Push Lasix To 24 Hours Pre-Race? Study Says ‘Hold Your Horses’

by | 01.29.2018 | 3:19pm

As the debate about race-day medication rages on, hay/oats/water advocates have pushed to eliminate furosemide from the American raceday. But researchers and veterinarians have been left wondering: Will furosemide (widely known as Lasix or Salix) work as well to control exercise-induced pulmonary hemorrhage (EIPH) if it's given the day before a race?

According to a pair of recent studies presented at the 2017 American Association of Equine Practitioners Convention in San Antonio, the science (for now) says no.

Currently, furosemide may be given up to four hours out from race time. Dr. Heather Knych and a team of researchers at the University of California wondered whether a dose 24 hours from race time would be equally good at stopping bleeding.

Knych and her team dosed 15 horses with either saline or 250 mg of furosemide. One group was given its dose four hours prior to a simulated five-furlong race; the other 24 hours before. The team collected blood samples before and after the simulated race and performed an endoscopic exam and a bronchoalveolar lavage (BAL) after the race. They then assigned the horses EIPH scores based on the diagnostic results. All horses received each treatment with a resting period of two weeks in between so researchers could understand how the same individual reacted under different protocols.

The researchers found there was a statistically significant difference in scores between the four-hour and 24-hour furosemide groups. Knych said 93 percent of horses receiving furosemide four hours before their runs were rated as Grade 0 for bleeding, while 60 percent of horses got a Grade 0 when given furosemide 24 hours out. All horses had some red blood cells in their lung lavages.

Grade 0 horses were those which showed no signs of blood on endoscopic exam. Grades range from 0 to 4.

Knych pointed out that the horses' history regarding EIPH wasn't known to researchers before they entered the study and it's possible selecting specifically for known bleeders might have made a difference in the results. Based on the final times of individual runners, Knych noticed there was a significant range of athletic ability within the group of 15 horses, which also may have impacted results.

Still, Knych doesn't think the results will exactly have regulators rushing to push the furosemide administration time to 24 hours pre-race.

“We did not see a significant reduction in either endoscopic or BAL red blood cell counts with 24 hours furosemide. By those criteria, this study did not support 24-hour furosemide as being effective,” she said.

As we reported in late 2017, experts view EIPH as a somewhat unpredictable condition – a horse's having bled once doesn't necessarily mean he will bleed every time he runs or that he will bleed enough to limit his performance. While this study wasn't designed to examine that problem, Knych said it did raise an interesting question for her.

“There are numerous studies looking at endoscopic EIPH prevalence. Our horses were a very healthy group. They had lower than expected EIPH scores, but all had (red blood cells) in their BAL's post-work, even the four hour furosemide runs,” said Knych. “Horses raced for centuries without furosemide and still do in many parts of the world. The unanswered question is whether U.S. horses racing with furosemide are healthier than horses racing internationally without furosemide. That study has not been done and would be hard to design.”

Could alternative management options work?

Also at the 2017 AAEP convention, Dr. Warwick Bayly of Washington State University presented the results of his study into prophylactic EIPH treatments. Since furosemide works by reducing blood pressure in the pulmonary artery through fluid loss, Bayly wanted to know if controlling a horse's water intake could produce a similar result. Bayly and his team gave six horses different doses of furosemide with and without controlled access to water 24 hours before a treadmill workout. The horses had BALs and were scoped after exercise.

Bayly found the combination of .5 mg/kg of furosemide (the lower of two doses he used), combined with controlled water access significantly reduced severity of EIPH compared to any other combination of furosemide dose and water control. Why did the lower dose with limited water do better than the higher dose? It's hard to say, but Bayly guesses it may have reached a ‘sweet spot' in keeping blood pressure in the pulmonary artery low while allowing the horse a better overall hydration level.

How do trainers implement water control into their pre-race regimens? We don't yet have enough information to say for sure. Finding that ‘sweet spot' for any individual horse can be tricky on a practical level and this study only provides a piece of the puzzle.

“There's definitely going to be individual differences. You can count on that,” said Bayly. “There was no question we only had six horses but there were differences in response amongst those horses.

“The other thing that's important is EIPH is a very complex condition. We have data from these horses on the treadmill and when they've been on the racetrack, breezing or doing simulated racing when they had no drugs or no treatment. Even then, there's considerable variation from exercise bout to exercise bout, especially on the track. On the racetrack, from a half mile on up, severity of the bleeding in all cases was a lot more severe than on the treadmill. That raises a number of questions with respect to research that might be done in the future and with respect to research that's been done in the past.”

Bayly admitted the sample size of six horses was too small to draw any broad conclusions. This was actually a follow-up study to one he had done earlier with four horses, in which he got a remarkably different result.

“It's rare, that in the world of scientific endeavor, you work out everything you want to know about a question in one experiment,” he said. “You go through a series of them, you get some data, you analyze that, you interpret it, and based on that you decide what to do next. This is just a good example. Scientific progress is incremental. It's rarely earth-shaking and like Superman jumping over a tall building in a single bound.”

Where does that leave trainers who may want to change their pre-race routines to avoid EIPH? Bayly said he's not sure, but he points out past research has shown furosemide doesn't always prevent EIPH in horses who are prone to it (Bayly recalled one study which indicated as many as 30 percent of horses receiving a dose of the drug either got worse EIPH or saw no change in their EIPH scores from when they went without).

“That just underlines that Lasix isn't the panacea and again there's a lot of variation in the extent to which an individual horse will respond to Lasix,” said Bayly.

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