WASHINGTON (AP) — British pharmaceutical firm AstraZeneca PLC said Friday it received approval to market its asthma drug for an additional use, boosting its ability to compete with competitor GlaxoSmithKline. The Food and Drug Administration approved Symbicort to treat chronic bronchitis and emphysema, which causes coughing, wheezing and shortness of breath. The additional approval means Symbicort is now available to treat both asthma and chronic bronchitis. That’s the same indication as Advair, the blockbuster drug from rival GlaxoSmithKline that dominates the market for inhalable respiratory drugs. Advair is the British drugmaker’s top product and was the third best-selling prescription in the U.S. for 2007 at $4.3 billion, according to research firm IMS Health. Both Advair and Symbicort come in inhalers containing two ingredients: one that relaxes muscles around stressed airways and another that reduces inflammation. AstraZeneca has struggled to take U.S. market share away from Glaxo since Symbicort was launched in 2007. However, AstraZeneca recently reported about one-fifth of newly treated asthma patients receive a Symbicort prescription. The company estimates about 12 million U.S. patients have chronic bronchitis. The disease, also known as chronic obstructive pulmonary disease, is the fourth leading cause of death in the U.S. In a separate development Friday, AstraZeneca PLC said the FDA asked for additional information about the company’s application to market Seroquel XR extended release tablets for anxiety.