a faulty section of gene for making dystrophin, so they can make enough of the critical protein to keep their muscles working.
Sarepta has already said that the results are promising enough to advance to the third and final phase of clinical trials, but much still needs to be determined before Sarepta can get there. The company needs to gather the 48-week data, discuss it with the FDA, and then agree on key ingredients of a pivotal study—like how many patients should enroll, the number of sites, the right dose, the right scientific and clinical measurements, and how long patients should be tracked.
It’s also too early to say whether the Sarepta finding is dose-dependent, that is, whether the drug works better at higher doses. But Sarepta did see a 69.4 meter difference in walking distance at 36 weeks among patients who got the high dose of 50 milligrams per kilogram of body weight, compared with a placebo. The benefit appeared to widen the longer the boys took the drug, as those same patients saw a 59.9 meter improvement in walking distance after 32 weeks of follow-up.
Sarepta doesn’t know if the improvements in walking ability are directly connected to greater dystrophin production, because the study wasn’t designed to capture muscle biopsies at that point—although that critical scientific measurement will be part of the final 48-week analysis. A lower dose of the Sarepta drug, at 30 milligrams per kilogram of body weight, didn’t appear to offer a statistically significant advantage over the placebo, although the performance of that quartet of patients was skewed by two boys who had particularly severe disease that left them unable to walk after 24 weeks. Given how long scientists say it takes for the Sarepta drug to help boost dystrophin production, the company believes those boys simply got too sick too fast for the drug to have a chance, Garabedian says.
If Sarepta’s data holds up after 48 weeks, and it can reproduce the data in a larger pool of patients, the improvements in 6-minute walk test could be medically meaningful. Other drugs for patients with rare genetic diseases that have been judged by that goal, including Genzyme’s alglucosidase (Myozyme) and BioMarin Pharmaceuticals’ laronidase (Aldurazyme) weren’t able to show such a large improvement in 6-minute walk distance, Garabedian says.
The company plans to hold a conference call at 8 am ET/5 am PT to discuss the latest results with investors.
