ACE inhibitors are among the most important life-saving cardiovascular drugs. They form the backbone of treatment for hypertension, heart failure, diabetic nephropathy, and post-myocardial infarction care. For MBBS, nursing, pharmacy, and exam aspirants, ACE inhibitors are extremely high-yield—especially questions on mechanism, side effects, and contraindications.
What Are ACE Inhibitors?
ACE inhibitors block the enzyme Angiotensin-Converting Enzyme (ACE), which converts angiotensin I → angiotensin II.
Angiotensin II is a powerful:
- Vasoconstrictor
- Aldosterone stimulator
- Promoter of cardiac and renal remodeling
Blocking ACE therefore reduces blood pressure and protects organs.
Renin–Angiotensin–Aldosterone System (RAAS): Quick Review
| Step | Action |
|---|---|
| Renin | Angiotensinogen → Angiotensin I |
| ACE | Angiotensin I → Angiotensin II |
| Angiotensin II | Vasoconstriction + Aldosterone release |
| Aldosterone | Sodium & water retention |
ACE inhibitors interrupt this pathway.
Mechanism of Action (Very High-Yield)
Step-by-Step
1. ACE inhibitors block angiotensin I → angiotensin IIOne-Line Exam Answer
ACE inhibitors lower BP and protect heart and kidneys by reducing angiotensin II and increasing bradykinin
Why ACE Inhibitors Are Special
Unlike many BP drugs, ACE inhibitors:
- Reduce mortality in heart failure
- Slow diabetic nephropathy
- Prevent post-MI remodeling
They are disease-modifying, not just symptom-relieving.
Individual Drugs Explained
Enalapril
Key Features
- Prodrug (converted to enalaprilat)
- Available in oral and IV form
Uses
- Hypertension
- Heart failure
- Post-MI patients
Exam Pearl
✔ Enalaprilat is used IV in emergencies
Ramipril
Key Features
- Long-acting
- Strong cardioprotective effects
Uses
- Hypertension
- Heart failure
- Post-myocardial infarction
- High-risk cardiovascular patients
Exam Pearl
✔ Proven mortality reduction in high-risk patients
Lisinopril
Key Features
- Not a prodrug
- Long duration of action
Uses
- Hypertension
- Heart failure
- Diabetic nephropathy
Advantage
✔ Predictable pharmacokinetics
Captopril
Key Features
- Short-acting
- Contains sulfhydryl (-SH) group
Uses
- Hypertension
- Heart failure
- Hypertensive emergencies (short-term)
Unique Side Effects (Exam Favorite)
- Metallic taste
- Skin rash
- More adverse effects than newer ACE inhibitors
High-Yield Comparison Table
| Drug | Prodrug | Duration | Special Feature |
|---|---|---|---|
| Enalapril | Yes | Moderate | IV form available |
| Ramipril | Yes | Long | Strong CV protection |
| Lisinopril | No | Long | Stable kinetics |
| Captopril | No | Short | Metallic taste |
Clinical Uses of ACE Inhibitors
Cardiovascular
- Hypertension (first-line)
- Heart failure (HFrEF)
- Post-myocardial infarction
Renal
- Diabetic nephropathy
- Proteinuric kidney disease
Endocrine / Metabolic
- Hypertension in diabetes
- Metabolic-friendly BP control
ACE Inhibitors in Heart Failure (Exam Gold)
Benefits include:
- ↓ Mortality
- ↓ Hospitalization
- ↓ Ventricular remodeling
ACE inhibitors are mandatory unless contraindicated.
Adverse Effects (Very Important)
Common
- Dry cough (due to bradykinin)
- Hypotension (first dose effect)
- Dizziness
Serious
- Angioedema (life-threatening)
- Hyperkalemia
- Acute kidney injury (in renal artery stenosis)
Contraindications (Must Remember)
❌ Pregnancy (teratogenic)
❌ Bilateral renal artery stenosis
❌ History of angioedema
❌ Severe hyperkalemia
ACE Inhibitors vs ARBs (Quick Contrast)
| Feature | ACE Inhibitors | ARBs |
|---|---|---|
| Cough | Common | Rare |
| Angioedema | Possible | Very rare |
| Mortality benefit | Yes | Yes |
| First choice | Yes | If ACEI intolerant |
Important Exam-Oriented Pearls
- ACE inhibitors increase bradykinin
- Cough ≠ allergy → switch to ARB
- Check serum creatinine & potassium
- Initial mild creatinine rise is acceptable
- Never use in pregnancy
Easy Memory Tricks
Mechanism
“ACE → Angiotensin Cut & Edema (bradykinin) builds”
Side Effects
“CAPTOPRIL causes CAPricious taste & rash”
Pregnancy
“-pril = prohibited in pregnancy”
FAQs
1. What is the main action of ACE inhibitors?
They block angiotensin II formation, causing vasodilation and reduced aldosterone.
2. Why do ACE inhibitors cause cough?
Due to increased bradykinin levels.
3. Which ACE inhibitor is short-acting?
Captopril.
4. Which ACE inhibitor is not a prodrug?
Lisinopril and captopril.
5. Can ACE inhibitors be used in pregnancy?
No, they are contraindicated.
6. Why are ACE inhibitors good in diabetes?
They protect kidneys and reduce proteinuria.
7. What electrolyte abnormality occurs with ACE inhibitors?
Hyperkalemia.
8. Which ACE inhibitor is available IV?
Enalaprilat.
9. What is angioedema?
Rapid swelling of lips, face, or airway—medical emergency.
10. Are ACE inhibitors first-line in heart failure?
Yes, unless contraindicated.
