Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Overview
Enalapril is an angiotensin-converting enzyme (ACE) inhibitor widely used in veterinary medicine for the management of cardiovascular and renal diseases in dogs and cats. It is administered as a prodrug and converted in the liver to its active metabolite, enalaprilat.
Enalapril has a relatively slow onset of action (approximately 4–6 hours) but a prolonged duration of effect lasting about 12–14 hours, allowing for once- or twice-daily dosing in clinical practice. It is commonly used as part of long-term therapy rather than for acute stabilization.
Mechanism of Action (MOA): Enalaprilat inhibits angiotensin-converting enzyme, preventing the formation of angiotensin II, a potent vasoconstrictor. This leads to reduced vasoconstriction, decreased aldosterone secretion, and modulation of the renin–angiotensin–aldosterone system (RAAS). As a result, there is decreased vascular resistance, improved cardiac output, and beneficial effects on renal hemodynamics, including reduced glomerular pressure and proteinuria.
Indications
Enalapril is used in dogs and cats primarily for the management of cardiovascular and renal diseases, particularly where modulation of the renin–angiotensin–aldosterone system (RAAS) provides clinical benefit. Its use varies between species and disease stages, and it is often administered as part of a multimodal treatment plan.
- Congestive heart failure (CHF): Used as adjunctive therapy in dogs and cats with CHF to improve hemodynamics and clinical signs. Commonly recommended in dogs with advanced (stage C and D) degenerative mitral valve disease, while its benefit in cats remains less clearly established.
- Chronic kidney disease (CKD) and proteinuria: Used to reduce proteinuria and provide renoprotective effects, particularly in dogs with protein-losing nephropathy. Often combined with dietary management for improved outcomes.
- Systemic hypertension: Considered a first-line option in dogs, especially when associated with CKD. In cats, it is less effective as monotherapy but may be used in combination with other antihypertensive agents (e.g. amlodipine) when additional control is needed.
- Adjunctive cardiovascular modulation: May improve cardiac loading conditions by reducing preload and afterload, contributing to improved cardiac output and exercise tolerance in some patients.
Dosage (Reference)
Dog
In dogs, enalapril is administered orally for long-term management of cardiac and renal diseases. Dosing varies depending on indication, renal status, and clinical response. Dehydration should be corrected before starting therapy.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Congestive heart failure (label) | PO | 0.5 mg/kg | Once daily (q24h) | Increase after 2 weeks if response inadequate. Many clinicians start directly at q12h dosing. |
| Proteinuria (non-azotemic) | PO | 0.25–1 mg/kg | q12h | Most start ≈0.5 mg/kg q12h. Goal: reduce UP:C by ≥50% (ideally <0.5). |
| Proteinuria (azotemic) | PO | 0.25 mg/kg | q12h | Increase after 7 days if stable. Monitor renal parameters closely. |
| Systemic hypertension (CKD) | PO | 0.5 mg/kg | q12h | Titrate to effect. Combine with amlodipine or ARB if needed. |
• Correct dehydration before starting therapy.
• Diuretics should ideally be started at least 1 day before enalapril in CHF cases.
• Twice-daily dosing may improve long-term outcomes compared to once-daily use.
• Monitor renal function, electrolytes (especially potassium), and blood pressure within 1–2 weeks of initiation or dose changes.
• If serum creatinine increases >0.2 mg/dL, consider dose reduction.
• Dose titration should balance proteinuria reduction and renal safety.
Cat
In cats, enalapril is used cautiously, primarily for cardiac disease and proteinuria. Dosing is typically lower and adjusted based on renal function and clinical response. Dehydration should be corrected before therapy.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Congestive heart failure | PO | 0.25–0.5 mg/kg or 1.25–2.5 mg/cat |
q24h | Common practical dosing uses fixed mg/cat dosing. |
| Proteinuria (non-azotemic) | PO | 0.25–0.5 mg/kg | q12-24h | Most start ≈0.25 mg/kg q12h. |
| Proteinuria (azotemic) | PO | 0.25 mg/kg | q12-24h | No fixed adjustment guidelines; monitor closely. |
| Systemic hypertension (adjunct) | PO | 0.5 mg/kg | q24h | Used with amlodipine if BP not controlled or with proteinuria. |
• Start at lower doses in CKD (≈50% reduction if creatinine >2.3 mg/dL).
• Goal in proteinuria: reduce UP:C by ≥50% (ideally <0.4).
• Monitor renal function and potassium closely after initiation and dose changes.
• Recheck labs within 1–2 weeks, then every ~3 months if stable.
• Amlodipine remains first-line for hypertension; enalapril is adjunctive.
Warnings & Precautions
Enalapril should be used with caution in patients with cardiovascular, renal, or fluid balance abnormalities. Careful patient selection and close monitoring are essential to minimize the risk of adverse effects, particularly those affecting renal function and blood pressure.
- Renal insufficiency: Use cautiously in patients with impaired renal function; dose reduction may be required. Monitor creatinine and renal parameters closely.
- Acute kidney injury (AKI): Not recommended in critically ill patients with AKI due to potential reduction in glomerular filtration rate; use only after stabilization.
- Dehydration and sodium depletion: Increased risk of hypotension; correct fluid and electrolyte imbalances before initiating therapy.
- Hypotension risk: May cause clinically significant hypotension, especially during anesthesia or when combined with other hypotensive agents.
- General anesthesia: Dogs receiving enalapril may experience significant hypotension under anesthesia; withholding the drug on the day of anesthesia is advisable.
- Electrolyte abnormalities: Use with caution in patients with hyperkalemia or hyponatremia due to potential worsening of electrolyte imbalance.
- Hematologic and autoimmune disorders: Use cautiously in patients with pre-existing hematologic abnormalities or conditions such as systemic lupus erythematosus (SLE).
- Hypersensitivity: Contraindicated in patients with known hypersensitivity to ACE inhibitors.
- Pregnancy and lactation: Avoid use during pregnancy due to risk of fetal harm; not recommended in nursing animals as the drug is excreted in milk.
Drug Interactions
Enalapril has multiple clinically relevant drug interactions, mainly related to additive hypotension, effects on renal function, and electrolyte disturbances. Careful monitoring and dose adjustment are required when used with the following:
- Anesthetic agents (e.g. isoflurane, propofol, alfaxalone): Increased risk of hypotension, especially during general anesthesia.
- Angiotensin receptor blockers (e.g. telmisartan): Additive RAAS inhibition may lead to hypotension, hyperkalemia, syncope, and acute kidney injury.
- Antacids (aluminum, calcium, magnesium): May reduce oral absorption; administer enalapril at least 2 hours apart.
- Other antihypertensives and vasodilators (e.g. amlodipine, hydralazine, nitrates, prazosin): Increased risk of hypotension; titrate doses carefully.
- Diuretics (e.g. furosemide): May enhance hypotensive effects; monitor blood pressure closely.
- Potassium or potassium-sparing diuretics (e.g. spironolactone): Increased risk of hyperkalemia; combination may be contraindicated in some guidelines.
- NSAIDs (e.g. carprofen, meloxicam): May reduce efficacy of ACE inhibitors and increase risk of nephrotoxicity; monitor renal function.
- Heparin and low-molecular-weight heparins (e.g. enoxaparin, dalteparin): Increased risk of hyperkalemia.
- Digoxin: Serum concentrations may increase; monitoring recommended.
- Lithium: Increased risk of lithium toxicity.
- Corticosteroids: May reduce antihypertensive effect of enalapril.
- Buspirone, cabergoline, opioids, diphenhydramine, doxepin, sildenafil: Additive hypotensive effects may occur.
- Probenecid: May decrease renal excretion of enalapril and enhance its effects.
- Cimetidine: May cause neurologic effects when combined (reported in humans).
- Darbepoetin alfa / epoetin alfa: ACE inhibitors may interfere with erythropoietin response.
- Disopyramide: May enhance hypoglycemic effects.
Side Effects & Overdose
Side Effects
Adverse effects of enalapril in dogs and cats are generally uncommon and often mild, but may involve gastrointestinal, cardiovascular, and renal systems.
- Gastrointestinal effects: Anorexia, vomiting, and diarrhea are the most commonly reported adverse effects.
- Hypotension and weakness: May occur, particularly in dehydrated patients or when combined with other hypotensive drugs.
- Renal effects: Increased BUN and creatinine, especially in patients with pre-existing renal disease.
- Electrolyte changes: Hyperkalemia may develop.
- Polyuria and polydipsia: Reported in some dogs.
- Cats: Lethargy and inappetence may occur.
- Rare effects: Rash, neutropenia, and agranulocytosis (reported in humans; uncommon in veterinary patients).
Overdose
Overdose of enalapril primarily affects cardiovascular function, with hypotension being the most significant concern. Due to the drug’s relatively long duration of action, prolonged monitoring may be required.
- Hypotension: Primary and potentially severe effect.
- Management: Supportive care with IV fluids (e.g. normal saline) to restore blood pressure.
- Decontamination: Gut-emptying protocols may be considered in acute oral overdose.
- Dialysis: The drug can be removed by dialysis.
- Monitoring: Extended monitoring is required due to prolonged drug action.
Key Notes
Practical clinical points that help optimize the safe and effective use of enalapril in dogs and cats:
- Prodrug activation: Enalapril requires hepatic conversion to enalaprilat; clinical response depends on adequate liver function.
- RAAS escape (aldosterone breakthrough): Continued aldosterone secretion may occur despite ACE inhibition, which can limit long-term effectiveness.
- Combination therapy importance: Often used as part of multimodal therapy (e.g. with diuretics or other cardiovascular drugs) rather than as a sole agent.
- Variable benefit in cats: Clinical benefit in feline CHF is less consistent compared to dogs, and its use remains debated.
- Proteinuria management goal: Treatment aims to significantly reduce protein loss rather than completely eliminate it.
- Partial RAAS blockade: ACE inhibition does not fully suppress RAAS activity, which may influence long-term outcomes.
- Limited efficacy as monotherapy (cats): Not highly effective alone for hypertension in cats; better used in combination therapy.
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