Therapeutic effect of PF1801 on muscle weakness, muscle weight loss, and muscle inflammation in CIM. (A) the grip strength of CIM mice treated therapeutically (therapeutic Tx) with PF1801 (5.0 mg/kg/day, n = 8), PSL (n = 8), combination of PF1801 (2.5 mg/kg/day) and PSL (n = 8), combination of PF1801 (5.0 mg/kg/day) and PSL (n = 8), or vehicle (n = 8) and that of non‐CIM mice (n = 4). Two‐way ANOVA test, followed by Dunnetts multiple comparison test. **P < 0.01. (B) The mean cross‐sectional area (CSA) of muscle fibres of rectus femoris (quadriceps) and biceps femoris (hamstrings) of the mice on day 21 of CIM (n = 5; vehicle, 5; PSL, 5; PF1801 5.0 mg/kg/day, 5; PSL + PF1801 2.5 mg/kg/day, 5; PSL + PF1801 5.0 mg/kg/day, 4; non‐CIM). Data are presented as mean ± SD. One‐way ANOVA test, followed by Bonferroni post hoc test (all pairs). *P < 0.05, **P < 0.01. (C) The area of necrotic muscle fibres on day 21 of CIM. Data are presented as median ± interquartile range. Kruskal–Wallis test, followed by Dunns test. **P < 0.01. (D) The histological scores of the severity of myositis on day 21 of CIM. Data are presented as median ± interquartile range. Kruskal–Wallis test, followed by Dunns test. *P < 0.05, **P < 0.01. (E) The weight of spleen of the CIM on day 21 of CIM. Data are presented as mean ± SD. One‐way ANOVA test, followed by Bonferroni post hoc test (all pairs). **P < 0.01. (F) The body weight of the mice. Data are presented as mean ± SD. Two‐way ANOVA test, followed by Dunnett's multiple comparison test. **P < 0.01. (A–F) Data represent two independent experiments.