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FDA gives speedy approval to another Duchenne drug

The Food and Drug Administration on Wednesday approved Viltepso, a drug from the Japanese firm NS Pharma, for patients with a form of the rare, inherited disease Duchenne muscular dystrophy.Viltepso, or viltolarsen, is cleared to treat the roughly 8% of Duchenne patients who have a certain genetic mutation that makes them likely to respond to treatment. The drug, like other Duchenne therapies approved by the agency, isn’t supported by proof it can change the course of the disease. NS Pharma has shown only that Viltepso can help patients produce dystrophin, a crucial protein they lack.

The approval sets Viltepso against Vyondys 53, a drug developed by Sarepta Therapeutics and controversially approved last year after an earlier FDA rejection. NS Pharma’s drug appears to help patients produce more dystrophin than does Sarepta’s, although directly comparing results across trials can be misleading.

The FDA’s approval of Viltepso would have been much more surprising four years ago.

But in 2016 the agency set a precedent by clearing Sarepta’s Exondys 51 based on three tiny studies involving some two dozen patients. Results were equivocal, suggesting treatment helped participants produce about 1% of normal dystrophin levels.

The decision was highly controversial, coming after a tense advisory panel meeting and an internal dispute among FDA staff, some of whom left the agency afterwards. Officials were forced to weigh the impassioned pleas of a desperate patient community against data that didn’t clearly show the drug would help.

Sarepta went back to the FDA last year with a similar drug, Vyondys 53, which is also an infusible, “exon-skipping” medicine for a targeted group of Duchenne patients. Approval was again dramatic, with Sarepta successfully appealing an initial rejection to senior agency officials.

For both drugs, Sarepta is required to run confirmatory trials to prove Exondys 51 and Vyondys 53 actually improve patient’s lives. The company doesn’t yet have that evidence; those studies are recruiting patients and are expected to deliver results within the next few years.

But their conditional approvals set the stage for Wednesday’s decision on Viltepso. Like Sarepta, NS Pharma must prove a functional benefit in a confirmatory study of its own.

Currently, the best information doctors and insurers can use to determine each drugs’ worth is how much dystrophin treated patients make.

Patients on Vyondys 53 produced, on average, 1.02% of normal dystrophin levels after 48 weeks of treatment, compared to 0.1% at the start of the study that led to its approval, according to the drug’s label.

Results from a 16-patient study of Viltepso, published recently in JAMA Neurology, showed dystrophin levels rose from an average of 0.6% at baseline to 5.9% of normal after 25 weeks.

In a statement to BioPharma Dive, a Sarepta spokesperson noted the higher baseline dystrophin production among patients in NS Pharma’s trial. Measured from baseline to study end, the spokesperson said, Viltepso and Vyondys treatment resulted in a similar fold change, by about 10 times.

NS Pharma priced Viltepso at a slight discount to Vyondys 53. List prices for both are based on a patient’s weight. Viltepso costs just over $733,000 per year for patients weighing 30 kilograms, or about 66 pounds, according to a spokesperson. Vyondys 53, by comparison, would cost about $748,000 per year for a patient of the same wieight.

As with Vyondys 53, the drug’s label includes a warning for potential kidney problems based on animal tests — one of the reasons the agency first rejected Sarepta’s drug. Those side effects weren’t seen in human tests, however.

The most common adverse events were cough, fever and upper respiratory tract infection.