Furosemide, used in the United States and Canada to treat bleeding into the airways in Thoroughbred racehorses, decreases the incidence of hemorrhage according to results of a recent study. The study, conducted by Colorado State University, the University of Melbourne and the University of Pretoria in the Republic of South Africa, provides a foundation for racing authorities to make decisions regarding use of this medication, which is the subject of heated debate and controversy around the world.
Furosemide is widely used in the horse racing industry in North America but is banned on race days in all other countries. More than 90 percent of racing Thoroughbreds and 50 percent of racing Standardbreds in the United States and Canada are given furosemide a few hours before racing to treat bleeding.
The study involved 167 horses randomly allocated to race fields of nine to 16 horses each. Each horse raced in two races, one week apart, in the same field and in races of the same distance. In the blinded study, each horse received furosemide before one race and saline solution before the other race. Horses raced under typical racing conditions. Endoscopy was performed within 30-90 minutes after racing to identify the presence of blood in airways. The study was released in the Journal of the American Veterinary Medicine Association on July 1.
The research showed that giving furosemide before a race dramatically decreased the incidence and severity of exercise-induced pulmonary hemorrhage, or EIPH. Horses were three to four times more likely to have any evidence of bleeding without furosemide, and were seven to 11 times more likely to have severe bleeding without it.
Because of their unique physiology, all horses running at racing speeds experience varying degrees of exercise-induced pulmonary hemorrhage, or bleeding into their airways. Because of blood pressure changes in the lung that are unique to horses during exercise, more than half of Thoroughbred racehorses have small amounts of blood in their trachea after a single race. While severe EIPH is uncommon, this same research group confirmed the widely held belief that bleeding into the airways impairs athletic performance of horses. Although furosemide has been used in the racing industry for several decades, no scientifically sound studies had been conducted to prove or disprove an effect on EIPH.
"The results of this study do not eliminate debate about the use of this medication in racehorses, but it does provide evidence needed to aid making sound policy decisions. Decisions are always easier when you have data," said Dr. Paul Morley, one of the principal investigators of the study and a veterinarian at Colorado State University in the Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences.
Dr. Kenneth W. Hinchcliff of the University of Melbourne and Dr. Alan J. Guthrie of the University of Pretoria, also veterinarians, were the other principle investigators in the study.