Ciafaloni E, et al. - Given that primary periodic paralyses are rare, hereditary skeletal muscle diseases characterized by episodic muscle weakness, researchers tested the safety and effectiveness of dichlorphenamide in adolescents (n = 7;10 to ≤ 17 years) and adults (n = 66) with primary periodic paralyses. In a double-blind, controlled, crossover study, patients with primary periodic paralyses were randomized to dichlorphenamide or placebo for 9 weeks, with a 9-week or longer between-treatment washout period. Total daily dose of dichlorphenamide in adolescents was 50 mg (n = 1) or 100 mg (n = 5), and in adults was 105.7 mg (mean; n = 61). Skin rash was the most common adverse event with dichlorphenamide in adolescents. The numbness was the most common adverse event in adults and skin rash occurred less frequently. Among a small number of adolescents as well as adults, dichlorphenamide was comparably effective and tolerated, although types of adverse events varied between groups.