Furosemide pharmacodynamics: effect of respiratory and acid-base disturbances

The aims of this study were to investigate the effect of changes in arterial blood gases and pH on furosemide pharmacodynamics and kinetics. Five groups of conscious rabbits were used: a control group breathing air with normoxia and normocarbia; a second group with hypercapnia and respiratory acidosis; a third with hypoxemia; a fourth with hypercapnia and respiratory acidosis combined with hypoxemia (HCHO); and the fifth group with metabolic acidosis. All experimental conditions, except hypoxemia, increased sodium tubular reabsorption and therefore, decreased urinary excretion of sodium. Renal blood flow was decreased by HCHO and metabolic acidosis. In response to 5 mg/kv i.v. of furosemide, natriuresis and diuresis were decreased by an average of 44% in animals with HCHO (P less than .05). The kinetics of furosemide were not affected by any of the experimental conditions except HCHO, in which the renal clearance of furosemide was reduced from 7.5 +/- 1.4 ml/min/kg (controls) to 2.7 +/- 0.7 ml/min/kg (P less than .05). The reduction in renal clearance of furosemide was associated with a decrease in urinary excretion of sodium (P less than .05). The reduction in renal clearance of furosemide was probably secondary to the decrease in renal blood flow and an increase in furosemide tubular reabsorption. Finally, HCHO did not decrease plasma volume, suggesting that the reduction in renal blood flow was secondary to blood flow distribution. In conclusion, only hypercapnia and respiratory acidosis combined with hypoxemia decreases the natriuretic and diuretic effect of furosemide.