Hesi 10: Ch. 31

Drugs Acting on the Autonomic Nervous System

Chapter 31: Adrenergic Antagonists

  • Adrenergic Antagonists are classified as follows:

    • Nonselective Adrenergic Blocking Agents

    • Nonselective Alpha-adrenergic Blocking Agents

    • Alpha 1 Selective Adrenergic Blocking Agents

    • Nonselective Beta-Adrenergic Blocking Agents

    • Beta 1 Selective Adrenergic Blocking Agents

Alpha-Receptors

  • Alpha-1 Receptors:

    • Responsible for processes such as:

    • Vasoconstriction leading to increased peripheral resistance and increased blood pressure.

    • Contraction of piloerection muscles, pupil dilation, thickened salivary secretions.

    • Closure of the urinary bladder sphincter and maintenance of male sexual emissions.

  • Alpha-2 Receptors:

    • Involvement in the negative feedback control of norepinephrine release from the presynaptic neuron and moderation of insulin release from the pancreas.

Beta-Receptors

  • Beta-1 Receptors:

    • Functions include:

    • Increased heart rate and conduction through the atrioventricular node.

    • Enhanced myocardial contraction.

    • Induction of lipolysis in peripheral tissues.

  • Beta-2 Receptors:

    • Actions entail:

    • Vasodilation, bronchial dilation, increased breakdown of muscle and liver glycogen.

    • Release of glucagon from the pancreas, relaxation of uterine smooth muscle.

    • Decreased gastrointestinal (GI) muscle tone and activity, reduced GI secretions, and relaxation of the urinary bladder detrusor muscle.

Non-Selective Adrenergic Blocking Agents (Antagonists)

  • Examples:

    • Amiodarone, Carvedilol, Labetalol.

  • Mechanism:

    • Blocks both alpha and beta receptor sites.

    • Notably, Labetalol is often mislabeled as a beta blocker as it also blocks alpha-1 receptors.

  • Actions:

    • Decreases heart rate (HR), lowers blood pressure (BP), and increases renal perfusion.

  • Uses:

    • Labetalol is used for hypertension (HTN).

    • Amiodarone is utilized in emergencies as part of ACLS drugs and as an antiarrhythmic (discussed in Pharm 3).

    • Carvedilol is used for HTN and heart failure; it possesses beneficial alpha-blocking activity despite most drugs in this class being contraindicated in heart failure.

Side Effects of Non-Selective Adrenergic Blocking Agents

  • CNS Effects:

    • Dizziness, insomnia, depression, fatigue.

  • GI Effects:

    • Nausea and vomiting (N&V), diarrhea, anorexia, flatulence.

  • Cardiac Effects:

    • Arrhythmias, hypotension, heart failure (HF), and stroke.

  • Respiratory Effects:

    • Bronchospasm, cough, rhinitis, bronchial obstruction.

  • Other Effects:

    • Decreased exercise tolerance, hypoglycemia, rash, and potential for hepatic failure with carvedilol and labetalol.

    • Amiodarone may lead to hepatic injury, pulmonary fibrosis, loss of vision, and thyroid issues.

Teaching/Nursing Considerations

  • Abrupt discontinuation should be avoided; taper dose slowly over 2 weeks to minimize risks of myocardial infarction (MI), stroke, or arrhythmias.

  • Consult a physician regarding any withdrawal drugs before surgery.

  • Patient monitoring includes:

    • Regular monitoring of heart rate and blood pressure.

    • Monitoring of GI system, particularly increased need for access to the bathroom due to diarrhea.

    • Observation for signs and symptoms (s/s) of liver failure.

  • Safety Precautions:

    • Given the aforementioned side effects and interactions, nurses and patients should be well informed.

    • Advisable to avoid herbal and alternative therapies.

Nonselective Alpha-Adrenergic Blocking Agents

  • Phentolamine (Regitine):

    • Currently, the only drug in this class still in use.

    • Exhibits specific affinity to alpha receptors.

  • Mechanism:

    • Blocking alpha-1 lowers blood pressure.

    • Blocking alpha-2 causes reflex tachycardia.

  • Uses:

    • Most often used for management of extravasation to prevent cell death and tissue sloughing; causes local vasodilation and restoration of blood flow to the area.

Alpha-1 Selective Adrenergic Blocking Agents

  • Examples: Alfuzosin, doxazosin (Cardura), prazosin (Minipress), silodosin, tamsulosin (Flomax), terazosin.

  • Characteristics:

    • Possess specific affinity to alpha-1 receptors.

    • Induce a decrease in blood pressure without eliciting reflex tachycardia; relax the bladder and prostate.

  • Uses:

    • Effective in managing benign prostatic hypertrophy (BPH) as described in Chapter 52.

  • Side Effects:

    • Related to alpha-1 blocking activity:

    • Common issues include hypotension, dizziness, tachycardia, and priapism.

    • Risk of orthostatic hypotension with the first dose.

  • Teaching/Nursing Considerations:

    • Close monitoring of vital signs (VS); implement safety precautions where necessary.

Nonselective Beta-Adrenergic Blocking Agents

  • Examples: Carteolol, levobunolol, nadolol, nebivolol, propranolol (Inderal), sotalol, timolol.

  • Mechanism:

    • These agents block both beta-1 and beta-2 receptors.

  • Uses:

    • Primarily employed in treating cardiovascular issues such as hypertension, angina, and preventing reinfarction after myocardial infarction. Also applied for migraine headaches.

  • Main Therapeutic Effects:

    • Cardiac Blockade:

    • Leads to decreased heart rate, contractility, and excitability, contributing to reduced arrhythmias, workload, and oxygen consumption.

    • Nephron Blockade:

    • Decreases renin release, subsequently lowering blood pressure.

Propranolol

  • Characteristics:

    • Highly effective in blocking all beta receptors. Other medications may offer more selectivity and fewer adverse effects.

    • Food increases the availability of propranolol while decreasing the absorption of some other drugs within the class.

    • Propranolol crosses the blood-brain barrier (BBB) while other drugs may not.

  • Cautions/Contraindications:

    • Propranolol is contraindicated in patients with bradycardia, heart failure, shock, heart block, bronchospasms, or acute asthma. Caution needed in diabetic, COPD/asthmatic, renal/hepatic dysfunction.

  • Side Effects:

    • Related to blockade of beta receptors:

    • CNS side effects: dizziness, fatigue, sleep disturbances.

    • Cardiac issues: bradycardia, hypotension.

    • Respiratory challenges: difficulty breathing, coughing, bronchospasm.

    • Gastrointestinal effects include nausea, vomiting, diarrhea, and colitis.

    • Genitourinary effects: decreased libido, impotence.

    • Other issues such as decreased exercise tolerance and variations in blood sugar levels (hypo/hyperglycemia).

Beta-1 Selective Adrenergic Blocking Agents

  • Examples: Acebutolol, atenolol (Tenormin), betaxolol, bisoprolol, esmolol, metoprolol (Lopressor).

  • Characteristics:

    • Typically do not block beta-2 receptors, thus preserving bronchodilation, making them preferred in patients who smoke or have asthma.

    • Becomes less selective when doses exceed therapeutic levels.

  • Uses:

    • Employed in treating hypertension, angina, and managing some cardiac arrhythmias. They also aid in preventing reinfarction after myocardial infarction.

  • Teaching/Nursing Considerations:

    • Abrupt cessation is discouraged; taper doses over a two-week period.

    • Oral administration of metoprolol with food enhances drug absorption.

    • Consider the possibility of increased CNS side effects with metoprolol due to its ability to cross the BBB.