WHAT is furosemide and how is it connected with exercise induced pulmonary haemorrhage (EIPH)?

Furosemide is a diuretic medicine that is used in both human and veterinary medicine. A diuretic is an agent or medicine that causes an increase in the passing of urine. Furosemide is a particularly effective diuretic and works by blocking the absorption of sodium in the kidneys (where urine is made). This results in higher amounts of sodium remaining behind in the urine.

In order the counter this water is drawn into the urine, diluting the sodium and generating a large volume of urine. The net result of all this is increased passing of urine and additional loss of fluids.

EIPH is a condition that can affect many racehorses. It typically occurs during strenuous exercise and is believed to result from an increase in pressure in the small blood vessels found in the lung wall of a horse. Such an increase in pressure can cause blood to abnormally enter the lung, referred to as a bleed, which in turn can negatively affect the horse’s performance.

USING FUROSEMIDE

In North America, furosemide has attracted significant attention as a possible preventive for EIPH where its use has been allowed on race day. However, it is still not fully understood how furosemide may be effective in reducing bleeding in the lungs of racehorses.

It is believed that furosemide may not actually treat or cure EIPH but instead reduce EIPH ‘scores’, meaning affected horses that have received furosemide appear to bleed less during exercise.

Possible explanations for the reduced EIPH ‘scores’ resulting from furosemide use include: (i) increased production of certain prostaglandins (biological chemicals with a hormone like effect) that dilate (open) blood vessels in the lung, or (ii) a reduction in blood volume due to the loss of fluids via the diuretic effect.

Either of these two explanations could reduce blood pressure in the lungs and hence may decrease the likelihood of an EIPH event.

It is worth remembering that horses who have been administered furosemide will pass more urine and hence lose additional fluids as well as valuable electrolytes. The importance of electrolytes for performance was discussed in a previous Science Matters column, where the role of electrolytes such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-) in maintaining nerve and muscle activity was examined.

It is critically important to note that while furosemide is a recognised veterinary medicine, it is also on the prohibitive substance list and as such its use should only be considered in consultation with one’s veterinary surgeon.