Officials emphasized that problems from the drug Serevent were rare, and they said the drug's benefits outweigh the risks. They cautioned that it is dangerous to abruptly stop taking the drug and recommended that concerned patients talk with their doctors.

Serevent, an aerosol spray made by GlaxoSmithKline, opens the airwaves to help asthma patients breathe more easily. Patients use it twice a day to prevent attacks.

Due to concerns about the drug, Glaxo launched a large study to compare the number of life-threatening experiences, such as intubations and mechanical ventilation, and the number of asthma-related deaths in patients taking the drug vs. the number of such occurrences in patients given a placebo.

The study found a greater risk of problems and a greater risk of death among black patients, and found a disparity in deaths among those who were not using a companion drug aimed at controlling inflammation.

As a result, the company and the FDA are emphasizing existing guidelines that say asthma patients whose disease is severe enough to require daily medication should also be using inhaled corticosteriods, which control inflammation.

"Someone who needs Serevent should be on something to control inflammation too," said Dr. Robert J. Meyer, director of one of the FDA's offices of drug evaluation.

The study was not designed to determine why certain Serevent patients were more likely to suffer problems, but rather to see if Serevent itself posed a threat, Meyer said.

The 28-week study included 26,000 patients. Originally designed to enroll 60,000 patients, Glaxo ended it early because of difficulty finding participants and because it was not designed to analyze the questions raised early in the study, company and FDA officials said.

When entering the study, 47 percent of all patients were using a corticosteroid. Black patients were less likely to be using these drugs than whites were, and that may explain at least part of why blacks using Serevent were more likely to have lung problems and more likely to die than whites were.

Officials at the company and the FDA did not know if other factors contributed to the racial disparities. Due to socioeconomic and other factors, blacks are more likely to face health problems. Overall, the severity of asthma is worse among blacks than whites.

Neither Glaxo nor FDA officials would say precisely how many people in each group had complications and how many died.

An estimated 16 million people in the United States have asthma, and about 1.3 million use Serevent.

The FDA approved Serevent, also known as salmeterol xinafoate, to treat asthma in 1994 and later extended its approval for treatment of chronic obstructive pulmonary disease.

On the Net:

FDA: http:/www.fda.gov

GlaxoSmithKline: http://www.gsk.com