1. Clinical Overview
Enalapril is an angiotensin-converting enzyme (ACE) inhibitor used primarily for the treatment of hypertension and heart failure. The 2.5mg strength is a low-dose formulation, often used for initiation of therapy, in heart failure management, or in patients with renal impairment. It is a prodrug that is hydrolyzed in the liver to its active metabolite, enalaprilat.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 1 hour. Peak plasma concentration of enalapril occurs in about 1 hour, but the peak antihypertensive effect may be delayed by 4-6 hours. | 24 hours. The antihypertensive effect is sustained for approximately 24 hours, permitting once-daily dosing. | Approximately 60%. |
2. Mechanism of Action
Enalapril competitively inhibits angiotensin-converting enzyme (ACE or kininase II). This enzyme is responsible for the conversion of angiotensin I to the potent vasoconstrictor angiotensin II. Inhibition results in decreased plasma angiotensin II, leading to vasodilation, reduced aldosterone secretion, and decreased sodium and water retention. It also increases plasma renin activity and decreases aldosterone secretion.
3. Indications & Uses
- Treatment of essential hypertension
- Management of symptomatic heart failure (as adjunctive therapy)
- Asymptomatic left ventricular dysfunction (to prevent progression to overt heart failure)
4. Dosage & Administration
Adult Dosage: Hypertension: Initial dose 5mg once daily, adjusted based on response. Usual range 10-40mg daily in 1-2 divided doses. (Note: 2.5mg is not a standard starting dose for uncomplicated hypertension). Heart Failure/Asymptomatic LV Dysfunction: Initiate at 2.5mg once daily under close medical supervision. Titrate to target maintenance dose of 10-20mg twice daily.
Administration: Can be taken with or without food. Swallow tablet whole with a glass of water. For hypertension, take at the same time each day. In heart failure, the 2.5mg starting dose is critical to avoid hypotension; monitor BP closely for first few hours and after dose increments.
5. Side Effects
Common side effects may include:
- Dizziness, lightheadedness
- Persistent dry, non-productive cough
- Headache
- Fatigue
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Diuretics (especially high-dose loop diuretics) | Potentiates hypotensive effect; risk of first-dose hypotension. | Major |
| Potassium-sparing diuretics (Spironolactone, Amiloride), Potassium supplements | Increased risk of severe hyperkalemia. | Major |
| Non-Steroidal Anti-Inflammatory Drugs (NSAIDs: Ibuprofen, Diclofenac) | May diminish antihypertensive effect and increase risk of renal impairment. | Moderate |
| Lithium | Decreased lithium excretion, leading to lithium toxicity. | Major |
| Aliskiren | Increased risk of hyperkalemia, hypotension, and renal impairment (contraindicated in diabetes/renal impairment). | Major |
| Antidiabetic agents (Insulin, Sulfonylureas) | Enhanced hypoglycemic effect. | Moderate |
| Gold (Sodium aurothiomalate) injections | Increased risk of nitritoid reactions (flushing, nausea, hypotension). | Moderate |
7. Patient Counselling
- DO take your medicine at the same time each day.
- DO get up slowly from sitting or lying down to avoid dizziness.
- DO inform all your doctors and dentists you are on Enalapril.
- DO monitor your blood pressure regularly as advised.
- DONT stop taking the medicine suddenly without consulting your doctor.
- DONT use potassium supplements or salt substitutes without doctor's advice.
- DONT take over-the-counter NSAIDs (like Ibuprofen) for pain without consulting your doctor.
8. Toxicology & Storage
Overdose: Profound hypotension, which may lead to circulatory shock, bradycardia, electrolyte disturbances (hyperkalemia), and acute renal failure.
Storage: Store below 30°C. Protect from light and moisture. Keep the tablet in the blister pack until use. Keep out of reach of children.