Pharmacology of Advanced Heart Failure and Hypertensive Medications

SA Node Modulating Drug for Hypertension and Heart Failure

  • General Classification and Function

    • This represents a newer class of medications specifically designed for hypertension and heart failure.
    • Unlike many other heart medications, it does not involve or affect heart muscle contraction.
    • Its primary site of action is the sinoatrial (SA) node, specifically slowing the electrical signals originating from the SA nerve.

  • Therapeutic Effects and Benefits

    • Heart Rate Reduction: The drug decreases the heart rate. By dropping the heart rate, it prevents tachycardia, which typically keeps the heart from resting sufficiently.
    • Cardiac Output (COCO): Slowing the heart rate can lead to a slight increase in cardiac output by allowing for more efficient filling and rest cycles.
    • Hospitalization Metrics: A significant clinical benefit of this medication is the decreased risk of hospitalization for heart failure patients.
    • CMS Metrics: This reduction in hospitalization is a key metric for the Center for Medicare and Medicaid Services (CMS). It helps hospitals satisfy the "thirty day readmissions" metric, ensuring the facility does not face financial penalties (is not "dinked").
    • Alternative for Beta-Blockers: This medication serves as a viable option for patients who cannot tolerate or take beta-blockers for various reasons.

  • Pharmacokinetics

    • Absorption: Absorbed through the gastrointestinal (GI) tract.
    • Peak Concentration: Reaches peak plasma levels in approximately 1 hour1 \, \text{hour}.
    • Metabolism: Metabolized in the liver and the intestines.
    • Specific Pathway: Metabolism involves the CYP3A4CYP3A4 enzyme system.
    • Excretion: Excreted through feces and bile.
    • Clinical Significance of Excretion: Because it is not excreted through the kidneys, it is a safe option for patients with kidney failure or impaired renal function.
    • Half-life: The medication has a half-life of 2.5 hours2.5 \, \text{hours}.
    • Duration: The drug has an approximate duration of 6 hours6 \, \text{hours}.

  • Contraindications and Cautions

    • Patient Instability: It is contraindicated in unstable patients, specifically those experiencing decompensated heart failure (actively in the middle of an episode).
    • Sinus Node Abnormalities: Contraindicated for any sinus node problems.
    • Bradycardia: It must not be used if the patient is already bradycardic or has any condition causing a heart rate less than 60 bpm60 \, \text{bpm}.
    • Sick Sinus Syndrome: Explicitly contraindicated.
    • Pacemakers: Contraindicated for patients who are dependent on a pacemaker.
    • Liver Function: The liver must be functioning well for proper metabolism.
    • Cautions: Atrial fibrillation is a caution; clinicians must weigh the risks and benefits in these cases.

  • Adverse Effects

    • Bradycardia.
    • Atrial fibrillation.
    • Luminous Phenomenon: A unique visual side effect characterized by sudden changes in brightness in portions of the visual field. Patients may report seeing colored lights, little flashes, or multiple images.

  • Drug Interactions

    • CYP3A4CYP3A4 Modulators: Any medication that inhibits or induces the CYP3A4CYP3A4 enzyme will affect the metabolism of this drug.
    • Heart Rate Modifiers: Any other medication that also drops the heart rate will interact and potentially cause severe bradycardia.

Angiotensin Receptor-Neprilysin Inhibitor (ARNI): Entresto

  • Composition and Identification

    • Components: A combination of two medications: Valsartan (an angiotensin receptor blocker or ARB) and Sacrovutriol (a neprilysin inhibitor).
    • Brand Name: Marketed under the name Entresto.
    • Target Population: Used in both adult and pediatric patients with symptomatic heart failure resulting from decreased ventricular function.

  • Mechanism of Action

    • Natriuretic Peptides: It blocks the breakdown of natriuretic peptides produced in the heart.
    • Excretion: This leads to increased excretion of sodium (Na+Na^+) and water.
    • RAAS Inhibition: The Valsartan component inhibits the Renin-Angiotensin-Aldosterone System (RAAS).
    • Cardiovascular Impact:
      • Decreased workload on the heart.
      • Decreased vascular volume (less fluid retention).
      • Decreased blood pressure.

  • Pharmacokinetics

    • Dissociation: Once administered, the drug separates into its two individual components: Dasartan and Sacrobutrinol.
    • Absorption and Timing:
      • Onset: Approximately 30 minutes30 \, \text{minutes}.
      • Peak: Reaches peak levels in 30 to 90 minutes30 \, \text{to} \, 90 \, \text{minutes}.
      • Steady State: Achieved within 3 days3 \, \text{days} of twice-daily dosing.
      • Duration: Approximately 12 hours12 \, \text{hours}.
    • Metabolism:
      • Valsartan: Does not undergo metabolism; it is excreted unchanged.
      • Sacrobutrin: Metabolized by an esterase enzyme.
    • Excretion: Excreted through the kidneys (urine) and feces.
    • Half-life: Approximately 10 hours10 \, \text{hours}.
    • Protein Binding: The drug is highly protein-bound. If a patient is protein-deficient, the effectiveness and distribution of the drug may be affected.
    • Food Interactions: Can be taken with or without food; food does not significantly affect absorption.

  • Contraindications

    • Angioedema History: Absolutely contraindicated in anyone with a history of angioedema caused by previous use of ACE inhibitors or ARBs.
    • Concurrent ACE Inhibitor Use: Cannot be taken with an ACE inhibitor due to the significantly increased risk of angioedema.
    • Pregnancy and Lactation: Contraindicated due to Valsartan's mechanism of blocking Angiotensin II, which is harmful to the fetus.
    • Renal Impairment & Aliskiren: Contraindicated in combination with Aliskiren for patients with poor renal function or a GFR less than 60 mL/min60 \, \text{mL/min}.

  • Adverse Effects and Risks

    • Hypotension (low blood pressure).
    • Hyperkalemia (high potassium levels), because ACE inhibitors and ARBs cause the body to retain potassium.
    • Renal impairment or failure.
    • Cough (similar to the side effect associated with ACE inhibitors).

  • Drug-Drug Interactions

    • ACE Inhibitors: Requires a mandatory washout period. ACE inhibitors must be discontinued at least 36 hours36 \, \text{hours} before starting Entresto to prevent angioedema.
    • Potassium-Sparing Diuretics: Significantly increases the risk of severe hyperkalemia.
    • Lithium: Increases the risk of lithium toxicity.
    • Nephrotoxic Agents: Use with other nephrotoxic medications (such as certain antibiotics) increases the risk of renal failure.

Questions & Discussion

  • Question: Is the first medication (the SA node drug) used as a standalone treatment?
  • Response: Yes, it is usually administered as a standalone medication.

Clinical Nursing Considerations

  • Assessment and Monitoring:
    • Obtain a complete patient history and physical exam.
    • Monitor cardiac status and all vital signs.
    • Maintain regular monitoring of laboratory values, specifically liver function tests (LFTs) and renal function.
    • Monitor potassium (K+K^+) levels closely, especially if the patient is on potassium-sparing diuretics.
  • Vital Thresholds:
    • Always verify the patient's heart rate before administration.
    • If the heart rate is less than 60 bpm60 \, \text{bpm}, the medication should be withheld and the prescribing provider must be notified.
  • Administration:
    • The SA node drug is oral (PO) and reaches peak effect in 1 hour1 \, \text{hour}.
    • Entresto is oral (PO), usually administered twice a day (BID) to maintain therapeutic levels.