Frusemide results in an extracellular to intracellular fluid shift in horses

Frusemide (Lasix) is commonly used diuretic in horse racing and equine clinical practice. While pharmacology, pharmacodynamics, renal and haematological effects of frusemide have been studied in horses, its effects on the distribution of fluid within the horse remain unknown.

To quantify the effects of frusemide on extracellular and intracellular fluid shifts.

Horses were infused with 1 mg/kg body mass (n = 7) or 2 mg/kg (n = 9) i.v. frusemide. Total body water (TBW), extracellular fluid volume (ECFV) and plasma volume (PV) were measured using D2O, NaSCN and Evans blue dilution. Change in ECFV was assessed from the change in plasma [protein] and from repeated infusion/dilution of NaSCN.

Frusemide resulted in a 0.020 +/- 0.002 l/kg decrease in TBW within 120 min. At 120 min after frusemide infusion the ECFV losses were nearly double the TBW losses, therefore ECFV loss in excess of TBW loss is seen as an increase in ICFV.

Frusemide resulted in a net shift of fluid (electrolytes and water) from the extracellular to intracellular fluid compartment.

The fluid shifts that occur within horses administered frusemide has not previously been characterised. The intracellular shift of fluid is of performance and clinical significance.