Captopril is the first orally active ACE inhibitor (Angiotensin-Converting Enzyme inhibitor), introduced in the late 1970s. It revolutionized the management of hypertension, heart failure, and diabetic nephropathy.
Like all drugs, it carries adverse effects and contraindications that clinicians must recognize. A simple way to remember them is through the CAPTOPRIL mnemonic.
Mechanism of Action
ACE inhibitors block the conversion of angiotensin I → angiotensin II.
This reduces:
- Vasoconstriction → lowers blood pressure.
- Aldosterone secretion → decreases sodium and water retention.
Therapeutic Uses of Captopril
- Hypertension – first-line in many patients.
- Congestive Heart Failure (CHF) – reduces afterload and improves survival.
- Post-Myocardial Infarction – prevents ventricular remodeling.
- Diabetic Nephropathy – slows progression of kidney disease.
- Chronic Kidney Disease (CKD) with proteinuria – protective effect.
Side Effects – CAPTOPRIL Mnemonic
C – Cough / C1 Esterase Deficiency
- Persistent dry cough in up to 20% of patients.
- Due to increased bradykinin and substance P.
- Contraindicated in hereditary angioedema related to C1 esterase deficiency.
A – Angioedema / Agranulocytosis
- Swelling of lips, tongue, face, airway obstruction → rare but potentially fatal.
- Agranulocytosis: rare, but requires monitoring in patients with collagen vascular disease.
P – Proteinuria
- Seen in high doses or in patients with kidney disease.
- Monitoring of urine protein is recommended.
T – Taste Change (Dysgeusia)
- Metallic or salty taste.
- Reversible upon discontinuation.
O – Orthostatic Hypotension
- Particularly after the first dose (“first-dose hypotension”).
- Common in patients on diuretics or with volume depletion.
P – Pregnancy Contraindication
- Teratogenic – causes fetal renal dysgenesis, oligohydramnios, skull hypoplasia.
- Contraindicated in all trimesters.
R – Renal Artery Stenosis Contraindication
- Bilateral renal artery stenosis → risk of acute renal failure due to reduced GFR.
- Monitor renal function and creatinine.
I – Increased Renin
- Reflex increase in plasma renin activity due to interruption of feedback loop.
L – Leukoplakia / Liver Toxicity
- Rare mucosal changes and hepatotoxicity.
- Reversible with drug discontinuation.
Other Common Side Effects
- Hyperkalemia (due to reduced aldosterone).
- Fatigue, dizziness.
- Rash (sulfhydryl group in captopril is associated with skin reactions).
Contraindications
- Pregnancy (all trimesters).
- History of angioedema.
- Bilateral renal artery stenosis.
- Severe hyperkalemia.
Drug Interactions
- NSAIDs – blunt antihypertensive effect.
- Potassium-sparing diuretics – risk of hyperkalemia.
- Lithium – risk of lithium toxicity.
- Diuretics – worsen first-dose hypotension.
Monitoring Parameters
- Blood pressure response.
- Serum creatinine and potassium.
- Urine protein levels in long-term therapy.
- Watch for signs of cough or angioedema.
Quick Reference Table – CAPTOPRIL Side Effects
| Letter | Effect |
|---|---|
| C | Cough / C1 esterase deficiency |
| A | Angioedema / Agranulocytosis |
| P | Proteinuria |
| T | Taste change |
| O | Orthostatic hypotension |
| P | Pregnancy contraindication |
| R | Renal artery stenosis contraindication |
| I | Increased renin |
| L | Leukoplakia / Liver toxicity |
FAQs
1. Why does captopril cause cough?
Because it increases bradykinin levels in the lungs, leading to irritation.
2. Can captopril be given in pregnancy?
No, it is contraindicated due to severe teratogenic effects.
3. Which is safer for chronic use – captopril or newer ACE inhibitors?
Newer ACE inhibitors (enalapril, lisinopril) have longer half-lives and fewer sulfhydryl-related side effects, making them more convenient.
4. What to do if a patient develops angioedema on captopril?
Stop the drug immediately, provide airway support, and consider switching to an ARB (with caution).
5. Is hyperkalemia a risk with captopril?
Yes, due to reduced aldosterone secretion, potassium can rise dangerously in some patients.
