NEW YORK (CNNMoney.com) -- Wal-Mart announced Thursday that it will extend its $4 generic prescription program to 12 more states three months ahead of a scheduled national rollout.

The program will now be available in an additional 1,008 stores throughout Alabama, Georgia, Iowa, Kansas, Maryland, Michigan, Mississippi, Missouri, New Hampshire, Ohio, South Dakota and Virginia.

The world's largest retailer has launched the program in 1,499 pharmacies in 15 states during the past month. Wal-Mart (Charts) originally planned a national rollout beginning January 2007 but said it pushed forward its schedule because of customer demand.

The program includes 314 generic prescriptions available for up to a 30-day supply at commonly prescribed dosages.

Currently the $4 prescriptions are not available by mail-order. The retailer is offering on-line or telephone requests for refills only for in-person pickup in Alabama, Alaska, Arizona, Arkansas, Delaware, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Maryland, Michigan, Mississippi, Missouri, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oregon, South Dakota, Texas, Vermont and Virginia.

According to Wal-Mart, more than 152,000 new prescriptions were filled by Wal-Mart pharmacies in all 15 initial states within four days of the program's Oct. 19 launch in Florida.

Wal-Mart's rival Target (Charts) has thus far committed to matching Wal-Mart's lower prices on a selection of generic drugs in those states where its pharmacy business competes directly with Wal-Mart.

Other retailers, too, are rushing to counter Wal-Mart's move. Midwest retailer Meijer this week announced the company had begun offering free generic antibiotics to anyone with a prescription in a handful of states.

Meijer said the plan covers antibiotics that are typically prescribed for flu and other ailments like strep throat.

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