Pharmacologic interaction of furosemide and phenylbutazone in horses.

The study investigates the impact of phenylbutazone premedication on the hemodynamic and diuretic effects of furosemide in horses, revealing that phenylbutazone considerably lessens but does not eliminate furosemide’s diuretic effect and completely inhibits its immediate impact on cardiac output and other parameters.

Research Methodology

• The research was conducted on six healthy, conscious mares. The horses were prepared for measuring systemic hemodynamics, which included parameters like cardiac output, pulmonary arterial pressure, systemic arterial pressure, intracardiac pressures, and urine flow.
• Three different treatments were given to these horses in a randomized and blinded study. These treatments included administering only furosemide, phenylbutazone before furosemide, or 0.9% Sodium Chloride (NaCl).
• Furosemide was given at a dosage of 1 mg/kg of body weight intravenously, while phenylbutazone was administered orally at 8.8 mg/kg, 24 hours before, and intravenously at 4.4 mg/kg, 30 minutes before giving furosemide.

Findings of the Study

• On administering phenylbutazone before furosemide, the diuretic effect of furosemide was significantly reduced, but it was not completely inhibited. This shows that phenylbutazone has the potential to decrease the diuretic activity of furosemide.
• Interestingly, phenylbutazone totally inhibited the immediate effect of furosemide on systemic hemodynamic measures such as cardiac output, stroke volume, total peripheral resistance, and peak pressure of the right ventricle. This demonstrated the drug’s ability to influence the cardiovascular response to furosemide.
• Results showed that the diuretic and hemodynamic effects of furosemide were not equally inhibited by premedication with phenylbutazone. This finding indicates that some of furosemide’s hemodynamic effects are mediated by an extrarenal activity of furosemide, suggesting that its effect isn’t solely limited to the kidneys.