Atlas Three · Medicine · Modern Pharmacology

ACE Inhibitors

Angiotensin-converting enzyme inhibitors — competitive blockers of ACE that interrupt the RAAS cascade, lowering angiotensin II, reducing aldosterone, and potentiating bradykinin.

First-line for HFrEF, hypertension, diabetic nephropathy, and post-MI LV dysfunction. CONSENSUS (1987) to HOPE (2000) — four decades of mortality benefit across cardiovascular and renal disease.

~27%Mortality ↓ in HFrEF
1987CONSENSUS Trial
10+Agents in Class
First-lineHFrEF / HTN / CKD
Medicine Atlas · Cardiovascular · RAAS Inhibitors

ACE Inhibitors

Class: ACE Inhibitor  ·  Antihypertensive  ·  Renoprotective  |  Route: Oral (most agents)  |  Status: First-line HFrEF, HTN with CKD/DM, diabetic nephropathy, post-MI

Competitive inhibitors of angiotensin-converting enzyme (ACE/kininase II) — the enzyme that converts angiotensin I to the potent vasoconstrictor angiotensin II. ACE inhibition also prevents bradykinin degradation, potentiating vasodilation. Net result: reduced afterload, preload, aldosterone-mediated sodium retention, and adverse ventricular remodelling. Landmark RCTs from CONSENSUS (1987) through HOPE (2000) established that ACEi reduce all-cause mortality in HFrEF by ~27% and confer cardiovascular protection broadly — including in patients with no heart failure but high vascular risk.

ACEi angiotensin-converting enzyme inhibitors captopril enalapril lisinopril ramipril

Overview

ACE inhibitors (angiotensin-converting enzyme inhibitors) are a class of drugs that competitively inhibit ACE (kininase II, EC 3.4.15.1) — the enzyme responsible for converting the inactive decapeptide angiotensin I into the potent vasoconstrictor angiotensin II in the renin-angiotensin-aldosterone system (RAAS). ACE also degrades bradykinin — a vasodilatory peptide — so ACE inhibition potentiates bradykinin effects, producing additional vasodilation (and the characteristic dry cough side effect via bradykinin-stimulated pulmonary C-fibres).

ACE inhibitors are among the most impactful drug classes in the history of cardiovascular medicine. Their landmark trials — beginning with CONSENSUS (1987) and SOLVD (1991) — established that RAAS blockade reduces all-cause mortality in heart failure with reduced ejection fraction (HFrEF) and transformed heart failure therapy. They are now first-line therapy for:

  • Heart failure with reduced ejection fraction (HFrEF, EF <40%): Class I, Level A recommendation in all major guidelines
  • Hypertension: Particularly with concurrent CKD, diabetes, or HF — where RAAS blockade confers organ-protective benefits beyond blood pressure lowering
  • Diabetic nephropathy: Reduce proteinuria 30–50% and slow CKD progression independent of BP lowering
  • Post-myocardial infarction with LV dysfunction (LVEF <40%): Prevent progressive adverse remodelling and reduce mortality (SAVE, AIRE trials)
  • High cardiovascular risk (secondary prevention): HOPE trial established benefit even in patients without HF or known LV dysfunction

Mechanism of Action

RAAS Cascade and ACE Inhibition

  Angiotensinogen (liver)
          │
          │  Renin (JG cells, kidney) — stimulated by ↓BP, ↓Na⁺, sympathetic activity
          ▼
  Angiotensin I (10 amino acids)
          │
          │  ACE (lung, vascular endothelium) ← ACE INHIBITOR BINDS HERE
          │  (zinc metalloprotease, EC 3.4.15.1)
          ▼
  Angiotensin II (8 amino acids)
          │
          ▼
  AT1 receptor → vasoconstriction · aldosterone release · norepinephrine release
                   sympathetic activation · cardiac fibrosis · LV remodelling

  Bradykinin → (normally degraded by ACE) → ACEi allows accumulation
                  → eNOS activation → NO → vasodilation
                  → pulmonary C-fibre stimulation → dry cough (25–40%)

ACE inhibitors bind the zinc-containing active site of ACE with high affinity, blocking angiotensin I cleavage. This produces a cascade of beneficial haemodynamic and structural effects:

  1. ↓Angiotensin II → less AT1 receptor stimulation → arterial and venous vasodilation (↓afterload, ↓preload) → ↓cardiac work
  2. ↓Aldosterone → less renal Na⁺/H₂O retention → ↓blood volume → ↓preload; renal K⁺ retention (risk of hyperkalaemia)
  3. ↑Bradykinin → bradykinin-mediated vasodilation (eNOS activation → NO → vasodilation); also responsible for the bradykinin-mediated cough (25–40%) and rare angioedema (<0.5%)
  4. Anti-fibrotic effects: Angiotensin II drives cardiac fibroblast activation, myocardial fibrosis, and ventricular remodelling. ACE inhibition reverses these processes over weeks-to-months → reverse remodelling in HFrEF, improving LVEF

Haemodynamic Effects

↓ Afterload

Arteriolar dilation via ↓angiotensin II. Reduces cardiac work — allows ventricular function to improve at the same energy cost in HFrEF

↓ Preload

Venodilation + ↓aldosterone. Reduces filling pressures and pulmonary venous congestion; relieves dyspnoea in HFrEF

↑ Cardiac Output

Net effect of ↓afterload and ↓preload in HFrEF: cardiac output increases despite ↓BP. Haemodynamic improvement correlates with clinical benefit

Renal Efferent Dilation

Angiotensin II preferentially constricts efferent arteriole. ACEi dilates it → ↓intraglomerular pressure → ↓proteinuria. Risk in bilateral renal artery stenosis: GFR may fall acutely

Clinical Use

Per the 2022 AHA/ACC/HFSA Guideline for the Management of Heart Failure and supporting trial evidence:

IndicationGuideline StrengthKey EvidencePreferred Agents
HFrEF (EF <40%) Class I Level A CONSENSUS, SOLVD — mortality reduction ~27% Enalapril, lisinopril, ramipril, captopril (titrate to target dose)
Hypertension Class I First-line with CKD, DM, or HF; HOPE trial (ramipril) Any ACEi; once-daily preferred for adherence
Post-MI with LV dysfunction Class I SAVE (captopril), AIRE (ramipril) — 19–27% mortality reduction Captopril (SAVE), ramipril (AIRE)
Diabetic nephropathy (T1DM with proteinuria) Class I Reduce proteinuria 30–50%; slow GFR decline independent of BP Any ACEi; titrate to maximum tolerated dose
High CV risk (without HF/LV dysfunction) Class IIa HOPE (ramipril): 22% reduction in CV death/MI/stroke Ramipril 10 mg/day (HOPE dose); perindopril (EUROPA)

Dosing principle: ACE inhibitors must be titrated to target dose in HFrEF — the same doses proven to reduce mortality in trials. Start at low dose (e.g., enalapril 2.5 mg BD) and double every 2 weeks to target (e.g., enalapril 10 mg BD). The mortality benefit is dose-dependent; under-dosing is a common clinical error.

Contraindications

  • Bilateral renal artery stenosis / severe aortic stenosis — efferent arteriolar dilation removes the pressure support driving GFR; may precipitate acute renal failure
  • Pregnancy (Category D/X): Fetal ACE is essential for kidney development — ACEi causes oligohydramnios, renal tubular dysplasia, skull hypoplasia ("ACE inhibitor fetopathy")
  • Hyperkalaemia (K⁺ >5.5 mmol/L): Significant risk, especially with concomitant MRA or ARB. Monitor potassium closely in CKD
  • Known angioedema from prior ACEi: Switch to ARB (slightly lower angioedema risk, but not zero). Do not rechallenge
  • Severe hypotension (SBP <90 mmHg): Contraindicated at initiation; start at very low dose in borderline cases

Key Agents

AgentProdrug?DosingKey Pharmacology & Clinical Distinguishing Features
Captopril No (active) 6.25–50 mg three times daily Oldest ACEi (1981); thiol group (SH) confers different side-effect profile (rash, dysgeusia more common); three-times daily dosing limits adherence; used in SAVE trial (post-MI)
Enalapril Yes (enalaprilat) 2.5–10 mg twice daily The SOLVD and CONSENSUS trial drug; twice daily; IV form (enalaprilat) available for hypertensive emergencies; longest track record in HFrEF
Lisinopril No (active) 2.5–35 mg once daily Once daily; hydrophilic — renally excreted, not metabolised; no CYP interactions; preferred in hepatic impairment; widely prescribed for HTN/HFrEF
Ramipril Yes (ramiprilat) 1.25–10 mg once daily HOPE trial drug (vascular protection in high-risk patients without HF); high tissue ACE selectivity; once daily; preferred for secondary prevention without HF
Perindopril Yes (perindoprilat) 4–8 mg once daily EUROPA trial (post-MI secondary prevention); long-acting; once daily; often combined with amlodipine (ADVANCE combination formulation)

ACEi vs ARB vs ARNI in HFrEF: ARBs (valsartan, candesartan) are non-inferior to ACEi and preferred when ACEi cough is intolerable; lower angioedema risk. ARNI (sacubitril/valsartan) is now preferred over ACEi alone in HFrEF — PARADIGM-HF showed 20% further reduction in CV death/HF hospitalisation vs enalapril. ACEi must be stopped 36 hours before starting ARNI to avoid angioedema from simultaneous bradykinin potentiation.

Evidence Base — Landmark Trials

TrialDrugPopulationKey Result
CONSENSUS (1987) Enalapril 253 patients, NYHA class IV HFrEF 40% reduction in 6-month mortality vs placebo; trial stopped early due to overwhelming benefit. First RCT to demonstrate mortality reduction with RAAS blockade in heart failure.
SOLVD (1991) Enalapril 2,569 patients, LVEF ≤35%, symptomatic HFrEF 16% reduction in all-cause mortality; 26% reduction in hospitalisations for HF. Confirmed mortality benefit across a broader HFrEF population.
SAVE (1992) Captopril 2,231 post-MI patients, LVEF ≤40% (asymptomatic LV dysfunction) 19% reduction in all-cause mortality; 25% reduction in HF hospitalisation. Extended ACEi indication to asymptomatic post-MI LV dysfunction.
HOPE (2000) Ramipril 10 mg/day 9,297 high-risk patients — no HF, no known LV dysfunction 22% reduction in composite of CV death, MI, stroke vs placebo. Established ACEi benefit in vascular protection beyond heart failure — patients with diabetes, peripheral arterial disease, prior MI, or stroke.

Why ACEi Work Across So Many Indications: The RAAS is activated in virtually all patients with cardiovascular disease — from heart failure to post-MI remodelling to diabetic nephropathy. By interrupting this maladaptive neurohormonal system, ACEi prevent the downstream cascades (fibrosis, volume retention, vasoconstriction, inflammation) that drive disease progression. The convergence of evidence across multiple agents, populations, and endpoints over three decades reflects a drug class acting on a fundamental pathophysiological pathway.

Side Effects

  • Dry cough (25–40%) — most common side effect; caused by bradykinin and substance P accumulation in the lung (ACE also degrades these). Predictable, class-specific. Often dose-independent. Switch to ARB (does not potentiate bradykinin) if intolerable. Not a contraindication to continuing if the patient tolerates it.
  • Angioedema (<0.5%) — potentially life-threatening swelling of the lips, tongue, larynx, or gut wall; also bradykinin-mediated. More common in Black patients (~4× risk) and with concomitant mTOR inhibitors. Absolute contraindication to reuse. Switch to ARB (lower risk, but not zero) or ARNI only after careful consideration.
  • Hyperkalaemia — reduced aldosterone leads to potassium retention. Clinically significant risk in CKD, with concomitant MRA (spironolactone/eplerenone), ARBs (dual RAAS blockade not recommended), or NSAIDs. Monitor potassium at 1–2 weeks after initiation or dose increase.
  • Acute kidney injury / creatinine rise — an initial rise in creatinine of up to 30% after initiation is expected (efferent arteriolar dilation reduces intraglomerular pressure and GFR). This is usually acceptable and not a reason to stop. >30% rise or creatinine >3.5 mg/dL: investigate for bilateral renal artery stenosis.
  • Hypotension (first-dose effect) — significant in volume-depleted patients or those on high-dose diuretics. Start at very low dose in heart failure initiation. Avoid in SBP <90 mmHg.
  • Teratogenicity (Category D/X) — contraindicated throughout pregnancy; fetal exposure leads to ACE inhibitor fetopathy (oligohydramnios, renal dysplasia, neonatal renal failure, limb contractures, lung hypoplasia). Stop before conception.

Connections

Acts on Cardiovascular System Used with Statins Used with Beta-blockers Used with Loop Diuretics Targets ACE / Kininase II (entry pending) Treats Kidney / CKD (entry pending)

References