Brand Name: Lasix, Disal
Available in oral solution (8 or 10 mg/ml), 12.5 mg tablets,20 mg
tablets, 40 mg tablet, 50 mg tablets, 80 mg tablets (and injectable)
Background
The kidney is one of the most complicated organs of the body. It is responsible
for maintaining one’s electrolyte balance, blood pressure, and fluid/hydration
status through its elaborate filtrating and excretion systems. It is not our
intention to review a system as complex as this here; with regard to furosemide,
what is important to know is that it acts on the kidney to increase the body’s
loss of water and assorted minerals and electrolytes (salt, potassium, calcium,
magnesium, bicarbonate, hydrogen and ammonium).
How this Medication is Used
Because furosemide leads to water loss via increased urine production it
is classified as a diuretic. This makes it a useful medication in conditions
where the removal of excessive fluids would be beneficial. Such conditions
include:
Congestive Heart Failure
By definition, congestive heart failure involves fluid congestion or accumulation
somewhere where there should not be excess fluids. This is usually in the
belly or chest cavity or actually within the lung tissue (pulmonary edema).
Furosemide causes an increase in urine production thus shifting the equilibrium
away from the accumulation of fluid in tissue. Injectable furosemide is needed
during acute heart failure crisis but oral is generally adequate for continued
management after stabilization.
Edema
Furosemide can also be used to remove fluid from body cavities or peripheral
tissues even when the cause is not heart failure. Swellings due to fluid accumulation
can be reduced through using this medication.
False Pregnancy
False pregnancy can be quite a nuisance for a female dog. The excess mammary
tissue can be reduced in some cases with the administration of furosemide.
Usually in this condition, simply waiting for the hormones to normalize is
adequate but furosemide administration would represent a conservative treatment
course.
Another important reason to stimulate urine production could be acute kidney
failure where the kidney is trying to shut down urine production permanently
and fatally. Obviously this is a dire emergency and frequently a combination
of diuretics is needed for treatment.
Furosemide can be used to reduce excessive blood calcium levels that are
inherently dangerous to the kidneys. Calcium is one of the minerals furosemide
encourages the body to lose. Often prednisone is used with furosemide for
this use as it too encourages calcium excretion.
Furosemide can also be helpful in reducing dangerously high potassium blood
levels and has been used in the horse to treat exercise induced pulmonary
hemorrhage (nose bleeds).
Side Effects
Inherent to all diuretics, including furosemide, are the following side
effects:
Increased thirst
Increased urination
Furosemide is associated with an increase in blood sugar levels. This is
not a problem for most patients but a different diuretic may be a better choice
for a diabetic patient.
Hearing loss has been reported, especially in cats, when large amounts of
injectable Lasix have been used in a crisis.
Urination is usually seen within 30 minutes of the administration of an
oral dose of furosemide. The drug peaks in strength after 1 to 2 hours after
it is given orally.
Interactions with other Drugs
One of the most common drug interactions to be aware of is the interaction
between furosemide and vasodilating heart medications (especially the angiotensin
converting enzyme inhibitors such as enalapril and captopril). Furosemide
will decrease circulating blood volume as it causes a depletion in body water.
This means that the kidney (and most other organs) will have a reduced blood
flow to them. The patient’s kidney and electrolyte balance must stabilize
before a vasodilator is added in. If the vasodilator is added too soon, it
too will reduce blood flow to the kidney and the kidney will fail, possibly
permanently. These medications are frequently used together in heart failure
patients. To avoid problems, the patient should be assessed biochemically
with a blood test prior to the addition of the vasodilator. If all is normal,
the vasodilator may be started and renal blood parameters should be rechecked
3 to 5 days later. If they are still normal, then the above kidney issues
should not be a problem; however, should another heart failure crisis arise
and large doses of injectable Lasix be required to resolve it, kidney values
should again be checked 3 to 5 days later.
The airway dilator theophylline may be able to reach higher blood levels
when used in conjunction with furosemide. This means that the theophylline
dose may need to be reduced.
Furosemide is often used concurrently with digitalis derivatives. If furosemide
leads to a significant drop in blood potassium levels, this can increase the
risk of heart rhythms disturbances and other signs of digitalis toxicity.
Furosemide is often used in combination with prednisone to reduce serum
calcium levels. It is possible for this combination of medication to lead
to a reduction in potassium level significant enough to require potassium
supplementation.
Aminoglycoside antibiotics (amikacin, gentamicin etc.) have properties that
make them toxic to the ear and to the kidney. These properties increase with
concomitant use of furosemide.
Concerns and Cautions
Obviously it is best not to use this medication in a dehydrated patient
if water is being restricted.
Weakness or lethargy could be an indicator that blood potassium has dropped
too low. Be sure to inform your veterinarian if your pet seems listless.
Because of the increased calcium excretion brought on by furosemide (i.e.,
an increase in urinary calcium levels), there could be a problem using this
medication in patients with a history of calcium oxalate bladder stone formation.
It is extremely difficult to overdose with this medication. Toxic doses
reported are over 100 times a typical oral dose of medication. It is important
to realize that in the treatment of heart failure (this drug’s primary use),
a crisis can arise at any time. Often giving an extra dose of oral medication
can be a life saving procedure. Be sure you understand what signs you are
to watch for to determine if an extra dose or two should be administered and
when you should definitely rush to the veterinarian’s office.
The loss of water-soluble vitamins or urine can be a problem for patients
receiving diuretics. Prescription diets for heart and kidney disease are vitamin-fortified
with these extra losses in mind. Patients that refuse to eat such prescription
diets should probably receive a vitamin supplement.
Copyright 2004 - 2008 by the Veterinary Information
Network, Inc. All rights reserved.
This work was originally published by Veterinary
Information Network, Inc. (VIN) and is republished with VIN's permission.
