Pharmacology · Cardiovascular

Natriuretic Peptides, NK1 Antagonists, and Integration

BNP biomarker guide, nesiritide, aprepitant, and vasoactive peptide clinical matrix

BNP and NT-proBNP are both released in response to ventricular wall stress, but they differ critically in one respect: neprilysin degrades BNP but not NT-proBNP — so patients on sacubitril-valsartan have artifactually elevated BNP regardless of heart failure status, making BNP uninterpretable in this population; NT-proBNP remains a reliable marker of cardiac filling pressures and is the preferred monitoring biomarker on sacubitril-valsartan therapy.
Nesiritide is recombinant human BNP that activates natriuretic peptide receptors to produce vasodilation, natriuresis, and RAAS suppression — it was tested in acute decompensated heart failure but ASCEND-HF showed only modest dyspnea benefit and no mortality improvement; it is not first-line and should not displace diuretics, which remain the cornerstone of acute decongestion.
Aprepitant and fosaprepitant block substance P at NK1 receptors in the area postrema, targeting the delayed phase of chemotherapy-induced nausea (24 to 120 hours post-chemotherapy) driven by substance P rather than the acute phase (0 to 24 hours) driven by serotonin; the standard three-drug antiemetic regimen combines an NK1 antagonist with a 5-HT3 antagonist and dexamethasone for highly emetogenic chemotherapy.
Aprepitant is a CYP3A4 inhibitor that roughly doubles dexamethasone plasma levels — the dexamethasone dose must be reduced by approximately half when co-administered; aprepitant also induces warfarin metabolism through a different CYP pathway, reducing warfarin levels, so INR should be monitored in the 7 to 10 days after a chemotherapy cycle.
The integration table in this module consolidates all six chapters of vasoactive peptide pharmacology into a single clinical decision framework: nine indications mapped to their peptide targets and the specific drug choices with key rules — from RAAS for heart failure and hypertension, through endothelin for pulmonary arterial hypertension and vasopressin for SIADH, to CGRP for migraine and substance P for chemotherapy-induced nausea.

Abbreviations: BNP = brain natriuretic peptide · NT-proBNP = N-terminal pro-BNP · HF = heart failure · HFrEF = heart failure with reduced ejection fraction · NK1 = neurokinin 1 · 5-HT3 = serotonin type 3 · RAAS = renin-angiotensin-aldosterone system · ERA = endothelin receptor antagonist · PDE5 = phosphodiesterase type 5 · CGRP = calcitonin gene-related peptide · vWD = von Willebrand disease · CYP3A4 = cytochrome P450 3A4

BNP and NT-proBNP in Heart Failure Diagnosis

Biomarker	Threshold	Clinical Notes
BNP	>100 pg/mL supports HF; <50 pg/mL makes HF unlikely	Falsely HIGH: renal impairment, atrial fibrillation. Falsely LOW: obesity, sacubitril-valsartan use
NT-proBNP	>300 pg/mL in acute setting	Not a neprilysin substrate — remains interpretable in patients on sacubitril-valsartan. Preferred biomarker in this population
Serial trend	Falling = improving	Monitor response to diuresis and heart failure therapy; rising level signals inadequate decongestion or deterioration

Nesiritide and NK1 Antagonists

Recombinant BNP · IV Only

Nesiritide (Natrecor)

Mechanism: activates natriuretic peptide receptors → vasodilation + natriuresis + renin-angiotensin-aldosterone suppression
Use: acute decompensated heart failure (adjunct to diuretics)
ASCEND-HF: modest dyspnea improvement; no mortality benefit
Not first-line — diuretics preferred
Dose-limiting adverse effect: hypotension
Contrast with sacubitril-valsartan: blocks BNP degradation (PARADIGM-HF: mortality benefit)

NK1 Receptor Antagonist · Antiemetic

Aprepitant / Fosaprepitant

Mechanism: blocks substance P at NK1 receptors in area postrema → prevents delayed nausea
Delayed phase (24–120 hrs): substance P / NK1; Acute phase (0–24 hrs): serotonin / 5-HT3
Given with: serotonin type 3 antagonist + dexamethasone (3-drug standard regimen)
Aprepitant: oral days 1–3; Fosaprepitant: single IV dose day 1
CYP3A4 inhibitor: doubles dexamethasone levels — use reduced dexamethasone dose
Induces warfarin metabolism — monitor INR after use

Vasoactive Peptide Clinical Decision Matrix — Chapter 24 Summary

Indication	Peptide Target	Drug(s) and Key Rule
HFrEF — chronic	RAAS + neprilysin	ACE inhibitor or ARB (mortality benefit) → upgrade to sacubitril-valsartan (PARADIGM-HF); 36-hr washout from ACE inhibitor required
HF — acute decompensation	Natriuretic peptide receptors	Nesiritide (adjunct to diuretics); no mortality benefit; use NT-proBNP to monitor if on sacubitril-valsartan
Hypertension / Diabetic nephropathy	RAAS (ACE or AT1)	ACE inhibitor first-line (renal protection); ARB if cough/angioedema; do not combine dual RAAS blockade
Pulmonary arterial hypertension	Endothelin (ETA/ETB)	ERA (bosentan/ambrisentan/macitentan) + PDE5 inhibitor; absolutely contraindicated in pregnancy
SIADH / Hyponatremia	Vasopressin V2	Vaptans (tolvaptan oral, conivaptan IV); aquaresis; tolvaptan: 30-day limit, no liver disease; correct ≤10 mEq/L/24 hr
Central DI / vWD / Hemophilia A mild	Vasopressin V2 (agonism)	Desmopressin; ineffective in nephrogenic diabetes insipidus; tachyphylaxis with repeated hemostatic dosing
Migraine — acute	CGRP receptor	Gepants (ubrogepant, rimegepant); no vasoconstriction; preferred over triptans in cardiovascular disease
Migraine — preventive	CGRP pathway	Anti-CGRP monoclonal antibodies (erenumab targets receptor; others target peptide); monthly/quarterly dosing
Chemotherapy nausea — delayed	Substance P / NK1	Aprepitant + serotonin type 3 antagonist + dexamethasone; reduce dexamethasone dose (CYP3A4 inhibition); monitor INR on warfarin

Suggested References

Author / Organization	Title	Source
Katzung BG, ed.	Basic and Clinical Pharmacology. 15th ed.	McGraw-Hill; 2021
Brunton LL, Knollmann BC, eds.	Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed.	McGraw-Hill; 2023
Maisel AS, Krishnaswamy P, Nowak RM, et al.	Rapid measurement of B-type natriuretic peptide in the emergency diagnosis of heart failure.	N Engl J Med. 2002;347(3):161–167
Heidenreich PA, Bozkurt B, Aguilar D, et al.	2022 AHA/ACC/HFSA guideline for the management of heart failure.	J Am Coll Cardiol. 2022;79(17):e263–e421
McMurray JJV, Packer M, Desai AS, et al; PARADIGM-HF Investigators and Committees.	Angiotensin-neprilysin inhibition versus enalapril in heart failure.	N Engl J Med. 2014;371(11):993–1004
O'Connor CM, Starling RC, Hernandez AF, et al.	Effect of nesiritide in patients with acute decompensated heart failure (ASCEND-HF).	N Engl J Med. 2011;365(1):32–43
Burnett JC Jr, Kao PC, Hu DC, et al.	Atrial natriuretic peptide elevation in congestive heart failure in the human.	Science. 1986;231(4742):1145–1147
Hesketh PJ, Kris MG, Basch E, et al.	Antiemetics: American Society of Clinical Oncology clinical practice guideline update.	J Clin Oncol. 2017;35(28):3240–3261
Navari RM, Aapro M.	Antiemetic prophylaxis for chemotherapy-induced nausea and vomiting.	N Engl J Med. 2016;374(14):1356–1367
Rademaker MT, Richards AM.	Cardiac natriuretic peptides for cardiac health.	Clin Sci (Lond). 2005;108(1):23–36