The government-funded study is one of the largest to delve into the biology of asthma.
Researchers collected data on nearly 1,000 people with asthma who were enrolled in nine clinical trials sponsored by the National Heart, Lung and Blood Institute.
Most of the studies followed patients over time and collected samples of mucus from the lower part of the lungs.
Researchers checked the samples for certain kinds of white blood cells, called eosinophils, that cause airway inflammation. Many asthma medications work by reducing inflammation.
Surprisingly, researchers found that nearly half (47%) of asthma sufferers did not have eosinophils in their mucus, indicating that something else was causing asthma in these patients.
They also found that people with this so-called non-eosinophilic asthma did not respond well to treatment with oral and inhaled corticosteroids, like prednisone, Aerobid, Azmacort, Flovent, and Symbicort, which fight inflammation.
“The currently used anti-inflammatories didn’t seem to be that effective, at least over a two-week period, in a subgroup of patients who had non-eosinophilic disease,” says researcher John V. Fahy, MD, a professor of medicine and director of the Airway Clinical Research Center at the University of California at San Francisco.
Patients with non-eosinophilic asthma also did respond to the drug albuterol. Albuterol works by relaxing the muscles around the airways, which helps them open up so the person can breathe easier. It’s usually prescribed as a rescue medication.
The study is published in the American Journal of Respiratory and Critical Care Medicine.