Drug Increases Risk of Sudden Death in Racehorses

Furosemide (also known as frusemide and by the trade name Lasix) has been used to prevent exercise-induced pulmonary haemorrhage (bleeding in the airways). It is also associated with enhanced racing performance. As a result, 94 percent of horse starts in the study were on furosemide. 

The results also suggest that it might be possible to identify horses at risk of sudden death before they experience it — for example, due to previous injury and interruption to training or racing. 

Amongst other findings were that the risk of sudden death was greater for stallions compared with mares, and for horses five years or older compared with horses three years old or younger. Other risk factors identified include season and value of race, and race distance. 

“Over the last 12 years, the overall risk of fatality within three days of racing has decreased by over 30 percent, but the incidence rate of sudden deaths has not changed significantly,” says Dr. Bennett. “This suggests that while interventions have been made which have contributed to a reduction in catastrophic injury, there are different sources of risk for sudden death which have not yet been identified.  

“This study suggests that a risk profile, identifying which horses are at the greatest risk of sudden death, may be possible. Given how rare the outcome is, further work is required to establish any potential interventions which might contribute to a reduction in sudden deaths. 

“On the association between furosemide use and sudden death, the fact that furosemide use is so common makes this result particularly remarkable given the statistical power of this large-scale study. Discussions around the ethics of race day administration of drugs should factor in potential risks such as those identified here, and further work is required to understand exactly why we identified this association.”