NEW YORK (AP) — Moody's Investor's Service maintained a positive view of the largest U.S. pharmacy benefits managers Tuesday, saying it has the highest opinion of CVS Caremark Corp.

Moody's holds investment-grade "Baa" ratings of the credit of CVS Caremark, Medco Health Solutions Inc., and Express Scripts Inc. It said all three companies will benefit from introductions of new generic drugs and from concerns about rising health care costs, but lower membership in commercial health plans could hurt all three companies.

The firm said it has the highest opinion of CVS Caremark because its retail business provides diversity. CVS Caremark, based in Woonsocket, R.I., is the second-largest drugstore chain in the U.S., with about 7,100 stores. The combination of a pharmacy benefit manager and a drugstore chain gives the company a unique business model, allowing it to save money by buying drugs in large quantities. It can also encourage pharmacy benefit members to go to CVS stores.