Objective: We conducted this study to be the first systematic review and meta-analysis to investigate the efficacy and safety of mexiletine in the treatment of patients with dystrophic and non-dystrophic myotonia.

Background: Myotonia is a rare genetic skeletal muscle sodium channelopathy in which the relaxation of a muscle is impaired. Mexiletine is a sodium channel blocker that has been prescribed for years for the treatment of myotonia nevertheless the evidence of its efficacy is limited by the small number of clinical trials which is attributed to the rarity of the disease.

Method: A thorough computer literature search was conducted in different medical electronic databases (PubMed, Cochrane, Scopus, EBSCO, and Web of Science) to identify all published randomized controlled trials. Relevant studies were selected and the risk of bias was assessed according to the Cochrane ROB tool. Data was extracted manually into a uniform data extraction sheet and analyzed using the RevMan software (version 5.4).

Results: Five studies were included in this meta-analysis (total n = 183 patients). Mexiletine was significantly superior to placebo regarding the improvement in stiffness score (SMD -1.19, 95% CI [-1.53 to -0.85]) and hand grip myotonia, 90%–5% (MD -1.36, 95% CI [-1.83 to -0.89]). Also, Mexiletine showed no significant impact on ECG outcomes when compared to placebo; PR interval (MD 1.12 ms, 95% CI [-3.65 to 5.89]), QRS interval (MD 1.12 ms, 95% CI [-1.27 to 3.52]), QTc interval (MD 1.64 ms, 95% CI [-6.96 to 10.24]). Results showed heterogeneity in SF-36 PCS and MCS outcomes, so we conducted subgroup analysis according to the type of disease to find that mexiletine improves SF-36 PCS (MD 6.83, 95% CI [4.29 to 9.37]) and SF-36 MCS (MD 5.19, 95% CI [2.88 to 7.49]) in non-dystrophic patients. Regarding adverse effects, there were no differences between the two groups in terms of tremors, headache, insomnia, and serious adverse events (all P>0.05). However, mexiletine significantly causes some GIT symptoms compared to placebo (RR 3.7, 95% CI [1.79 to 7.64]).

Conclusion: The results of this systematic review and meta-analysis support that mexiletine is effective and safe in myotonic patients; however, it is associated with a higher risk of GIT symptoms. Owing to the limited number of published RCTs, we recommend further well-designed RCTs.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/efficacy-and-safety-of-mexiletine-versus-placebo-in-patients-with-myotonia-a-systematic-review-and-meta-analysis/