The FDA unexpectedly reversed course Thursday, approving the second treatment developed by Sarepta Therapeutics for the rare disease Duchenne muscular dystrophy just a few months after rejecting the drug. 

Sarepta announced Thursday evening that the agency had approved its second drug, called Vyondys 53. After the drug was originally rejected by the FDA in August due to concerns over the risk of infection at the infusion site and renal toxicity, the company filed an appeal. The company said that “the matters raised in the CRL were rapidly evaluated and resolved by Dr. Peter Stein, director of the office of new drugs,” after which an application was resubmitted.

Vyondys 53, like Sarepta’s first commercial treatment Exondys 51, was developed to skip over a specific gene mutation that prevents young boys with the disease from producing a protein called dystrophin, which is vital to muscle health. Where Exondys 51 works in 13 percent of patient with the most common mutation, Vyondys 53 is aimed at patients with the second most-common mutation, which acoiunts for about 8 percent of all patients.

Duchenne affects roughly 15,000 boys in the United States.

Sarepta contended that the renal toxicity concerns had been in pre-clinical data at a dose 10 times higher than what was submitted to the FDA.

CEO Doug Ingram said in a statement that the agency acted with “unprecedented timing”. 

“Today is monumental for Sarepta and, more importantly, for the DMD community,” Ingram said. “In the span of four months, we commenced and completed the formal dispute resolution process culminating in the grant of our appeal, resubmitted our NDA and obtained an approval — a great benefit to DMD patients awaiting treatment.”

A spokeswoman told the Business Journal Thursday evening that Vyondys 53 will be priced at $300,000 a year per 20 kilograms, which equals about 44 pounds. Than means a cost of $900,000 for a child weighing 132 pounds.

The drug was approved under an accelerated timeline, meaning that Sarepta will need to conduct follow-up studies to verify its effectiveness. The company is currently enrolling patients in the confirmatory trial and expects to release results by 2024.