Mallinckrodt plc, the drugmaker spun off by Covidien plc, agreed to buy Cadence Pharmaceuticals Inc. for about $1.3 billion to add a pain treatment used in hospitals.

Mallinckrodt will begin a tender offer for Cadence shares at $14 each, the companies said in a statement today. The price is 26 percent above Cadence’s closing level yesterday in Nasdaq trading.

The purchase will accelerate Mallinckrodt’s growth in specialty pharmaceuticals, said the company, which is domiciled in Dublin and run from Hazelwood, Missouri. Cadence, based in San Diego, makes Ofirmev (pictured), an intravenous form of acetaminophen for pain management that had an estimated $110.5 million of sales last year.

Mallinckrodt’s financial advisor for the transaction is Deutsche Bank Securities Inc., and its legal advisors are Wachtell, Lipton, Rosen & Katz in the U.S. and Arthur Cox in Ireland. Cadence’s advisors are Lazard and Centerview Partners and its legal advisor is Latham & Watkins LLP.