WASHINGTON (AP) -- Three U.S. senators are raising concerns about the Food and Drug Administration's approval of a powerful painkiller called Zohydro, which experts say could add to the national epidemic of prescription drug abuse.

Republicans Mitch McConnell of Kentucky, Tom Coburn of Oklahoma and Lamar Alexander of Tennessee sent a letter to the head of the FDA Wednesday asking how the agency will prevent misuse and abuse of Zohydro and similar drugs in development.

The FDA approved Zohydro from Zogenix Inc. in October, making it the first single-ingredient hydrocodone drug ever cleared for U.S. patients. The pill is significantly more potent than currently available hydrocodone combination pills, such as Vicodin.

The approval surprised many doctors, since an FDA advisory panel voted overwhelmingly against the drug, citing its potential for abuse.