Forest Laboratories Inc., a New York City drugmaker with major operations in Suffolk County, Wednesday announced it is acquiring closely held pharmaceutical firm Aptalis for $2.9 billion.

The cash deal requires regulatory approval in the United States and Canada, and is expected to close in the first half of 2014.

Forest, granted tax breaks totaling $2.16 million over 10 years by the Suffolk County Industrial Development Agency in 2011 after agreeing to keep operations in Commack and Hauppauge, has 5,800 employees worldwide. Officials declined to provide a Long Island head count.

Gastrointestinal and cystic fibrosis drugmaker Aptalis, with operations in Birmingham, Ala., Montreal and in Europe, is owned by private equity firm TPG.

Shares of Forest soared almost 18 percent Wednesday, closing at $69.30.

The deal is expected to add nearly $700 million in revenue and 78 cents to Forest's earnings per share in fiscal 2015 when special items are included, chief executive Brent Saunders said in a statement.

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"The acquisition of Aptalis helps diversify Forest while advancing our strategy to create blockbuster therapeutic areas," he said. "Because there is such a strong fit, we expect to grow the sales of products from both Forest and Aptalis, while realizing $125 million in cost synergies from combining the two companies."

Forest makes drugs that treat illnesses of the central nervous, cardiovascular, gastrointestinal and respiratory systems.

In October, Forest posted diluted earnings per share of 26 cents in the second quarter versus 8 cents a year earlier. Net sales for the quarter grew 17.3 percent to $811.4 million.