Short- and long-term effects of hydrochlorothiazide in dogs with relapsing congestive heart failure due to myxomatous mitral valve disease: a retrospective analysis of 38 cases

Introduction/objectives: Information on the use of hydrochlorothiazide (HCTZ) in dogs with relapsing congestive heart failure (CHF) due to myxomatous mitral valve disease (MMVD) is limited. Therefore, the aim of this study was to provide data on HCTZ's short- and long-term effects in canine MMVD. Animals, materials and methods: Signalment, clinical, diagnostic, therapeutic, and outcome data of dogs with relapsing CHF due to MMVD treated with HCTZ were retrospectively reviewed. The initial time point was the day HCTZ was introduced for a CHF relapse. Optimized criteria were used to determine the appropriate timings for evaluating HCTZ's short-term effects on laboratory and echocardiographic variables and its long-term impact on CHF management. Results: Thirty-eight dogs were included. The initial median dose of HCTZ was 0.8 mg/kg/die. At a median of seven days after HCTZ prescription, creatinine, urea, and total calcium levels significantly increased, while sodium and potassium levels significantly decreased (P: from 0.045 to <0.0001). While no dog developed severe electrolyte abnormalities, some dogs showed severe increases in creatinine and urea. After a median of 95 days, no significant echocardiographic changes developed (P: from 0.74 to 0.13). Episodes of CHF were more frequent before (median: one every 68 days) than after (median: one every 124 days) HCTZ prescription (P=0.006). Study limitations: The study limitations included the retrospective design of the study; not all dogs were included both in the short- and long-term analysis. Conclusions: In canine MMVD, HCTZ is useful in long-term management of relapsing CHF. However, in the short term, HCTZ can cause laboratory abnormalities, primarily increased creatinine and urea.