This retrospective study evaluated the use of pimobendan in cats with heart disease. The dose and frequency of pimobendan were recorded, along with other medications given. During the study period, 170 client-owned cats received pimobendan. Of these, 164 were diagnosed with congestive heart failure (CHF) and 119 were started on pimobendan at the time of diagnosis. The remaining 45 cats were initially started on furosemide; pimobendan was initiated >1 week later. Most cats had hypertrophic cardiomyopathy (HCM) or unclassified cardiomyopathy (UCM) (40% and 37%, respectively). Median pimobendan dose was 0.24 mg/kg q12h (range, 0.08–0.42). Furosemide was administered concurrently to 98% of cats with CHF, and 84% of cats received an ACE inhibitor, along with pimobendan. An additional 7.1% of the cats received spironolactone and hydrochlorothiazide simultaneously, and most cats (80%) received antithrombotics.

Survival analyses were available for the 164 CHF cats. Median survival time after initial examination was 151 days (range, 1–870), with 43 cats still alive at last contact. Potential side effects of pimobendan were noted in 5 cats, but only 1 case was considered severe enough for discontinuation. Serum BUN and creatinine concentration did not change significantly despite concomitant use of furosemide—possibly indicating that pimobendan has a positive effect on renal function. Study results indicated that pimobendan was well tolerated in cats; further studies may help determine its role in survival and quality of life in these patients.

Commentary
Cardiologists are now using pimobendan in the long-term management of heart failure in cats, and although its use may be safe and well tolerated, some important points should be noted. First, because this was a retrospective study, it did not show a survival benefit for cats treated with pimobendan in addition to standard therapy with an ACE inhibitor and furosemide. Second, the majority of these cats (73%) had evidence of systolic dysfunction/myocardial failure and pimobendan was likely added to the treatment protocol to provide positive inotropic support. Myocardial failure can occur in the latter stages of HCM and in cats with UCM or restrictive cardiomyopathy but is not typically a feature early in the course of the disease or at the first episode of heart failure in cats with HCM. In addition, many cats with HCM and heart failure often have left ventricular outflow tract obstruction (LVOT), and as a positive inotropic agent pimobendan could potentially worsen this obstruction.

At this time, pimobendan should not be considered standard therapy for the treatment of heart failure in cats. Therapy with pimobendan should only be considered if there is evidence of systolic dysfunction and absence of LVOT obstruction. A randomized, controlled clinical trial is required to more accurately assess efficacy of pimobendan.—Amara Estrada, DVM, DACVIM (Cardiology)

Source
Use of pimobendan in 170 cats (2006-2010). MacGregor JM, Rush JE, Laste NJ, et al. J VET CARDIOL 13:251-260, 2011.