Less than two weeks after acquiring a 45% interest in Alliance Boots, Walgreens will purchase USA Drug, a 144-store chain, for $438 million. USA Drug gives Walgreens access to stores in the mid-Southern U.S. markets. The Little Rock-based firm operates in Arkansas, Kansas, Mississippi, Missouri, New Jersey, Oklahoma and Tennessee under the Super D Drug, May’s Drug, Med-X and Drug Warehouse nameplates. But after the buying spree, Walgreens may be faced with a tad of a hangover, The comp...