A study funded in part by North American racing groups and conducted using South African racehorses has indicated that furosemide, the diuretic administered prerace to about 90 percent of all horses racing at North American tracks, plays a significant role in reducing the severity of bleeding in the lungs.\nThe study, conducted by researchers at Colorado State University, the University of Melbourne in Australia, and the University of Pretoria in South Africa, involved postrace tracheal examinations in 167 horses that were administered either a saline solution or furosemide - which is marketed under the trade name Salix but is better known as Lasix - prior to performing in races at Vaal Racecourse in South Africa. The researchers found that horses administered furosemide were far less likely to suffer "severe" episodes of bleeding than those that were injected with the saline solution.\nThe conclusions appear to confirm results that had previously been largely anecdotal. In the United States and Canada, the only two major racing jurisdictions that allow the use of furosemide on race day, veterinarians have long contended that the drug effectively reduced the severity of bleeding, or exercised-induced pulmonary hemorrhage, but previous studies had relied only on laboratory results, rather than the study of horses under actual racing conditions.\n"It does back up the clinical impressions of practitioners on the backstretch that furosemide does help in the reduction of EIPH," said Dr. Scot Waterman, the executive director of the Racing Medication and Testing Consortium, a North American research group that co-funded the study. "The current literature is equivocal about that."\nThe researchers used a scale from 0 to 4 to grade the severity of bleeding in the postrace tracheal examinations, with a 0 indicating that the horse did not show any evidence of bleeding and a 4 indicating the most severe episode. The researchers used the results from horses that were administered furosemide prior to one race and saline solution prior to a different race.\nThough the results did not show a significant difference in the percentage of horses that experienced a bleeding episode rated a one by the researchers, the postrace tracheal examinations of horses that were administered furosemide were far more likely to be rated a 0 and far less likely to be rated a 2, 3, or 4. In fact, no horse that was administered furosemide had a postrace tracheal examination that rated either a 3 or 4, whereas approximately 10 percent of the untreated horses received a 3 rating. Two postrace tracheal examinations of the 152 conducted for untreated horses were rated a 4, or 1.3 percent.\nIn addition, the researchers concluded that "81 of the 120 horses that had EIPH after administration of saline solution had a reduction in EIPH severity score of at least 1 when treated with furosemide," according to the study.\nBecause furosemide is a diuretic, many veterinarians have theorized that the drug reduces capillary pressure in the lungs and makes blood vessels less likely to burst. The study did not seek to determine why furosemide reduces bleeding, however. \nConsistent with the clinical effects of a diuretic, the study showed that horses administered furosemide experienced a much greater weight loss after administration than horses that were not injected with the drug. According to the study, treated horses lost an average of 27.9 pounds between the injection and a weight measurement following the race, while untreated horses lost an average of 11.9 pounds.\n"However, weight loss does not appear to be directly related to the mechanism by which furosemide prevents EIPH," the study's authors wrote, "in that we did not identify an association between amount of weight lost and prevention of EIPH in the present study."\nThe most rigorous study about the effects of furosemide on racing performance - conducted in 1999 using an analysis of past-performance data - had concluded that horses treated with the drug ran faster than untreated horses. That study, which was co-authored by one of the co-authors of the just-released study, Dr. Paul Morley, did not delve into the efficacy of the drug in treating bleeding.