Revenue from established stores slipped last month for Walgreen Co., as generic drugs once again chipped away at the drugstore chain’s top line.

The Deerfield company said Tuesday that revenue from stores open at least a year fell 0.6 percent in February. Pharmacy revenue came in flat even though prescriptions filled at those stores climbed 6.5 percent. Revenue from the front-end, or rest of the store, fell 1.4 percent.

Revenue from stores open at least a year is considered a key indicator of retailer health because it leaves out results from locations that have opened or closed in the last year.