Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

DIURETICS
metabolic acidosis due to poor perfusion. Despite the
increase in net acid excretion, urinary pH falls slightly
after furosemide administration, while urine specific
gravity is generally reduced to around 1.006–1.020.
In addition to its diuretic effects, furosemide acts as
a mild systemic venodilator, decreasing systemic venous
pressure before diuresis takes place (especially after
intravenous administration). Furosemide decreases renal
vascular resistance. Thus, it acutely increases renal
blood flow (in the order of 50%) without changing
glomerular filtration rate.
Furosemide increases thoracic duct lymph flow in
dogs following high doses (8–10 mg/kg IV). This
effect is independent of renal function as it occurs in
nephrectomized animals. The basis for this effect is
unexplained.
Furosemide acts as a bronchodilator in humans,
horses and guinea-pigs. It can be administered as an
inhalant in humans with asthma. Its bronchodilatory
effects in dogs and cats are unknown. If it does have
bronchodilatory effects in cats and dogs, it could have
beneficial effects in cats with asthma and in dogs with
chronic bronchitis but its use should not replace conventional
therapy for these diseases. It does, however,
offer an explanation for why some dogs with chronic
valve disease that are not truly in heart failure and are
coughing due to chronic bronchitis (small airway
disease) may experience a reduction in their cough when
treated with furosemide. Thus resolution or improvement
of a cough following trial therapy with furosemide
does not prove the patient was in heart failure. One
needs to document radiographic resolution of a characteristic
infiltrate in the therapeutic trial of this nature.
It is important that dogs with heart disease (preclinical)
that will not benefit from furosemide are not administered
the drug chronically.
Formulations and dose rates
Furosemide is available in oral (tablets, suspensions) and parenteral
formulations.
CANINE
Chronic heart failure
1 mg/kg PO q.12 h for mild heart failure to 5 mg/kg q.8 h (doses
should be separated by at least 3 h but do not have to be exactly 8 h)
for severe heart failure. When this dose fails to keep the patient free
of clinical signs of congestion a second diuretic may be added (see
hydrochlorothiazide). The need for the addition of a rescue diuretic is
clinically relatively rare. In general, the goal with furosemide is to use
the minimum dose necessary to keep the patient free of clinical signs
of congestion. Dogs with mitral regurgitation secondary to CVD that
are refractory to furosemide administration may also benefi t from the
administration of a systemic arteriolar dilator, such as amlodipine or
hydralazine.
Acute heart failure
Severe pulmonary edema requires immediate intensive intravenous
or intramuscular administration in dogs. Intravenous is preferred if
feasible.
FUROSEMIDE DOSE SCHEDULE FOR SEVERE LIFE-THREATENING
CARDIOGENIC PULMONARY EDEMA IN THE DOG
• Dependent on severity of respiratory clinical signs
• Guided by resting respiration rate with oxygen supplementation
and thoracic radiographs when available
• For severe life-threatening cardiogenic pulmonary edema in the
dog:
Initial dose: 4–6 mg/kg IV (IM if IV not feasible)
Then: 2–4 mg/kg IV q.1 h (or 1 mg/kg min CRI) until resting
respiration rate (RR) ↓ by 20%
Then: 2–4 mg/kg IV q.2 h (or 0.5 mg/kg min CRI) until resting RR ↓
by 50%
Then: 2–4 mg/kg IV q.6–8 h (discontinue CRI at this time)
Then: switch to oral 2–4 mg/kg q.8–12 h
Note: For less severe edema use the lower end of the dose range and
in older patients who are concurrently azotemic reduce the lower
range doses in the schedule by 50%.
If dogs with respiratory distress fail to demonstrate a trend for
improvement (reduced respiration rate) following 4–6 doses or 4–6 h
of a furosemide CRI alternative differentials for respiratory distress
should be considered and/or additional heart failure therapy should
be initiated.
FELINE
Chronic heart failure
1 mg/kg PO every 1–3 d (mild heart failure) to 2 mg/kg twice to three
times daily (severe heart failure) in most cases (doses should be
separated by at least 3 h but do not have to be exactly 8 h). In general
the goal with furosemide is to use the minimal dose necessary to keep
the patient free of clinical signs of congestion. Some cats that are not
amenable to oral administration may benefi t from chronic clientadministered
subcutaneous injections. A higher oral dose may be
considered in some cats that are not responding to a conventional
dose. The need for the addition of rescue diuretics in the cat is
exceedingly rare.
Acute heart failure
Severe pulmonary edema requires immediate intensive intravenous
or intramuscular administration in cats. Intravenous is preferred if
feasible.
FUROSEMIDE DOSE SCHEDULE FOR SEVERE LIFE-THREATENING
CARDIOGENIC PULMONARY EDEMA IN THE CAT
• Dependent on severity of respiratory clinical signs
• Guided by resting respiration rate with oxygen supplementation
and thoracic radiographs when available
• For severe life-threatening cardiogenic pulmonary edema in the
cat:
Initial dose: 2–4 mg/kg IV (IM if IV not feasible)
Then: 1–2 mg/kg IV in 1–2 h
Then: 1–2 mg/kg IV in 2–4 h if resting respiration rate is not ↓ by
50%
Then: switch to oral at 1–2 mg/kg q.8–12 h once RR reduced by
50%
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