EIPH: Common Drug Less Effective Than Thought

The results of a recent study have revealed that a drug commonly used to treat exercise-induced pulmonary hemorrhage (EIPH) is not as effective as veterinarians previously thought.

Belinda M. Buchholz, BS, a second year veterinary student at Washington State University, and colleagues set out to determine if aminocaproic acid (ACA), a drug that helps blood clot, decreases the amount of bleeding occurring in the respiratory tracts of horses with EIPH.

Exercise-induced pulmonary hemorrhage causes bleeding in the lungs during strenuous exercise. Clinical signs of EIPH in a horse range from a reddish tinge in the horse's mucus to a severe nosebleed. Veterinarians are generally concerned that repeated episodes of EIPH cause inflammation and scarring that reduces the elasticity of the lungs and makes it harder for the horses to breathe optimally during high-speed exercise.

"If the horse can't take in as much air, it takes in less oxygen and fatigues faster and performs less well," Buchholz said. "A single episode of EIPH is unlikely to end a career in a horse, but if repeated episodes occur, the length of a horse's career as a successful athlete may be shortened."

"We have to focus our efforts to deal with EIPH on medications that might reduce the amount of bleeding associated with each hemorrhagic episode," said Warwick Bayly, BVSc, MS, PhD, Dipl. ACVIM, a co-author on the study and the provost at Washington State University's veterinary school. "We are fooling ourselves if we think we can truly prevent bleeding. About the only way to do that is to force them to run more slowly so their blood pressure doesn't get as high and the pressure associated with breathing is also reduced. Given the intent of racing, which is to run as fast as possible and win, intentionally running slower makes no sense."

In the study, Buchholz examined the effects of ACA on eight Thoroughbreds with EIPH. After working the horses on a treadmill (once without ACA and twice with two different doses of ACA; adequate time was allowed between ACA works to assure there was no residual drug in the bloodstream), she and her colleagues determined there was little difference in EIPH severity when working with or without ACA.

Previous studies suggest that EIPH affects virtually all racehorses at one time or another, with its severity varying on a horse-by-horse basis. Another study revealed that 13% of upper-level three-day event horses are bleeders.

"We only used horses that had mild EIPH," Buchholz cautioned. She added that she and her colleagues believed the outcome would be similar if the study was performed on horses with severe EIPH.

Other medications to control EIPH are available to horse owners, but veterinarians recommend resting horses with EIPH to allow the lungs to heal, rather than running the risk of inducing more severe inflammation because of repeated bouts of EIPH. Any underlying respiratory condition, such as laryngeal hemiplegia (when one of the arytenoid cartilages obstructs a part of the windpipe, also known as roaring), dorsal displacement of the soft palate, or inflammatory airway disease, also should be treated.

The study "Effects of intravenous aminocaproic acid on exercise-induced pulmonary hemorrhage," was published in November online ahead of print in the Equine Veterinary Journal.

About the Author

Marie Rosenthal, MS

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