Ranbaxy might lose a key six-month exclusivity period for the generic version of Nexium – a blockbuster drug from AstraZeneca – if it fails to get regulatory clearance for the US market by the end of November. The drug maker is awaiting approval for the drug, which treats heartburn, from the US Food and Drug Administration (US FDA). The exclusivity period could imply an opportunity worth $170-$180 million for Ranbaxy, analysts said. The ban on selling drugs manufactured at the Punjab and Himachal units of Ranbaxy has resulted in the regulatory delay, experts added. The company, which is in the process of being acquired by Sun Pharma, is preparing to make the generic version of Nexium from its plant at New Jersey in the US.