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Enalapril Maleate (Enacard, Vasotec)
Revised: May 08, 2024
Published: January 01, 2001

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Vasotec

Available in 2.5 mg, 5 mg, 10 mg, and 20 mg tablets; oral solution 


Enalapril is an “Angiotensin Converting Enzyme Inhibitor” also called an ACE inhibitor or simply an ACEI. Angiotensin Converting Enzyme is an enzyme involved in the final stage of angiotensin II production, angiotensin II being an extremely powerful constrictor of blood vessels. The ACE inhibitor blocks angiotensin II production and is helpful in the treatment of heart failure, high blood pressure, and in urinary protein loss.

Angiotensin II constricts blood vessels. If blood pressure drops (as with serious blood loss or shock), blood pressure must be restored as soon as possible so as to preserve circulation to the heart, brain, and kidneys (the most important organs). This is, in part, done by constricting blood vessels supplying less important body parts and shunting blood flow "centrally" to the important areas. The body possesses the Renin-Angiotensin System, so as to perceive a blood pressure drop and begin life-saving hormone cascades to restore blood pressure quickly.

Why Should We Ever Want to Block Angiotensin II?

As you might guess, an Angiotensin Converting Enzyme Inhibitor blocks the production of angiotensin II. If angiotensin II is such a good thing, why might we want to stop making it? The Renin-Angiotensin system turns out not to be such a good thing when blood pressure drops more chronically as in heart disease.

When blood pressure drops from heart failure, there is no blood loss; the amount of blood is the same as always.  The problem in heart failure is that the heart is not pumping enough blood forward. When the Renin-Angiotensin system centralizes the blood, it effectively confines the same amount of blood to a smaller circulatory route, essentially forcing the already diseased heart to pump blood faster to keep up. This amounts to more work for the already overworked heart.

Enalapril acts as a dilator of blood vessels. This effect opens up circulation peripherally. (If one thinks of the circulation as a roadway system, this is analogous to achieving less highway congestion by opening more side streets). Blood pressure drops to normal and the heart has less work. This makes enalapril a good choice for heart failure as well as a good medication for the treatment of high blood pressure.

Enalapril for Urinary Protein Loss

The effect of enalapril in the kidney bears a special discussion. The kidney consists of millions of tiny filtration units called glomeruli, which are part of larger excretory units called nephrons.

Image of a cross section of a glomerulus
Graphic Courtesy of MarVistaVet.

A tiny blood vessel enters each glomerulus, carrying blood to be filtered, and another tiny blood vessel carries blood out after it has been filtered. ACE inhibitors dilate the exiting vessel without dilating the entering vessel. (Think of a sink full of water with the faucet on and the drain open. As long as the water coming in matches the water draining, the sink stays full. The ACE inhibitor opens the drain further. The sink doesn't empty all the way, but there is less water maintained in the sink than there was before.) This effect amounts to less blood pressure inside the glomerulus (the sink), which means less filtration. When the glomerulus is leaking protein, less filtration means less urinary protein loss, which is good. If the kidney is failing or if the patient is dehydrated, less filtration means less kidney function, which is bad. This makes ACE inhibitor use a bit tricky in heart failure patients where we do not want to treat the heart disease at the expense of the kidneys. For patients without heart failure, where you are treating high blood pressure or renal protein loss, the drop in kidney function that comes with ACE inhibitor use is not significant.

How this Medication is Used

Enalapril is used to treat congestive heart failure; and kidney protein loss (such as glomerulonephritis). It has not been found to be effective in treating high blood pressure.

In heart failure patients, when enalapril is commonly given in conjunction with a diuretic (like furosemide), kidney parameters (BUN, creatinine, and electrolytes) should be measured prior to enalapril use again three to seven days after enalapril therapy has started and periodically thereafter. Kidney function should also be rechecked after any dose change in the heart failure patient.

Enalapril may be given with or without food.

Enalapril is given once or twice daily, and the dose is commonly altered depending on response. 

Do not double up on the next dose if you miss a dose. Simply give the medication when it is remembered and schedule the next dose accordingly.

Side Effects

Nausea, appetite loss, or diarrhea are sometimes seen with this medication. In some patients, these effects are severe enough to preclude the use of enalapril. The situation is usually improved by giving the medication with some food.

More seriously, in some patients, blood pressure can drop too low as the peripheral blood vessels are dilated. This manifests as listlessness and lethargy. Often the dose of enalapril can be modified should this side effect occur. Enalapril may lead to elevations in potassium blood levels. This has potential to be a serious side effect and is one of the reasons electrolytes should be monitored with enalapril use. As mentioned, enalapril use alters kidney blood flow and monitoring to ensure normal kidney function will be needed. Enalapril may lead to elevations in potassium blood levels.

Interactions with Other Drugs

Enalapril is commonly used in combination with diuretics, especially furosemide. In this situation, monitoring kidney parameters is especially important as both these medications serve to decrease blood supply to the kidney as they support the heart. Should a heart failure crisis occur while a patient is on these two medications, it will become necessary to rely on the diuretic to resolve the crisis. High doses of diuretics are typically needed. This can potentially lead to significant kidney failure, although there is no alternative when the heart is failing.

Blood potassium levels can become dangerously high when enalapril is used with other medications that elevate it. Such drugs might include potassium supplements (Polycitra, or Urocit-K) or spironolactone (a potassium-sparing diuretic).

Enalapril is less effective when used with aspirin or other NSAIDs (non-steroidal anti-inflammatory drugs).

Enalapril may increase the risk of hypoglycemia (low blood sugar) when used concurrently with insulin.

The risk of creating an accidental low blood pressure situation is increased when enalapril is used with diphenhydramine (more commonly known as Benadryl®), buspirone, or sildenafil.

Concerns and Cautions

Enalapril is inactive when it is consumed and must be activated into enalaprilat (its active form) by the liver. If the patient’s liver is in failure and cannot reliably perform this conversion, an ACE inhibitor that does not require conversion can be used.

Enalapril probably should not be used in patients with impaired kidney function.

This medication should not be used in pregnancy or lactation.

Store enalapril at room temperature and away from light.

Enalapril should not be used in dehydrated patients.

If a dose of enalapril is accidentally skipped, do not double up on the next dose but give the next dose when it is remembered normally.

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