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If Lasix is the answer...what question are we asking?

By Dr David Marlin
First Published: 07 December 2009 - Issue Number: 28

The impetus for the statements was the publication of a long-awaited study into the effect of Lasix on exercise-induced pulmonary haemorrhage (EIPH or “bleeding”) in thoroughbred racehorses in South Africa.
The South African study was led by Prof Ken Hinchcliff, Dean of the Veterinary School in Melbourne, Australia. Additional investigators included Prof Paul Morley, a veterinary statistician from Colorado State University, and Prof Alan Guthrie, Dean of the Veterinary School in Pretoria, South Africa. Ken Hinchcliff is rightly considered a world leader in the field of EIPH.  He and I organised and co-chaired the first Havemeyer International Workshop on EIPH in Vancouver in March 2006. The recent study was entitled “Efficacy of furosemide for prevention of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses” and was published on 1st July 2009 in the Journal of the American Veterinary Medical Association. What was relatively unusual about this study was the number of horses involved – an incredible 167 racehorses. The funding to undertake this study came from the racing industry in South Africa, including the track operators, US funding bodies and private donors. I shudder at the thought of the true bottom line figure. The authors utilised all the appropriate techniques to ensure accurate results, including such things as placebos, not telling the jockeys which horses had which treatment, and running half the horses with Lasix first and half without, and then running them again but 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 bleed...

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