1. Clinical Overview
Enalapril is a prodrug that is hydrolyzed in the liver to its active metabolite, enalaprilat. It is a potent, long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor used primarily in the management of hypertension, heart failure, and asymptomatic left ventricular dysfunction. It reduces the formation of angiotensin II, a potent vasoconstrictor, leading to decreased systemic vascular resistance and blood pressure.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 1 hour; Peak hypotensive effect: 4-6 hours. | Dose-dependent, typically 24 hours for a single dose. | Approximately 60%. |
2. Mechanism of Action
Enalapril is a prodrug de-esterified to enalaprilat, which competitively inhibits angiotensin-converting enzyme (ACE, kininase II). This inhibition prevents the conversion of angiotensin I to the potent vasoconstrictor angiotensin II and decreases the degradation of bradykinin, a potent vasodilator. The result is a reduction in systemic vascular resistance, blood pressure, aldosterone secretion, and cardiac afterload.
3. Indications & Uses
- Essential Hypertension
- Chronic Heart Failure (NYHA Class II-IV)
- Asymptomatic Left Ventricular Dysfunction (to prevent progression to overt heart failure)
4. Dosage & Administration
Adult Dosage: Hypertension: Initial: 5 mg once daily; Usual maintenance: 10-20 mg once daily; Max: 40 mg/day in 1-2 divided doses. Heart Failure/Asymptomatic LV Dysfunction: Initial: 2.5 mg once daily under close medical supervision; Titrate to target dose of 10-20 mg twice daily.
Administration: Can be taken with or without food. Administer at the same time each day. For heart failure, the first dose should be given under supervision if possible due to risk of first-dose hypotension. Tablet should be swallowed whole with a glass of water.
5. Side Effects
Common side effects may include:
- Persistent dry, non-productive cough (up to 20%)
- Dizziness, lightheadedness
- Headache
- Fatigue
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Diuretics (especially loop/thiazide) | Potentiates hypotensive effect; risk of first-dose hypotension. | Major |
| Potassium-sparing diuretics (Spironolactone, Amiloride) | Increased risk of severe hyperkalemia. | Major |
| Potassium supplements / Salt substitutes | Increased risk of hyperkalemia. | Major |
| NSAIDs (e.g., Ibuprofen, Diclofenac) | May attenuate antihypertensive effect and increase risk of renal impairment. | Moderate |
| Lithium | Decreased renal clearance of lithium; risk of lithium toxicity. | Major |
| Aliskiren | Increased risk of hyperkalemia, hypotension, and renal impairment (contraindicated in diabetes/renal impairment). | Major |
| Antidiabetics (Insulin, Sulfonylureas) | Enhanced hypoglycemic effect. | Moderate |
| Allopurinol, Procainamide, Immunosuppressants | Increased risk of hypersensitivity reactions, including Stevens-Johnson Syndrome. | Moderate |
7. Patient Counselling
- DO take your medicine at the same time every day.
- DO inform all your doctors and dentists you are on Enalapril.
- DO get regular blood tests for kidney function and potassium as advised.
- DONT stop taking the medicine suddenly without consulting your doctor.
- DONT take over-the-counter NSAIDs (like ibuprofen) or potassium supplements without asking your doctor.
- DONT use salt substitutes containing potassium.
8. Toxicology & Storage
Overdose: Profound hypotension, which may lead to shock, stupor, bradycardia, electrolyte disturbances (hyperkalemia), and acute renal failure.
Storage: Store below 30°C. Protect from light and moisture. Keep the container tightly closed. Keep out of reach of children.