In its first test against cystic fibrosis, high doses of a drug called NAC were safe for short-term use, researchers report.

NAC, or N-acetylcysteine, has a “proven safety record over long-term use at high doses in several chronic inflammatory conditions and has minimal interaction with other drugs,” write the researchers. They included Rabindra Tirouvanziam, PhD, of Stanford University.

However, they aren’t recommending NAC for cystic fibrosis. NAC needs more testing as a cystic fibrosis treatment, note Tirouvanziam and colleagues.

“It is important to warn patients against uncontrolled use of the drug,” they write in Proceedings of the National Academy of Sciences.

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Why NAC?

In their report, the researchers trace their interest in NAC as a cystic fibrosis treatment.

Cystic fibrosis is a chronic, progressive condition that primarily affects the body’s respiratory and digestive systems. It is due to a gene defect that causes the body to produce abnormally thick mucus.

That mucus clogs the lungs, leading to recurring infections of the lungs and sinuses. It also makes breathing difficult.

In cystic fibrosis, the lungs have an unusually high number of neutrophils, a type of white blood cell. Those neutrophils prompt inflammation, setting the stage for more damage.

Tirouvanziam and colleagues noticed that neutrophils in cystic fibrosis patients were short on an antioxidant called glutathione. NAC is a building block for glutathione. The scientists wanted to see if NAC could boost glutathione, which in turn might curb lung inflammation.

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The researchers checked NAC’s short-term safety. Participants were 18 children with cystic fibrosis who were at least 10 years old.

Every day for four weeks, the patients took three high doses of NAC by mouth. “We used doses in excess of 1.8 grams per day, which had never been used in [cystic fibrosis patients] before,” write Tirouvanziam and colleagues.

The treatment appeared to be safe. The scientists note “very mild and infrequent drug-related adverse effects” including heartburn, nausea, and a bad taste from the drug.

Especially in patients with lung inflammation before taking NAC, neutrophils in the lungs became less active and had a rise in glutathione during NAC treatment. Lung function didn’t improve, which didn’t surprise the researchers because the test was so short.

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Next Steps

Those findings could be an important cellular link in understanding cystic fibrosis, write the researchers.

However, they note that they didn’t test NAC’s effectiveness and long-term safety. That work will come later.

NAC’s structure “prevents proper quality control of most commercial formulations available over the counter,” the researchers caution. They call for “carefully designed and controlled clinical studies” of NAC and cystic fibrosis.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Tirouvanziam, R. Proceedings of the National Academy of Sciences, online early edition, week of March 13-17, 2006. News release, Proceedings of the National Academy of Sciences.