Federal regulators on Thursday approved a new drug that treats the underlying cause of cystic fibrosis and eventually might be used to help nearly half of the 30,000 patients in the United States with the fatal genetic disease.

The drug, known as Orkambi, is manufactured by Boston-based Vertex Pharmaceuticals.

In 2012, Vertex also won approval for the first drug aimed at counteracting the genetic defect behind cystic fibrosis, which causes the body to produce excess amounts of thick mucus that leads to loss of lung function and chronic infections. The disease kills most patients by their 40s.

That initial treatment, Kalydeco, was considered a breakthrough drug because of its ability to dramatically improve the lung function of patients. However, it is approved to treat only about 2,000 patients in the United States with certain mutations.

Orkambi, which combines Kalydeco and another compound called lumacaftor, is targeted toward patients who have two copies of the most common mutation, called F508del. While nearly half of the estimated 30,000 cystic fibrosis patients in the United States fall into that category, Thursday's approval applies only to the 8,500 who are 12 and older. Vertex, which said the drug would be available in a matter of days, also has been testing the drug in younger patients, in hopes of eventually expanding its approved usage.

"Today is a remarkable day for science, medicine and the CF community," Vertex President Jeffrey Leiden said in a statement Thursday. "While we celebrate this important step forward, we also recognize that two out of three patients in the U.S. still do not have a medicine to treat the underlying cause of their disease. We share their urgency and are committed to continuing our significant investment in research and development."

An FDA advisory committee in May voted 12 to 1 in favor of approving Orkambi, despite concerns that the treatment showed only modest effectiveness in clinical trials. Officials said that the drug appeared safe and that even small improvements could help fill a significant unmet need for a disease that has no cure.

Patients also pleaded with the FDA to approve the drug, with some testifying that Orkambi had made a significant difference in their daily lives.

Aaron Stocks, who participated in a trial for Orkambi, said that's certainly the case for him. The 30-year-old Maryland man said the drug gave him a noticeable improvement in lung function and helped him to gain weight, which is difficult for many cystic fibrosis patients. He recalled going on his normal run not long after starting the drug, only to be surprised to the point of tears when he realized how much easier he could breathe and how much farther he could go.

"Now, when I exercise, my legs give out before my lungs do," Stocks said. "I'm functioning like a normal human being."

Stocks now works for the Bethesda-based Cystic Fibrosis Foundation, a group whose significant investments in Vertex over the past 15 years have helped bring Kalydeco and Orkambi to market.

"We applaud the FDA for its swift approval of Orkambi," Robert J. Beall, the group's president, said in a statement Thursday. "It is our hope that everyone who is prescribed this drug will have immediate access to it so they can begin to live longer, healthier lives."

The FDA had granted Orkambi expedited review because it is intended to treat a life-threatening illness and potentially offers a substantial improvement over existing therapies. The agency also designated it an "orphan" drug, meaning Vertex will receive seven years of market exclusivity because Orkambi treats a rare disease. “Today’s approval significantly broadens the availability of targeted treatments for the specific defects that cause cystic fibrosis," John Jenkins, director of the agency’s Office of New Drugs, said in a statement.

Kalydeco costs more than $300,000 a year, and Orkambi isn't far behind. Vertex said Thursday that it plans to charge $259,000 a year for Orkambi, meaning the drug is likely to bring in billions of dollars in annual sales, even as its price causes consternation among patients and insurers. The two treatments have become examples of both the promise and perils of precision medicine, which has resulted in a growing number of specialty drugs that represent long-awaited medical advances but also are hugely expensive.

"They are not cures. They are being priced as if they are, but they are not," said Carlos Milla, director of the Stanford Cystic Fibrosis Center in California, said of the Vertex drugs. "It’s a pretty high price for something that you’re proposing as a life-long therapy."

Miller said that if the treatments ultimately reduce hospitalizations, improve quality of life and help patients to live longer, they could prove their value over time. But he said it's difficult to predict how much the drugs, particularly Orkambi, will do to replace the current standards of care.

In its statement Thursday, Vertex said it understands "that medicines can only help patients who can get them." It noted that the company maintains a patient support program dedicated to making sure any patients who need the drugs get access to them. The CF Foundation runs a similar assistance program.

Read more: