How Does Furosemide Work?By Dr. Bryan Waldridge · January 4, 2012
Furosemide is a commonly used and very effective diuretic in human and veterinary medicine. The pharmacologic action of furosemide is to block the absorption of sodium from the small tubules that produce urine in the kidney. Water follows sodium, so the increased sodium draws more water into the urine. The overall result is to produce a larger volume of dilute urine. Most horses will begin urinating within 30 minutes after an intravenous dose of furosemide.
Furosemide is prescribed for heart disease, hypertension, edema or swelling, or stimulation of urine production with kidney disease. In horses, furosemide has attracted much attention as a preventive for exercise-induced pulmonary hemorrhage (EIPH or bleeders). It is still not completely understood how furosemide may be effective to reduce bleeding from the lungs in racehorses. Possible mechanisms for furosemide use in EIPH include reduced blood volume or stimulated production of certain prostaglandins that dilate blood vessels in the lung. Either of these two mechanisms reduce blood pressure in the lungs and should decrease the likelihood of bleeding.