Enalapril

Introduction Overview

Generic Name

enalapril

Brand Name

Epaned, Vasotec

Dosage Form

intravenous solution (1.25 mg/mL), oral liquid (1 mg/mL), oral tablet (2.5 mg, 5 mg, 10 mg, 20 mg)

Drug Class

Angiotensin Converting Enzyme Inhibitors (ACE inhibitors)

Pharmacokinetics

Absorption:
Enalapril is administered orally or intravenously. When taken orally, enalapril is rapidly absorbed from the gastrointestinal tract, with peak plasma concentrations typically achieved within 1 to 2 hours after dosing. The oral bioavailability of enalapril is approximately 60%, reflective of first-pass metabolism in the liver. Food does not significantly affect the extent of absorption, allowing administration with or without food. Upon absorption, enalapril acts as a prodrug that is converted hepatically to its active metabolite, enalaprilat.

Distribution:
Following absorption and conversion to enalaprilat, the active metabolite exhibits a volume of distribution of about 0.15 L/kg, indicating limited tissue distribution. Enalaprilat binds moderately to plasma proteins (~60%), which influences its pharmacokinetic profile. Distribution into the central nervous system is minimal due to low lipid solubility and active efflux transport, which may help reduce central adverse effects. Enalaprilat accumulates in renal tissue, which may contribute to its therapeutic effects on the kidney.

Metabolism:
Enalapril undergoes rapid hepatic hydrolysis by esterases to form the active diacid metabolite, enalaprilat. This conversion is critical as enalapril itself lacks pharmacologic activity. Enalaprilat exerts ACE inhibition, the principal mechanism of the drug's blood pressure-lowering effects. The metabolism does not involve cytochrome P450 enzymes significantly, reducing potential drug-drug interactions mediated via CYP pathways.

Elimination:
Enalaprilat is predominantly eliminated by the kidneys via glomerular filtration and tubular secretion. The elimination half-life of enalaprilat ranges from 11 to 14 hours in individuals with normal renal function, supporting once or twice daily dosing. In renal impairment, clearance is markedly reduced, necessitating dosage adjustments to prevent accumulation and toxicity. Approximately 60% of administered enalapril dose is excreted as active enalaprilat in the urine. Minimal fecal excretion occurs. Intravenous enalapril has a rapid onset, with clinical effect onset noted within 15 minutes post-administration. Pharmacokinetics are further influenced by patient-specific factors including age, renal and hepatic function.

Dosage Forms

Available Dosage Forms:
- Intravenous solution: 1.25 mg/mL
- Oral liquid (solution): 1 mg/mL
- Oral tablets: 2.5 mg, 5 mg, 10 mg, 20 mg

Dosages for Adults and Adolescents:
- Hypertension (oral tablets or solution):
Initial dose: 5 mg once daily
Maintenance dose: 10 to 40 mg per day, either as a single dose or divided into two doses
Maximum dose: 40 mg daily
- Hypertension in combination with diuretics:
Initial dose: 2.5 mg once daily
Diuretics ideally discontinued 2 to 3 days prior; may be resumed gradually if needed
- Congestive heart failure:
Initial dose: 2.5 mg once daily
Maintenance dose: 2.5 to 20 mg daily in 2 divided doses
Maximum dose: 40 mg daily in 2 divided doses
Typically combined with diuretics and digitalis; titrate dose upward gradually as tolerated
- Left ventricular dysfunction:
Initial dose: 2.5 mg twice daily
Maintenance dose: 20 mg daily in 2 divided doses
Observe patient 2 hours post first dose for blood pressure stabilization
- Parenteral (intravenous) dosing:
1.25 to 5 mg IV over 5 minutes every 6 hours
Clinical response generally seen within 15 minutes after IV administration

Specific Patient Populations:
- Pediatrics (1 month to 17 years) with hypertension:
Initial dose: 0.08 mg/kg/day (up to 5 mg) in 1 to 2 divided doses
Dose adjustments based on response
Maximum studied dose: 0.58 mg/kg/day or 40 mg daily (whichever is less)
Not recommended in neonates or pediatric patients with glomerular filtration rate <30 mL/min
- Renal impairment:
Dosage adjustment required with careful titration due to decreased clearance of enalaprilat
- Hepatic impairment:
Use with caution; monitor for adverse effects
- Elderly:
May require dosage modifications based on renal function and tolerability

Administration Notes:
- Oral tablets and solution may be taken with or without food
- Liquid solution should be measured with supplied dosing device
- Intravenous administration reserved for patients unable to take oral formulations
- Tablets stored at room temperature away from moisture and heat
- Oral solution stored refrigerated; can be stored at room temperature for up to 60 days

Mechanism Of Action

Enalapril is a prodrug that, after oral administration, is metabolized hepatically to enalaprilat, the active angiotensin-converting enzyme (ACE) inhibitor. Enalaprilat competitively inhibits ACE, the enzyme responsible for the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. By blocking this conversion, enalapril decreases levels of angiotensin II, resulting in vasodilation, reduced aldosterone secretion, and decreased sodium and water retention.

At the molecular level, inhibition of ACE reduces angiotensin II-mediated stimulation of AT1 receptors, which are involved in vasoconstriction, aldosterone release, sympathetic activation, and cellular proliferation. This leads to decreased vascular resistance and lower systemic blood pressure. Furthermore, ACE inhibition elevates bradykinin levels by preventing its degradation, contributing to vasodilation through release of nitric oxide and prostacyclin.

Cellular pathways affected include diminished activation of protein kinase C and downstream signaling cascades that promote vascular smooth muscle hypertrophy and fibrosis. The renoprotective effects of enalapril derive from improved glomerular hemodynamics via efferent arteriole vasodilation, reducing intraglomerular pressure and proteinuria.

Clinically, these actions translate to effective treatment of hypertension and heart failure, improving cardiac output and reducing afterload. Enalapril’s mechanism is similar to other ACE inhibitors but differs from angiotensin receptor blockers (ARBs) in targeting the enzyme rather than the receptor. Clinical studies have shown enalapril reduces morbidity and mortality in heart failure and post-myocardial infarction settings, emphasizing its efficacy and role in cardiovascular care.

Pharmacological Actions

Inhibition of angiotensin-converting enzyme leading to decreased angiotensin II levels
Reduction of systemic vascular resistance through vasodilation
Decreased aldosterone secretion resulting in reduced sodium and water retention
Elevation of bradykinin levels promoting vasodilation via nitric oxide and prostacyclin pathways
Improvement in cardiac output by reducing afterload in heart failure
Renoprotective effects by decreasing intraglomerular pressure and proteinuria
Modulation of sympathetic nervous system activity through reduced angiotensin II signaling
Anti-proliferative effects on vascular smooth muscle cells reducing remodeling
Reduction in blood pressure beneficial in hypertension management
Improvement of endothelial function through ACE inhibition
Decreased progression of diabetic nephropathy through renal hemodynamic effects
Mitigation of adverse cardiovascular remodeling post-myocardial infarction
Minimal cytochrome P450 involvement reducing drug interaction risk
Rapid onset of action with intravenous administration
Synergistic effects when combined with diuretics and other antihypertensives

Therapeutic Or Clinical Uses

Treatment of hypertension in adults and children aged 1 month and older
Management of congestive heart failure to improve symptoms and reduce hospitalizations
Prevention and treatment of left ventricular dysfunction following myocardial infarction
Reduction of cardiovascular mortality and morbidity in heart failure patients
Renal protection in diabetic nephropathy and chronic kidney disease
Adjunct therapy in combination with diuretics for better blood pressure control
Reduction of proteinuria in kidney disorders
Use in hypertensive patients with concomitant diabetes mellitus
Acute blood pressure management via intravenous administration in hospitalized patients
Control of blood pressure in patients with cardiac and renal comorbidities
Potential use in slowing progression of certain glomerular diseases
Improvement of endothelial dysfunction in vascular disorders
Treatment of high-renin hypertension particularly responsive to ACE inhibition
Management strategy after heart attacks to prevent remodeling and failure
Off-label use in pediatric hypertension based on clinical evidence

Side Or Adverse Effects

Persistent dry cough due to increased bradykinin levels
Hyperkalemia characterized by elevated blood potassium levels, potentially life-threatening
Hypotension manifesting as dizziness, lightheadedness, and syncope
Angioedema presenting as swelling of face, lips, tongue, or throat, requiring emergency care
Renal impairment or acute kidney injury especially in susceptible patients
Neutropenia or agranulocytosis indicated by low white blood cell counts and infection risk
Gastrointestinal disturbances including nausea, diarrhea, and abdominal pain
Headache and fatigue commonly reported during therapy initiation
Chest pain or palpitations indicative of cardiovascular effects
Elevated liver enzymes and, rarely, hepatic dysfunction or cholestatic jaundice
Skin rash or photosensitivity reactions
Dizziness or syncope especially after first dose or dose escalation
Elevated blood urea nitrogen (BUN) and serum creatinine reflecting renal effects
Muscle cramps or weakness associated with electrolyte imbalance
Rare reports of taste disturbances or oral mucosal irritation

Precautions

Discontinue enalapril immediately if pregnancy is detected due to teratogenic risk
Monitor serum potassium closely, avoiding potassium supplements or salt substitutes unless prescribed
Use with caution in patients with renal impairment or on dialysis; adjust dose accordingly
Avoid combination with aliskiren in diabetic or renal impairment patients due to risk of adverse effects
Screen for history of angioedema prior to initiating therapy; contraindicated if present
Monitor blood pressure regularly to prevent excessive hypotension especially in hypovolemia
Evaluate renal function periodically during treatment to detect potential nephrotoxicity
Exercise caution in patients with low sodium or on restrictive salt diets
Consider close monitoring when combined with diuretics to prevent hypotension
Avoid use within 36 hours before or after sacubitril-containing medications to prevent angioedema
Educate patients to avoid sudden position changes to minimize dizziness and falls
Use cautiously in patients with liver disease as metabolism may be affected
Avoid breastfeeding during enalapril therapy due to potential adverse effects on the infant
Regular blood counts are recommended to monitor for leukopenia in susceptible individuals
Advise patients on signs of allergic reactions and to seek emergency care promptly

Warnings

Contraindicated during pregnancy due to risk of fetal injury or death, especially in second and third trimesters
Increased risk of angioedema that can be life-threatening, particularly in African American patients
Risk of profound hypotension in volume- or salt-depleted patients
Potential for hyperkalemia, especially when used with potassium-sparing diuretics or potassium supplements
Risk of renal function deterioration, particularly in patients with bilateral renal artery stenosis
Avoid use with aliskiren in patients with diabetes or renal impairment due to increased adverse events
Concomitant use with sacubitril is contraindicated due to possible angioedema
May cause neutropenia or agranulocytosis, necessitating regular blood monitoring
NSAIDs may reduce antihypertensive effect and increase risk of renal dysfunction
Hypotension risk heightened in patients undergoing major surgery or general anesthesia
Caution in patients with a history of hypersensitivity to ACE inhibitors
Enalapril may mask certain signs of hypoglycemia in diabetic patients
Inform patients about potential dizziness and advise avoidance of driving or operating machinery if affected
Elevation of liver enzymes indicative of hepatotoxicity requires prompt medical evaluation
Not recommended in neonates or patients with low glomerular filtration rate due to lack of safety data

Contraindication

Known hypersensitivity or allergy to enalapril or any ACE inhibitor
History of angioedema related to previous ACE inhibitor therapy
Second and third trimesters of pregnancy due to fetal toxicity
Concomitant use with sacubitril-containing medications (e.g., Entresto) within 36 hours
Use of aliskiren in patients with diabetes or renal impairment concurrently
Severe bilateral renal artery stenosis due to risk of renal failure
Patients with hereditary or idiopathic angioedema
Use in neonates or pediatric patients with glomerular filtration rate below 30 mL/min
Hypersensitivity to any component of the formulation
Use cautiously or avoid if hypersensitivity to medications with similar chemical structures

Drug Interactions

Potassium-sparing diuretics (e.g., spironolactone, triamterene) increase risk of hyperkalemia
Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, naproxen may reduce antihypertensive efficacy and increase risk of renal impairment
Combination with aliskiren is contraindicated in diabetic or renal impairment patients due to enhanced risk of adverse renal or cardiovascular effects
Sacubitril-containing medications contraindicated within 36 hours due to angioedema risk
Immunosuppressants like sirolimus, everolimus, and temsirolimus may potentiate nephrotoxicity
Concurrent use with diuretics may increase first-dose hypotension risk
Other antihypertensive agents may have additive hypotensive effects
Lithium levels may be elevated increasing risk of lithium toxicity
Use with systemic corticosteroids may attenuate the antihypertensive effect
Use with other drugs affecting renal function like aminoglycosides can increase renal adverse effects
Combination with potassium supplements or salt substitutes increases hyperkalemia risk
Drugs that reduce renal perfusion (e.g., cyclosporine) may exacerbate renal dysfunction
May interfere with diagnostic tests such as renal function markers; interpret results cautiously
Concomitant use with drugs causing bone marrow suppression may amplify neutropenia risk
Concurrent use with certain diabetic medications may require glucose monitoring for hypoglycemia mask

Preparations Of The Drug

Oral tablet formulations available in 2.5 mg, 5 mg, 10 mg, and 20 mg strengths
Oral solution at concentration of 1 mg/mL for weight-based dosing and pediatric use
Intravenous solution at concentration of 1.25 mg/mL for acute administration in hospitalized patients unable to take oral therapy
Tablets are formulated for stable room temperature storage; include proprietary excipients ensuring bioavailability
Oral solution supplied with calibrated measuring device to ensure accurate dosing
IV formulation is preservative-free solution intended for slow intravenous administration
Available branded preparations include Vasotec and Epaned
Manufactured to comply with Good Manufacturing Practices (GMP) and rigorous quality controls
Packaging includes blister packs and bottles depending on formulation and dose form
Formulations designed to ensure stability and shelf life per FDA-approved standards
Oral liquid formulation suitable for both adult and pediatric populations with dosing flexibility
Various preparations adapted for use in different clinical scenarios including hypertension and heart failure
Approved for use in hospital and outpatient settings based on route and indication
Standard labeling includes dosing guidelines, warnings, and storage instructions
Multiple generic versions available ensuring accessibility and cost-effective therapy