Horse Care: Furosemide Facts

Why veterinarians recommend the use of Lasix as a race-day medication

story by Kimberly French

Patented for human medicine in 1959 and approved for use in 1964, furosemide, also known as Lasix or Salix, was first implemented in the racing industry in the late 1960s and early 1970s. Its purpose, then as it is now, was to manage the effects of exercise-induced pulmonary hemorrhage (EIPH).

Over the course of the last four to five decades, this drug’s use in North American Thoroughbred, Standardbred and Quarter Horse racing has been frequently employed. Yet the presence of furosemide in the sport has been a hot-button issue and continues to be so. While certainly more research can and will be performed to develop other treatments for EIPH, the current and past stance by the American Association of Equine Practitioners (AAEP) is that administering furosemide on race day remains the most effective method to combat EIPH.

“The AAEP’s current policy on race-day medication administration endorses the use of furosemide to help mitigate the occurrence of exercise-induced pulmonary hemorrhage in the racehorse,” wrote former AAEP president R. Reynolds Cowles in a June 5, 2017, statement from the organization. “This policy is based on the overwhelming body of international scientific and clinical evidence.

“H.R. 2651 seeks to end the administration of furosemide on race day, which conflicts with the AAEP’s long-held position. While we are optimistic that current research projects will yield an alternative treatment for EIPH which does not require race-day administration, as doctors of veterinary medicine we cannot abandon our current policy until science provides an efficacious option for protecting the health and welfare of the horse.”

Cowles’ response was to the introduction of legislation referred to generally as the Horse Racing Integrity Act, which would ban the use of furosemide as a race-day medication. The act, now referred to as H.R. 1754, was reintroduced this March after failing to advance out of committee and is virtually identical to its predecessor.


What Is Epistaxis and/or EIPH?

According to a 2012 study published in The International Journal of Applied Research in Veterinary Medicine evaluating the use of furosemide to prevent epistaxis, this condition is “bleeding from the nose in racing horses” and it “has been observed by horsemen since the 17th century.”

It is estimated more than 90 percent of all racehorses experience some type of bleeding, with 3 to 5 percent presenting with epistaxis, or bleeding from the nose.

When furosemide first was used, bleeding from the nose was the primary symptom of EIPH. With the introduction of endoscopic evaluations, veterinarians learned EIPH could cause a horse to bleed deep within the lungs without blood ever coming through the nasal cavity. They also learned EIPH occurred much more frequently in horses than was originally thought and could present itself in any horse, including performance and show horses, that engage in rigorous exercise.

“Exercise-induced pulmonary hemorrhage refers to the condition in which blood is present in the airways following exercise,” states a 2009 presentation from the Proceedings of the Geneva Conference on Equine Medicine. “The most frequent classification of horses as EIPH positive or negative is currently based on post-exercise endoscopy of the upper airways, including trachea. Until the introduction of endoscopy and surveys of horses following racing, it was generally considered that only few horses experienced EIPH, as the occurrence was essentially based only on the appearance of blood at the nostrils (epistaxis).

“Even today, the lay perception of a horse classified as a ‘bleeder’ is frequently that which either has profuse amounts of blood in the trachea following training or racing or exhibits epistaxis. However, EIPH should now be considered ubiquitous in horses undertaking fast or intense exercise. The severity of the condition varies from horses showing a small increase in the number of red blood cells in the lower airways only detectable using sensitive techniques such as bronchoalveolar lavage (BAL) to those showing marked epistaxis, with all grades in between.”

Many theories have been advanced to determine exactly what caused EIPH and/or epistaxis, yet none have fully explained the condition. Some scientists have claimed a horse bleeds while engaging in rigorous exercise because of the high pulmonary vascular pressures in the lungs, but this hypothesis does not explain where the bleeding begins or how EIPH can become more severe over time.

Another theory is based on locomotory forces through which bleeding begins in the bottom of the lung, near its back. Its basis lies in the fact a horse has no bone attachment to the spine from his or her forelegs and when galloping the spine causes the shoulder to compress into the rib cage. Due to the nature and area of this compression, capillary disruption begins in the lungs.

Representatives at the Geneva Conference, however, had their own point of view on what causes EIPH and/or epistaxis.

“A more pragmatic view of EIPH may be that it is a multi-factorial condition involving airway, vascular, cardiac and locomotory components and that the contribution of different factors varies between individual horses and possibly even within the same horse over time,” the presentation states.


How Does Lasix Help?

Furosemide aids in preventing EIPH and/or epistaxis because it is a diuretic, meaning it eliminates excess fluid buildup created by liver or kidney disease, heart conditions or high blood pressure. It operates by prohibiting the kidney from absorbing minerals, which in turn increases urine production.

The urine release spurred by furosemide lowers hydrostatic pressures, which are those pressures exerted by intravascular fluid (such as blood plasma) or extravascular fluid on the wall of a blood vessel in a horse’s body. The release of this pressure can reduce the severity of pulmonary bleeding by 50 to 70 percent, but does not eradicate the risk entirely.

A 2009 study which appeared in the Journal of the American Veterinary Medical Association evaluated 167 Thoroughbreds in South Africa to determine whether race-day administration of furosemide did reduce the risk of EIPH under normal racing conditions.

“Horses were substantially more likely to develop EIPH or moderate to severe EIPH, following administration of saline solution than following administration of furosemide,” stated the article. “In addition, 81 of the 120 (67.5 percent) horses that had EIPH after administration of saline solution had a reduction in EIPH severity score when treated with furosemide.

“Results indicated that prerace administration of furosemide decreased the incidence and severity of EIPH in Thoroughbreds racing under typical conditions in South Africa.”

Lasix Saves Lives

According to the 2012 evaluation in The International Journal of Applied Research in Veterinary Medicine, administering furosemide could prevent or eliminate acute/sudden deaths from EIPH while a horse is competing or training, which in turn could save the lives of their human handlers.

“Acute/sudden deaths during racing due to EIPH occur when the hemorrhage is sufficiently voluminous to acutely interfere with respiration/blood oxygenation such that the horse collapses and dies acutely on the racetrack,” the article states. “Although acute/sudden death from EIPH has long been known to equine practitioners, more recent work has shown that acute/sudden death from EIPH can occur without blood being visible in the nostrils as shown by the work of Gunson and her colleagues and others.

“Review of the relevant literature, including the 1988 paper by Gunson and coworkers suggests that in the U.S. such acute deaths during racing or training occur approximately once per every 1,500 Thoroughbred races, and that a substantial proportion, approximately 60 percent of acute deaths during racing, are due to EIPH. As such the data presented here suggests that pretreatment with furosemide is likely to reduce the instance of such EIPH related sudden deaths during racing by approximately 80 percent, a very significant contribution to equine and human safety in racing.”

The evaluation concluded with a concise, yet stout, recommendation in the use of furosemide on race day.

At the conclusion of its 2012 board of directors meeting, the USTA issued its official stance on the use of furosemide, which echoed the opinion of the AAEP and that of The International Journal of Applied Research in Veterinary Medicine’s 2012 evaluation.

“The use of the therapeutic substance furosemide (Salix, Lasix) under controlled conditions should be continued as the most effective and humane treatment of the racehorse.” HB

To comment on this story, email us at

360 More posts in Hoof Beats Magazine category
Recommended for you
Recipe for Success

Managing older stallions means accommodating their quirks with excellent care by Kimberly A. Rinker In...