WASHINGTON (AP) – The Food and Drug Administration warned Friday that three asthma drugs may increase the risk of severe asthma attacks and even death.

The agency asked the manufacturers of Advair, Serevent and Foradil to strengthen the warning labels to reflect this risk.

The FDA said that even though the drugs decrease the frequency of asthma attacks, they can make the attacks more severe when they occur. The agency said the drugs should be prescribed only if other medicines do not control patients’ asthma.

Advair had sales of $4.7 billion in 2004, making it one of GlaxoSmithKline’s top-selling drugs.

The FDA cautioned patients not to stop taking the drugs without consulting their doctors. The agency asked the drug makers to update product labels and medication guides for patients and doctors outlining the dangers.

GlaxoSmithKline PLC, which also makes Serevent, issued a statement disagreeing with the FDA’s public health advisory. The company said the drugs already come with sufficient safety information, though the company said it would work with the FDA to “address the differences of opinion.”

Schering-Plough Corp., which markets Foradil in the United States, said it is working with the FDA to update the warning label.

“Once that is final we will be communicating with physicians,” said Schering-Plough spokeswoman Mary-Fran Faraji.

The drug is manufactured by Novartis AG.

Friday’s advisory was a request for new warnings. But ultimately, drugs must contain FDA-approved labels.

The FDA said a recent study found that more people using the asthma drugs died from their asthma, compared with those taking placebos, though the number of asthma deaths in the study was small.

The drugs are used for long-term control and prevention of asthma symptoms. They do not relieve sudden wheezing. Patients should use short-acting inhalers to relieve sudden wheezing, according to the FDA’s public health advisory.