Co-trainers Ciaron Maher and David Eustace have been charged by Racing Victoria stewards over a positive swab from a stable runner.

A raceday blood sample taken from Piccatric after winning a maiden at Sale on February 28 contained the diuretic substance Frusemide.

The matter will be heard by the Victorian Racing Tribunal at a date to be fixed.

Under RV rules, the substance is permitted to be used in training but has a withholding period and is not allowed to be in a horse's system on raceday.

Maher and Eustace issued a statement saying the highly successful stable had already held an internal review into the swab.

" ... (it) led to a clear finding that human error led to the treatment of Piccatric with Furosemide, instead of the intended horse Stardayz," the statement said.

"The review was provided to RV Stewards along with other evidence.

"As expected, RV stewards have today notified Ciaron Maher Racing of their charge that Piccatric has been presented at the races with a prohibited substance.

"We accept the RV Stewards charge and will assist at the Victorian Racing Tribunal hearing.

"While the incident is regrettable, we are pleased that the internal review has identified the exact cause and has led to implementation of improvements to strengthen our controls to prevent a recurrence."