U.S. court temporarily blocks a competitor to AstraZeneca's Nexium NEW YORK (Reuters) - A federal U.S. judge issued a temporary injunction against Hanmi Pharmaceutical Co Ltd on Friday, preventing the South Korean drugmaker from launching a close relative of AstraZeneca Plc's Nexium stomach-acid drug in the United States. Judge Timothy Dyk of the U.S. Court of Appeals for the Federal Circuit approved AstraZeneca's request for the injunction on Friday. He ordered Hanmi to respond within a week and AstraZeneca to reply no later than September 24. AstraZeneca has accused its South Korean rival of patent infringement for developing Esomezol, a drug that treats gastroesophageal reflux disease, which is caused by stomach acid moving up into the esophagus. In August, Hanmi received tentative approval from the U.S. Food and Drug Administration for Esomezol, which was developed based on Nexium. Hanmi's potential encroachment poses a threat to AstraZeneca, which is facing the near-term expiration of U.S. patents covering its two top-selling drugs - Nexium, which loses U.S. protection in 2014, and the cholesterol pill Crestor, which will go off-patent in 2016. As a result, sales at the company are set to fall by several billion dollars. Reporting by Lauren Tara LaCapra in New York, Deena Beasley in Los Angeles and Zeba Siddiqui in Bangalore; Editing by Tim Dobbyn