DEERFIELD, Ill. — Walgreen Co. has signed a definitive agreement with Madison Dearborn Partners, a private equity firm based in Chicago, under which MDP will acquire a majority interest in Walgreens Infusion Services.

One of the nation’s largest providers of home and alternate treatment site infusion services, Walgreens Infusion Services has a footprint that includes 89 infusion pharmacies and 110 alternate treatment sites in 40 states, around 4,700 employees and the ability to serve over 90% of the U.S. population.

“This agreement will enable us to continue to strengthen the Walgreens infusion offering as part of our broad health care portfolio as we work closely with the new company, which will have a dedicated focus on this $14 billion and growing U.S. market,” said Mike Ellis, vice president of Walgreens specialty pharmacy and infusion services.

“With Walgreens and MDP’s expertise, capabilities and resources, the new company will have an opportunity to play an even greater role in improving the quality and cost of infusion services.”

When the transaction closes, Walgreens Infusion Services will become a new independent, privately held company. The transaction supports Walgreens’ focus on accelerating its core retail and specialty ­offerings.

Paul Mastrapa, current divisional vice president of Walgreens Infusion Services, will serve as the new company’s chief executive officer.

Financial terms of the agreement were not disclosed.

“The new company, which will have an industry-leading management team supported by MDP and Walgreens, will be positioned to provide even greater value to patients, local health systems, health plans and pharmaceutical manufacturers,” commented ­Mastrapa.