Nov. 23 (Bloomberg) -- GlaxoSmithKline Plc's asthma drugs Serevent and Advair, the company's biggest-selling medications, may have rare and deadly side effects for children, safety officials at the U.S. Food and Drug Administration said.

Nine patients under age 16 were harmed, including five who died, while taking Serevent in the 13 months after it was approved in the U.S. for children in 2006, a safety review found. An advisory panel of pediatricians is slated to discuss side effects from Serevent and other medications on Nov. 27.

The FDA strengthened the warning labels for Serevent, Advair and Novartis AG's Foradil almost two years ago, limiting use to patients who don't benefit from other drugs. A study found patients using Serevent had a fourfold increase in asthma- related deaths, while others showed it and Foradil increased asthma exacerbations and hospitalizations in adults and children, according to the FDA staff memo Oct. 24, 2007.

``There is no available pediatric data to indicate that the increased risk of asthma death and life-threatening exacerbations observed in adults does not also apply to children,'' the FDA staff members wrote in a report posted on its Web site today. While the review didn't identify any adverse reactions unique to children, Serevent may have more risks than benefits for the youngest users, they said.

Glaxo officials weren't immediately available to comment.

The drugs are used long-term to relax the airway, control symptoms and prevent exacerbations of asthma. Almost one in 10 Americans will be diagnosed with asthma at some time, according to the National Institutes of Health. About 21 million adults and 9 million children in the U.S. currently have the condition.

Global Revenue

Global revenue for Serevent and Advair rose 12 percent to $6.13 billion last year, making the medicines the second-best- selling in the world behind Pfizer Inc.'s cholesterol drug Lipitor. Advair is a combination of the salmeterol, the chemical in Serevent, and a steroid.

Asthma is a chronic respiratory disease that causes inflammation and narrowing of airways in the lungs. Asthma attacks can be caused by changes in the weather, allergies, exercise, smoking or exposure to toxic air. Attacks can cause shortness of breath, cough, chest pain and other symptoms.

The FDA staff members said a study looking at the drugs' safety may be warranted, thought it would be difficult to enroll enough children. A more ``formal'' analysis of their risks and benefits in treating asthma in children is needed, they said.

To contact the reporter on this story: Michelle Fay Cortez in Minneapolis at mcortez@bloomberg.net

Last Updated: November 23, 2007 17:56 EST