Enalapril maleate

Tablets for Heart Failure in Dogs.

Federal (U.S.A.) law restricts this drug to use by or on the order of a licensed veterinarian.

Enalapril maleate contains the maleate salt of enalapril, a derivative of two amino-acids, L-alanine and L-proline. Following oral administration, enalapril (a prodrug) is rapidly absorbed and then hydrolyzed to enalaprilat, which is a highly specific, long-acting, non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor. ACE is a dipeptidase that catalyzes the conversion of angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor which stimulates aldosterone secretion by the adrenal cortex. Inhibition of ACE results in decreased plasma angiotensin II levels, which leads to decreased vasopressor activity and to decreased aldosterone secretion. ACE inhibitors are neurohormonal antagonists that are balanced (both arterial and venous) vasodilators resulting in decreased preload and afterload. The overall effect of enalapril treatment is a decrease in the workload of the heart resulting from both arterial and venous dilation and decreased fluid retention.
Enalapril maleate is indicated for the treatment of mild, moderate, or severe [modified NYHA Class II(a), III(b), IV(c)] heart failure in dogs.

a) A dog with modified New York Heart Association Class II heart failure develops fatigue, shortness of breath, coughing, etc., which becomes evident when ordinary exercise is exceeded.
b) A dog with modified New York Heart Association Class III heart failure is comfortable at rest, but exercise capacity is minimal.
c) A dog with modified New York Heart Association Class IV heart failure has no capacity for exercise and disabling clinical signs are present at rest.
Dosage and administration:
The recommended starting dose of Enalapril maleate in dogs is 0.5 mg/kg administered orally s.i.d. (once daily) with or without food. In the absence of an adequate clinical response within 2 weeks, the dosing frequency may be increased to b.i.d. (twice daily) for a total daily dose of 1 mg/kg. The clinical response should be evaluated based on criteria that include a physical exam, degree of pulmonary congestion/edema demonstrated on chest radiographs, the level of activity displayed by the dog, and exercise tolerance. This dose increase may be initiated earlier if indicated by worsening signs of heart failure such as increased pulmonary congestion/edema, decreased level of activity or decreased exercise tolerance. Dogs should be observed closely for 48 hours following initial dosing or after increasing the dosing frequency for clinical signs consistent with hypotension such as weakness or depression. In addition, renal function should be monitored closely both before and 2 to 7 days after starting treatment with Enalapril maleate.
Dogs should be receiving standard heart failure therapy including stable doses of furosemide, with or without digoxin. Dogs should be receiving a stable dose of furosemide for at least two days before treatment with Enalapril maleate and, if included in the treatment regimen, a stable dose of digoxin should be administered for four days prior to initiation of therapy with Enalapril maleate.
In the event that clinical signs of hypotension or reduced kidney function occur or that a significant increase in the concentration of blood urea nitrogen (BUN) and/or serum creatinine (CRT) over pretreatment levels is detected, refer to the PRECAUTIONS section for appropriate response.

Case Management:
Because of the complexity of the treatment of dogs with heart failure, it may be necessary to consult with a veterinary cardiologist or internist.
Enalapril maleate is indicated for the treatment of dogs in heart failure due to mitral regurgitation (chronic valvular disease) and/or reduced ventricular contractility (dilated cardiomyopathy). Conjunctive therapy which should be used with Enalapril maleate consists of furosemide and digoxin in the treatment of dilated cardiomyopathy, and furosemide with or without digoxin in the treatment of chronic valvular disease. Enalapril maleate acts to ameliorate the clinical signs associated with heart failure rather than to reverse the degeneration of the atrioventricular valves or to resolve the underlying myocardial disease in dilated cardiomyopathy. Efficacy against heart failure caused by etiologies other than mitral regurgitation or dilated cardiomyopathy has not been demonstrated.

Diagnosis and Monitoring:
As the heart failure disease syndrome is complex and usually requires multiple therapies, it is important to establish an accurate diagnosis. Diagnosis is based on procedures such as a complete physical examination, auscultation, electrocardiography, radiography, echocardiography, and pertinent laboratory tests, including hematology, clinical chemistry and urinalysis. Client observations are important in the successful monitoring of treatment. During long-term therapy, dogs were evaluated approximately every three months unless conditions required that individual dogs be monitored more frequently. For dogs receiving digoxin therapy, serum digoxin concentrations were also measured at these times or if indicated by inappetence, vomiting or diarrhea.

Concomitant Therapy:
As established during clinical studies, Enalapril maleate may be used concomitantly with other therapy, which may include furosemide, digoxin, antiarrhythmics, beta-blockers, bronchodilators and cough suppressants, for the treatment of heart failure in dogs. Enalapril maleate may be used in combination with sodium-restricted diets. The safety of Enalapril maleate when used concomitantly with other cardiovascular drugs (e.g., vasodilators) has not been established.

Renal Function:
 The use of diuretics is considered an important part of therapy for heart failure. The result is that some dogs are kept in a volume-depleted (slightly dehydrated) state to control their heart failure. If cardiac function is impaired, the relative volume of blood reaching the kidneys is decreased, leading to pre-renal azotemia. If the renal flow, already impaired by heart failure, is further compromised by volume depletion, pre-renal azotemia is exacerbated. In normal dogs, pre-renal azotemia is confirmed by examination of urine specific gravity; however, administration of diuretics renders this diagnostic test invalid.

Clinical manifestations of the heart failure syndrome may include pre-renal azotemia, which is defined as an elevation in BUN and/or CRT with a normal urinalysis. This usually results from decreased renal blood flow induced by impaired cardiovascular performance. Compounds that cause volume depletion, such as diuretics or angiotensin converting enzyme inhibitors, may lower systemic blood pressure, which may further decrease renal perfusion and lead to the development of azotemia. Dogs with no detectable renal disease may develop minor and transient increases in BUN or CRT when Enalapril maleate is administered concomitantly with a furosemide.

1. If clinical signs of hypotension or signs of azotemia develop, the dose of furosemide should be reduced first.
2. If signs of azotemia continue, it may be necessary to further reduce the daily dose of the furosemide or discontinue administration.
3. If there is still no improvement in clinical signs, dosing with Enalapril maleate should be decreased in frequency to once daily if being given twice daily, or discontinued.
4. Renal function (BUN and CRT) should be monitored periodically until it returns to pretreatment levels.
5. Appropriate fluid therapy, carefully monitored, should be considered if the above steps do not reverse azotemia.

Use in Breeding Animals: Safety of enalapril in breeding dogs has not been established. Use of enalapril in pregnant bitches is not recommended.
Keep this and all drugs out of the reach of children.

Chemistry: Enalapril maleate tablets contain the maleate salt of enalapril, the ethyl ester of the parent diacid, enalaprilat. Enalapril maleate is chemically described as (S)-1(N-(1-(ethoxycarbonyl)-3-phenylpropyl)-L-alanyl)-L-proline, (Z)-2-butenedioate salt (1:1). The empirical formula is C20H28N2O5?C4H4O4.

PROTECT FROM MOISTURE. Store below 30°C (86°F) and avoid transient temperatures above 50°C (122°F). When not in use keep container tightly closed. Bottle contains dessicant. 

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