Study Finds Phenylbutazone a Risk Factor in Breakdowns

Based on the groundbreaking results of a recently published study, the epidemiologist who oversees The Jockey Club Equine Injury Database will add phenylbutazone as a risk factor for catastrophic breakdowns and will call for policies that require the non-steroidal anti-inflammatory to be completely clear from a horse's system before it races.

In an essay scheduled to be published in an upcoming issue of BloodHorse, Tim Parkin, senior lecturer in clinical epidemiology at the University of Glasgow who has studied the Equine Injury Database for 10 years, recommends the race-day threshold for phenylbutazone be lowered to zero—no tolerance. 

The recommendation, which would be more restrictive than the current policy in every U.S. racing jurisdiction except California, follows a study by one of Parkin's graduate students, Teresita Zambruno, that found a link between phenylbutazone, commonly referred to as bute, and equine injuries—both catastrophic and nonfatal.

Zambruno's study, published online and scheduled for print publication in the Journal of the American Veterinary Medical Association in late 2020, examined data from 500,000 starts at four tracks in South America. While it found some risk factors observed in other studies, it was the first study to find a link between bute and breakdowns. 

Zambruno concludes: "This study is the first to clearly demonstrate an association between racing, having recently been administered phenylbutazone, and the risk of fatality. The next challenge is to attempt to turn this information into policy or regulatory change in the racing jurisdictions in which such practices are permitted."

In his upcoming essay for BloodHorse, Parkin says horses racing with bute in their systems are 50% more likely to sustain a fatal or nonfatal musculoskeletal injury than those racing without a recent administration of the non-steroidal anti-inflammatory. 

Zambruno's study offered some potential reasons for the increased injury risk of horses administered bute. Those reasons suggest restrictions in the use of bute ahead of timed workouts also could be helpful.

"The increased odds of fatality for the (bute) group is probably because those horses need anti-inflammatories or analgesics to have a good performance or to make it to the race," Zambruno said. "This could be due to clinical or sub-clinical preexisting injuries or pain. Thus phenylbutazone administration may allow horses to continue training and racing, accumulating damage to their musculoskeletal structures and increasing the odds of fatalities due to fatal (injury) during performance."

The closest thing to a national standard in the United States, the National Uniform Medication Program's list of controlled therapeutic substances, allows a race-day presence of bute (threshold) up to 2.0 micrograms per milliliter of serum or plasma. It recommends a withdrawal time of 24 hours or more for the commonly used NSAID. 

As is typical of many medication rules in the U.S., bute rules lack uniformity from state to state. For instance, according to the RMTC, Wyoming and South Dakota still allow bute to be administered on race day. Arizona allows a 5.0 micrograms per milliliter threshold, even though at the beginning of the decade most states lowered the threshold to 2.0 to allow for more effective pre-race examinations.

California has already put new restrictions in place on bute in line with what Parkin is advocating—ahead of races and workouts. This year, in an effort to reduce equine injuries after a rash of catastrophic breakdowns during the winter/spring meet at Santa Anita Park, The Stronach Group—as a house rule—adopted the standard Parkin is now calling for when it eliminated thresholds for bute as well as two other previously permitted NSAIDs: flunixin and ketoprofen. The new standard recommended a withdrawal time for bute of seven days, which is in line with many international racing jurisdictions, and ensures it will be completely out of the horse's system on race day.

Also, The Stronach Group prohibited the administration of any NSAID within 48 hours of a workout—retaining the current 2.0 thresholds in blood for those works. 

In March, the California Horse Racing Board approved The Stronach Group's new medication rules for its tracks and in April approved applying those more restrictive rules to all the state's Thoroughbred tracks for 12 months.

While there's no way to break out a single change to measure impact in California, which besides overhauling its medication rules also put in safety measures such as additional pre-race exams, catastrophic breakdowns during racing have been greatly reduced under the new standards. Since Santa Anita reopened March 29 and through the Los Alamitos Race Course, Del Mar, and Santa Anita fall meet that followed, the equine fatality rate in Southern California has been 1.09 per 1,000 starts. Based on Equine Injury Database numbers, that 1.09 rate is 35% lower than the rate for the United States and Canada in 2018 of 1.68.

During the time period the zero-tolerance policy has been in place in California, the average starters per race in Southern California is 7.13, down from the 7.62 average at these tracks in 2018. Again, in terms of determining impact, it's difficult to break out a single change from the many new rules and protocols put in place in California this year.

The study also provided some insight on the always-hot topic of race-day Lasix (or Salix). The South American study found no link between Lasix use and breakdowns. Zambruno noted that one of the racecourses in the study prohibited bute but allowed Lasix, administered by regulatory vets. In looking at numbers for that track, the study found no correlation between Lasix and breakdowns.

A group of leading track owners has announced new restrictions for race-day Lasix beginning in 2020, and some industry leaders support federal legislation that would prohibit the race-day use of the diuretic, which is used to prevent or reduce the severity of exercise-induced pulmonary hemorrhage.