The Journey of Sacubitril-Valsartan

Sacubitril-valsartan (Entresto) is supplied as a sodium salt complex
and dissociates in the GI tract to release sacubitril and valsartan, which are absorbed separately.
Sacubitril has oral bioavailability of approximately 60% and is rapidly hydrolyzed by esterases to
its active form LBQ657 (sacubitrilat) within hours of absorption. Valsartan in Entresto has
significantly higher bioavailability (approximately 60%) compared to valsartan tablets alone
(approximately 23%) — approximately 2-fold difference attributed to the supramolecular complex
formulation that improves dissolution and absorption. Peak plasma concentrations of sacubitril
occur within 0.5 hours, LBQ657 within 2 hours, and valsartan within 1.7 hours. The drug should
be separated from ACE inhibitors by at least 36 hours before switching (to prevent excessive
bradykinin accumulation causing angioedema). Food has minimal effect on sacubitril absorption
but modestly reduces valsartan Cmax without affecting total AUC.

LBQ657 (sacubitrilat, active neprilysin inhibitor) distributes
to a volume of approximately 103 L. Plasma protein binding of LBQ657 is approximately 97%, primarily
to albumin. Valsartan has a small volume of distribution of approximately 75 L and is 94-97% protein
bound. Sacubitril-derived LBQ657 is not expected to cross the blood-brain barrier significantly —
an important safety consideration, as neprilysin in the brain degrades amyloid-beta, and concerns
existed that neprilysin inhibition might promote amyloid accumulation. Long-term clinical data
have not demonstrated increased Alzheimer's risk, but ongoing surveillance is maintained. Valsartan
distributes primarily to the vascular compartment and interstitium. Both components achieve
tissue concentrations in the heart, kidney, and vasculature sufficient for pharmacological effect.

Sacubitril-valsartan provides dual complementary blockade of the
renin-angiotensin system and augmentation of the natriuretic peptide system. LBQ657 (sacubitrilat)
is a competitive inhibitor of neprilysin (neutral endopeptidase, NEP, enkephalinase; encoded by
MME), a zinc metalloprotease that degrades natriuretic peptides (ANP, BNP, CNP), bradykinin,
substance P, and other vasoactive peptides. Neprilysin inhibition raises ANP and BNP concentrations,
activating particulate guanylyl cyclase (GC-A receptor for ANP/BNP), generating cGMP, reducing
cardiac preload and afterload (vasodilation), promoting sodium and water excretion (natriuresis/
diuresis), inhibiting cardiac fibrosis and hypertrophy (antiremodeling), and enhancing baroreceptor
sensitivity. Valsartan simultaneously blocks AT1 receptors (angiotensin II signaling) — preventing
vasoconstriction, aldosterone release, and fibrotic cardiac remodeling. Neprilysin also degrades
angiotensin II; its inhibition alone would increase angiotensin II levels (as with sacubitril
monotherapy) — the valsartan component counteracts this angiotensin II excess. ACE inhibitors
cannot be combined with sacubitril-valsartan because neprilysin inhibition raises bradykinin (also
a NEP substrate), and ACE inhibition further prevents bradykinin degradation, causing dangerous
angioedema.

Sacubitril is rapidly hydrolyzed in the intestinal mucosa and plasma
by carboxylesterases (CES1 primarily) to LBQ657. LBQ657 is minimally metabolized and excreted
primarily as the glucuronide conjugate in urine. Valsartan undergoes minimal metabolism — the primary
pathway is glucuronidation by UGT2B17 with a minor valeryl 4-hydroxy valsartan metabolite formed
by CYP2C9 (pharmacologically inactive). Neither sacubitril/LBQ657 nor valsartan are significant
CYP450 substrates or inhibitors, limiting pharmacokinetic drug interactions. However, valsartan
inhibits OATP1B1 and OATP1B3, the hepatic uptake transporters for statins — a potential interaction
increasing statin concentrations. The absence of ACE inhibitor use eliminates the major angioedema
risk from bradykinin accumulation, though ARNI-associated angioedema does occur (estimated ~0.5%
incidence), particularly in patients with prior ACE inhibitor-associated angioedema.

LBQ657 is excreted predominantly in urine (52-68%) as glucuronide
conjugate and unchanged drug; valsartan is excreted primarily in feces (83%) via biliary excretion.
Elimination half-life of sacubitril is approximately 1.4 hours, LBQ657 approximately 11.5 hours,
and valsartan approximately 9.9 hours — all supporting twice-daily dosing. No dose adjustment
is required for mild-moderate renal impairment. In severe renal impairment (eGFR <30 mL/min),
a starting dose of 24/26 mg twice daily (half the standard starting dose) is recommended. Hepatic
impairment reduces valsartan clearance (predominantly biliary elimination). Entresto is initiated
at 49/51 mg twice daily (sacubitril 49 mg / valsartan 51 mg) and titrated to the target dose of
97/103 mg twice daily as tolerated. Hypotension is the primary tolerability limiting factor.

Sacubitril-valsartan (Entresto) demonstrated superiority over enalapril
in the PARADIGM-HF trial (20% relative risk reduction in CV death or HHF in HFrEF, EF ≤35%)
— the first cardiovascular outcome trial in decades to show superiority over an ACE inhibitor.
PARAGON-HF evaluated HFpEF (EF ≥45%) and showed near-significant reduction in HHF in women and
patients with EF 45-57%. Sacubitril-valsartan is now guideline-recommended as the RAAS blocker of
choice in HFrEF (class I recommendation) if tolerated. Adverse effects include hypotension (17%),
hyperkalaemia, renal impairment, and angioedema. It is contraindicated in pregnancy (like all RAAS
blockers), and cannot be combined with ACE inhibitors or within 36 hours of any ACE inhibitor due
to angioedema risk. The PIONEER-HF trial supported in-hospital initiation in stabilized acute
decompensated HF.