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Enalapril for Veterinary Use
by Barbara Forney, VMD
Enalapril is an ACE inhibitor that blocks the formation of angiotensin II. It is used as a vasodilator to treat CHF and systemic hypertension. It also is used in animals with chronic renal failure and protein-losing nephropathies.
Enalapril acts as a competitive inhibitor of the ACE responsible for converting angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor and when its concentrations are decreased, peripheral vascular resistance decreases, blood pressure decreases, aldosterone levels are reduced and plasma renin activity is increased.
Dogs and Cats
Enalapril is used in dogs and cats to treat CHF, occult dilated cardiomyopathy and systemic hypertension. In large studies of dogs with moderate to severe heart disease due to mitral regurgitation or dilated cardiomyopathy, enalapril improved survival by greater than 100%, improved quality of life, improved exercise tolerance and decreased pulmonary edema. When treating CHF in dogs, enalapril frequently is combined with other drugs, such as furosemide, spironolactone or a positive inotropic drug. Enalapril may be combined with beta blockers to treat occult dilated cardiomyopathy or systemic hypertension. The value of enalapril to treat degenerative mitral valve disease of small breed dogs is still being investigated. While enalapril may be used to treat mild hypertension in cats, alodipine may be more effective for cats with severe hypertension.
Enalapril is used to treat chronic renal failure and proteinuria. By blocking the production of angiotensin II, enalapril causes vasodilation of the glomerular efferent arterioles, decreases intraglomerular pressure and reduces the glomerular filtration rate (GFR). The improvement in renal function is postulated to be due to the anti-hypertensive effect, the reduction in mesangial cell proliferation and renal vasodilation, which causes a decrease in renal-filtration pressure and decreased proteinuria.
Enalapril Side Effects
The most common side effects are hypotension, weakness, lethargy, GI upset (anorexia, vomiting or diarrhea), hyperkalemia and renal dysfunction. Although enalapril is used to treat chronic renal failure, there are instances of mild to moderate reversible renal failure, which may be precipitated by volume depletion superimposed on dilatation of the efferent arterioles.
- Patients receiving enalapril should be monitored regularly for arterial blood pressure, renal function and serum electrolytes.
- If an animal shows adverse effects due to enalapril, withdrawal followed by a lower dose or a longer dosing interval may be helpful.
- Severely azotemic animals should start with once a day dosing while being monitored closely for renal function.
- Some dogs appear to be dependent on the effects of angiotensin II for maintaining GFR. While this is unusual, this subpopulation will not tolerate ACE inhibitor drugs.
- Diuretics and other vasodilators may increase the incidence of hypotension or hyperkalemia. Careful monitoring and adjustment of drug therapies may be necessary to reach the optimal therapeutic balance.
- NSAIDs, including aspirin, should be avoided in animals on enalapril.
If an overdose is recognized promptly, gut emptying protocols should be attempted. Hypotension is the most clinically significant problem when managing an overdose of enalapril. Hospitalization with volume expansion, blood pressure monitoring and supportive care may be necessary.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
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