ACE inhibitors and angiotensin receptor blockers are two drug classes that target the renin-angiotensin-aldosterone system, a hormonal cascade central to blood pressure regulation, fluid balance, and cardiovascular remodeling. Both classes are cornerstones of therapy for hypertension, heart failure, chronic kidney disease, and post-myocardial infarction management, though they achieve their effects through distinct mechanisms within the same pathway.
What Are ACE Inhibitors and ARBs?
The renin-angiotensin system begins with renin release from the kidney, which cleaves angiotensinogen to angiotensin I. Angiotensin-converting enzyme then converts angiotensin I to angiotensin II, a potent vasoconstrictor that also stimulates aldosterone release, promotes sodium retention, and drives pathological cardiac and vascular remodeling. ACE inhibitors block the conversion of angiotensin I to angiotensin II, while ARBs directly antagonize the angiotensin II type 1 receptor, providing more complete blockade of angiotensin II effects regardless of its source.
Mechanism of Action
ACE inhibitors such as lisinopril, enalapril, and ramipril competitively inhibit angiotensin-converting enzyme, reducing angiotensin II levels and decreasing aldosterone secretion. This leads to vasodilation, reduced blood pressure, decreased cardiac afterload, and diminished sodium and water retention. ACE inhibitors also prevent the degradation of bradykinin, a vasodilatory peptide that contributes to their antihypertensive effects but also to their characteristic adverse effect of dry cough.
ARBs such as losartan, valsartan, and candesartan selectively block the angiotensin II type 1 receptor, preventing angiotensin II from exerting its vasoconstrictor and aldosterone-stimulating effects. Because ARBs do not affect bradykinin metabolism, they are not associated with cough and are better tolerated in patients who cannot tolerate ACE inhibitors. Both drug classes reduce proteinuria and slow the progression of chronic kidney disease through favorable effects on glomerular hemodynamics.
Therapeutic Uses
Both drug classes are first-line therapies for hypertension, particularly in patients with diabetes, chronic kidney disease, or heart failure. They reduce mortality and hospitalizations in heart failure with reduced ejection fraction and prevent adverse ventricular remodeling after myocardial infarction. The renoprotective effects of ACE inhibitors and ARBs make them essential in diabetic nephropathy and proteinuric kidney disease, slowing progression to end-stage renal disease.
Adverse Effects
The most common adverse effect of ACE inhibitors is a persistent dry cough, occurring in up to twenty percent of patients, which results from bradykinin accumulation. Angioedema, though rare, is a potentially life-threatening adverse effect shared by both drug classes. Hyperkalemia can occur, particularly in patients with renal impairment or those taking potassium-sparing diuretics or potassium supplements. Acute kidney injury may result from reduced glomerular filtration pressure in patients with bilateral renal artery stenosis or volume depletion.
Contraindications
Both ACE inhibitors and ARBs are contraindicated in pregnancy due to risks of fetal renal dysplasia, oligohydramnios, and neonatal hypotension. They should be used with caution in patients with bilateral renal artery stenosis, where glomerular filtration depends on angiotensin II-mediated efferent arteriolar constriction. Caution is also required in patients with hyperkalemia or severe renal impairment. ARBs are often substituted when ACE inhibitors cause intolerable cough.
Conclusion
ACE inhibitors and ARBs are among the most effective and widely prescribed cardiovascular medications. Their complementary mechanisms within the renin-angiotensin system allow for therapeutic flexibility, and their proven benefits across multiple cardiovascular and renal conditions make them indispensable in modern pharmacotherapy.
