Captopril !
The first ACE inhibitor, short-acting and with a sulfhydryl group. Used for high blood pressure, heart failure and diabetic kidney disease.
Updated 2026-11-01
The figure shows captopril bound to the zinc active site of human testicular ACE (the C-domain form).
Mechanism of action
Captopril binds the zinc in the active site of ACE through its sulfhydryl (thiol) group. Less angiotensin II is made, so arterioles dilate, aldosterone falls and the efferent arteriole of the glomerulus relaxes. Bradykinin, which ACE normally degrades, builds up and adds vasodilation, cough and angioedema. Unlike enalapril, it is active as given, not a prodrug.
- Captopril's thiol group binds the zinc of ACE
- Less angiotensin II and aldosterone; bradykinin builds up
- Arterioles dilate and blood pressure falls
Pharmacokinetics
- Absorption
- Rapidly absorbed; food in the stomach reduces absorption, so it is given before meals
- Elimination
- Mainly by the kidneys
- Half-life
- Short, so it is given several times a day
Indications
- High blood pressure Arterial hypertension →
- Heart failure Heart failure →
- Left ventricular dysfunction after myocardial infarction Myocardial Infarction (Heart Attack) →
- Diabetic nephropathy with proteinuria Chronic kidney disease →
Adverse effects
Common
- Dry cough
- Loss or change of taste
- Rash
- Hypotension, especially with the first dose in salt-depleted patients
- Hyperkalaemia
Contraindications
- Pregnancy
- Previous angioedema or hypersensitivity with any ACE inhibitor
- Use with sacubitril/valsartan or within 36 hours of it
- Use with aliskiren in people with diabetes
Key interactions
- Potassium-sparing diuretics, potassium supplements or potassium salt substitutes
- Hyperkalaemia
- NSAIDs, including COX-2 inhibitors
- Weaker effect and risk of kidney injury
- Lithium
- Higher lithium levels and toxicity
What is monitored
- Blood pressure
- Potassium and creatinine
- White cell count, especially with kidney or autoimmune disease
- Urine protein
Administration and safety
- Given by mouth before meals, because food lowers absorption
- The first dose can drop blood pressure sharply in patients on diuretics or salt-depleted: the patient lies down and is observed
- Several «-pril» names look alike: the name is checked on every order
Nursing care
- Check blood pressure before and after the first dose
- Watch for swelling of the lips, tongue or throat and act at once if it appears
- Teach the patient to report fever or sore throat (possible neutropenia)
- Avoid potassium salt substitutes unless prescribed
Pregnancy and breastfeeding
Contraindicated: drugs acting on the renin-angiotensin system can injure and kill the developing fetus; it is stopped as soon as pregnancy is detected.
Test yourself
Think of the answer, then tap the question to see it.
Which chemical group of captopril binds ACE and is linked to its special side effects?
The sulfhydryl (thiol) group; captopril is linked to taste changes, rash and neutropenia.
Why is captopril given before meals?
Food in the stomach reduces its absorption.
Why is captopril given several times a day, unlike lisinopril?
It has a short half-life, while lisinopril acts much longer.
Which blood test is watched with captopril in a patient with lupus and kidney disease?
The white cell count, because of the risk of neutropenia or agranulocytosis.
Related drugs
Related conditions
← Back to the class: ACE inhibitors
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CAPTOPRIL tablet (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.