Veterinarians have used furosemide (often referred to as Salix) since the 1970s to reduce bleeding into the lungs in racehorses, a condition known as exercise-induced pulmonary hemorrhage (EIPH). While frequently used on race day in the United States, it’s banned in most other countries due to its potential performance-enhancing effects. The United States racing industry is under mounting pressure to prevent race-day use of furosemide. In fact, it could become prohibited under the Horse Racing Integrity Act (HR 2651) that is currently before Congress. Therefore, there is a need to find other potential race-day therapies that can be used to manage EIPH if, in fact, medication administration is prohibited in the 24 hours preceding a race.
A group of researchers from Washington State University, in Pullman, investigated the impact of several treatments on EIPH during treadmill exercise tests. Warwick Bayly, BVSc, MS, PhD, presented their findings at the 2017 American Association of Equine Practitioners convention, held Nov. 17-21 in San Antonio, Texas.
The exact cause of EIPH is unknown, but many veterinarians believe increases in pulmonary blood pressure during intense exercise cause the lungs’ capillaries to rupture.
The exact way in which furosemide acts on EIPH is also unclear. But it is likely in part due to its action as a diuretic (a medication that increases urine production), even though maximum diuretic impact occurs within 30 minutes of administration. Furosemide is also associated with a lesser increase in pulmonary vascular pressure during exercise, which persists for at least four hours. Furthermore, it can act as a bronchodilator in acute equine asthma cases.
In their study, Bayly and his colleagues administered each of the following seven treatment protocols to six horses exercising on a treadmill to the point of fatigue:
- 0.5 mg/kg furosemide administered intravenously (IV) 24 hours before exercise, with free access to water until four hours before exercise (LD);
- 0.5 mg/kg furosemide administered IV 24 hours before exercise, with 6 mL/kg water every four hours until four hours before exercise (LDW);
- 1.0 mg/kg furosemide administered IV 24 hours before exercise, with free access to water until four hours before exercise (HD);
- 1.0 mg/kg furosemide administered IV 24 hours before exercise with 6 mL/kg water every four hours until four hours before exercise (HDW);
- Controlled water consumption for 24 hours before exercise and 6 mL/kg of water given every four hours up until eight hours before exercise (W);
- 0.5 mg/kg furosemide administered IV four hours before exercise and water withheld starting at time of injection (F); and
- Control (C), where 5 mL saline was administered IV 24 hours pre-exercise and water was removed four hours before exercise.
The researchers measured the number of red blood cells contained in bronchoalveolar lavage (BAL, or a “lung wash”) before and 45 to 60 minutes after exercise. They also performed endoscopic examinations to determine the horses’ EIPH scores.
Bayly said his team found a statistically significant difference between individual horses’ EIPH scores (in other words, how they compared to each other), but no significant effect of treatment on EIPH score when looking at the group. However, the LDW treatment resulted in significantly lower numbers of pre- vs. post-exercise BAL red blood cells as compared to controls.
Based on these results, the researchers then administered compared the LDW treatment to controls in a racetrack simulation, in which horses trained for 12 weeks and then competed in two simulated 1,100-meter races 12 days apart. After the simulated races the LDW treatment group showed a significantly reduced EIPH score, said Bayly.
He concluded that if the use of race-day furosemide is banned, 0.5 mg/kg of furosemide administered 24 hours before racing, combined with controlled access to water, might reduce EIPH severity.