Page 218 - Clinical Small Animal Internal Medicine

186 Section 3 Cardiovascular Disease

Drugs for Treatment of Chronic Heart Failure results, and presence of concomitant conditions such as
VetBooks.ir (Table 19.1) renal insufficiency. The authors recommend checking
serum blood profiles within the first 10 days after starting
Diuretics
Diuretics increase production of urine through affect- or changing an existing dose of furosemide, after which
routine rechecks every 3–6 months are performed.
ing the kidney’s physiologic handling of water and Doses of furosemide might also be adjusted after adding
electrolytes. Diuretics result in an increased loss of concomitant agents that can affect renal perfusion (i.e.,
sodium (natriuresis) that is followed by water and vasodilators, positive inotropes, other diuretics, non-
other electrolytes. Diuretics are the first‐line therapy steroidal antiinflammatory agents, etc.).
in patients with chronic CHF, but despite their efficacy
in resolving and preventing congestion, they are not Spironolactone
typically used as monotherapy due to their activation Spironolactone is a diuretic as well as a neurohormonal
of the renin‐angiotensin‐aldosterone system (RAAS). blocking agent due to its inhibition of aldosterone. In
One instance when diuretics are contraindicated for chronic CHF, benefits of spironolactone involve modest
the treatment of CHF is in patients with pericardial diuresis and antiremodeling effects on the myocardium,
effusion and cardiac tamponade. In this group, cardiac kidneys, and vasculature through its blockade of aldos-
output is markedly dependent on preload, and aggres- terone receptors. In humans and experimental animal
sive diuresis will worsen cardiac output, potentially models, spironolactone reduces pathologic tissue hyper-
leading to cardiogenic shock.
trophy and fibrosis. In both human and veterinary
patients, spironolactone improves survival times in
Furosemide patients with chronic CHF. Based on anecdotal experi-
Furosemide is first‐line therapy in the management of ence, one author (SR) recommends considering spirono-
chronic CHF. The goal of therapy is to prescribe the low- lactone therapy in patients with progressive heart
est diuretic dose required to control the clinical symp- enlargement that have not yet experienced CHF, as well
toms of congestion and edema. Compared to treatment as those patients with chronic heart failure. In dogs with
of pulmonary edema, relatively higher diuretic dosages abdominal or pleural effusion, spironolactone is often
are often required to help resolve body cavity effusions, co‐administered with furosemide to help slow the recur-
such as pleural or abdominal effusion. In these instances, rence of the effusion. Typical spironolactone dose in
routine thoracocentesis or abdominocentesis can aid in dogs is 2 mg/kg/day. Monitoring of renal function and
minimizing the dose of furosemide needed. electrolytes is recommended in a fashion similar to furo-
There is a wide range of doses reported in the veteri- semide. The benefit of spironolactone in cats with CHF
nary literature. In the authors’ experience, furosemide is unknown. Previous study in cats suggests that 1.7–
doses of 1–4 mg/kg orally every 8–24 hours are utilized 3.3 mg/kg/day was well tolerated.
in treating chronic CHF in the dog. The typical starting In dogs, adverse reactions include anorexia and hyper-
dose of oral furosemide for a dog with first‐time CHF is salivation that may be mitigated by administration with
2–3 mg/kg/day. Cats are particularly sensitive to the food or in a gelatin capsule, azotemia, and electrolyte
dehydrating effects of furosemide and dosages of 1–2 mg/ imbalances. Reformulated and flavored preparations of
kg every 12–48 hours are preferred, with most cats spironolactone are difficult to administer due to their
receiving a total of 1–2 mg/kg/day for first‐time CHF. still unpleasant taste. Due to its potassium‐sparing
Lower doses spread over shorter dosage intervals may effects, spironolactone can also predispose to hyper-
result in less diuretic resistance as high doses can lead to kalemia. This is most common when spironolactone is
rebound effects and resistance due to greater stimulation used in combination with an ACEI.
of the RAAS. Pet owners who become adept at monitor-
ing respiratory rates and effort can often make small Vasodilators
adjustments in furosemide dosing at home to prevent In the late 1980s and early 1990s, the use of vasodilators
recurrent CHF symptoms. became part of the standard CHF treatment in both
Adverse effects of diuretics include electrolyte imbal- human and veterinary medicine. The benefits for the
ances such as hypokalemia (often mitigated with the hemodynamic and, in the case of ACEI, neurohormonal
concurrent use of angiotensin converting enzyme inhibi- aspects of heart failure contributed to widespread use
tors (ACEI) or spironolactone), hyponatremia, azotemia, across many different species and many types of heart
dehydration, and urinary incontinence. Renal function disease. ACEI, nitrates, amlodipine, hydralazine, and
and serum electrolytes should be routinely monitored. sildenafil are the most common agents utilized in veteri-
The frequency of monitoring is based on furosemide nary patients. The majority of clinical data in veterinary
dosage, concurrent medications, previous bloodwork medicine involves ACEI for the treatment of chronic