Enzyme dissolves cystic fibrosis phlegm.

An experimental drug that cystic fibrosis patients inhale in aerosol form can cut through the thick mucus that clogs their lungs, allowing them to breathe more easily and deeply, according to the results of a preliminary study.

A team led by National Institutes of Health researcher Ronald G. Crystal found that twice-daily inhalations of the drug, called DNase I, improved the lung functions of all 16 of the adult subjects. Moreover, the treatment had no noticeable side effects, the researchers report in the March 19 NEW ENGLAND JOURNAL OF MEDICINE.

DNase I is a naturally occurring body enzyme that chops up DNA, a major constituent of the sticky phlegm that accumulates in the lungs and other organs of cystic fibrosis patients. The DNA is left behind by infection-fighting white blood cells that migrate to the lining of these organs, only to die after finishing their job. Because DNA is very viscous, it makes the mucus hard to cough up, increasing patients' vulnerability to further lung infections.

DNase I treatment thinned the lung mucus of all of the patients participating in the new study, Crystal and his colleagues found. They also detected higher levels of degraded DNA in the patients' sputum following DNase I therapy.

"This is very exciting," says Robert J. Beall, vice president for medical affairs of the Cystic Fibrosis Foundation in Bethesda, Md. "It's the first [mucus-degrading drug] for which we've had such encouraging preliminary data."

Crystal and his colleagues reported early results from the DNase I study at a conference on cystic fibrosis last year (SN: 3/2/91, p.132). Genentech, Inc., the South San Francisco, Calif., biotechnology company that produces DNase I through genetic engineering, is now expanding tests of the drug to include 900 cystic fibrosis patients at 50 U.S. medical centers. If the additional tests confirm DNase I's efficacy, the company plans to file for Food and Drug Administration approval of the drug early next year.