A recent study indicates that phenylbutazone, commonly called bute, is a risk factor for breakdown injuries in racehorses.  Breakdown injuries include are those that are catastrophic and non-fatal while racing. A grad student named Teresita Zambruno at the University of Glasgow published a paper that examined 500,000 horse racing starts in South America. She found multiple risk factors for breakdown injuries that had been found previously, but hers was the first study to find the association between phenylbutazone and breakdown injuries.  After looking at this study, the epidemiologist for the Jockey Club, Dr. Tim Parkin, indicated that he will call for policies that will allow zero phenylbutazone to be in the horse’s blood on race day.  This is a stricter recommendation than every state has at this time except California.  Dr. Parkin said that horses with phenylbutazone in their systems were 50% more likely to sustain a fatal or nonfatal musculoskeletal injury than those racing without a non-steroidal drug in their system. 

The author of the study believes the increased odds of fatality in the horses using phenylbutazone are because these horses need pain medication to race and bute may allow the horses to continue racing and training.  Various states have different legal limits for bute in the horse’s blood on race day and California adopted a new limit due to the increased number of breakdown injuries at the Santa Anita Race Track.  After California changed their regulations to not allow any bute in the horse’s blood before the race, breakdown injuries have decreased. However, California made several other changes as well so it is impossible to say all of the decreased numbers of breakdowns were due to changes in the bute regulations.