Branched chain amino acids in the treatment of polymyositis and dermatomyositis: a phase II/III, multi-centre, randomized controlled trial

Objectives: To assess the efficacy and safety of branched chain amino acids (BCAAs) in the treatment of PM/DM prior to official approval of their use in Japan. Methods: Treatment naïve adults with PM/DM were enrolled in a randomized, double-blind trial to receive either TK-98 (drug name of BCAAs) or placebo in addition to conventional treatment. After 12 weeks, patients with an average manual muscle test (MMT) score <9.5 were enrolled in an open label extension study for a further 12 weeks. The primary endpoint was the change of the MMT score at 12 weeks. The secondary endpoints were the clinical response and the change of functional index (FI). Results: Forty-seven patients were randomized either to the TK-98 (n = 24) or placebo (n = 23) group. The changes of MMT scores at 12 weeks were 0.70 (0.19) [mean (s.e.m.)] and 0.69 (0.18), respectively (P = 0.98). Thirteen patients from the TK-98 group and 12 from the placebo group were enrolled in the extension study. The MMT scores in both groups improved similarly. The increase of the FI scores of the shoulder flexion at 12 weeks was significantly greater in the TK-98 group [27.9 (5.67) vs 12.8 (5.67) for the right shoulder flexion, and 27.0 (5.44) vs 13.4 (5.95) for the left shoulder; P < 0.05]. Frequencies of adverse events up to 12 weeks were similar. Conclusion: BCAAs showed no effect on the improvement of the muscle strength evaluated by MMT and the clinical response. However, they were partly effective for improving dynamic repetitive muscle functions. Trial registration: UMIN-CTR Clinical Trial, https://center6.umin.ac.jp/,