NEW YORK (Reuters Health) - Difficult-to-control asthma has been linked to stomach acid backing up into the esophagus, but treatment with a heartburn drug doesn't seem to improve asthma symptoms, investigators report.

Dr. Robert Wise at Johns Hopkins University, Baltimore, and colleagues note in this week's New England Journal of Medicine that drugs to suppress stomach acid production are recommended for people with poorly controlled asthma and gastric acid reflux, even when heartburn symptoms are absent.

Whether or not this costly strategy improves asthma symptoms has not been verified, however.

Wise's group ran a 24-week clinical trial with 412 adult patients with inadequate control of their asthma, despite treatment with asthma inhalers, and who had few symptoms of gastric acid reflux. The participants were randomly assigned to take Nexium or an inactive "placebo" pill twice daily.

There was no difference between the groups in how often the patients experienced episodes of poor asthma control, the investigators found. They also saw no differences in other aspects of lung function, how often patients were woken at night by breathing problems, or in their quality of life.

Even in a subgroup of these patients who had measurable acidity in the esophagus, Nexium was of no greater benefit than it was in the other subjects.

Wise and his team conclude that gastric acid reflux that doesn't cause heartburn symptoms "is not a likely cause of poorly controlled asthma."

SOURCE: New England Journal of Medicine, April 9, 2009.