Yankee Rose's trainer David Vandyke has been hit with a $25,000 fine and the horse has been disqualified from the Group One Flight Stakes after returning a positive test to banned anti-inflammatory Ketorolac.

Vandyke pleaded guilty at a Racing NSW stewards' inquiry on Friday to allowing Ketorolac to be administered to Yankee Rose and presenting the horse with a prohibited substance on race day.

Yankee Rose's owners will have to forfeit the $99,000 prize money won from the race at Randwick on October 1, while the Chris Waller-trained Sezanne has been promoted to second place.

Vandyke said he would consider appealing the penalty.

"It's disappointing to lose a second in a Group One for the owners and myself and obviously disappointing to get fined," Vandyke said.

Yankee Rose was being treated for fetlock soreness which she has suffered from throughout her career.

Veterinarian David Garth was also fined $15,000 for administering the drug which he said was injected into Yankee Rose's joints eight days before the race, one day more than the required seven.

"I asked him to give an extra day because I didn't want to end up in this sort of situation," Vandyke told the hearing.

Racing NSW senior veterinarian Craig Suann said he was not familiar with Ketorolac being used on horses with the drug primarily used to treat humans.

But Garth said he had used it successfully on racehorses while working in Victoria and knew of its use in other jurisdictions.

Garth's explanation for the positive centred on Yankee Rose eating straw in her box contaminated with her urine.

"Yankee Rose is the first that I have treated that has been kept on straw," Garth said.

"She was eating quite a lot of straw in her box and (Ketorolac) is excreted in the urine."

Vandyke said he had complete faith in Garth's ability to treat the horse while she was stabled in Sydney after being brought down from his Sunshine Coast base.

"I pretty much left the ball in his court in respect to looking after the filly," Vandyke said.

Chief steward Marc Van Gestel said Vandyke's 2015 presentation charge for Ipratropium for which he was fined $12,000 was taken into account.

"The treatment is somewhat unconventional and not without risk and therefore this does aggravate the penalty," Van Gestel said.