Tolvaptan substitution for torsemide is associated with improved renal biomarkers in dogs with advanced myxomatous mitral valve disease and concurrent azotemia

Objective: To evaluate the safety and preliminary efficacy of substituting torsemide with tolvaptan on renal biomarkers in dogs with myxomatous mitral valve disease (MMVD) and concurrent azotemia. Methods: This retrospective observational study reviewed medical records of dogs with American College of Veterinary Internal Medicine stage C or D MMVD and azotemia. Three 60-day cohorts were analyzed: group 1, torsemide dose reduction (25% to 50%); group 2, 50% replacement of torsemide with tolvaptan; and group 3, complete replacement of torsemide with tolvaptan. Renal biomarkers (BUN, creatinine, and symmetric dimethylarginine [SDMA]) were evaluated at baseline, day 30, and day 60. Results: 41 dogs were included. Groups 2 (50% torsemide replacement with tolvaptan) and 3 (complete replacement) showed significant reductions in BUN, creatinine, and SDMA at days 30 and 60 versus baseline. In group 2, mean creatinine decreased from 2.4 ± 1.5 mg/dL at baseline to 1.6 ± 1.2 mg/dL (day 30) and 1.7 ± 1.0 mg/dL (day 60), whereas SDMA decreased from 29.9 ± 17.5 µg/dL to 21.5 ± 5.7 µg/dL and 23.6 ± 11.1 µg/dL, respectively. No significant changes occurred in group 1 (torsemide reduction). Sodium increased modestly in the tolvaptan groups, potassium remained within reference ranges, and echocardiographic and hepatic parameters remained stable. Conclusions: Substituting torsemide with tolvaptan was associated with significant improvement in renal biomarkers in dogs with MMVD and azotemia. Clinical Relevance: These findings suggest that tolvaptan substitution may represent a potential therapeutic option for managing azotemia in dogs with congestive heart failure receiving loop diuretics, although prospective controlled studies are needed to confirm clinical benefit.