NEW YORK (AP) — Wal-Mart says it is expanding its discount prescription drug program, testing a program that will allow customers to get 90-day supplies of generic prescription drugs through the mail for as little as $10. The Bentonville, Ark., company will pilot the program in Michigan. With the announcement, Wal-Mart Stores Inc. enters a territory primarily occupied by pharmacy benefit managers. Pharmacy benefits managers like Medco Health Solutions Inc. have been encouraging their clients to fill their prescriptions through the mail, and to replace monthly prescriptions with 90-day orders, which are both cheaper for patients and more profitable for the pharmacy benefits manager. The companies say the programs save money for both health plans and plan members, and the pharmacy benefits managers themselves make larger profits. The announcement comes the same day as CVS Caremark posted solid results for a program that lets customers order 90-day supplies of drugs but pick them up at a retail pharmacy rather than getting them through the mail. Wal-Mart said its program will have no membership or enrollment fees. Customers will be able to get any of 300 common prescriptions for $10 per 90-day order, and will be able to get more than 3,000 other prescriptions, both brand-name and generic, for higher prices. In 2006, the company launched a program though which customers could fill a 30-day prescription of a low-cost generic drug for $4. It began testing the program in September of that year and took it nationwide by early 2007. Wal-Mart shares slid 58 cents to $50.26 in afternoon trading.