LOUISVILLE, Ky. (AP) - Kentucky horse racing regulators say no traces of a powerful painkiller were found in samples taken from horses running in this year's Kentucky Derby.

The Kentucky Horse Racing Commission said Wednesday the Derby horses were tested for dermorphin, a substance more powerful than morphine.

An outbreak of positive tests for the painkiller at Louisiana tracks has resulted in suspensions for several trainers.

The Association of Racing Commissioners International lists dermorphin among the most harmful substances that might be given to horses. Regulators say the drug has no legitimate use in horses.

The Kentucky announcement follows a story by The New York Times that says Derby and Preakness winner I'll Have Another was treated with painkillers before the Belmont Stakes, but does not name the drug. The colt was retired from racing the day before the Belmont.