By Kim L. Kuhlmann, DVM

Of all the questions posed to veterinarians by owners, the most common one concerns the use of Furosemide (Lasix). Lasix is one of the most discussed and sometimes controversial, yet least understood, drugs used in racing. 

For years, states argued over its use for treatment of exercise-induced pulmonary hemorrhage (EIPH) “bleeding”. Fortunately, in recent years the states have begun to agree on the dosage, route, and time of administration. Most notably, New York has finally approved its use in racehorses, which is scheduled to begin this fall. These events are due primarily to the efforts and recommendations of the American Association of Equine Practitioners.

With the introduction of the flexible fiber optic endoscope, studies have shown that as much as 70% to 80% of horses have visible evidence of EIPH. While many treatment modalities have been tried to remedy EIPH, the most common and successful remedy has been Lasix. Other drug treatments include coagulant and conjugated estrogens (Premarin). Yet, none have been proven to be totally effective in stopping EIPH. 

How does Lasix work? Well, Lasix is thought to decrease bleeding by reducing pulmonary edema via fluid loss in the lungs as well as decreasing the horse’s pulmonary blood pressure. Some argue that this has not been totally proven. Nevertheless, Lasix does reduce the amount of hemorrhage seen in most horses. 

What causes EIPH? Several studies have been don to determine the cause of bleeding in horses. Although many theories have come forth, none has set itself apart as identifying the definitive cause. Until there is an identified, proven cause, no “perfect” treatment for EIPH will be found. Remember, Lasix is not a cure. What it is is the most widely accepted and effective treatment developed to date.

Dr. Kuhlmann is a licensed veterinarian practicing in Northern California, and is a principal in Equine Veterinary Services, Inc.