Enalapril: An ACE inhibitor for hypertension and heart failure

What it is

Enalapril is an angiotensin-converting enzyme inhibitor (ACE inhibitor) that blocks the conversion of angiotensin I into angiotensin II (a powerful vasoconstrictor). It lowers blood pressure, reduces afterload and reduces left ventricular remodelling.

It is first line in hypertension (especially with comorbidities such as diabetes or heart failure). It has a proven kidney benefit in diabetes. It is very well tolerated, although with some characteristic effects (dry cough).

Mechanism of action

It inhibits:

Angiotensin-converting enzyme (ACE): it blocks the conversion of Ang I → Ang II
It reduces systemic and renal vasoconstriction
It reduces aldosterone synthesis, reducing sodium retention

At the counter

When to recommend it

Essential hypertension (first line)
Heart failure with reduced ejection fraction (it reduces mortality)
Kidney protection in diabetes (it reduces proteinuria)
Ischaemic heart disease after a heart attack

When not to

Previous angioedema with an ACE inhibitor
Severe uncontrolled hyperkalaemia
Pregnancy (not advised in the first trimester and contraindicated in the second and third) and breastfeeding
Bilateral renal artery stenosis

What to say at the counter. The line that prevents someone giving up: 'If you get a dry cough that won't go away, it isn't a cold or an allergy: it's the medicine, and your doctor can change it.' And the warning that cannot be missed: if the lips, tongue or throat swell, go to A&E.

Warnings

Important Angioedema: rare but serious. Swelling of the lips, tongue or throat. Stop immediately and seek urgent care.
Important Hyperkalaemia: especially with NSAIDs or potassium-sparing diuretics. Monitor potassium.
Caution Dry cough: common, caused by bradykinin build-up. It is not an allergy; if it is bothersome, the doctor can switch to an ARB.
Caution Low blood pressure: especially with the first dose. Gradual dose increases are recommended.

Pharmacokinetics

Absorption: Around 60% oral absorption, unaffected by food. Enalapril peaks at 1 hour; enalaprilat (the active form) at 3–4 hours.
Distribution: Wide distribution. Plasma protein binding of 50–60%. It crosses the placenta.
Metabolism: Enalapril is a prodrug: it is converted in the liver into enalaprilat (the active form). Enalaprilat is not absorbed orally (it is very polar).
Elimination: Renal elimination of enalaprilat. Half-life of 11 hours.

Enalapril vs losartan (ARB)

Aspect	Enalapril	Losartan (ARB)
Mechanism	Blocks ACE	Blocks the Ang II AT1 receptor
Blood pressure effect	High	Similar
Dry cough	Common	Rare
Kidney protection	Very good	Very good (including diabetic nephropathy)
First line	Yes	Yes (if the ACE inhibitor causes cough)

Enalapril is first line. An ARB if the ACE inhibitor causes an intolerable cough.

Self-assessment

Three questions. When you check your answers you will see the explanation for each one.

What exactly is enalapril's mechanism? It raises blood pressure It inhibits ACE, preventing the conversion of Ang I into Ang II (a vasoconstrictor) It blocks angiotensin II receptors
A patient on enalapril develops a dry cough. What do you tell them? It is an expected effect (bradykinin), not an allergy. If it is tolerable, carry on; if it is bothersome, talk to their doctor about switching to an ARB It is an allergy, stop immediately Take an antihistamine
Why is enalapril especially beneficial in people with diabetes? Because it lowers blood glucose Because it improves insulin Because as well as lowering blood pressure, it reduces proteinuria and protects the kidneys

Training content. It does not replace the summary of product characteristics or clinical judgement.

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