(AP) The asthma medication Advair and a related drug will bear stronger warnings of an increased risk of death associated with one of their ingredients.

The revised warnings apply to Advair and Serevent, Food and Drug Administration spokeswoman Laura Alvey said Monday. Advair is GlaxoSmithKline's best-selling product, and Serevent is another of the British company's drugs.

The updated versions of the "black-box" warnings on both drugs caution that salmeterol, one of the active ingredients in Advair and the active ingredient in Serevent, may increase the risk of asthma-related death. Black-box warnings are the most severe warnings the FDA can require of prescription drugs.

Advair should be used only by patients when other asthma drugs, such as low- to medium-dose inhaled corticosteroids, don't work or if their asthma is severe enough to merit use of two medications, the revised warning says.

As for Serevent, it should only be used as an additional medication when the low- to medium-dose inhaled corticosteroids aren't sufficient or, again, if the asthma is serious enough to merit use of two drugs.

The FDA in November asked that the labels be updated for the two drugs, along with a third, Foradil.

Foradil's manufacturer, Novartis, remains in talks with the FDA and no final decision has been reached, said Julie Lux, a spokeswoman for Schering-Plough Corp., which markets Foradil in the United States.

GlaxoSmithKline said in a statement that it was pleased to reach an agreement with the FDA on the label changes to its two drugs.

"The new product labels communicate the benefit-risk profile of Serevent and Advair and help guide physicians in making appropriate prescribing decisions," the company said. In November, however, it maintained that the drugs already came with sufficient warning. The company reported in February that sales of Advair, sold as Seretide in the United Kingdom, rose 22 percent last year to $5.2 billion.

The FDA last Friday released new medications guides for patients using the two GlaxoSmithKline drugs. The letters urge asthmatics using the drugs to talk to their doctors about the relative risks and benefits of the medicines.

The agency said a large U.S. study found that more people using the asthma drugs died from their asthma compared with those taking dummy medication. The number of asthma deaths in the study was small, however: just 13 out of 13,176 patients.

The drugs help with long-term control and prevention of asthma symptoms like wheezing and shortness of breath. They help the muscles around the airways in the lungs stay relaxed.

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On the Net:

Food and Drug Administration: http://www.fda.gov/cder/drug/infopage/LABA/default.htm