Doping-hit Kentucky Derby winner Medina Spirit has passed three rounds of blood testing without a doping positive and is cleared to race in Saturday's 146th Preakness, race officials said Friday.

After the Bob Baffert-trained colt tested positive for traces of a banned steroid in a post-race sample at the Derby, the Maryland Jockey Club required extra testing before allowing him to race at Pimlico in Baltimore in the second jewel of US flat racing's Triple Crown.

Medina Spirit, the 9-5 oddsmaker favorite, and another Baffert entry, Concert Tour, were clear in three out-of-competition blood tests for the Preakness.

But Medina Spirit still could be disqualified from its victory at the Kentucky Derby if a second sample taken at Churchill Downs in Louisville tests positive for the banned steroid betamethasone.

Preakness test samples were drawn May 6 and Monday by the Maryland Racing Commission and were screened by Industrial Laboratories in Colorado.

A third sample was drawn on Tuesday by the Maryland Jockey Club and track owners 1/ST Racing and screened by the University of California at Davis Maddy Laboratory.

The additional tests and monitoring were part of the extra conditions of entry deal made with Baffert to, as a Preakness statement Friday put it, "ensure the fairness and integrity of the races with horses entered by Baffert."

Baffert, who has had a history of doping issues with champion horses in recent years, said he had no idea how the banned substance betamethasone got into the horse's system last Sunday, then said Monday that he had unknowingly treated the horse with a medication ointment for a rash that included the banned substance.

Baffert's horses will remain under veterinary observation and security surveillance until the Preakness.

The third race of the treble is next month's Belmont Stakes in New York.