Why are ARBs less likely than ACE inhibitors to cause cough?

ARBs block the angiotensin II receptor rather than the converting enzyme, so they do not raise bradykinin levels, and bradykinin accumulation is the mechanism thought to drive ACE-inhibitor cough.

Do ARBs and ACE inhibitors target the same system?

Yes, both inhibit the renin-angiotensin system, but at different points: ACE inhibitors reduce formation of angiotensin II, while ARBs block its action at the AT1 receptor.

Angiotensin II Receptor Antagonists

Angiotensin II receptor antagonists, commonly called angiotensin receptor blockers (ARBs), lower blood pressure by blocking the angiotensin II type 1 (AT1) receptor. Acting one step downstream of ACE inhibitors, they prevent angiotensin II from causing vasoconstriction and aldosterone release regardless of how the peptide was generated, without raising bradykinin.

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Definition

Angiotensin II receptor antagonists are drugs that selectively block the angiotensin II type 1 (AT1) receptor, preventing angiotensin II from exerting its vasoconstrictor and aldosterone-stimulating effects and thereby lowering blood pressure.

Scope

This entry covers receptor-level blockade of the renin-angiotensin system, how ARBs differ from ACE inhibitors in mechanism and tolerability, and the trial evidence for cardiovascular and renal outcomes. It is reference material on pharmacology, not a prescribing guide.

Core questions

How does blocking the AT1 receptor differ from inhibiting angiotensin-converting enzyme?
Why do ARBs generally not cause the cough associated with ACE inhibitors?
What does outcome evidence show for ARBs in hypertension and diabetic nephropathy?

Key concepts

Angiotensin II type 1 (AT1) receptor
Receptor-level versus enzyme-level renin-angiotensin blockade
Bradykinin-independent action
Aldosterone suppression
Renal protection in diabetic nephropathy
Unopposed AT2 receptor signalling

Mechanisms

Angiotensin II acts mainly through the AT1 receptor to cause arteriolar vasoconstriction, aldosterone secretion, and sodium retention. ARBs block this receptor, so the downstream effects of angiotensin II are inhibited regardless of whether the peptide is formed by ACE or by alternative pathways. Because they act at the receptor rather than on the converting enzyme, ARBs do not impair bradykinin breakdown and therefore seldom produce the dry cough seen with ACE inhibitors. By blocking AT1, they may leave angiotensin II free to act at the AT2 receptor. As with ACE inhibitors, reduced AT1 signalling lowers efferent arteriolar tone in the kidney, contributing to renal protection in proteinuric disease.

Clinical relevance

ARBs are a principal class for studying renin-angiotensin pharmacology and are examined across hypertension, heart failure, and diabetic kidney disease, often as an alternative to ACE inhibitors when cough or intolerance occurs. This entry is educational reference on their mechanism and evidence and does not give dosing or individualised advice.

Evidence & guidelines

Guidelines treat ARBs as a first-line antihypertensive class alongside ACE inhibitors, calcium channel blockers, and diuretics, generally advising against combining an ARB with an ACE inhibitor. The RENAAL trial showed losartan reduced renal endpoints in type 2 diabetic nephropathy, the LIFE trial showed cardiovascular benefit of a losartan-based regimen versus atenolol in hypertension with left ventricular hypertrophy, and ONTARGET established that an ARB was comparable to an ACE inhibitor while their combination added risk without benefit.

History

Losartan, introduced in the 1990s, was the first orally active non-peptide AT1 receptor antagonist, followed by other sartans. Their development offered a receptor-selective alternative to ACE inhibition, and subsequent outcome trials defined their roles in hypertension, nephropathy, and heart failure.

Debates

Are ARBs and ACE inhibitors interchangeable, and should they be combined?: ARBs and ACE inhibitors produce broadly similar cardiovascular outcomes, with ARBs better tolerated regarding cough; however, ONTARGET showed that combining the two classes increased adverse events without improving outcomes, so dual blockade is generally discouraged.

Seminal works

brenner-2001
dahlof-2002
ontarget-2008

Frequently asked questions

Why are ARBs less likely than ACE inhibitors to cause cough?: ARBs block the angiotensin II receptor rather than the converting enzyme, so they do not raise bradykinin levels, and bradykinin accumulation is the mechanism thought to drive ACE-inhibitor cough.
Do ARBs and ACE inhibitors target the same system?: Yes, both inhibit the renin-angiotensin system, but at different points: ACE inhibitors reduce formation of angiotensin II, while ARBs block its action at the AT1 receptor.