ACE Inhibitors and Angiotensin II Receptor Blockers

The Renin-Angiotensin-Aldosterone System (RAAS) Physiology

• Angiotensinogen → Renin (released by juxtaglomerular cells in response to decreased renal perfusion pressure, sodium depletion, or sympathetic stimulation) → Angiotensin I (decapeptide)
• Angiotensin-converting enzyme (ACE), a dipeptidyl carboxypeptidase located on endothelial surfaces (especially pulmonary vasculature), catalyzes conversion of Angiotensin I → Angiotensin II (octapeptide)
• Angiotensin II binds to two primary receptors: AT₁ receptor (mediates pathologic effects) and AT₂ receptor (generally protective, vasodilatory)

Pathologic Effects of Angiotensin II (AT₁-Mediated)

• Vasoconstriction: Direct smooth muscle contraction via phospholipase C activation and IP₃/DAG signaling
• Sodium retention and volume expansion: Direct proximal tubule reabsorption and aldosterone stimulation
• Sympathetic nervous system activation: Increased norepinephrine release and reuptake inhibition
• Aldosterone secretion: Promotes distal tubule sodium reabsorption and potassium excretion
• Cardiac and vascular remodeling: Promotes fibroblast proliferation, collagen deposition, left ventricular hypertrophy (LVH), and arterial stiffness via TGF-β and other growth factor pathways
• Endothelial dysfunction: Reduced nitric oxide bioavailability, increased oxidative stress, and inflammation
• Thrombosis promotion: Enhanced platelet aggregation and tissue factor expression

Mechanism of ACE Inhibitors

• Competitive inhibition of ACE at the catalytic site containing zinc and sulfhydryl groups
• Decreases Angiotensin II formation and increases Angiotensin I and inactive metabolites
• Increases bradykinin levels (since ACE also catalyzes bradykinin degradation), contributing to vasodilation, reduced LVH, and antifibrotic effects—and explaining the characteristic persistent dry cough (15-20% of patients) due to increased bronchial bradykinin
• Relative shift toward AT₂ receptor signaling, which promotes vasodilation and beneficial remodeling

Mechanism of Angiotensin II Receptor Blockers

• Selective competitive antagonism of the AT₁ receptor without affecting ACE activity
• Prevents Angiotensin II binding to AT₁ receptors while allowing unopposed AT₂ activation
• Does NOT increase bradykinin levels, explaining the absence of cough
• Allows continued Angiotensin II synthesis with potential "aldosterone breakthrough" phenomenon (temporary rise in aldosterone despite initial suppression)
• May have advantages in specific populations: absence of cough improves tolerability; some data suggest superior renal protection in certain diabetic populations

Tissue-Specific Effects

• Cardiovascular: Reduced LVH, improved diastolic function, decreased myocardial fibrosis, reduced atherosclerosis progression
• Renal: Preferential efferent arteriole dilation (reducing glomerular capillary hypertension), reduced proteinuria/albuminuria, slowed GFR decline
• Vascular: Reduced arterial stiffness, improved endothelial function, decreased atherosclerotic plaque inflammation
• Systemic: Anti-inflammatory effects, improved insulin sensitivity, reduced sympathetic activity

Indications for ACEI/ARB Use (Evidence-Based)

• Hypertension (essential or secondary): First-line agents for uncomplicated hypertension and mandated in patients with CKD or diabetes

• Heart failure with reduced ejection fraction (HFrEF): Foundational therapy shown to reduce mortality by ~20% in multiple landmark trials (CONSENSUS, SOLVD, AIRE); all patients without contraindications should receive ACEIs or ARBs

• Acute myocardial infarction with systolic dysfunction: ACEI reduces mortality when initiated early post-MI, particularly in anterior MI with reduced EF; standard post-MI therapy

• Diabetic nephropathy (Type 1 and Type 2 diabetes): Both ACEIs and ARBs reduce proteinuria and slow progression to ESRD independent of blood pressure effects; considered renal protective agents

• Non-diabetic chronic kidney disease: Slow GFR decline and reduce proteinuria across all stages (1-4); particularly beneficial in proteinuric CKD

• Hypertension with left ventricular hypertrophy: Regress LVH and reduce cardiovascular events more effectively than other antihypertensive classes

• Coronary artery disease (CAD) with preserved systolic function: Reduce secondary events and mortality in stable CAD

• Prevention of atrial fibrillation: May reduce AF burden in certain settings (post-MI, HFrEF)

Patient Factors Influencing ACEI vs. ARB Selection

• ACEI cough intolerance → ARB preferred
• Angioedema history with one class → switch to other class with caution
• Pregnancy status (teratogenic; contraindicated 2nd and 3rd trimester)
• Prior adverse reactions, comorbidities

Clinical Manifestations of Untreated RAAS Activation (Indications for Therapy)

Hypertension-Related Symptoms

• Often asymptomatic; detected on routine screening
• Headache, dizziness, or dyspnea may reflect severe or acute hypertension
• Angina pectoris from demand ischemia in CAD patients

Heart Failure Symptoms (in HFrEF)

• Dyspnea on exertion and orthopnea from pulmonary congestion
• Fatigue and exercise intolerance from reduced cardiac output
• Peripheral edema and abdominal distension from volume overload
• Tachycardia and gallop rhythm (S₃) on auscultation

Renal Disease Manifestations

• Asymptomatic hematuria or proteinuria detected on urinalysis
• Gradually rising serum creatinine and declining GFR
• Foamy urine suggesting nephrotic-range proteinuria

Physical Examination Findings

• Elevated blood pressure (systolic and/or diastolic >140/90 mmHg or goal-directed threshold)
• Left ventricular hypertrophy: Laterally displaced point of maximal impulse (PMI), prominent S₄ gallop (atrial contribution to hypertrophied ventricle)
• Signs of heart failure: Pulmonary crackles (bibasilar rales), elevated jugular venous pressure (JVP), hepatomegaly, peripheral edema
• Retinopathy: Flame hemorrhages, cotton-wool spots, microaneurysms (hypertensive or diabetic retinopathy)
• Brisk reflexes and other signs of hyperadrenergic state in secondary hypertension (e.g., pheochromocytoma)

Diagnostic Framework for Conditions Requiring ACEI/ARB

Blood Pressure Measurement

• Office BP: Measured in seated position after 5 minutes of rest; ≥140/90 mmHg confirms hypertension (or ≥130/80 mmHg per 2017 ACC/AHA guidelines for higher-risk patients)
• Home BP monitoring: Reduces white-coat effect; ≥135/85 mmHg threshold
• 24-hour ambulatory BP: Gold standard; confirms diagnosis and quantifies burden

Cardiac Assessment

• Echocardiography:
• Measures left ventricular ejection fraction (LVEF) to classify HF severity
• HFrEF: LVEF ≤40% (mildly reduced 41-49% also benefits)
• Assesses chamber size, wall thickness (LVH quantification), and diastolic parameters
• Reduced LVEF is key indication for mandatory ACEI/ARB therapy

• 12-lead ECG:
• LVH voltage criteria (Sokolow-Lyon, Cornell)
• Signs of prior MI (pathologic Q waves)
• Ischemic changes

• Cardiac biomarkers (in acute decompensation):
• B-type natriuretic peptide (BNP) or N-terminal pro-BNP (NT-proBNP): Elevated in HF; BNP >100 pg/mL or NT-proBNP >125 pg/mL suggests HF

Renal Function and Electrolytes

• Serum creatinine and calculated GFR (using MDRD or CKD-EPI equation):
• Establishes baseline renal function
• CKD staging guides ACEI/ARB dosing and monitoring intensity

• Baseline serum potassium:
• Normal range 3.5-5.0 mEq/L
• ACEI/ARBs increase potassium by 0.3-0.5 mEq/L on average
• Hyperkalemia (>5.5 mEq/L) is major adverse effect; risk increases with GFR <30, diabetes, concurrent potassium-sparing diuretics, NSAIDs

• Urinalysis and urine albumin-to-creatinine ratio (UACR):
• UACR <30 mg/g: Normoalbuminuria
• UACR 30-300 mg/g: Microalbuminuria (ACEI/ARB indicated for diabetes)
• UACR >300 mg/g: Macroalbuminuria; ACEI/ARB mandatory
• Reduction in UACR by ≥30% during first 3 months indicates renoprotection

Blood Pressure Target and Diagnostic Criteria

• Non-diabetic CKD without albuminuria: <120 mmHg systolic (ACCORD BP trial supports more intensive control)
• Diabetic patients: <130/80 mmHg per current guidelines (previously <140/90 mmHg)
• CAD patients: <130/80 mmHg
• HFrEF: Lower blood pressures tolerated if symptomatic hypotension absent

• Renal artery stenosis: Doppler ultrasound, CT/MR angiography, captopril renography
• Pheochromocytoma: 24-hour urine metanephrines or plasma free metanephrines
• Primary aldosteronism: Aldosterone-to-renin ratio, salt suppression testing
• Thyroid dysfunction: TSH level

First-Line ACEI/ARB Therapy

ACE Inhibitor Agents (Common Examples)

• Lisinopril: Initial 10 mg daily; target 20-40 mg daily (renal excretion; adjust for GFR)
• Enalapril: Initial 5 mg daily; target 10-20 mg daily (prodrug; hepatic activation)
• Ramipril: Initial 2.5 mg daily; target 5-10 mg daily (tissue-bound ACE inhibition; longer half-life)
• Perindopril: Initial 2-4 mg daily; target 4-8 mg daily
• Captopril: Initial 6.25-12.5 mg TID; target 25-50 mg TID (short-acting, so useful when rapid titration or quick withdrawal is needed; contraindicated in pregnancy, like all ACE inhibitors)

Angiotensin II Receptor Blockers (Common Examples)

• Losartan: Initial 50 mg daily; target 50-100 mg daily (hepatically metabolized to active metabolite)
• Valsartan: Initial 80 mg daily; target 160 mg daily (minimal metabolism)
• Olmesartan: Initial 20 mg daily; target 20-40 mg daily (potent; renally cleared)
• Telmisartan: Initial 40 mg daily; target 40-80 mg daily (longest half-life; once daily dosing)
• Irbesartan: Initial 150 mg daily; target 150-300 mg daily
• Candesartan: Initial 16 mg daily; target 16-32 mg daily

Mechanism of Benefit by Indication

Starting and Target Dosing Strategy

1. 1.Initiation in HFrEF:

• Start low dose (e.g., lisinopril 2.5-5 mg daily) in hospitalized or volume-overloaded patients
• Uptitrate every 2-4 weeks toward target doses if tolerated
• Monitor BP, renal function (Cr, GFR), and potassium at each adjustment
• Target moderate to high doses (lisinopril ≥20 mg, enalapril ≥10 mg) for mortality benefit

1. 1.Initiation in Hypertension:

• Start standard dose (e.g., lisinopril 10 mg daily)
• Check BP response in 2-4 weeks
• Uptitrate if SBP remains >130 or DBP >80 mmHg per guidelines
• Often combined with diuretics, calcium channel blockers, or thiazide-type agents

1. 1.Initiation in CKD:

• Start lower dose in GFR <30; dose-adjust by renal clearance
• Expect small initial increase in creatinine (typically <30%) due to hemodynamic effects
• Benefit (proteinuria reduction) persists despite serum creatinine rise
• Achieve maximum tolerated dose for maximal renoprotection

Monitoring During ACEI/ARB Therapy

• Baseline: Serum creatinine, potassium, blood pressure, urinalysis
• 1-2 weeks after initiation or dose change: Recheck BP, creatinine, potassium (critical window for hyperkalemia/azotemia)
• 1 month: Assess response; continue monitoring if uptitrating
• 3 months: Confirm tolerability and BP/proteinuria response
• Ongoing (every 6-12 months): Monitor creatinine, potassium, BP, and UACR to assess renoprotection

Expected Changes in Lab Values

• Potassium: ↑ by 0.3-0.5 mEq/L (concerning if baseline >5.0

Bradykinin-mediated (ACEI-specific)

• Dry cough: ACE (kininase II) normally degrades bradykinin and substance P; accumulation in the bronchial mucosa sensitizes afferent C-fibers. Onset ranges from days to months; resolves within days to weeks of discontinuation. Not a class effect of ARBs.
• Angioedema: non-pruritic, non-urticarial swelling of lips, tongue, larynx, or bowel wall from bradykinin-driven vascular permeability. Disproportionately affects Black patients and can occur years into therapy. Management is airway-first (intubation threshold should be low), permanent discontinuation, and avoidance of rechallenge; antihistamines/glucocorticoids/epinephrine target histamine pathways and are unreliable here.

Hemodynamic and metabolic (both classes)

• Hyperkalemia: loss of aldosterone-driven principal-cell K⁺ secretion. Risk multiplies with reduced GFR, diabetes, MRAs (spironolactone), potassium-sparing diuretics, NSAIDs, and trimethoprim. Treat with membrane stabilization (IV calcium), intracellular shift (insulin with dextrose, beta-2 agonist), and potassium binders (patiromer, sodium zirconium cyclosilicate); dose reduction rather than reflexive discontinuation is favored by the KDIGO CKD guideline.
• Acute kidney injury / azotemia: angiotensin II maintains GFR by efferent arteriolar constriction; blockade drops filtration pressure. A creatinine rise up to roughly 30% is expected and acceptable; larger or progressive rises suggest volume depletion, NSAID co-administration, or bilateral renal artery stenosis.
• First-dose hypotension: pronounced in high-renin states — aggressive diuresis, hyponatremia, HFrEF. Start low, monitor, per the ACC/AHA heart failure guideline.
• Captopril-specific: sulfhydryl group causes dysgeusia, rash, and rarely neutropenia/agranulocytosis.

Contraindications and monitoring

• Pregnancy: FDA boxed warning for fetal toxicity — fetal RAAS blockade causes oligohydramnios, renal dysgenesis/anuria, skull hypoplasia, and limb contractures. ACOG endorses alternatives (labetalol, nifedipine, methyldopa).
• Prior angioedema, bilateral renal artery stenosis, hyperkalemia, hereditary/idiopathic angioedema: absolute or near-absolute.
• Do not combine ACEI + ARB or add a direct renin inhibitor: more hyperkalemia, hypotension, and renal failure without mortality benefit.
• Sacubitril/valsartan: requires a 36-hour ACEI washout to avoid overlapping bradykinin accumulation.
• No specific antidote; overdose is managed with IV crystalloid and vasopressors.

• Cough on lisinopril → switch to an ARB: the single most tested substitution. The mechanism is bradykinin/substance P accumulation, not angiotensin II blockade, which is why ARBs are cough-free. Common distractor: switching to a different ACEI.
• Angioedema is a bradykinin problem, not a mast-cell problem: the stem shows tongue/lip swelling without urticaria or pruritus. Best next step is airway assessment and permanent ACEI discontinuation; do not rechallenge. ARB substitution is possible but only with caution and after weighing risk.
• **Rising creatinine after starting an ACEI in a patient with an abdominal bruit → bilateral renal artery stenosis**. Angiotensin II was doing the filtering via efferent constriction; blocking it collapses GFR. The classic exam pairing is fibromuscular dysplasia (young woman) or atherosclerotic disease (older smoker).
• A creatinine bump of roughly ≤30% is expected and you continue the drug: the renoprotective benefit derives from the very drop in intraglomerular pressure that raises creatinine. Stopping the drug is the trap answer.
• Hyperkalemia is the monitoring endpoint: recheck potassium and creatinine within about 1–2 weeks of initiation or uptitration. Watch for NSAIDs, MRAs, potassium supplements, and trimethoprim–sulfamethoxazole layered on top.
• Pregnancy is an absolute contraindication (fetal renal maldevelopment, oligohydramnios, skull hypoplasia). Any reproductive-age woman on an ACEI/ARB in a stem is a discontinuation question; ACOG-favored alternatives are labetalol, nifedipine, and methyldopa.
• HFrEF quadruple therapy is four classes, not three: ARNI (or ACEI/ARB), beta blocker, MRA, and SGLT2 inhibitor, per the ACC/AHA/HFSA heart failure guideline. ACEI/ARB alone is incomplete guideline-directed therapy.
• Never combine ACEI + ARB, and never add a direct renin inhibitor to either — dual RAAS blockade increases hyperkalemia, hypotension, and renal failure without survival benefit. Also remember the 36-hour washout between an ACEI and sacubitril/valsartan.