With asthma medication Symbicort, pharmaceutical corporation AstraZeneca aims to take away market share from GlaxoSmithKline’s Advair. Glaxo is the world’s dominant maker of asthma treatments and Advair is the company’s top-selling drug. Both companies are based in the United Kingdom.

AstraZeneca’s introduction of Symbicort comes at a time when the market for asthma treatments has reached $11 billion and is currently growing by 15%, the Wall Street Journal reported.

“It’s very difficult to overtake a product you’re not a lot better than,” said Paul Diggle, a pharmaceutical analyst with London investment bank Nomura Code Securities. “Especially if you’re up against a bigger marketing force.” Glaxo spent $146 million in advertising Advair last year, making it the seventh-most advertised drug in the United States.

Until Symbicort was introduced, Advair was the only treatment that combined two asthma medications into a single inhaler. Both Advair and Symbicort contain a coticosteroid and a long-acting beta agonist.

Astra is banking on Symbicort’s faster acting relief against symptoms to give it an edge over Advair. “We know that Symbicort delivers improved control as soon as the first day of use, said Tony Zook, president and CEO of AstraZeneca U.S. “And it has a fairly rapid onset of action, within 15 minutes. We believe that will be a point of differentiation for us.”

Analysts predict Glaxo will maintain its dominant market share because it treats a broader range of ailments. Advair is prescribed for asthma in adults and children as well as for COPD in adults. Symbicort is approved only for adult asthmatics.

AstraZeneca plans to apply for FDA approval to sell Symbicort for pediatric asthma and COPD next year.