The drug works to restore the balance of salt and water on the surface of the patient's airways, a process that is crucial for CF patients because their bodies produce a thick, sticky mucus which makes it hard to breathe.
However it is only for people who have a specific G551D gene mutation, or about 1,200 of the 70,000 people worldwide who have cystic fibrosis.
More than 90 percent of CF patients have genetic basis, or two copies of the F508 mutation in the CFTR gene. The drug does not work for those people, the FDA said.
"Kalydeco is an excellent example of the promise of personalized medicine -- targeted drugs that treat patients with a specific genetic makeup," said FDA Commissioner Margaret Hamburg.
A phase III trial published in November 2011 in the New England Journal of Medicine was hailed as a promising breakthrough after results showed the oral twice-daily medication could improve lung function, growth and sweat chloride levels over a span of 11 months.
The clinical trial involved 213 patients, some as young as six years old. Results showed "significant and sustained improvement in lung function," the FDA said.
It remains unclear if longer-term exposure to the drug could halt the deterioration of lung function.
If a CF patient does not know his or her genetic status, an FDA-cleared CF mutation test should be used to determine whether the G551D mutation is present, the US regulator said.
Common side effects included upper respiratory tract infection, headache, stomach ache, rash, diarrhea, and dizziness.
Cystic fibrosis mainly affects the lungs, where excess mucus builds up causing inflammation and infection. While other organs such as the pancreas are also susceptible to complications from CF, most patients die of lung disease.
The average lifespan of people with CF is 37 years.
Source: AFP
