LONDON: The U.S. Food and Drug Administration had directed that drugmaker GlaxoSmithKline’s biggest selling asthmatic drug Advair should be made available to asthmatics only as a last resort. The ruling is likely to hit the drug major really hard as Advair is its single most important drug.

The drug, which had recorded a worldwide sale of 3.43 billion pounds last year, is predicted to become a 5-billion-pound-a-year earner for the company by 2010. In the U.S., almost a quarter of the drug’s sales come from prescriptions as a first line of treatment.

Experts feel that while FDA rulings carry extreme importance and are likely to be followed, U.S. doctors would continue to prescribe the drug and patients, who are used to the benefits of the dual-action inhaler, may not leave it.

In Europe, where regulators are stricter, Advair sales are currently 15 per cent ahead of last year.

The ruling naturally brought the company’s shares down by almost 4 per cent yesterday.

The FDA has acted in the wake of recent clinical trials, which showed Advair and similar drugs had occasionally triggered sudden asthma attacks in its patients, some of which were fatal. It proposed a more restrictive labelling system for the drug.

Glaxo has criticised the ruling, saying the drug has been a boon to millions of patients worldwide and the recommendation that it can be used as a second line of treatment could lead to deaths of those who are best suited to receive it immediately.

The company’s vice president for clinical development and medical affairs, Dr Kathy Rickard, said FDA’s proposed labelling changes would reserve the most effective asthma treatment until after a patient has failed on other treatment options and therefore may be at risk for severe outcomes, such as exacerbations and potentially death.

A company spokesperson said the existing U.S. label for the drug contains a strong enough caveat in the form of a “black box” warning, introduced in 2003.

The company has a month to respond to the FDA ruling before the final text for the product’s labels are agreed. Glaxo has confirmed it intends to appeal.