PHARMACOLOGICAL INTERACTION OF FUROSEMIDE AND PHENYLBUTAZONE IN HORSES

The effect of premedication with phenylbutazone on systemic hemodynami c and diuretic effects of furosemide was examined in 6 healthy, consci ous, mares. Mares were instrumented for measurement of systemic hemody namics, including cardiac output and pulmonary arterial, systemic arte rial, and intracardiac pressures, and urine flow. Each of 3 treatments was administered in a randomized, blinded study; furosemide (1 mg/kg of body weight, IV) only, phenylbutazone (8.8 mg/kg, PO, at 24 hours a nd 4.4 mg/kg, IV, 30 minutes before furosemide) and furosemide, or 0.9 % NaCl. Phenylbutazone administration significantly attenuated, but di d not abolish, the diuretic effect of furosemide. Phenylbutazone compl etely inhibited the immediate effect of furosemide on cardiac output, stroke volume, total peripheral resistance, and right ventricular peak pressure. Premedication with phenylbutazone did not inhibit equally t he diuretic and hemodynamic effects of furosemide, indicating that som e of furosemide's hemodynamic effects are mediated by an extrarenal ac tivity of furosemide.