NEW YORK (The Deal) -- Dublin, Ireland-based Mallinckrodt Pharmaceuticals has broadened its strategic product growth platform with the $5.6 billion acquisition of Questcor Pharmaceuticals (QCOR).

Questcor's major product is Acthar gel, a depot injectable corticosteroid approved by the Food and Drug Administration for 19 conditions, mostly autoimmune and inflammatory. Mallinckrodt executives say they plan to expand the market for Acthar internationally.

Questcor's net sales grew 57%, to $799 million, in 2013.

Anaheim, Calif.-based Questcor shareholders will receive $30 in cash and 0.897 Mallinckrodt shares for each share of Questcor common stock they own.

The parties expect the deal to close in the third calendar quarter this year, although it is contingent on shareholder acceptance and regulatory approvals. Former Questcor shareholders would own 49.5% of the merged company.

Mallinckrodt, which has been exceptionally active in M&A over the past year, says this deal is its "high-water market" for the time being. However, it will continue to look at smaller acquisitions of companies and products that would help it meet its goal of becoming a top-tier specialty pharmaceuticals company.

"We wouldn't rule out any type of transaction," Matthew Harbaugh, Mallinckrodt chief financial officer, said in a conference call with investors Monday, April 7.

Mallinckrodt says its business is characterized by creating and selling difficult-to manufacture, complex and highly specialized drugs. It is focused on markets in the rheumatology, nephrology, pulmonology and other therapeutic spaces.

Mallinckrodt will remain domiciled in Ireland. It expects that Questcor business will gain an immediate benefit of about 10% decline in tax rate due to Ireland's significantly lower business taxes.