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The Vital Role of Antibiotics in Treating Horses That Bleed Through Furosemide

Updated: Oct 28, 2023

Furosemide, commonly known as Lasix, is a diuretic medication often used in the horse racing industry to control exercise-induced pulmonary hemorrhage (EIPH), a condition where horses experience bleeding in the lungs during intense physical activity. While furosemide is widely accepted as an effective treatment for EIPH, it is essential to recognize that horses that bleed through furosemide may be at an increased risk of secondary infections. In such cases, the use of antibiotics becomes crucial to ensure the health and well-being of these equine athletes. This article explores the importance of administering antibiotics when a horse experiences EIPH while on furosemide.

Understanding EIPH and Furosemide

Exercise-induced pulmonary hemorrhage is a significant concern in the horse racing industry. When horses push their physical limits during races or strenuous workouts, the pressure on their cardiovascular system can lead to bleeding in the small blood vessels within their lungs. This condition not only compromises the horse's health but also affects their performance and overall career.

Furosemide, a loop diuretic, is often administered to manage EIPH. It works by reducing the volume of fluid in the horse's circulatory system, subsequently lowering the pressure in the lung capillaries and helping to prevent or minimize bleeding. While furosemide is effective in controlling EIPH, it can also lead to several important secondary issues, particularly the suppression of the immune system and the potential for bacterial infections.

The Need for Antibiotics

  1. Immune System Suppression: Furosemide is known to suppress the horse's immune system temporarily. This immunosuppressive effect can make them more susceptible to infections, including those of bacterial origin. In a weakened state, horses may struggle to mount an effective defense against invading pathogens, increasing the likelihood of infection. This is a critical concern when horses are exposed to crowded racing environments, which can be breeding grounds for bacteria.

  2. Respiratory Health: When a horse bleeds through furosemide, it signifies an existing vulnerability in the respiratory system. Blood in the airways can create an ideal environment for bacteria to thrive, as it provides the necessary nutrients and moisture for growth. Without intervention, bacterial infections can exacerbate the existing lung issues, causing further damage and hampering the horse's overall well-being.

  3. Preventing Complications: Bacterial infections in horses can quickly lead to complications such as pneumonia, pleuritis, and abscess formation in the lungs. These complications not only pose a significant threat to the horse's health but also can result in a prolonged recovery period and even the end of a racing career.

  4. Antibiotics as a Preventive Measure: Administering antibiotics when a horse bleeds through furosemide serves as a preventive measure to mitigate the risk of bacterial infections. By addressing potential infections promptly, veterinarians can help horses recover more quickly and reduce the chances of long-term damage.


The administration of furosemide has proven to be a valuable tool in managing EIPH in horses, allowing them to perform at their best. However, it is essential to recognize that this medication's immunosuppressive effect, coupled with the vulnerability caused by bleeding in the lungs, makes horses susceptible to secondary bacterial infections. Treating horses that bleed through furosemide with antibiotics is a crucial step in ensuring their overall health and longevity as competitive athletes. Veterinarians play a pivotal role in assessing the condition of these horses, diagnosing any infections, and implementing the appropriate antibiotic treatments. By doing so, we can protect these remarkable animals and safeguard their futures in the racing world.

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