Amitriptyline -- commercialized under such names as Elavil, Endep and Vanatrip -- reduces levels in the lung of a fatty molecule called ceramide, they found.

A buildup of ceramide leads to the death of lung cells and inflammation, causing bacterial infection, which is the leading cause of mortality among people with cystic fibrosis, they discovered.

The study, which appears on Sunday in the journal Nature Medicine, was conducted on cells taken from 18 adult volunteers with cystic fibrosis and on mice that had been genetically modified to reproduce the symptoms of the disease.