Loop diuretics provide symptomatic relief for congestive heart failure, yet stimulate the renin-angiotensin-aldosterone system (RAAS). We hypothesized that the two potent loop diuretics, torsemide and furosemide, at approximately equipotent dosages (similar diuresis), would have comparable effects on the circulating RAAS.
Six, healthy, middle-aged, male beagles were randomized to receive torsemide (0.1mg/kg PO q12h), furosemide (2.0mg/kg PO q12h), or placebo for 10 days during 3 separate experiments, in a crossover design with a 10-day washout period between experiments. Blood was collected on days 1, 5, and 9 and 24-hour urine collection ended on days 2, 6, and 10. After repeated measures analysis and Bonferonni correction, variables with an adjusted P < 0.05 were investigated further, using Tukey’s method.
Twenty-four hour urine production differed significantly between the diuretics only on day 10, with torsemide causing a 38% greater diuresis than furosemide. There was, however, no significant difference in average 3-day diuresis. There were no significant differences between diuretics in the 24-hour urinary excretion of Na+, Cl-, or K+, though furosemide caused less kaliuresis than torsemide. Serum renin, angiotensin II, and aldosterone and the urine aldosterone-to-creatinine ratio were significantly increased in the diuretic groups, as compared to placebo on days 5/6 and 9/10. There were no significant differences in these parameters between diuretics. Creatinine and BUN concentrations rose comparably in the 2 diuretic groups, remaining within reference intervals in all dogs.
At approximately equipotent dosages (20:1), torsemide and furosemide produced comparable RAAS activation. This, and torsemide’s greater kaliuretic effect decrease support for torsemide’s hypothesized mineralocorticoid-receptor blocking capability.
Colorado State University
Dr. Brianna Potter received her DVM from the University of Tennessee College of Veterinary Medicine. She then completed a small animal medicine and surgery rotating internship at the Ohio State University. She is now in her second year of a cardiology residency at Colorado State University.
Thursday, June 14
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