Mallinckrodt Plc agreed to acquire Ikaria Inc. for about $2.3 billion from a group of investors led by Madison Dearborn Partners to expand in neonatal intensive care treatments.

The acquisition bolsters Mallinckrodt’s hospital business by adding to its current base of diagnostic radiology and pain management in surgical specialties, the company said in a statement on Thursday. Ikaria’s top product, INOmax, treats premature infants with breathing difficulties.

Chief Executive Officer Mark Trudeau has been using acquisitions to broaden Mallinckrodt’s collection of health-care assets since the company was spun off from Covidien Plc in 2013. Mallinckrodt acquired pain-drug maker Cadence Pharmaceuticals Inc. last year for about $1.3 billion, then followed up by buying Questcor Pharmaceuticals Inc. for $5.6 billion.

Mallinckrodt rose 5.2 percent to $122.24 at 9:51 a.m. in New York. The company is domiciled in Dublin with U.S. headquarters in St. Louis. The transaction will add about $150 million in net sales and at least 25 cents a share in adjusted earnings in fiscal 2015, the company said.

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