Adrenergic Antagonists

Learning Objectives

  • Upon completion of this chapter, you will be able to:

    • 1. Describe the effects of adrenergic blocking agents on adrenergic receptors, correlating these effects with their clinical effects.

    • 2. Discuss the use of adrenergic blocking agents across the lifespan, noting variations in response due to age, weight, and concomitant medical conditions.

    • 3. Describe the therapeutic actions, indications, pharmacokinetics, contraindications, and cautions, the most common adverse reactions, and important drug-drug interactions associated with adrenergic blocking agents, including specific populations like pediatrics and geriatrics.

    • 4. Compare and contrast the prototype drugs labetalol, phentolamine, doxazosin, propranolol, and atenolol with other adrenergic blocking agents in terms of mechanism of action, clinical applications, side effects, and patient demographics.

    • 5. Outline the nursing considerations, including important teaching points, for patients receiving an adrenergic blocking agent, addressing the importance of adherence, monitoring for adverse effects, and lifestyle modifications that may be needed.

Key Terms

  • Adrenergic receptor-site specificity: A drug's affinity for only adrenergic receptor sites; certain drugs may have specific affinity for only alpha- or only beta-adrenergic receptor sites.

  • Alpha-Selective Adrenergic Blocking Agents: Drugs that block the postsynaptic alpha-receptor sites, causing a decrease in vascular tone and vasodilation that leads to a fall in blood pressure; these drugs do not block the presynaptic alpha-receptor sites, thereby reducing the likelihood of reflex tachycardia that might occur with hypotension.

  • Beta-Adrenergic Blocking Agents: Drugs that, at therapeutic levels, specifically block the beta-receptors of the sympathetic nervous system, affecting heart rate and contractility.

  • Beta-Selective Adrenergic Blocking Agents: Drugs that, at therapeutic levels, specifically block the beta-receptors in the sympathetic nervous system while sparing beta-receptors with respiratory effects, useful in patients with asthma.

  • Bronchodilation: Relaxation of the smooth muscles in the bronchi, resulting in a widening of the bronchi, an essential therapeutic effect in managing conditions like asthma and COPD.

  • Pheochromocytoma: A rare tumor of chromaffin cells of the adrenal medulla that causes excessive release of norepinephrine and epinephrine, leading to severe hypertension and associated symptoms like headaches and palpitations.

  • Sympatholytic: A class of drugs that inhibit the effects of the sympathetic nervous system, providing therapeutic effects in conditions like hypertension and anxiety.

Drug List

  • Nonselective Adrenergic Blocking Agents:

    • Amiodarone

    • Carvedilol

    • Labetalol

Nonselective Alpha-Adrenergic Blocking Agents

(Further details not provided in the transcript)

Prototype Summary: Phentolamine

  • Indications:

    • Prevention or control of hypertensive episodes associated with pheochromocytoma.

    • Test for diagnosis of pheochromocytoma, validated through observation of blood pressure changes.

    • Prevention and treatment of dermal necrosis and sloughing linked to IV extravasation of norepinephrine or dopamine, critical for avoiding complications in emergency settings.

  • Actions:

    • Competitively blocks postsynaptic alpha- and presynaptic alpha-receptors, causing significant vasodilation and lowering of blood pressure, often accompanied by increased reflex tachycardia, necessitating careful monitoring during administration.

Pharmacokinetics:

  • Route: Intramuscular, IV.

  • Onset:

    • Intramuscular: Rapid

    • IV: Immediate

  • Peak Duration:

    • Intramuscular: 20 min

    • IV: 2 min

  • T1/2: Metabolism and excretion are unknown, highlighting the need for individualized patient care based on clinical response and side effects.

Adverse Effects:

  • Acute and prolonged hypotensive episodes, requiring vigilance in monitoring.

  • Myocardial Infarction (MI) although rare; patients should be educated about signs and symptoms.

  • Tachycardia, potentially leading to arrhythmias.

  • Nausea and flushing, which may impact compliance with medication regimens.

Nursing Considerations for Patients Receiving Nonselective Alpha-Adrenergic Blocking Agents
Assessment: History and Examination

  • Assess for contraindications or cautions:

    • Known allergies to the drug, which may vary by patient.

    • Presence of cardiovascular diseases, which may be exacerbated by the use of this drug, guiding individualized treatment plans.

    • Current status of pregnancy or lactation due to potential adverse effects, crucial for maternal-fetal medicine consultations.

  • Perform a physical assessment to establish baseline data for determining effectiveness of the drug and occurrence of adverse effects, ensuring a comprehensive approach to drug therapy.

  • Assess orientation, affect, and reflexes for CNS changes related to drug therapy, considering the potential impact on safety and coordination.

  • Monitor cardiovascular status, including pulse, blood pressure, peripheral perfusion, and cardiac output; also, monitor urine output to reflect kidney perfusion as an assessment of cardiac function, reinforcing interdisciplinary communication.

Nursing Conclusions Related to Drug Therapy:

  • Injury risk related to CNS and CV effects of the drug must be communicated to patients, ensuring understanding and awareness.

  • Altered cardiac function necessitates ongoing assessment and potential adjustments in therapy based on individual patient needs, including education on lifestyle modifications to improve outcomes.