Preakness officials are allowing Kentucky Derby winner Medina Spirit to enter Saturday's race subject to additional testing and monitoring, in the wake of the colt's failed drug test.

Medina Spirit and two other horses trained by Bob Baffert will be under extra scrutiny in the days leading up to the second jewel of the Triple Crown.

The Maryland Racing Commission and Baffert have agreed to the conditions for Medina Spirit, fellow Preakness runner Concert Tour and Beautiful Gift, who is expected to run in the Black-Eyed Susan Stakes on Friday.

Medina Spirit drew the No.3 post in a field of 10 horses and is listed as the favourite.

Concert Tour drew the outside 10th post and is the second choice in the wagering.

Baffert earlier on Tuesday said it was brought to his attention that a veterinarian treated Medina Spirit with an antifungal medication to treat dermatitis that includes the steroid betamethasone.

"My investigation is continuing, and we do not know for sure if this ointment was the cause of the test results, or if the test results are even accurate, as they have yet to be confirmed by the split sample," Baffert said.

"I have been told that a finding of a small amount, such as 21 picograms, could be consistent with application of this type of ointment."

Medina Spirit failed a Kentucky Derby post-race drug test due to the presence of betamethasone.

Maryland Racing's chief veterinary officer, Dr. Dionne Benson, said at the draw for the Preakness that tests on the three Baffert horses are expected back on Friday.

This is an additional layer of blood testing added to the usual post-race tests.

"(The tests) will allow us to ensure that if there is or was any betamethasone or any other medications, whether therapeutic or illegal, in the horse, we will know about them before the race," Benson said.

Benson said if betamethasone is detected by laboratory testing in any of the horses, officials will ask Baffert to scratch that horse.