DAYTONA BEACH, Fla. (AP) -- NASCAR has temporarily suspended driver AJ Allmendinger after he failed a drug test.

Allmendinger won't be allowed to drive Saturday night in the Sprint Cup race at Daytona international Speedway. Instead, Sam Hornish Jr. will be behind the wheel of the No. 22 Dodge for Penske Racing.

Allmendinger has 72 hours to request that his B sample be tested.

"AJ Allmendinger has been temporarily suspended from NASCAR competition based upon notification of a positive A test NASCAR received from its medical review officer," said Steve O'Donnell, NASCAR's senior vice president of racing operations.

Driving his first season for Roger Penske, Allmendinger ranks 23rd in Cup points. He is the most prolific driver to be suspended under NASCAR's substance-abuse policy since Jeremy Mayfield in 2009.