Three GlaxoSmithKline Plc and Novartis AG Asthma drugs are safe enough to stay on the market amid concerns they raise the risk of severe asthma attacks in rare cases, a U.S. advisory panel unanimously said on Wednesday.

Glaxo’s drugs Serevent and Advair already come with “black box” warnings about one study showing Serevent patients had a higher, albeit small, risk of life-threatening Asthma attacks and deaths.

Novartis’ medicine Foradil, part of the same category of drugs, should carry a similar warning about the study, the Food and Drug Administration advisory panel ruled.

“Until proven otherwise, we have to make ourselves believe (Foradil) may act the same way,” said panel member Dr. Steven Gay, medical director of critical care medicine at the University of Michigan Health System.

Novartis said Foradil, which Schering-Plough Corp. markets in the United States, acted differently than the Glaxo drugs and may be safer. But Novartis said it would “work with the FDA to finalize appropriate language” if the agency asked for a new warning.

The FDA usually follows recommendations from its advisory panels.

Asthma is a chronic lung disease that afflicts about 15 million Americans, nearly 5 million of them children. The disease can cause episodes of wheezing, coughing and breathing difficulty. Severe asthma attacks can kill.

Serevent, Advair and Foradil are inhaled drugs known as long-acting beta agonists that patients take daily to relax bronchial muscles and prevent asthma attacks.

Panel members said the drugs’ benefits of controlling asthma symptoms and improving lung function outweighed the small possibility of a life-threatening asthma attack.

In a Glaxo study detailed on the drug labels, there were 13 deaths among about 13,000 patients treated for 28 weeks with Serevent, compared with three deaths among about 13,000 people given a placebo.

Severe asthma attacks also were seen when Foradil was given at a higher dose that the FDA refused to approve. Another study done after approval was too small to draw conclusions about the safety concern, FDA reviewers said.

Advair is a combination of Serevent, known generically as salmeterol, and another asthma drug. Global Advair sales were $4.5 billion in 2004, making it Glaxo’s top-selling product. Serevent sales were $639 million. Foradil’s global sales were $320 million in 2004. The generic name for Foradil is formoterol.