Zenica says the pill is the first new treatment of its kind to come onto the UK market in twenty years.

Accolate is one of a new class of drugs known as leukotriene receptor antagonists (LTRAs), which act by blocking the effects of leukotrienes - natural substances which trigger inflammation, mucus secretion and which cause bronchoconstriction typical of an asthmatic attack.

Accolate, also known as Zafirlukast, has been used in the US for the past two years where it has already been prescribed to over one million patients.

Chronic disease

Around three million people are affected with asthma in the UK, including 750,000 school children, and it is estimated that more than 100 million worldwide suffer from the chronic lung disease.

The inhaler is the standard treatment for many sufferers

The company says the drug is suitable for patients in the mild to moderate asthma category - the vast majority of cases - and should be prescribed to adults and children over the age of 12.

It will normally be used alongside inhalers, but for some people it may even replace the old steroid delivery systems. But like all asthma treatments, it will need to be taken regularly to be effective.

Dr Dermot Ryan, a GP and chair of the General Practitioners on Asthma Group, said: "Adequate compliance is a key element in the success of any treatment.

"This is particularly important for asthma 'preventer' treatment. Accolate treatment has shown high patient preference and compliance, making it a useful addition to asthma treatment."

Big market

Worldwide sales for Accolate in 1997 were £53m. Zeneca says the international market for anti-asthma medicines is worth an estimated £4bn.

"Unlike many current asthma therapies, Accolate, is taken as a tablet, which may be an important factor in the success of the product, since there are sometimes disadvantages and difficulties associated with the usage of inhalers," the company says.

It added that research showed that UK patients preferred tablets to inhalers and were more likely to keep up with the treatment if it was in pill form.

'Useful treatment'

The new tablet has been welcomed by the National Asthma Campaign.

Professor Duncan Geddes, a spokesman for the NAC, said: "Existing treatments for asthma such as inhaled steroids are, in the main, extremely effective and extremely safe for most people with asthma.

"However, Accolate and the recently introduced Singulair, along with several other existing products such as long acting bronchodilators, may well be useful as treatments additional to inhaled steroids in those whose asthma is not well controlled on inhaled steroids alone."

Asthma is the only treatable chronic condition in the West which is increasing in prevalence.

According to the NAC, asthma causes 2,000 deaths a year in the UK, 80% of which could be avoided.