Cost-effectiveness is seen as a challenge for a new group of biotech lung drugs that have produced promising results in clinical tests, of which the first is likely to be launched next year by GlaxoSmithKline. Rival firms are racing to develop similar injectable drugs for patients with severe asthma, who do not respond adequately to traditional inhalers, in pursuit of a new market that analysts believe may be worth around $7.5 billion in annual sales.