Amneal Pharmaceuticals Llc., a fast-growing drugmaker with factories in Hauppauge and South Yaphank, announced plans Monday to sell an acid-reflux drug that would challenge the popular Nexium in the United States.

New Jersey-based Amneal has reached an agreement with Hanmi Pharmaceutical Co. of South Korea, which created the esomeprazole strontium delayed-release medicine.

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The drug is being reviewed by the U.S. Food and Drug Administration and is the subject of a lawsuit between Hanmi and AstraZeneca, maker of Nexium.

An Amneal spokeswoman said the company hopes to begin selling the drug in the second half of this year, before generic versions of Nexium go on the market next year. The IMS Health news service estimated Nexium's U.S. sales totaled $6 billion per year.

Citing the lawsuit, the Amneal spokeswoman said the company could not discuss where the new drug would be manufactured or by whom.

Amneal president Chirag Patel said the agreement "gives Amneal the opportunity to introduce potentially before other generic competitors."

Amneal is in the midst of quadrupling the size of its factory in South Yaphank, which would add 400 jobs there over five years.