study's application to postoperative care. Although myalgia and fasciculation have clearly been associated with succinylcholine administration, [2],[3] the side-effect of myalgia is less specific to the drug. Therefore, it may be more challenging to determine how gabapentin affects postoperative myalgia specifically caused by succinylcholine. In the United States, between 75-80% of patients report postoperative pain. [4] The incidence of postoperative pain varies greatly depending on the nature of the procedure and patient-related factors. Postoperative pain is likely multi-factorial and separating myalgia ("muscle pain not related to surgical intervention") from surgical pain would seem a difficult distinction. More so, differentiating succinylcholine-induced postoperative myalgia from multi-factorial postoperative myalgia (surgical positioning, stasis, baseline disease, etc.) would seem even more difficult to achieve.

The incidence of postoperative myalgia after the use of succinylcholine has been estimated at 1.5-92%. [2],[5] With such a wide variation in incidence, it is likely that differences in methodology across studies could blur the lines between myalgia due to succinylcholine vs. other postoperative causes of myalgia not specified. Therefore, the effect of gabapentin on myalgia that is specifically attributable to succinylcholine may be equally difficult to define. Pandey CK et al, showed that pre-treatment with gabapentin lowered fentanyl requirements after succinylcholine. The effect of gabapentin on reducing opioid requirements postoperatively has been well-demonstrated previously. [6] It is difficult to say whether patients used less fentanyl because they had less succinylcholine-induced myalgia after gabapentin, or because gabapentin decreased their surgical-site pain. It is also possible that gabapentin decreased their need for opioids by another unidentified mechanism.

Succinylcholine is a depolarizing neuromuscular blocking agent. It acts by continuously depolarizing the plasma membrane of the muscle fiber, preventing any further stimulation by acetylcholine at the nicotinic receptor. By keeping the membrane potential above threshold, it does not allow the fiber to repolarize, which leads to paralysis. In this study, succinylcholine was given with thiopentone and fentanyl at induction, and after intubation, vecuronium was given as well. A non-depolarizing neuromuscular blocking agent, vecuronium works as a competitive inhibitor of acetylcholine at the receptor, preventing the membrane from being depolarized and causing paralysis. Vecuronium does not cause fasciculations, but it does clearly have an effect on membrane potential (relative hyperpolarization). In this study, it is not clear when the fasciculation assessments took place in relation to the administration of vecuronium. Vecuronium could theoretically cause decreased succinylcholine-induced fasciculation by altering the muscle cell membrane potential across the succinylcholine dose-response curve. Pre-treatment with vecuronium prior to succinylcholine induction has been shown to decrease fasciculation. [3],[7] Vecuronium given after succinylcholine induction could have similar effects. Therefore, the incidence of fasciculation could be confounded by the administration of vecuronium, depending on the timing of drug administration and fasciculation assessment.

This study included patients who were relatively healthy, weighed less than 120% of their ideal body weight, and had no prior adverse reactions to any medications. The study population may not be entirely representative of the population of patients undergoing cholecystectomy (who are typically overweight with other obesity-related medical co-morbidities), and that selection bias could possibly underestimate the incidence of postoperative myalgia/pain. For example, succinylcholine-induced myalgia is less common in physically fit individuals. [8] It is also unclear why the use of some medications excluded patients. All calcium channel blockers and antidepressants were excluded, but only gabapentin and pregabalin have specific α-2-λ-subunit activity. On the other hand, the use of other medications that were previously studied in the prevention of succinylcholine-induced myalgia (phenytoin, ketorolac, etc.) did not specifically exclude patients. The possible effect of these other drugs on enrolled patients may have been an uncontrolled variable. Considering the use of a specific patient population and modest sample size, the study may have limitations in how it can be applied to other populations. Despite these drawbacks, it serves as an important step in understanding how preoperative gabapentin may be helpful in postoperative care. Overall, we agree that the use of gabapentin as a single prophylactic dose is a well-tolerated, low-risk intervention. The study by Pandey CK et al., suggests that gabapentin could have a significant role in preventing postoperative pain and succinylcholine-induced myalgia.

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