Phenylbutazone is a nonsteroidal anti-inflammatory drug, which has been a useful pain-killing tool in racehorses away from racing, but is a prohibited substance in competition at both barrier trials and on raceday.
New Zealand does not have a standard withholding period before raceday, but it is understood the Veterinary Association recently published guidelines that a withholding period be extended from 10 days to 14 days.
For years, when banned elsewhere, it continued to be legal in many states in America, but its raceday use is now almost universally banned.
It was found that the drug was so successfully masking pain, horses were shattering legs in races and many dangerous situations resulted.
Apprentice Chris Dell, who rode the horse that broke its legs at Ruakaka, was hospitalised with head injuries.
He is recovering, but has yet to resume riding two months later.
Interestingly, in the United States recent fines for what is described as over-use of phenylbutazone have resulted mainly in fines of US$500.
In many American states the drug is permitted to be administered up to 24 hours before racing. On September 19 last year trainer Adolfo Ortiz was fined US$8500 on each of six charges of over-use of the drug flunixin, a pain-killer similar to phenylbutazone.
• The 1968 Kentucky Derby winner Dancer's Image was disqualified after traces of phenylbutazone were allegedly discovered in a post race urinalysis.
Owned by prominent Massachusetts businessman Peter Fuller, Dancer's Image remains the only horse to win the Kentucky Derby and then be disqualified.
Phenylbutazone was legal on most tracks around the United States in 1968, but had not yet been approved by Churchill Downs.
Controversy and speculation still surround the incident.
In the weeks before the race, Peter Fuller had given previous winnings to Coretta Scott King, the widow of slain civil rights activist Martin Luther King, which brought both praise and criticism.
The previous year, King held a sit-in against housing discrimination which disrupted Derby week. Forty years later, Fuller still believes Dancer's Image was disqualified due to those events.