Page 221 - Clinical Small Animal Internal Medicine

19 Management of Heart Failure 189

higher dose over the first 7–10 days of treatment. Blood will diets high in fiber. Certain antibiotics like tetracy-
VetBooks.ir pressure, renal function, and electrolyte monitoring is clines will alter the bacterial flora and may increase
serum digoxin levels.
performed every 3–6 months thereafter. In humans, idi-
The primary indication for digoxin in dogs (and to a
osyncratic nocturnal cough is an important adverse
effect, but this has not been reported in dogs, and any much lesser extent in cats) with heart disease is to slow
coughing is usually due to concurrent chronic airway AV nodal conduction and ventricular response rate in
disease. patients with atrial fibrillation. Digoxin is indicated for
the treatment of atrial fibrillation, persistent atrial and
Other Vasodilators sinus tachycardias, and progressive myocardial dysfunc-
Other vasodilators used for treatment of chronic CHF tion. It may also help reduce syncope in patients with
include hydralazine, amlodipine, and nitrates. These severe mitral regurgitation due to its pharmacologic
agents are discussed in the section regarding treatment effects, including its effects on baroreceptors.
of refractory heart failure. Contraindications for use include complex ventricular
arrhythmias, renal disease, atrioventricular block, cer-
Positive Inotropes tain types of ventricular preexcitation, and sinus node
Use of positive inotropes for the treatment of heart fail- dysfunction.
ure has been a subject of controversy due to a potential Due to the risk of toxicity, serum digoxin levels are
increase in the risk of sudden death due to arrhythmias. typically monitored 10–14 days after initiation or any
Conventional positive inotropes such as digoxin, dobu- dose changes. Blood should be drawn 6–8 hours post pill
tamine, and dopamine act by increasing cytosolic cal- to assess “trough” concentrations. Traditionally, serum
cium that improves cardiac contractility but might also digoxin levels between 0.8 and 2.0 ng/dL have been con-
precipitate cardiac arrhythmias. The objective of posi- sidered to be therapeutic. Based on recent data in
tive inotropic therapy is to increase myocardial contrac- humans, the authors commonly target a lower serum
tility and improve cardiac output and organ perfusion. level of 0.6–1.2 ng/dL as lower levels remain beneficial
Digoxin and pimobendan are the two most commonly but with a lower incidence of adverse reactions. In the
used agents for the treatment of chronic CHF in the vet- authors’ experience, gastrointestinal upset and anorexia
erinary patient. can occur at levels as low as 1.5 ng/dL. Anecdotally, min-
iature schnauzers and Doberman pinschers are more
Digoxin sensitive to digoxin and lower starting doses are recom-
Digoxin is one of the oldest cardiac medications known mended for these breeds (no greater than 0.125 mg q12h
and has positive inotropic and negative chronotropic as a starting dose in Dobermans regardless of their body
(slowing conduction through the atrioventricular [AV] weight). Pet owners are recommended to administer the
node) effects, as well as beneficial effects on the barore- digoxin along a consistent interval and regimen. Since
ceptors and neurohormonal axis such as the RAAS. certain foods and medications can alter absorption, the
Even though it has been used for over 200 years, its ben- owner should continue the same feeding and dosing reg-
efits for survival have not been proven. In dogs, imen once therapeutic serum levels are achieved.
pimobendan has largely supplanted digoxin as the posi- Changes in renal function will affect digoxin excretion,
tive inotrope of choice. Digoxin is associated with a high and digoxin and electrolyte levels are routinely evaluated
incidence of adverse reactions including gastrointestinal every six months or when changes are made in concur-
upset and cardiac arrhythmias. The recommended rent medications.
canine dose is 0.005–0.0075 mg/kg q12h. In cats, digoxin
is not commonly used, in part due to the drug’s long half‐ Pimobendan
life. The feline dose is ¼ of a 0.125 mg tablet (0.03125 mg) Pimobendan is widely used for the treatment of canine
every other day for smaller cats and once a day for larger heart failure secondary to dilated cardiomyopathy
cats. The dosage in patients with renal disease is reduced (DCM) and myxomatous mitral valve disease (MMVD).
since digoxin is excreted by the kidneys. Dosage should Recently, studies have shown the benefits of this agent in
be based on lean body mass and reduced in obese pets or the preclinical stage of MMVD once a moderate degree
those with significant ascites. Oral absorption of digoxin of radiographic and echocardiographic cardiac enlarge-
can be altered by the formulation, concurrent medica- ment has developed.
tions, or food. The elixir (0.05 mg/mL) is better absorbed Pimobendan is a calcium sensitizer and phosphodies-
than the tablet formulation although is not palatable to terase inhibitor and its benefits are a result of the combi-
most cats. As such, slightly lower doses are often pre- nation of positive inotropic properties along with effects
scribed when using the elixir over tablets. Antacid agents as a vasodilator. Its dual action is often indicated by the
like sucralfate will reduce the absorption of digoxin, as term “inodilator.” Pimobendan is used as the first‐line