Ireland-based Mallinckrodt will buy US rival Questcor Pharmaceuticals in a roughly $5.6bn cash-and-stock deal expected to expand the firm's drive in the speciality drugs field, the companies have announced.

The acquisition was unanimously approved by the boards of directors of both companies and should be completed in the third quarter.

Questcor, headquartered in Anaheim, California, is a biopharmaceutical company specialised in the treatment of autoimmune and inflammatory disorders.

Its main revenue-maker is Acthar, an injectable drug approved by the US Food and Drug Administration for 19 indications, including multiple sclerosis, rheumatoid arthritis and infantile spasms.

Dublin-based Mallinckrodt Pharmaceuticals less than a month ago completed its $1.4bn takeover of another US drug company, Cadence, adding its pain product Ofirmev, an injectable acetaminophen.

"With Questcor, combined with our recently completed acquisition of  Cadence Pharmaceuticals, the new  Mallinckrodt will have a significant, established presence with perscribers, payers and hospitals," Mark Trudeau, the Irish firm's president and chief executive, said in the joint statement.

"We believe we are now well on our way to becoming a leader in the development and commercialisation of speciality therapeutics around the world."  
Under the terms of the transaction with Questcor, Mallinckrodt will pay $30.00 in cash and 0.897 Mallinckrodt shares for each Questcor common stock, in a total payout of about $86.10 per share.

The payment represents a premium of about 27% over Questcor's stock price, based on the closing prices of Mallinckrodt and Questcor on Friday.

Questcor, which closed Friday at $72.17, soared 25% to $84.98 in pre-market trade.