More than 90% of amyotrophic lateral sclerosis (ALS) patients have muscle cramps, but evidence-based treatments have not been available.

A multicenter, double-blind, placebo-controlled crossover trial of mexiletine 150 mg twice daily was conducted in ALS patients requesting treatment of symptomatic muscle cramps.

Muscle cramp frequency was reduced in 18 of 20 patients; 13 reductions were attributed to treatment (P < 0.05). The average reduction, based on t tests, was 1.8 cramps per day (a reduction from 5.3 with placebo to 3.5 with mexiletine). The estimated reduction of cramp severity was 15 units on a 100-unit scale (P = 0.01) from a baseline average of 46. No effect on fasciculations was noted. One patient discontinued the study because of dizziness, and another patient discontinued the study to start open-label mexiletine therapy. No serious adverse event occurred.

Mexiletine is a well tolerated and effective medication for controlling the symptom of muscle cramps in ALS. Muscle Nerve, 2018.