Pharmacology2000
1. BNP & NT-proBNP · 2. Nesiritide · 3. Substance P & NK1 · 4. Integrative Framework · 5. Clinical Decision Matrix · Infographic · References ↑ Top
Contents of this module
Section 1
BNP and NT-proBNP in Heart Failure: Biomarker Thresholds, Age Adjustment, and Clinical Utility
Quantifying myocardial wall stress and guiding diagnosis, prognosis, and treatment titration

Brain natriuretic peptide (BNP) and its amino-terminal prohormone fragment (NT-proBNP) are the two circulating biomarkers of myocardial wall stress in routine clinical use. Both derive from the same precursor, proBNP, which is cleaved by corin and furin proteases in cardiomyocytes subjected to stretch, volume overload, or pressure overload: the cleavage yields the biologically active 32-amino-acid BNP and the inactive 76-amino-acid NT-proBNP fragment in equimolar amounts. Their measurement, now universally available and performed with high-sensitivity immunoassays, has transformed the evaluation of dyspnea and the monitoring of heart failure therapy.1

The clinical distinction between BNP and NT-proBNP rests principally on their respective half-lives and renal clearance characteristics. BNP has a half-life of approximately 20 minutes, cleared by neutral endopeptidase (neprilysin) and natriuretic peptide clearance receptors (NPR-C), making it highly sensitive to acute changes in cardiac filling pressures. NT-proBNP has a half-life of 60 to 120 minutes and is eliminated primarily by renal filtration, so its levels are substantially higher than BNP in the same patient and are more profoundly affected by renal impairment. The 2019 ESC/HFA guideline and the 2022 AHA/ACC heart failure guideline both recognize BNP and NT-proBNP as Class I biomarkers for the diagnosis and prognosis of heart failure, with the understanding that the two assays are not interchangeable and that reference ranges differ substantially between them.2

The diagnostic cut-points for ruling out acute heart failure in the emergency department have been validated in the BREATHING NOT PROPERLY and PRIDE multinational studies. For BNP, a level below 100 pg/mL has a negative predictive value exceeding 90 percent for ruling out acute heart failure as a cause of dyspnea in the emergency setting; levels above 400 pg/mL are highly specific for heart failure. For NT-proBNP, age-stratified cut-points are used: values below 300 pg/mL rule out acute heart failure regardless of age, while diagnostic thresholds for confirming heart failure vary by age group (450 pg/mL for age below 50 years; 900 pg/mL for age 50 to 75 years; 1800 pg/mL for age above 75 years). The age stratification of NT-proBNP thresholds reflects the progressive decline in glomerular filtration rate with aging, which reduces renal clearance and elevates baseline NT-proBNP levels independent of cardiac pathology.2

Sacubitril-Valsartan and BNP Measurement: A Critical Assay Pitfall

Sacubitril-valsartan (Entresto) contains sacubitril, a neprilysin inhibitor that substantially reduces BNP degradation. Patients taking sacubitril-valsartan have markedly elevated BNP levels that do not reflect worsening heart failure; BNP levels may rise three- to fivefold from baseline within weeks of initiation, rendering BNP measurements uninterpretable for diagnostic or monitoring purposes in these patients. NT-proBNP, which is not a neprilysin substrate, is the appropriate natriuretic peptide biomarker in patients receiving sacubitril-valsartan, and monitoring should be switched to NT-proBNP at the time sacubitril-valsartan is started. This distinction has become a frequent source of clinical error as sacubitril-valsartan use has expanded following the PARADIGM-HF trial results.3

Natriuretic Peptide-Guided Heart Failure Therapy

Beyond their diagnostic role, serial BNP or NT-proBNP measurements are used to guide up-titration of heart failure pharmacotherapy and to assess prognosis. Failure to achieve a substantial reduction in NT-proBNP (target below 1000 pg/mL, or greater than 30 percent reduction from admission level) during a hospitalization for acute decompensated heart failure predicts a high 90-day readmission and mortality risk. The GUIDE-IT randomized trial tested whether serial NT-proBNP-guided therapy produced better outcomes than standard symptom-guided management in patients with HFrEF: while NT-proBNP-guided patients achieved greater NT-proBNP reductions, the trial did not demonstrate a significant difference in the primary composite outcome of time to first cardiovascular death or HF hospitalization. These results suggest that natriuretic peptide measurement adds most value as a diagnostic tool and prognostic risk stratifier rather than as a mandatory therapeutic target in all patients.2

BNP vs. NT-proBNP: Which to Use When
Use BNP when: (1) acute assessment is needed with rapid turnaround; (2) the patient is not taking sacubitril-valsartan; (3) point-of-care testing is available. Use NT-proBNP when: (1) the patient is taking sacubitril-valsartan (BNP is unreliable); (2) serial monitoring over weeks to months is planned (longer half-life reduces noise from acute hemodynamic perturbations); (3) age-adjusted thresholds need to be applied. Never use BNP levels to assess response to sacubitril-valsartan therapy — they will falsely suggest worsening.
Section 2
Nesiritide: Recombinant BNP, Mechanism, and the ASCEND-HF Trial
From physiological rationale to clinical evidence and current positioning

Nesiritide (Natrecor) is a recombinant human BNP produced by Escherichia coli expression and identical in structure to endogenous BNP. Its development was predicated on the physiological rationale that exogenous BNP would restore the natriuretic peptide axis that is overwhelmed and relatively deficient in decompensated heart failure: providing pharmacological natriuretic peptide activity would reduce preload and afterload, promote natriuresis and diuresis, and alleviate dyspnea without the arrhythmogenic or vasoconstrictor liabilities of inotropes. The clinical evidence, culminating in the ASCEND-HF trial, revealed a more complicated picture that substantially narrowed nesiritide's clinical role.4

Nesiritide acts by binding to natriuretic peptide receptor A (NPR-A), a guanylyl cyclase-coupled receptor on vascular smooth muscle cells, endothelium, and renal tubular cells. NPR-A activation generates cyclic guanosine monophosphate (cGMP), which activates protein kinase G (PKG). In vascular smooth muscle, PKG phosphorylates myosin light chain phosphatase and opens large-conductance calcium-activated potassium channels, producing profound vasodilation of both venous (preload reduction) and arterial (afterload reduction) circulations. In the kidney, NPR-A signaling in the inner medullary collecting duct suppresses the sodium-hydrogen exchanger and the epithelial sodium channel (ENaC), producing natriuresis and diuresis that is mechanistically distinct from loop diuretic action. In the sinoatrial node, cGMP/PKG signaling modulates pacemaker current, producing a modest negative chronotropic effect.510

The ASCEND-HF trial (Acute Study of Clinical Effectiveness of Nesiritide in Decompensated Heart Failure) randomized 7,141 patients hospitalized for acute decompensated heart failure to nesiritide (2 mcg/kg bolus followed by 0.01 mcg/kg/min infusion) or placebo for up to 7 days, in addition to standard care. The co-primary endpoints were dyspnea status at 6 and 24 hours and a 30-day composite of rehospitalization for heart failure or death from any cause. Nesiritide produced a modest but statistically significant improvement in self-reported dyspnea at 6 hours compared with placebo. However, there was no significant difference in the 30-day rehospitalization or mortality endpoint, and nesiritide-treated patients had a significantly higher rate of symptomatic hypotension (26.6 percent vs. 15.3 percent). No worsening of renal function was detected, addressing the concern raised by earlier smaller trials that nesiritide might impair renal outcomes. The overall conclusion of ASCEND-HF was that nesiritide provides modest symptomatic benefit but no outcome benefit and increases hypotension risk; it should not be used routinely in acute decompensated heart failure.4

Current Clinical Position of Nesiritide

Following ASCEND-HF, nesiritide is not recommended as a routine agent for acute decompensated heart failure by either the 2022 AHA/ACC or 2021 ESC heart failure guidelines. It remains an option in highly selected patients with volume overload and acute dyspnea who are intolerant of or refractory to high-dose loop diuretics, where its hemodynamic unloading effects may provide symptomatic relief as a bridge strategy. It should not be combined with vasopressors or other vasodilators without careful hemodynamic monitoring. In pediatric congenital heart disease centers, nesiritide has retained a niche application in postoperative management, where some evidence supports its hemodynamic benefits in a population that differs substantially from the adult HF population studied in ASCEND-HF.

Parameter Nesiritide (Natrecor)
Mechanism Recombinant human BNP; binds NPR-A → cGMP → PKG → venous and arterial vasodilation + natriuresis
Dose 2 mcg/kg IV (intravenous) bolus; then 0.01 mcg/kg/min continuous infusion; up to 7 days
Half-life ~18 minutes (neprilysin and NPR-C clearance)
ASCEND-HF result Modest dyspnea improvement at 6 h; no 30-day mortality or rehospitalization benefit; higher hypotension rate (26.6% vs. 15.3%); no renal worsening
Current guideline position Not recommended for routine use (AHA/ACC 2022, ESC 2021); reserved for highly selected patients
Key interaction Additive hypotension with ACE (angiotensin-converting enzyme) inhibitors, ARBs (angiotensin receptor blockers), other vasodilators; monitor blood pressure continuously during infusion
Nesiritide and BNP Assays: Second Pitfall
Because nesiritide is identical to endogenous BNP, its infusion elevates measured BNP levels dramatically. Clinicians monitoring heart failure therapy with BNP during a nesiritide infusion will observe falsely elevated values that reflect the drug rather than the patient's cardiac status. As with sacubitril-valsartan, NT-proBNP (N-terminal pro-B-type natriuretic peptide; not a neprilysin substrate and not the infused peptide) should be used for monitoring during and after nesiritide therapy.
Section 3
Substance P and NK1 Receptors: Aprepitant and Fosaprepitant in CINV
Tachykinin pharmacology and the neurokinin-1 pathway in chemotherapy-induced nausea and vomiting

Substance P (SP) is an 11-amino-acid neuropeptide of the tachykinin family encoded by the preprotachykinin A (TAC1) gene, expressed in primary sensory neurons of the dorsal root ganglia, enteric neurons, and brainstem nuclei involved in emesis regulation. Its preferred receptor, the neurokinin-1 receptor (NK1R), is a Gq/11-coupled seven-transmembrane receptor that mediates several of SP's central emetic effects, particularly the delayed phase of chemotherapy-induced nausea and vomiting (CINV). The NK1 receptor antagonists aprepitant and fosaprepitant represented a pharmacological breakthrough in CINV prophylaxis because they specifically addressed a component of the emetic cascade that 5-HT3 antagonists and corticosteroids alone could not adequately control.6

The neuropharmacology of CINV involves at least three mechanistic arms that have been exploited therapeutically. The acute phase (occurring within 24 hours of chemotherapy) is driven predominantly by serotonin (5-HT) released from enterochromaffin cells in the intestinal mucosa acting on 5-HT3 receptors on vagal afferents, which project to the nucleus tractus solitarius and the area postrema (chemoreceptor trigger zone). The delayed phase (24 to 120 hours post-chemotherapy) is driven predominantly by substance P acting on NK1 receptors in the nucleus tractus solitarius and area postrema, and is the primary therapeutic target of NK1 receptor antagonists. Anticipatory nausea involves central conditioning mechanisms rather than peripheral receptor activation and responds to anxiolytics rather than antiemetics. This mechanistic tripartite framework explains why contemporary highly emetogenic chemotherapy (HEC) prophylaxis requires at least three drug classes: a 5-HT3 antagonist, an NK1 antagonist, and dexamethasone, with or without a fourth agent (olanzapine) in the highest-risk protocols.67

Aprepitant (Emend) is an orally bioavailable NK1 receptor antagonist with approximately 67 percent oral bioavailability and a terminal half-life of 9 to 13 hours. It is extensively metabolized by CYP3A4, making it a moderate CYP3A4 inhibitor as well as a substrate, which creates important drug interactions: aprepitant increases plasma concentrations of CYP3A4 substrates including corticosteroids (requiring dexamethasone dose reduction from 12 to 8 mg when given with aprepitant), warfarin (monitor INR), vincristine (increased neurotoxicity risk), and imatinib. It also induces CYP2C9, potentially reducing warfarin efficacy several days after the aprepitant course ends. The standard aprepitant regimen for HEC prophylaxis is 125 mg on day 1, followed by 80 mg on days 2 and 3. Fosaprepitant (Emend for Injection) is an IV phosphate prodrug of aprepitant that achieves equivalent systemic exposure after a single 150 mg IV dose on day 1, offering a single-dose intravenous option that avoids the 3-day oral regimen.7

Netupitant is a second-generation NK1 antagonist combined in a fixed-dose capsule with palonosetron (a second-generation 5-HT3 antagonist) as the combination product netupitant/palonosetron (NEPA; Akynzeo). Rolapitant is a third-generation NK1 antagonist distinguished by its exceptionally long half-life of approximately 180 hours, enabling a single pre-chemotherapy dose to provide NK1 receptor coverage through the entire delayed CINV window without the CYP drug interaction concerns of aprepitant, since rolapitant does not inhibit or induce CYP3A4 but does inhibit CYP2D6. Understanding the CYP interaction profile of each NK1 antagonist is clinically essential because oncology patients receive complex polypharmacy regimens where these interactions have direct patient safety consequences.7

Agent Route / Dose (HEC) Half-life CYP Interactions Key Clinical Notes
Aprepitant (Emend) Oral: 125 mg day 1; 80 mg days 2–3 9–13 h Moderate CYP3A4 inhibitor + substrate; CYP2C9 inducer (delayed) Reduce dexamethasone to 8 mg; monitor INR on warfarin; vincristine neurotoxicity risk
Fosaprepitant (Emend IV) IV: 150 mg single dose day 1 Same as aprepitant (prodrug) Same CYP3A4 inhibition as aprepitant (single dose) Single-dose IV option; equivalent efficacy to 3-day oral aprepitant
Netupitant / Palonosetron (NEPA; Akynzeo) Oral: 1 capsule (300/0.5 mg) day 1 Netupitant ~90 h Moderate CYP3A4 inhibitor (netupitant); no clinically significant CYP2C9 induction Fixed NK1 + 5-HT3 combination; single capsule day 1 only; less day 2–3 NK1 needed
Rolapitant (Varubi) Oral: 180 mg single dose day 1 ~180 h Does NOT inhibit/induce CYP3A4; inhibits CYP2D6 Ultra-long half-life; no dexamethasone dose adjustment; CYP2D6 substrates require monitoring
Standard HEC Antiemetic Regimen (Day 1)
Five-drug regimen for highly emetogenic chemotherapy (e.g., cisplatin-based): (1) Aprepitant 125 mg or fosaprepitant 150 mg IV; (2) Palonosetron 0.25 mg IV or ondansetron 8–24 mg IV; (3) Dexamethasone 8 mg IV (dose reduced from 12 mg because of CYP3A4 inhibition by aprepitant); (4) Olanzapine 10 mg oral (added in highest-risk protocols per NCCN and ASCO 2020 guidelines); (5) Lorazepam 0.5–2 mg for anticipatory nausea as needed. On days 2–3: aprepitant 80 mg + dexamethasone 8 mg + olanzapine 10 mg (if included).
Section 4
Integrative Vasoactive Peptide Framework: RAAS, ET-1, AVP, Natriuretic Peptides, CGRP, and Substance P
How six vasoactive peptide systems interact in cardiovascular and neuroendocrine homeostasis

The six vasoactive peptide systems covered in Chapter 24 do not operate in isolation; they form an interlocking regulatory network in which activation or blockade of one system perturbs the others in predictable ways. Understanding these interactions is pharmacologically essential because many patients requiring RAAS blockade, endothelin receptor antagonism, or vasopressin antagonism carry multiple conditions simultaneously, and the drug interactions within this network are not merely pharmacokinetic but genuinely pharmacodynamic: one vasoactive peptide system modulates the expression, release, or receptor sensitivity of another.8

The RAAS and the natriuretic peptide system are the most directly antagonistic pair in this network. Angiotensin II (via AT1 [angiotensin type 1] receptors) promotes sodium retention, vasoconstriction, aldosterone secretion, and myocardial fibrosis; BNP (B-type natriuretic peptide) and ANP (atrial natriuretic peptide) counteract each of these effects by promoting natriuresis, vasodilation, aldosterone suppression, and anti-fibrotic signaling through NPR-A/cGMP. In decompensated heart failure, the RAAS predominates because the baroreceptor-mediated volume signals that normally suppress it are overwhelmed by reduced cardiac output; natriuretic peptides rise in response to wall stress but are insufficiently potent to overcome the activated RAAS. The sacubitril-valsartan combination exploits this biology by simultaneously blocking AT1 receptors (valsartan) and neprilysin (sacubitril), thereby both reducing angiotensin II activity and amplifying endogenous natriuretic peptide levels — a dual mechanism that accounts for the mortality benefit seen in PARADIGM-HF that exceeds that of ACE (angiotensin-converting enzyme) inhibitor therapy alone.39

Endothelin-1 (ET-1) and AVP act in concert as neurohormonal vasoconstrictors that are co-activated in heart failure and pulmonary arterial hypertension. Both peptides are upregulated by hypoxia, shear stress, and angiotensin II; both produce vasoconstriction through Gq-coupled receptors on vascular smooth muscle; and both contribute to the adverse remodeling and hemodynamic deterioration seen in these conditions. The natriuretic peptides suppress ET-1 secretion from endothelial cells, providing a feedback brake on endothelin-mediated vasoconstriction. Correspondingly, ET-1 stimulates AVP release from the posterior pituitary through central hypothalamic effects, creating a loop in which endothelin receptor antagonism reduces AVP-driven fluid retention in addition to its direct pulmonary vascular effects. These interactions explain why multiple vasoactive peptide pathways must be engaged simultaneously in pulmonary arterial hypertension management — monotherapy targeting only one system is rarely adequate for disease control in advanced PAH.8

CGRP and the natriuretic peptide system share important functional overlap in vasodilatory signaling: both reduce peripheral vascular resistance, both are released in response to myocardial stress or vascular injury, and both appear to serve cardioprotective roles during ischemia. CGRP signals through Gs/cAMP (cyclic AMP)/PKA (protein kinase A), while natriuretic peptides signal through NPR-A/cGMP (cyclic GMP)/PKG — two parallel second-messenger pathways that converge on similar downstream smooth muscle relaxation targets. Substance P, through NK1 receptor-mediated Gq signaling, acts as a modulatory signal in both the enteric nervous system and central pain and emesis pathways but has comparatively limited direct cardiovascular effects in physiological concentrations; its pharmacological relevance in this chapter is primarily through NK1 receptor antagonism for CINV control. These functional distinctions should inform how clinicians combine therapies: the cGMP and cAMP vasodilatory pathways are not redundant, and drugs acting on them may have additive hemodynamic effects that require monitoring.910

Counterregulatory and Amplifying Interactions

Several specific pharmacodynamic interactions within this network carry direct prescribing implications. ACE inhibitors not only reduce angiotensin II but also increase bradykinin levels by blocking kinase II (the same enzyme as ACE), which in turn stimulates endothelial production of nitric oxide and prostacyclin — explaining why ACE inhibitors reduce mortality in heart failure beyond pure angiotensin blockade alone, and why ARBs (angiotensin receptor blockers), which do not affect bradykinin, produce somewhat different organ protection profiles despite similar blood pressure lowering. Vaptans (AVP V2 antagonists) produce aquaresis without natriuresis, meaning that correction of hyponatremia in heart failure with tolvaptan does not reduce the volume overload driven by RAAS activation — diuretics remain necessary for volume management even when vaptans correct the serum sodium. Neprilysin inhibition with sacubitril raises not only BNP but also ANP, bradykinin, substance P, and adrenomedullin, since all are neprilysin substrates; the cough and angioedema observed with sacubitril-valsartan (though lower than with ACE inhibitors) reflects bradykinin accumulation from this shared substrate mechanism.9

Section 5
Clinical Decision Matrix: Targeting Vasoactive Peptide Pathways by Indication
Selecting the right vasoactive peptide intervention for HFrEF, PAH, hyponatremia, migraine, and CINV

The six vasoactive peptide pharmacology systems reviewed in Chapter 24 map onto a distinct and non-overlapping set of clinical indications. Framing therapeutic selection as a peptide-pathway decision matrix clarifies the mechanistic rationale for each agent class, reduces the risk of under-treatment (failing to engage a relevant pathway) or over-treatment (redundantly blocking the same pathway with multiple agents), and consolidates the pharmacological principles of the entire chapter into an actionable clinical framework.10

Clinical Indication Primary Peptide Pathway First-Line Intervention Second-Line / Add-On Monitoring / Caution
HFrEF (LVEF [left ventricular ejection fraction] <40%) RAAS (renin-angiotensin-aldosterone system; excess Ang II, aldosterone); Deficient natriuretic peptides ACE (angiotensin-converting enzyme) inhibitor or ARB (angiotensin receptor blocker) + beta-blocker + MRA; upgrade to sacubitril-valsartan if tolerated SGLT2 inhibitor; loop diuretic for volume; CRT/ICD per guideline Use NT-proBNP (N-terminal pro-B-type natriuretic peptide; not BNP [B-type natriuretic peptide]) for monitoring on sacubitril-valsartan; check K⁺ and creatinine with RAAS agents
Pulmonary Arterial Hypertension (PAH) Excess ET-1 (endothelin-1; ETA/ETB); Deficient PGI2 and NO (nitric oxide) ERA (endothelin receptor antagonist; ambrisentan or macitentan) + PDE5i (phosphodiesterase type 5 inhibitor; sildenafil) combination; add prostacyclin analog in WHO FC III–IV Selexipag (IP receptor agonist); IV (intravenous) epoprostenol for advanced disease LFTs monthly for bosentan; avoid ERAs in pregnancy (teratogenic); avoid PDE5i with nitrates
Euvolemic / Hypervolemic Hyponatremia Excess AVP (arginine vasopressin; V2-mediated AQP2 insertion) Fluid restriction; tolvaptan (V2 antagonist) if refractory; conivaptan (V1a + V2) for in-hospital use Salt tablets; urea in refractory cases Inpatient initiation mandatory; monitor Na q6–8 h; ceiling 10–12 mEq/L per 24 h; CI in hypovolemia
Central Diabetes Insipidus Deficient AVP secretion (V2 pathway inactive) Desmopressin (V2-selective agonist): intranasal 10–40 mcg or oral 0.1–0.4 mg Chlorpropamide (potentiates AVP; rarely used); thiazide diuretics in partial central DI Allow breakthrough polyuria between doses; monitor serum Na; ineffective in nephrogenic DI
Acute Migraine Excess CGRP (trigeminovascular release; CLR/RAMP1 activation) Triptans (5-HT1B/D agonists) if no CV (cardiovascular) contraindication; gepants (ubrogepant, rimegepant, zavegepant) if CV CI or triptan failure NSAIDs (non-steroidal anti-inflammatory drugs); dihydroergotamine; IV (intravenous) antiemetics (metoclopramide, prochlorperazine) Triptans CI in IHD, stroke, uncontrolled HTN (hypertension), hemiplegic/basilar migraine; gepants: CYP3A4 interactions
Migraine Prevention Excess CGRP (chronic trigeminovascular sensitization) Anti-CGRP mAbs (erenumab, fremanezumab, galcanezumab, eptinezumab) after ≥2 failed oral preventives; gepants (rimegepant, atogepant) as oral preventive option Beta-blockers (propranolol, metoprolol); topiramate; amitriptyline; valproate Avoid anti-CGRP agents within 3–6 months of major CV event; monitor BP (blood pressure) on erenumab 140 mg
CINV (Highly Emetogenic Chemotherapy) Excess SP at NK1 receptors (delayed phase); Excess 5-HT at 5-HT3 receptors (acute phase) Aprepitant 125/80/80 mg or fosaprepitant 150 mg IV + palonosetron 0.25 mg IV + dexamethasone 8 mg + olanzapine 10 mg (days 1–4) Lorazepam for anticipatory nausea; haloperidol for breakthrough Reduce dexamethasone dose with aprepitant (CYP3A4 inhibition); monitor INR if on warfarin; CYP2D6 substrates with rolapitant
Integrative Pharmacological Principles for the Vasoactive Peptide Series

Several overarching principles unify the pharmacology of vasoactive peptide systems and should guide clinical reasoning. First, most vasoactive peptide systems function as homeostatic pairs: the RAAS (vasoconstrictive, sodium-retaining) is counterbalanced by natriuretic peptides (vasodilatory, natriuretic); ET-1 (vasoconstrictive) is counterbalanced by prostacyclin and nitric oxide; AVP (antidiuretic) is counterbalanced by vaptans when its action becomes pathological. Effective pharmacotherapy generally involves either restoring a deficient counterregulatory system (desmopressin in central DI, nesiritide as supplemental BNP) or blocking an excessively active vasoconstrictive system (ACE inhibitors, ARBs, ERAs, vaptans). Second, the receptor signal transduction pathway of each system predicts its hemodynamic effects: Gq-coupled peptides (ET-1, AVP V1a, SP) produce vasoconstriction or cellular excitation through IP3 (inositol trisphosphate)/Ca2+; Gs-coupled peptides (CGRP, natriuretic peptides) produce vasodilation through cAMP (cyclic AMP) or cGMP (cyclic GMP) second messengers; NPR-A (natriuretic peptides) and the NO/sGC pathway converge on cGMP, explaining why PDE5 inhibitors (which prevent cGMP degradation) potentiate both natriuretic peptide and nitric oxide vasodilatory signaling in the pulmonary vasculature.10

Third, the half-life and route of administration of vasoactive peptide drugs have direct implications for how they should be used in acute versus chronic clinical contexts. Short half-life drugs (nesiritide, vasopressin, intravenous nitrates) are suited to acute hemodynamic management under continuous monitoring. Intermediate half-life drugs (vaptans, gepants, oral RAAS agents) require regular dosing but allow day-to-day titration based on clinical response. Long half-life drugs (anti-CGRP monoclonal antibodies, macitentan) enable infrequent dosing with stable receptor occupancy, making them ideal for chronic prevention where patient adherence to daily regimens is a limiting factor. Fourth, drug interactions within this network are not merely additive but sometimes synergistic: sacubitril-valsartan's superior outcomes relative to RAAS monotherapy, the superiority of triple-pathway PAH therapy over monotherapy, and the superiority of three-drug CINV prophylaxis over two-drug regimens all reflect synergistic pharmacodynamic interactions at mechanistically distinct targets.910

Chapter 24 Summary: Six Systems, One Network
The vasoactive peptide pharmacology covered in PEP-01 through PEP-06 constitutes the most clinically impactful expansion of cardiovascular and neurological pharmacotherapy of the past three decades. RAAS inhibition (PEP-01/02) is the cornerstone of HFrEF management. Sacubitril-valsartan (PEP-02) represents the first pharmacological amplification of the natriuretic peptide system. Endothelin receptor antagonism (PEP-03) transformed PAH from a uniformly fatal disease to one where survival can be measured in decades. Vasopressin antagonism (PEP-04) enabled the first mechanism-specific treatment for hyponatremia. CGRP pathway blockade (PEP-05) produced the first migraine-specific drug class without vasoconstriction. NK1 antagonism (PEP-06) closed the gap in CINV control that 5-HT3 antagonists alone could not bridge. Taken together, these six systems demonstrate that precise receptor-level pharmacological targeting of endogenous peptide signals, rather than broad physiological manipulation, is the direction in which cardiovascular and neurological pharmacotherapy continues to evolve.
Visual Summary
Infographic — PEP-06
A visual synthesis of natriuretic peptides, nesiritide, NK1 pharmacology, and the integrative vasoactive peptide framework
References
Selected References
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  2. 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. doi:10.1016/j.jacc.2021.12.012

  3. McMurray JJV, Packer M, Desai AS, et al. Angiotensin-neprilysin inhibition versus enalapril in heart failure. N Engl J Med. 2014;371(11):993–1004. doi:10.1056/NEJMoa1409077

  4. O'Connor CM, Starling RC, Hernandez AF, et al. Effect of nesiritide in patients with acute decompensated heart failure. N Engl J Med. 2011;365(1):32–43. doi:10.1056/NEJMoa1100171

  5. 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. doi:10.1126/science.2935937

  6. 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. doi:10.1200/JCO.2017.74.4789

  7. Navari RM, Aapro M. Antiemetic prophylaxis for chemotherapy-induced nausea and vomiting. N Engl J Med. 2016;374(14):1356–1367. doi:10.1056/NEJMra1515442

  8. Kemp CD, Conte JV. The pathophysiology of heart failure. Cardiovasc Pathol. 2012;21(5):365–371. doi:10.1016/j.carpath.2011.11.007

  9. Packer M, McMurray JJV, Desai AS, et al. Angiotensin receptor neprilysin inhibition compared with enalapril on the risk of clinical progression in surviving patients with heart failure. Circulation. 2015;131(1):54–61. doi:10.1161/CIRCULATIONAHA.114.013748

  10. Rademaker MT, Richards AM. Cardiac natriuretic peptides for cardiac health. Clin Sci (Lond). 2005;108(1):23–36. doi:10.1042/CS20040253

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