Abstract
Background: The use of thiazide diuretics is recommended in the American College of Veterinary Internal Medicine guidelines for advanced heart failure due to mitral insufficiency (MI) in dogs. However, there are no large-scale reports of the use of thiazide diuretics in dogs with advanced heart failure.
Aim: This retrospective study evaluated the therapeutic effect of concomitant hydrochlorothiazide (HTCZ) with loop diuretics in dogs with heart failure.
Methods: The study included 14 dogs that were diagnosed with advanced pulmonary edema with MI at two facilities. In all cases, high-dose loop diuretics (torsemide; 0.78 – 4 mg/kg/day) did not improve pulmonary edema. The results of the echocardiography and renal function tests before and after the administration of HTCZ (0.2–0.84 mg/kg/day) in addition to torsemide were statistically compared.
Results: The echocardiographic data demonstrated significant improvement in relation to cardiac stress; left atrium to the aorta ratio, normalized left ventricular internal dimension in diastole, and E wave velocity (m/s) after HTCZ administration. However, blood urea nitrogen and creatinine levels increased and potassium level decreased, indicating a decline in renal function following HTCZ administration.
Conclusion: This study suggests that the administration of HTCZ in combination with loop diuretics may be beneficial during advanced heart failure due to MI in dogs. The results can also be extended to patients who are resistant to loop diuretics, resulting in the improvement of cardiac function. However, as the combination of HTCZ and loop diuretics can deteriorate renal function, caution should be exercised prior to making recommendations regarding its use, and renal function should be monitored.

Key words: echocardiology, hydrochlorothiazide, loop diuretic, mitral insufficiency, pulmonary edema,