* GSK drug ahead of similar ones from Teva and AstraZeneca
* Under-the-skin injection set for filing this year
* NEJM editorial questions cost-effectiveness of new drugs
* Analysts see fragmented market for biotech lung treatments (Adds more detail on Teva drug, analyst comment on fragmented market)
By Ben Hirschler
LONDON, Sept 8 (Reuters) - A new group of biotech lung drugs that have produced promising results in clinical tests are now up against the issue of how cost-effective that are.
The first is likely to be launched next year by GlaxoSmithKline. Rival firms including Teva Pharmaceutical Industries and AstraZeneca are racing to develop similar injectable drugs for patients with severe asthma, who do not respond adequately to traditional inhalers.
It is all in pursuit of a new market that analysts believe may be worth around $7.5 billion in annual sales.
But some analysts have estimated the new class of drugs might cost $10,000 to $15,000 per patient a year.
GSK, the leader in asthma treatments since launching its Ventolin inhaler in 1969, consolidated its position in the new field by presenting late-stage Phase III data on its experimental drug mepolizumab at the European Respiratory Society congress in Munich on Monday.
The company plans to submit an under-the-skin mepolizumab injection for regulatory approval before the end of 2014, while Teva, which also unveiled positive Phase III data in Munich, aims to file its drug reslizumab in the first half of 2015.
AstraZeneca's benralizumab is further behind, although it is seen as a potentially potent competitor.
Other drugs are also in development from several rival companies, suggesting the market for the new treatments may become fragmented, according to analysts at Credit Suisse.
GSK had already said in March that mepolizumab reduced serious asthma attacks, known as exacerbations, by around 50 percent compared to placebo and cut the need for potentially damaging oral steroids, without giving full details.
An editorial in the New England Journal of Medicine (NEJM), where the results were also published, said the data were promising and the drug's side effects looked acceptable, but it was unclear how widely it should be used.
Mepolizumab is an anti-interleukin-5 antibody drug that depletes a type of white blood cells known as eosinophils involved in lung disorders and is expected to help around half the estimated 2 million patients in developed markets with severe, difficult-to-treat asthma.
Parameswaran Nair, an asthma expert at Canada's McMaster University, said in the NEJM editorial that the data did not suggest all patients with eosinophil-related severe asthma would need such a treatment, which he expected to be "expensive".
He noted that patients on placebo in one of two studies also had a "remarkable" 50 percent drop in exacerbations, simply by adhering properly to prescribed conventional therapies, which was likely to be more cost-effective.
"This finding would suggest that most patients in this clinical trial might have had improvement in symptoms without mepolizumab simply by the institution of good clinical practice," he wrote.
GSK, which faces slowing sales of its conventional inhaled lung treatment Advair, said it was premature to talk about price but added it planned cost-effectiveness studies to show the value of its new product.
"There are currently no options, so we will be the first into the marketplace," said Steve Yancy, GSK's development leader for mepolizumab.
Xolair, from Novartis and Roche, is the only biotech asthma drug sold at present, but it works in a different way to the new batch of products and is only indicated for allergic asthma.
The new class of medicines are also being investigated for the treatment of chronic obstructive pulmonary disease (COPD), which is linked to smoking.
AstraZeneca earlier reported that benralizumab did not reduce COPD exacerbations in a mid-stage trial, although it did demonstrate clinically significant improvements in lung function. (Editing by Jeremy Gaunt)