Angiotensin receptor blockers competitively and selectively block the angiotensin type 1 receptor on vascular smooth muscle, the adrenal cortex, the kidney, and the heart. By occupying the receptor, they prevent angiotensin II from producing its downstream effects: vasoconstriction, aldosterone secretion, sodium and water retention, and cardiac and vascular remodeling. Because the blockade occurs at the receptor level — not at the enzymatic step that converts angiotensin I to angiotensin II — angiotensin-converting enzyme remains fully active. Bradykinin continues to be degraded normally, and bradykinin levels do not rise.

This single mechanistic difference explains the entire adverse effect distinction between the two classes. No elevated bradykinin means no dry cough and no bradykinin-mediated angioedema. Angiotensin receptor blockers are therefore the standard alternative when a patient develops cough on an angiotensin-converting enzyme inhibitor. They are used cautiously rather than freely in patients with a history of angiotensin-converting enzyme inhibitor angioedema, since the angioedema risk is substantially lower but not completely absent with angiotensin receptor blockers.

Despite the bradykinin distinction, angiotensin receptor blockers share all of the angiotensin-converting enzyme inhibitor adverse effects that derive from reduced angiotensin II and aldosterone activity rather than from bradykinin. Hyperkalemia occurs because aldosterone suppression reduces potassium excretion in the collecting duct — the same mechanism as with angiotensin-converting enzyme inhibitors. The same renal hemodynamic risk applies in bilateral renal artery stenosis: removing angiotensin II-dependent efferent arteriolar constriction collapses filtration pressure and can precipitate acute kidney injury.

The pregnancy contraindication is absolute and identical to that of angiotensin-converting enzyme inhibitors. The developing fetal kidney depends on its own renin-angiotensin-aldosterone system for normal tubular development; angiotensin receptor blockers suppress fetal angiotensin II signaling and cause the same spectrum of fetal harm — oligohydramnios, fetal anuria, and pulmonary hypoplasia — as angiotensin-converting enzyme inhibitors.

The indications for angiotensin receptor blockers mirror those for angiotensin-converting enzyme inhibitors: hypertension, heart failure with reduced ejection fraction, post-myocardial infarction left ventricular dysfunction, and diabetic nephropathy with proteinuria. The CHARM-Alternative trial established that candesartan reduces cardiovascular mortality and hospitalizations in heart failure patients who are intolerant of angiotensin-converting enzyme inhibitors, providing the evidence base that made angiotensin receptor blockers a guideline-endorsed alternative rather than just a substitute of convenience.

In diabetic nephropathy, the Reduction of Endpoints in Non-Insulin Dependent Diabetes Mellitus with the Angiotensin II Antagonist Losartan (RENAAL) and Irbesartan Diabetic Nephropathy Trial (IDNT) trials demonstrated that losartan and irbesartan reduce progression to end-stage renal disease in type 2 diabetes with established nephropathy, mirroring the renal protective effects of angiotensin-converting enzyme inhibitors through the same mechanism of efferent arteriolar dilation and reduced intraglomerular pressure.

Unlike most angiotensin-converting enzyme inhibitors, angiotensin receptor blockers are not prodrugs — they are pharmacologically active as administered. Most are metabolized hepatically and eliminated via biliary/fecal routes, with less dependence on renal excretion than angiotensin-converting enzyme inhibitors. This means dose adjustment in renal impairment is generally less critical for angiotensin receptor blockers than for renally eliminated angiotensin-converting enzyme inhibitors, though the pharmacodynamic risks of hyperkalemia and acute kidney injury apply equally.

Combining an angiotensin-converting enzyme inhibitor with an angiotensin receptor blocker — so-called dual renin-angiotensin-aldosterone system blockade — was tested in the ONTARGET trial. The combination did not reduce cardiovascular outcomes compared to either agent alone but significantly increased rates of acute kidney injury, hyperkalemia, and hypotension. Dual blockade is contraindicated for this reason. The one apparent exception — adding an angiotensin receptor blocker to an angiotensin-converting enzyme inhibitor in heart failure with reduced ejection fraction — was also evaluated and found to produce more harm than benefit compared to adding a mineralocorticoid receptor antagonist instead. Current guidelines recommend mineralocorticoid receptor antagonists as the preferred add-on to angiotensin-converting enzyme inhibitor or angiotensin receptor blocker therapy in heart failure.

Atrial natriuretic peptide is released from atrial cardiomyocytes in response to atrial wall stretch — the kind caused by volume overload. Brain natriuretic peptide (the name is historical; it is made primarily in the ventricles, not the brain) is released from ventricular cardiomyocytes in response to ventricular wall stretch and increased filling pressure. In heart failure, chronically elevated ventricular wall stress drives sustained brain natriuretic peptide secretion, which is why plasma brain natriuretic peptide and its inactive cleavage fragment NT-proBNP rise in proportion to the severity of heart failure and fall with effective treatment.

Both peptides act through natriuretic peptide receptors coupled to cyclic guanosine monophosphate signaling, producing three key effects: natriuresis and diuresis (increased sodium and water excretion by the kidney), vasodilation (both arterial and venous), and suppression of aldosterone secretion from the adrenal cortex. These effects directly oppose the sodium retention, vasoconstriction, and aldosterone excess of the activated renin-angiotensin-aldosterone system in heart failure.

Neprilysin is a zinc metallopeptidase expressed on vascular endothelium and in the kidney that cleaves and inactivates natriuretic peptides, along with bradykinin and several other vasoactive peptides. In the context of heart failure, neprilysin activity limits the beneficial compensatory response of elevated natriuretic peptides. Inhibiting neprilysin allows natriuretic peptide levels to rise, amplifying their vasodilatory and natriuretic effects. This is the mechanism exploited by sacubitril, the neprilysin inhibitor component of sacubitril-valsartan.

Sacubitril is a prodrug that is hydrolyzed after absorption to its active neprilysin-inhibiting metabolite. By blocking neprilysin, sacubitril prevents the degradation of natriuretic peptides, bradykinin, and other vasoactive peptides, raising their circulating and tissue levels. The consequence is enhanced natriuresis, vasodilation, and suppression of aldosterone and sympathetic activation — all beneficial in heart failure with reduced ejection fraction.

Valsartan, the angiotensin receptor blocker component, blocks the AT1 receptor and reduces vasoconstriction, aldosterone secretion, and cardiac remodeling. The combination produces complementary suppression of the renin-angiotensin-aldosterone system while amplifying the opposing natriuretic peptide system. Neither mechanism alone produces the same magnitude of benefit, and the two together are superior to angiotensin-converting enzyme inhibitor monotherapy in head-to-head comparison.

The PARADIGM-HF trial compared sacubitril-valsartan to enalapril in over 8,000 patients with heart failure with reduced ejection fraction (ejection fraction 40 percent or below) who were already on standard therapy. Sacubitril-valsartan reduced the primary composite endpoint of cardiovascular death or heart failure hospitalization by 20 percent relative to enalapril. It also reduced all-cause mortality and cardiovascular mortality individually. The trial was stopped early because the benefit was so clear that continuing would have been ethically problematic.

Based on PARADIGM-HF, current heart failure guidelines recommend sacubitril-valsartan as the preferred agent over angiotensin-converting enzyme inhibitors or angiotensin receptor blockers alone in patients with heart failure with reduced ejection fraction who can tolerate it. It effectively replaces, rather than adds to, angiotensin-converting enzyme inhibitor or angiotensin receptor blocker therapy — this distinction matters for the contraindications discussed in Section 5.

Sacubitril inhibits neprilysin, which is one of the enzymes that degrades bradykinin. Angiotensin-converting enzyme inhibitors reduce bradykinin degradation through a completely separate mechanism. When both drugs are present simultaneously, bradykinin accumulates to levels that can trigger severe, potentially fatal angioedema. This combination is absolutely contraindicated — the two drugs must never be used together.

Because sacubitril and its active metabolite have a prolonged tissue half-life, simply stopping one drug and starting the other on the same day does not eliminate the risk. A mandatory 36-hour washout period is required in both directions: a patient switching from an angiotensin-converting enzyme inhibitor to sacubitril-valsartan must wait at least 36 hours after the last angiotensin-converting enzyme inhibitor dose before starting sacubitril-valsartan, and vice versa. This 36-hour rule is one of the most commonly tested clinical pharmacology facts about this drug.

Pregnancy is an absolute contraindication shared with all renin-angiotensin-aldosterone system-blocking agents. The valsartan component suppresses fetal angiotensin II signaling with the same consequences as angiotensin-converting enzyme inhibitors — oligohydramnios, fetal renal tubular dysgenesis, and potential neonatal death.

Hypotension is the most common adverse effect in practice, particularly at initiation. Starting at a low dose and up-titrating slowly is important, especially in patients who are already on diuretics or who have borderline low blood pressure. Hyperkalemia occurs via the same mechanism as with angiotensin receptor blockers — aldosterone suppression reducing potassium excretion — and requires monitoring.