Enalapril is a blood pressure-lowering medicine that belongs to a group of drugs called ACE inhibitors. It is one of the oldest and most extensively studied ACE inhibitors and is on the WHO Model List of Essential Medicines. It is used to treat high blood pressure (hypertension), heart failure and to protect the kidneys in patients with diabetes. Enalapril is a prodrug, converted in the liver to its active form (enalaprilat) after absorption.

Drug Class

ACE stands for angiotensin-converting enzyme. This enzyme is found in the lungs and blood vessels and its job is to produce a chemical called angiotensin II that is a powerful blood vessel constrictor. When angiotensin II is produced in high amounts, it tightens blood vessel walls and raises blood pressure. ACE inhibitors like enalapril block this enzyme. When the enzyme is blocked less angiotensin II is produced, blood vessels relax & widen and blood pressure falls.

How Enalapril Lowers Blood Pressure

Enalapril works in two main ways. By blocking ACE enalapril reduces the production of angiotensin II, which causes blood vessels to relax and widen. Blocking ACE also reduces the breakdown of bradykinin, which dilates blood vessels further. Enalapril also reduces aldosterone (a hormone that causes the kidneys to retain salt and water) gently reducing the amount of fluid in the bloodstream. The blood pressure-lowering effect begins within 1 hour of taking a dose and peaks at 4 to 6 hours.

Medical Uses

Doctors prescribe enalapril for:

• High blood pressure (hypertension): Used as a first-line or add-on treatment; particularly useful in patients who also have diabetes, heart failure or kidney disease

• Heart failure: Enalapril reduces the workload on the heart by widening blood vessels and reducing fluid retention

• Diabetic kidney disease (diabetic nephropathy): ACE inhibitors reduce the pressure inside the tiny kidney filters (glomeruli), slowing the progression of kidney damage caused by diabetes; this benefit applies even in patients with normal blood pressure

• Left ventricular dysfunction: Used after a heart attack to prevent progression to full heart failure in patients with reduced heart pumping capacity

• Hypertension in children: One of the few antihypertensive drugs with safety data in children, including those with kidney-related hypertension.

Side Effects 

Common side effects are:

• Dry, persistent cough is the most common side effect

• Dizziness or lightheadedness when standing up quickly (postural hypotension)

• Fatigue 

• Headache 

• Nausea and mild abdominal discomfort 

• Elevated potassium (hyperkalaemia) particularly in patients with kidney disease or those taking potassium supplements.

Serious Side Effects

Angioedema is the most serious side effect of enalapril. It causes sudden swelling of the face, lips, tongue or throat - the result of bradykinin accumulation. Throat swelling can obstruct breathing and is a medical emergency. Angioedema can occur at any point during treatment. Any patient who develops sudden facial or throat swelling while on enalapril should stop the drug immediately and seek emergency medical care. 

Kidney function changes are expected at the start of enalapril treatment - a small rise in serum creatinine (up to 30% from baseline) is acceptable and reflects the intended protective mechanism. A rise above 30% or a sudden large rise in creatinine may indicate renal artery stenosis and requires reassessment.

Who Should Not Take Enalapril?

• In pregnant women enalapril is strictly contraindicated in pregnancy as ACE inhibitors cause serious foetal kidney damage in the second and third trimesters (foetal renal dysgenesis, oligohydramnios, limb contractures and neonatal death)

• History of ACE inhibitor-induced angioedema

• Bilateral renal artery stenosis 

• Severe hyperkalaemia (very high potassium levels)

• Patients on sacubitril/valsartan (Entresto) as combining with an ACE inhibitor significantly increases angioedema risk; a 36-hour washout is required between stopping sacubitril/valsartan and starting an ACE inhibitor.

Drug Interactions That Matter

Key interactions are:

Aliskiren 

Antidiabetic drugs

• NSAIDs like ibuprofen, diclofenac, naproxen

• Other antihypertensive medicines

• Potassium-sparing diuretics like spironolactone, amiloride

• Potassium supplements 

• Lithium

• Sacubitril/Valsartan

• Trimethoprim. 

Enalapril During Pregnancy - Important Warning

Enalapril must never be used during pregnancy. In the second and third trimesters, it causes foetal renal dysgenesis (the baby's kidneys fail to develop properly) leading to oligohydramnios, foetal limb contractures and can cause death. Women of childbearing age who are prescribed enalapril must use effective contraception and switch to a pregnancy-safe antihypertensive if they plan to conceive or become pregnant. Enalapril is also present in breast milk so breastfeeding is generally not recommended.

Enalapril vs Lisinopril vs Ramipril - Key Differences

All three are ACE inhibitors and share the same mechanism, core benefits, and safety concerns including the cough and angioedema risk. Enalapril is often given twice daily whereas lisinopril and ramipril are once daily. Enalapril and ramipril are prodrugs converted in the liver to their active forms; lisinopril is active as taken. Ramipril has the strongest evidence for post-heart attack cardiovascular protection whereas enalapril has the strongest historical heart failure evidence. All three are on India's National List of Essential Medicines.

FAQs

1. What is enalapril used for?

   Enalapril is used to treat high blood pressure (hypertension), heart failure and to protect the kidneys in patients with diabetes. It is also used after a heart attack to prevent progression to full heart failure. 

2. Why does enalapril cause a dry cough?

   ACE inhibitors like enalapril block the enzyme that breaks down bradykinin - a chemical that accumulates in the throat and lungs. When bradykinin builds up it irritates the airways, causing a dry, persistent, tickling cough. The cough is not dangerous but does not improve over time and it resolves only when the drug is stopped. 

3. Is enalapril safe for diabetic patients with kidney disease?

   Yes enalapril is particularly beneficial for diabetic patients with kidney disease. ACE inhibitors reduce the pressure inside the kidney's tiny filtering units (glomeruli), slowing the progression of diabetic nephropathy and reducing protein leakage in the urine. This benefit is independent of blood pressure and ACE inhibitors protect the kidney even in diabetic patients with normal blood pressure. Potassium levels and creatinine must be monitored, as enalapril can raise potassium and cause a small rise in creatinine at the start of treatment.

4. What is angioedema and can enalapril cause it?

   Angioedema is sudden swelling of the face, lips, tongue or throat that is caused by bradykinin accumulation, which makes blood vessels leak fluid into surrounding tissue. Throat swelling can be life-threatening. Angioedema can occur at any point during treatment, not only at the start. Any patient who develops sudden facial swelling or difficulty breathing must stop the drug immediately and seek emergency medical care. Once angioedema has occurred, all ACE inhibitors are permanently contraindicated.

5. Can enalapril be stopped suddenly?

   Enalapril can be stopped without tapering as there is no withdrawal syndrome. However, blood pressure will rise again after stopping, which can be dangerous in patients with hypertension or heart failure. Stopping enalapril in heart failure patients can cause rapid deterioration. Any decision to stop enalapril should involve the treating doctor, who will arrange an alternative drug or monitoring plan before discontinuation.

6. Is enalapril safe during pregnancy?

   Enalapril is strictly contraindicated in pregnancy. In the second and third trimesters, enalapril causes the baby's kidneys to fail to develop properly (foetal renal dysgenesis), leading to dangerous reduction in amniotic fluid (oligohydramnios), foetal limb deformities and potentially death. Women of childbearing age prescribed enalapril must use effective contraception and switch to a safe alternative like methyldopa, nifedipine or labetalol as soon as pregnancy is confirmed or planned.

7. Can enalapril raise potassium levels?

   Yes enalapril reduces aldosterone, a hormone that normally tells the kidneys to excrete potassium. When aldosterone is reduced, the kidneys retain more potassium, raising potassium levels in the blood (hyperkalaemia). This is usually mild in patients with normal kidney function. It becomes more important in patients with kidney disease, diabetes or those taking potassium-sparing diuretics or NSAIDs. 

8. What is the difference between enalapril and other ACE inhibitors?

   All ACE inhibitors share the same main benefits and risks including the dry cough and angioedema. Practical differences include dosing frequency (enalapril is often twice daily; lisinopril and ramipril are once daily), and prodrug status (enalapril and ramipril are converted in the liver to active forms; lisinopril is not). 

References

1. CONSENSUS Trial Study Group. Effects of enalapril on mortality in severe congestive heart failure. N Engl J Med. 1987;316(23):1429–35. https://doi.org/10.1056/NEJM198706043162301

2. The SOLVD Investigators. Effect of enalapril on survival in patients with reduced left ventricular ejection fractions and congestive heart failure. N Engl J Med. 1991;325(5):293–302. https://doi.org/10.1056/NEJM199108013250501

3. Israili ZH, Hall WD. Cough and angioneurotic edema associated with angiotensin-converting enzyme inhibitor therapy. Ann Intern Med. 1992;117(3):234–42. https://doi.org/10.7326/0003-4819-117-3-234

4. Lewis EJ, Hunsicker LG, Bain RP, Rohde RD. The effect of angiotensin-converting-enzyme inhibition on diabetic nephropathy. N Engl J Med. 1993;329(20):1456–62. https://doi.org/10.1056/NEJM199311113292004

5. Yusuf S, Sleight P, Pogue J, et al. Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients (HOPE trial). N Engl J Med. 2000;342(3):145–53. https://doi.org/10.1056/NEJM200001203420301