TUESDAY, Jan. 31 (HealthDay News) -- Kalydeco, the first drug that targets the defective protein behind a rare form of the deadly lung disorder cystic fibrosis, was approved Tuesday by the U.S. Food and Drug Administration.

One patient advocate group applauded the decision.

"Today marks an important milestone in our journey to find a cure for cystic fibrosis," Robert Beall, president and CEO of the Cystic Fibrosis Foundation, said in a news release. "Kalydeco addresses the underlying cause of cystic fibrosis, and the science behind the drug has opened exciting new doors to research and development that may eventually lead to additional therapies that will benefit more people."

People with cystic fibrosis have mutations in a gene that produces a protein called CFTR, which regulates the movement of ions (such as chloride) and water in the body. This defect causes sticky mucus to accumulate in the lungs and other organs, resulting in infections, digestive problems and usually death in early adulthood.

Cystic fibrosis affects an estimated 30,000 people in the United States and is the most common fatal genetic disease in the white population. About 1,200 (4 percent) of cystic fibrosis patients have a rare form of the disease caused by a specific G551D mutation in the cystic fibrosis transmembrane regulator (CFTR) gene, the FDA explained in a news release.

The twice-a-day pill Kalydeco (ivacaftor) was approved for patients with this rare form of cystic fibrosis. The pill, which is taken with fat-containing food, helps the protein made by the CFTR gene function better, the FDA explained.

Two 48-week clinical trials involving 213 patients -- one with patients ages 12 and older and the other with patients ages 6 to 11 -- showed that the drug improved lung function and reduced other symptoms of cystic fibrosis.

The most common side effects of the drug were upper respiratory tract infection, headache, stomach ache, rash, diarrhea and dizziness, said the FDA, which approved the drug under its priority review program.

The drug will come with a hefty price tag, however: Kalydeco, which is made by Massachusetts-based Vertex Pharmaceuticals Inc., costs almost $300,000 a year.

"Kalydeco is the first available treatment that targets the defective CFTR protein, which is the underlying cause of cystic fibrosis," Dr. Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research, said in the news release. "This is a breakthrough therapy for the cystic fibrosis community because current therapies only treat the symptoms of this genetic disease."

Kalydeco is not effective in cystic fibrosis patients with two copies of the F508 mutation in the CFTR gene, which is the most common mutation that causes cystic fibrosis, the FDA stressed. If a patient's mutation isn't known, an FDA-approved cystic fibrosis mutation test should be used, the agency said.

The Cystic Fibrosis Foundation said there is an ongoing phase 2 trial for people with the more common CFTR gene mutation, using Kalydeco alongside a second experimental drug, VX-809. Findings from the first part of this trial have been encouraging, with the second part still underway.

More information

The U.S. National Heart, Lung, and Blood Institute has more about cystic fibrosis.