ST. LOUIS — Keller Apothecary opened in 1933 and nearly a century later was still filling up to 200 prescriptions a day. It had $2 million in sales last year. Customers were known by name. Help-yourself containers of candy and dog treats sat on the glass countertop. Thank-you notes and neighborhood news filled a corkboard inside the small shop. Then the reimbursements for prescriptions started to drop. When the little south St.