March 4 (HealthDay News) -- A new type of asthma therapy might be especially helpful for people with severe asthma who often have to take oral steroids to control their symptoms.

The drug is called mepolizumab, and two small studies in the March 5 issue of the New England Journal of Medicine have found that, when taken regularly, it can reduce asthma exacerbations. Additionally, people taking the drug had lower levels of eosinophils, a type of white blood cell that has been implicated as a potential cause of asthma.

"This is a new treatment which substantially reduces the risk of asthma attacks in a severe asthma population," said the senior author of one of the studies, Dr. Ian Pavord, a consultant physician and an honorary professor of medicine at Glenfield Hospital, University Hospitals of Leicester, England.

Dr. Paul O'Byrne, the senior author of the other study, added that "we now have a likely new treatment modality that will improve outcomes and reduce exacerbations in severe prednisone-dependent asthma, and this is not a small population -- it's probably 2 to 4 percent of the asthmatic population." O'Byrne is chairman of the Department of Medicine at McMaster University and executive director of the Firestone Institute for Respiratory Health at St. Joseph's Hospital in Hamilton, Ontario, Canada.

Both studies were funded by GlaxcoSmithKline, the pharmaceutical company that is developing the drug.

He said that mepolizumab works by blocking a protein called interleukin-5, which is essential for the development of eosinophils. Eosinophils have long been implicated in asthma, though their exact role remains unclear. However, scientists do know that when an asthma exacerbation occurs, eosinophil levels usually rise.

In the first study, Pavord and his colleagues randomly placed 61 people with severe asthma on either 750 milligrams of mepolizumab or a placebo for a year. The drug and placebo were administered intravenously once a month for a year.

Over the study period, those on mepolizumab had fewer asthma exacerbations than those on placebo -- 2 versus 3.4. People taking the drug also reported a greater improvement in their quality of life than did people taking the placebo.

The second study was smaller, including just 20 patients. Nine received 750 mg of mepolizumab, and 11 were given a placebo. Again, the drug and placebo were administered in intravenous doses once a month.

Everyone in this study had severe, prednisone-dependent asthma. Prednisone is an oral steroid that is generally quite effective in treating asthma but has numerous and serious side effects.

In the six-month trial, there were 12 asthma exacerbations in 10 people on placebo. Nine had evidence of eosinophils during their exacerbations. During the study, just one person in the treatment group had an exacerbation, but no eosinophils were present. Additionally, those taking the drug were able to reduce their dosage of prednisone more than people on placebo could.

Mepolizumab was not associated with a serious side effect in either study, though both authors pointed out that the studies were small and no more than six months to a year long.

"If you are one of those people [who has eosinophils] and your asthma is pretty severe, this may be a relatively promising treatment to prevent exacerbations, though it's still experimental," said the author of an accompanying editorial in the same issue of the journal, Dr. Sally Wenzel, director of the Asthma and Allergy Center at the University of Pittsburgh Medical Center.

But, she pointed out that not everyone who has asthma also has eosinophils.

All three experts said they were not sure if mepolizumab would have a place in treating less severe asthma, at least for awhile. O'Byrne said that the drug needs to be studied in larger populations and it's currently very expensive, which would limit its use by people who have other treatment options.

SOURCES: Paul O'Byrne, M.B., professor and chairman, department of medicine, McMaster University, and executive director, The Firestone Institute, St. Joseph's Hospital, Hamilton, Ontario, Canada; Ian Pavord, D.M., consultant physician and honorary professor, medicine, Glenfield Hospital, University Hospitals of Leicester, U.K.; Sally E. Wenzel, M.D., director, Asthma and Allergy Center, University of Pittsburgh and University of Pittsburgh Medical Center; March 5, 2009, New England Journal of Medicine