DRUGS group GlaxoSmithKline has won approval in the US for an asthma treatment for children as young as four.

The decision means more than 3.8 million children with chronic breathing difficulties can be treated with Advair, which was first launched in the US in 2001.

The US Food and Drug Administration was previously only prepared to make the treatment available to patients older than 12.

But trials children showed the drug was as safe as other asthma products on the US market.

The announcement will boost GSK's balance sheet at a time when the company is suffering a slowdown in introducing new drugs to the market and sales of many bestselling medicines are coming under pressure from generic copies.

It also follows a £297.5m deal for two treatments for acute heart disease. The group announced an agreement earlier this month with Sanofi-Synthelabo to buy injectable drugs Fraxiparine and Arixtra.

Advair is an inhaled treatment that attacks two causes of asthma - airway inflammation and the tightening of muscles in the tubes that carry oxygen into the lungs.

It is the most commonly prescribed inhaled treatment for asthma in the US.

A report by the US Centers for Disease Control found that nine million children under 18 have the disease.