BY JOHN KELL

Walgreen Co.'s same-store sales slid 4.6% in January, missing Wall Street's expectations for a 2.7% decline, as the drugstore chain's prescriptions sales were battered by the loss of major customer Express Scripts Inc.

The retailer reported that prescriptions it filled at same-store sales decreased 8.6% last month, worse than the 4.6% drop feared by analysts and reflecting the loss of pharmacy-benefits manager Express Scripts members and a milder cough, cold and flu season. Prescriptions processed by Express Scripts comprised roughly 12% of Walgreen's total a ...