LASIX ISSUE 15:Jerkins feature.qxd
27/1/10
15:46
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LASIX
the ones that had Lasix the first time ran without it the second time. There is no doubt that this study has set a standard which others will find hard to match, at least if the cost is taken into account. But what were the results and how should we interpret them? Horses that were given Lasix had less blood in the trachea (windpipe) when scoped after racing than when they were given a placebo (salt water). Lasix did not, however, abolish EIPH completely. The degree of bleeding is most commonly scored by grading the amount of blood in the trachea after exercise on a 0-4 scale, with 0 being no blood and 4 meaning the trachea would be awash with blood. In this study there was a small number of horses that had severe bleeding (grades 3 and 4) when running without Lasix, but none when running with Lasix. In addition, twice the number of horses had no blood in the trachea when they ran with Lasix compared to when they ran without it. This does not mean that Lasix abolished bleeding completely. Blood would still have been present in the smaller airways of the lung, but would not have been visible with a scope in the windpipe. This study is very fortunate for the U.S. racing authorities who originally changed the rules to allow Lasix in the absence of any data on efficacy. So is this study sufficient grounds for a
reconsideration of Lasix? If so, what could be some of the added complications of such a change in race day medication rules? There is never such a thing as a perfect experiment. We all strive for it, but usually there are limitations and many of these are not apparent until after we have completed the work. In this study there are very few obvious flaws. The first may be that the use of Lasix in this population of horses before they took part in the study was not described. Therefore some horses would have been trained on Lasix and some would not. This could potentially affect the response to Lasix in the study. Even though Lasix is not permitted for use on race days in South Africa, like the U.K., regulated use of Lasix in training to manage the more severe bleeders is common A second observation concerns the reliability of a single post-race or posttraining scoping to classify a horse’s grade of bleeding. Studies over the past 30 years have suggested that if any population of racehorses anywhere in the world is scoped once after racing, between 40-75% of horses will have some blood in the trachea. But, in a 2002 study by Dr. Ric Birks in the USA, it was shown that if any horse was scoped on three separate occasions after racing, it would have blood in the trachea after at least one of those races. Therefore bleeding is
variable and a single scoping may not be as accurate as multiple assessments in terms of classifying a horse as a bleeder or a horse’s “normal” grade of bleeding. My third observation is that the dose of Lasix given was 500mg (or 10ml). The normal dose permitted in most U.S. racing jurisdictions is 250mg (or 5ml). Why was double the normal dose chosen for this study? There is no explanation of this as far as I can see in the published paper. Certainly, one could speculate that a higher dose of Lasix would give a better chance of success. But if other racing jurisdictions decided to implement Lasix in racing, would they choose the commonly used 250mg dose or the 500mg dose used in this study? If they wanted to be sure of obtaining the same effect as demonstrated in this study then they should go with the 500mg dose. And now to my major concerns. This study showed that when Lasix was given ONCE it produced a small but significant reduction in the amount of blood in the trachea. But it didn’t show what happens when Lasix is used in training and in racing repeatedly over the course of a number of weeks, months or even a racing season. Does it have the same effect every time? At present there are no studies that show that Lasix produces the same effect with repeated use. Therefore, we have no evidence that it reduces EIPH by the same amount with repeated use over time. Many racetrack vets have reported that they see a reduction in urine production with long term repeated use of Lasix. This would be consistent with the tolerance that develops from repeated use of many drugs. This fact is particularly well established with Lasix use in humans and other species where repeated use causes the kidney to adapt, resulting in reduced efficacy. That means you give the same dose of furosemide but you get less urine produced and therefore less beneficial effect in terms of reduction in bleeding. Another major concern is the use of the term “prevention of EIPH” in the Hinchcliff paper. The authors use the words “prevent,” ”prevention,” “preventing,” or “preventative” in the title and throughout the paper a total of 16 times, but we know that Lasix reduces EIPH but has never been shown to prevent it. In fact the authors use “reduction” themselves in relation to their results on around five separate occasions. Am I being picky? Yes. Is this just semantics? No. Prevention and reduction are not interchangeable words. Lasix may prevent the appearance of blood in the trachea but it will not prevent EIPH. This is because even when there is no blood in the trachea there can still be significant amounts of blood in the smaller airways – it’s just not visible when you scope the horse. In fact, we have observed that normal healthy horses at rest have as few as 10 red blood cells per ISSUE 15 TRAINERMAGAZINE.com 23