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Lasix Study Backs Four-Hour Administration Time

Pair of Lasix studies of interest outline results.

A study that has some potential to reshape the timing of Salix administration ahead of racing determined that the current four-hour timeframe is more effective than administering 24 hours out in reducing the severity of exercise-induced pulmonary hemorrhage.

The study, led by Dr. Heather Knych, was one of two studies on Salix (furosemide, commonly referred to as Lasix) with results outlined at the American Association of Equine Practitioners convention in late November. The other study, led by Dr. Warwick Bayly, found some potential for a low dosage of Salix 24 hours out combined with controlled access to water in reducing EIPH in racing.

The Paulick Report first posted a story on the results of both studies Jan. 30.

According to the AAEP’s 2017 Convention Proceedings document, the study by Dr. Knych of the Ken L. Maddy Equine Analytical Chemistry Laboratory looked at the efficacy of administering Lasix 24 hours out, instead of the current four hours out called for in racing’s model rules. The study concluded that administering furosemide four hours before a race was more effective in reducing the severity of EIPH than going to 24 hours out.

The Knych study saw 15 Thoroughbreds administered furosemide either four or 24 hours prior to a five-furlong simulated race. Blood samples were collected before and after the simulated race for determination of furosemide, lactate, hemoglobin, and electrolyte concentrations.

One hour after the race, an endoscopic exam and bronchoalveolar lavage (BAL) was performed. Horses were assigned an EIPH score based on previously published criteria. The number of red blood cells in in BAL fluid was also determined.

“There was a statistically significant difference in EIPH scores between the four-hour and 24-hour furosemide administrations,” the study determined. The study noted that none of the treatments prevented EIPH in the horses but that reducted red blood cell counts in bronchoalveolar fluid post-race indicated that administering furesomide four hours before a race was the most effective.

According to its introduction, the study came together following anecdotal reports that suggested furosemide administration 24 hours prior to strenuous exercise could be equally effective at decreasing EIPH.

The United States is one of the few countries that allows the raceday administration of Lasix. A study showing efficacy in preventing EIPH at 24 hours or beyond had potential to reshape current raceday policy of administration four hours before the race.

In the study led by Bayly, it was determined that a 0.5 mg/kg administration of furosemide 24 hours before strenuous exercise combined with controlled access to water shows potential for reducing the severity of EIPH.

The study used six horses who underwent treadmill exercise to fatigue after seven different protocols that adjusted the dosage amount of the Lasix and timing of the administration. The study concluded that, “Furosemide, 0.5 mg/kg, combined with controlled access to water, significantly reduced the severity of EIPH,” adding that, “No ill effects were detected in the horses.”

In its AAEP presentation outline, the study noted that “Although the findings were promising, the number of horses used was small. The effects of furosemide on water and ion excretion were evident for 24 hours but did not adversely affect the horses, likely because of increased absorption of wager and ions from the colon.”

In September 2015, Grayson Jockey Club Foundation announced it had launched funding of the two projects. The AAEP also played a prominent role in funding the projects, along with a number of racetracks.

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