The accelerated approval of Exondys 51 (eteplirsen) for the treatment of patients with Duchenne muscular dystrophy (DMD) amenable to exon 51 skipping therapy was a hard fought battle and one that is not finished. The company still needs to conduct additional studies to confirm that the drug is effective. And while doing those studies, the company is teasing out some additional data from their phase 2 clinical trial that got the drug approved in the first place.
At the ACMG Annual Clinical Genetics Meeting in Phoenix, AZ, O’Rouke et al presented data showing eteplirsen to slow the progression of pulmonary dysfunction in 12 boys who have been on the drug for 4 years (216 weeks).
Twelve boys with DMD amenable to exon 51 skipping therapy received 30 or 50 mg/kg/wk intravenous (IV) eteplirsen treatment for 216 weeks. Forced vital capacity (FVC) and maximum expiratory pressure (MEP) and minimum expiratory pressure (MIP) were assessed twice a year.
In the eteplirsen-treated boys, mean decline in FVC, MEP, and MIP was 2.8%, 2.6%, and 1.0% per year , respectively. These numbers are lower than the declines observed in similar boys receiving standard of care (mean FVC, MEP, and MIP annual decline by ≥5%, ≥2.7% and ≥3.8%, respectively).
About Duchenne Muscular Dystrophy
Duchenne muscular dystrophy is caused by lack of a functional dystrophin protein, a protein that helps keep muscle cells intact. Patients with progressive muscle disorder experience symptoms in early childhood, losing the ability to walk as early as age 10. These patients, mostly boys, experience life-threatening heart and lung complications in their late teens and twenties.
There are many subsets of the Duchenne population based on the type of mutation found in the dystrophin gene. The only approved drug for DMD is Sarepta’s eteplirsen which only treats those with a specific mutation that makes them amenable to exon 51 skipping treatment (approximately 13% of the DMD population).
O’Rourke E, Mayer O, Lowes L, et al. Respiratory Function in Eteplirsen-treated Duchenne Muscular Dystrophy Patients Compared to Natural History. Poster presented at the ACMG Annual Clinical Genetics Meeting; Phoenix, AZ; March 21-24, 2017. Abstract 828