angiotensin receptor blocker
An angiotensin receptor blocker, or ARB, works one step further downstream than an ACE inhibitor. If angiotensin II is a key that locks arteries tight, the ARB does not stop the key from being made; instead it covers the keyhole. With the receptor occupied by a blocker, the hormone can circulate but cannot deliver its vessel-tightening, salt-retaining message.
Specifically, ARBs are competitive antagonists at the angiotensin II type 1 (AT1) receptor. Blocking AT1 prevents vasoconstriction, aldosterone release and sodium retention, so blood pressure falls and the workload on the heart and kidneys eases. Members carry the suffix -sartan, including losartan, valsartan, candesartan and irbesartan. Because they do not interfere with bradykinin breakdown, they rarely cause the dry cough seen with ACE inhibitors.
ARBs are often the preferred choice for patients who cannot tolerate an ACE inhibitor cough, and they share the same broad uses in hypertension, heart failure and diabetic kidney protection. They carry the same cautions: they can raise potassium, reduce kidney filtration in renal artery stenosis, and are contraindicated in pregnancy because of fetal harm. Combining an ARB with an ACE inhibitor is generally avoided because the added risk outweighs the benefit.
After developing a nagging cough on lisinopril, a hypertensive patient is switched to losartan, an ARB, and the cough resolves while blood pressure stays controlled.
ARBs offer ACE-like benefits without the bradykinin-driven cough.
Both ACE inhibitors and ARBs interrupt the renin–angiotensin–aldosterone system, but ARBs block the receptor while ACE inhibitors block the enzyme that makes the hormone.