Effects of glucocorticoids and idebenone on respiratory function in patients with duchenne muscular dystrophy

In Duchenne muscular dystrophy (DMD) progressive weakness of respiratory muscles leads to a restrictive pulmonary syndrome that contributes to early morbidity and mortality. Currently no curative treatment exists for DMD. In a Phase II randomized placebo-controlled study (DELPHI) in 21 DMD boys at age 8-16 years, idebenone (450mg/d) showed trends of efficacy for cardiac and respiratory endpoints. Since the DELPHI study population comprised both glucocorticoid-naive subjects and glucocorticoid-users, we now report a post-hoc analysis investigating the effects of glucocorticoids and idebenone on markers of respiratory weakness, particularly peak expiratory flow (PEF) percent predicted (PEF%p). Baseline values of PEF%p correlated well with the percent predicted values for maximal inspiratory mouth pressure (MIP%p), forced vital capacity (FVC%p), and forced expired volume in 1sec (FEV1%p). Baseline PEF%p and FVC%p were significantly higher in patients on concomitant glucocorticoids compared to glucocorticoid-naive patients. In the latter subgroup, idebenone caused a 8.0 +/- 12.1% improvement in PEF%p, whilst patients on placebo declined by -12.3 +/- 17.9% (P<0.05) in the course of the 12 month study. In patients receiving concomitant glucocorticoids, PEF%p remained stable (-0.4 +/- 14.6%) in the idebenone group compared to a decline by -6.2 +/- 12.4% (P=0.24) in the placebo group. Idebenone showed a trend for efficacy on FVC%p only in glucocorticoid-naive patients. Because of the study limitations, these data are exploratory and preclude any firm conclusions. In conclusion, PEF appears to be a sensitive respiratory function parameter that could be a valid and clinically relevant endpoint in intervention studies in DMD. In DELPHI the effect size of idebenone on PEF%p was significantly larger in steroid-naive patients, possibly indicating a maximum treatment effect reached by steroids or steroid-mediated suppression of idebenone's effects. The impact of standard care glucocorticoids on respiratory function will have to be considered in the planning of future interventional trials in DMD. Pediatr Pulmonol. 2013; 48:912-920. (c) 2012 Wiley Periodicals, Inc.