WASHINGTON – A widely used asthma medicine, Serevent, appears to slightly increase the risk of a serious or fatal asthma attack in a few people who use it, the Food and Drug Administration said Thursday. The agency emphasized that it remains a useful drug for most asthma patients.

The announcement was triggered by partial results of a large study that was launched as a result of earlier concerns over the safety of the drug, whose chemical name is salmeterol.

The risk appears to be greatest in African Americans and in patients who are not also taking an inhaled corticosteroid drug for their asthma, according to the joint announcement by the FDA and the manufacturer, GlaxoSmithKline.

It is not clear whether the study results will change use of the drug, which is used by about 1.3 million of the nation’s 14 million asthmatics. But it appeared unlikely the drug will be withdrawn from the market.

“We still feel that from the data at hand that this drug is safe and effective,” said Robert Meyer, one of the FDA’s directors of drug evaluation. “But if part of what we are seeing is because the drug is not being used as part of a well-thought-out asthma care plan, then it behooves us to emphasize … that it really does need to be used in that setting.”

Both he and GlaxoSmithKline officials warned users of Serevent not to stop taking the medicine, and urged them to consult their physicians.

The incomplete study, known as the SMART trial, followed 28,000 asthmatics who were randomly assigned to get their usual care and take Serevent, or to get usual care only. All patients in the study were observed for about half a year.

Overall, there were slightly fewer than 30 deaths from asthma, with about twice as many in the group taking Serevent as in the control group, Meyer said. The Serevent group also had more cases of asthma attacks requiring intensive care treatment, although those numbers also were very small. In both cases, the differences were not statistically significant.

Asthma is a condition in which the lung’s airways swell and fill with mucus, making breathing difficult. In severe attacks, people go into “respiratory arrest” and must be put on breathing machines to survive.

Serevent and other beta-agonist drugs – which are chemically related to the hormone epinephrine (also called adrenaline) – help relieve an attack by rapidly shrinking the swollen tissue. Serevent is a long-acting drug that is taken twice a day, rather than four or more times for most beta-agonists.