Pharmacology · Cardiovascular

ARBs, Natriuretic Peptides, and Sacubitril-Valsartan

Mechanism comparison, natriuretic peptide physiology, and key safety rules

ARBs and ACE inhibitors block the RAAS at different points with one key pharmacological consequence: ACE inhibitors raise bradykinin (by blocking its degradation) while ARBs leave ACE intact, so ARBs produce no dry cough and only rare angioedema — making ARBs the standard substitute when ACE inhibitor cough or angioedema is intolerable; both classes share contraindications in pregnancy, hyperkalemia risk, and the bilateral renal artery stenosis problem.
The natriuretic peptide system provides counter-regulation to the RAAS: ANP is released from atrial stretch, BNP from ventricular stretch; both cause natriuresis, vasodilation, and aldosterone suppression; neprilysin is the endopeptidase that degrades them — its inhibition by sacubitril amplifies these beneficial effects in heart failure with reduced ejection fraction.
Sacubitril-valsartan works through two simultaneous mechanisms: sacubitril (a prodrug converted to LBQ657) inhibits neprilysin, raising natriuretic peptides and bradykinin; valsartan blocks AT1 receptors, reducing angiotensin II-driven vasoconstriction and aldosterone; PARADIGM-HF showed a 20 percent reduction in cardiovascular death or heart failure hospitalization versus enalapril, establishing it as the preferred RAAS agent in HFrEF.
The most important safety rule is absolute: sacubitril-valsartan must never be combined with an ACE inhibitor because both raise bradykinin through different mechanisms, dramatically increasing angioedema risk; a 36-hour washout is required in both switching directions because the active sacubitril metabolite LBQ657 persists; the same washout applies before starting an ACE inhibitor after stopping sacubitril-valsartan.
Monitoring on sacubitril-valsartan requires using NT-proBNP rather than BNP: sacubitril blocks neprilysin-mediated BNP degradation, so BNP rises artifactually regardless of heart failure status; NT-proBNP is not degraded by neprilysin and remains a reliable marker of cardiac filling pressures during therapy.

Feature	ACE Inhibitors	Angiotensin Receptor Blockers
Site of action	Blocks ACE enzyme (Step 2)	Blocks AT1 receptor (Step 3)
Bradykinin effect	Rises — ACE also degrades bradykinin	No change — ACE unaffected
Dry cough	Yes — 5–20% of patients	No
Angioedema	Yes — bradykinin-mediated	Rare — not bradykinin-driven
Hyperkalemia	Yes	Yes
Pregnancy	Contraindicated	Contraindicated
Prodrug	Most agents yes	No — active as given
Elimination	Primarily renal	Primarily hepatic/biliary

Rule	Reason
Never combine with ACE inhibitor	Both raise bradykinin → additive angioedema risk, potentially fatal
36-hour washout (both directions)	Sacubitril metabolite persists; overlap with ACE inhibitor causes bradykinin surge
Contraindicated in pregnancy	Valsartan suppresses fetal renin-angiotensin-aldosterone system → fetal renal dysgenesis
Monitor for hypotension	Most common adverse effect — titrate dose slowly, especially with diuretics
Use NT-proBNP, not BNP	Sacubitril blocks brain natriuretic peptide degradation → brain natriuretic peptide falsely elevated regardless of heart failure status

Suggested References

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