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release product. The pharmacokinetics has been described for both formulations. The doses described in cats are diltiazem 7.5mg/cat q 8h PO and sustained release diltiazem (Dilacor XR) 30 mg/cat q12 h PO and (Cardizem CD) 10 mg/kg q24h PO. In many European countries, diltiazem is only available in 60 mg tablets, which is very impractical.
The pharmacokinetics of oral pimobendan has
been studied in cats, and the drug appears to have longer elimination half-time and higher maximal drug concentrations in cats compared to dogs. The dose most frequently used is 0.625-1.25 mg PO q12h. The drug does produce similar cardiovascular effects, i.e. increased inotropy and a reduction in systemic arterial resistance, in cats as in other species. The drug has become more frequently used, particularily in cardiomyopathic non-obstructed cats. One case series report of worsening of syncopal episodes in severely obstructed cats receiving pimobendan. To the contrary, another retrospective study showed a significant survival benefit in pimobendan treated cats versus those receiving other treatments. There is one placebo controlled clinical trial completed in cats with cardiomyopathy, but the results are not yet published.
Clinical cardiomyopathy
Cats with clinical signs of CHF should be managed symptomatically. The required dose of furosemide depends on the severity of dyspnea. In the acute phase, cats often require an approximate dose of 2-3 mg/kg
IV, SC or IM q 2-6h to reduce the resting respiratory
rate to less than 50/min. Oxygen supplementation is often required, and cats with significant pleural effusion may require thoracocentesis. It is important that cats with significant dyspnea is not stressed, for example struggling during acquisition of thoracic radiographs. These procedures should preferably wait until the condition has stabilized. Some cats may need sedation with a low dose of acepromazine (0.05 to 0.1 mg/kg IV) to produce anxiolysis. Once the condition has stabilized, the furosemide dose should be reduced as much as possible to avoid dehydration, electrolyte disturbances and renal failure, which should all be monitored. Should the cat be severely dehydrated, small volumes of intravenous fluid may be administered, but with caution because of the significant risk of aggravating the pulmonary edema. Oftentimes the maintainance dose
of furosemide is approximately 1-4 mg/kg q 8-24h PO or lower. It is useful to instruct the owner to count the respiratory rate at home in order to monitor the cat. It is controversial which other drugs that could be added to the furosemide treatment: beta-blocker, calcium-channel blocker, ACE-inhibitor or pimobendan. There is currently one, unpublished study, comprising 118 cats receiving one of atenolol, diltiazem, enalapril or placebo together
An Urban Experience
with furosemide. Study end-points were recurring heart failure and death. The results showed no significant benefit of any of these 3 treatments over furosemide treatment alone. However, there was a trend for a worse prognosis for cats receiving beta-blocker together with furosemide did worse than the other 3 groups, a finding that drastically reduced the use of beta-blockers in cats with signs of CHF. Again, pimobendan has become an increasing popular choice of treatment, particularly in non-obstructed cats. With aggravating heart failure, the addition of a second diuretic, such as spironolactone
1-2 mg/kg PO q12-24h, or hydrochlorothiazide 1-4 mg/ kg PO q12h, could be considered. At this stage, it is common for cats to be mildly dehydrated and mildly to moderately azotemic, as a consequence of the disease and the diuretic therapy, but otherwise act normally and eat and drink. However, it is often not possible to lower the diuretic dose because that would lead to recurrence of pulmonary edema. Potassium supplementation should be considered in cases where clinical signs are present that could indicate clinically significant hypokalemia.
Concluding remarks
The level of evidence for different treatments of cats
with cardiomyopathy is low, and there is a general lack of large prospective placebo-controlled clinical trials. Treatment is therefore often based on opinions and
own experiences. For the adjunctive treatments to furosemide, beta-blockers and calcium channel blockers are less frequently used, whereas pimobendan has become more popular. Cats in CHF should be handled gently, to minimize stress, be administered furosemide and have pleural effusion evacuated (if present).
Selected References
Fox PR, Schober KA. Management of asymptomatic (occult) feline cardiomyopathy: Challenges and realities. J Vet Cardiol 2015;17 Suppl 1:S150- 158.
Gordon SG, Cote E. Pharmacotherapy of feline cardiomyopathy: Chronic management of heart failure. J Vet Cardiol 2015;17 Suppl 1:S159-172.
Fox PR. Prospective, double-blinded multicenter evaluation of chronic therapies for feline diastolic heart failure: Interim analysis. Proc 21st Annual ACVIM Forum. Charlotte, NC. Abstract 78. J Vet Intern Med 2003;17:398.
Bright JM, Golden AL, Gompf RE, et al. Evaluation of the calcium channel- blocking agents diltiazem and verapamil for treatment of feline hypertrophic cardiomyopathy. J Vet Intern Med 1991;5:272-282.
Schober KE, Zientek J, Li X, et al. Effect of treatment with atenolol on 5-year survival in cats with preclinical (asymptomatic) hypertrophic cardiomyopathy. J Vet Cardiol 2013;15:93-104.
Hanzlicek AS, Gehring R, Kukanich B, et al. Pharmacokinetics of oral pimobendan in healthy cats. J Vet Cardiol 2012;14:489-496.
Reina-Doreste Y, Stern JA, Keene BW, et al. Case-control study of the effects of pimobendan on survival time in cats with hypertrophic cardiomyopathy and congestive heart failure. J Am Vet Med Assoc 2014;245:534-539.

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