Study Notes on Peripheral Nervous System Medications

Peripheral Nervous System Medications by Katie Knott, MSN, RNC-OB

Course: NUR 3305

WEEK 5 / 6 TOPICS

  • Peripheral/Autonomic Nervous System Overview

  • Sympathetic Nervous System (SNS) Medications

  • Parasympathetic Nervous System (PSNS) Medications

STUDENT LEARNING OBJECTIVES

  1. Define key terminology relevant to medications that affect the Sympathetic Nervous System (SNS).

  2. Differentiate between catecholamines and non-catecholamines and how their properties influence the pharmacokinetics of adrenergic medications.

  3. Explain the physiological and adverse effects that result from stimulating alpha 1, alpha 2, beta 1, and beta 2 receptors.

  4. Describe the concept of drug selectivity and how it impacts the therapeutic effects of adrenergic medications.

  5. Identify the mechanism of action, therapeutic effects, indications, side/adverse effects, drug interactions, and key considerations for each of the adrenergic agonists and antagonists.

SYMPATHETIC NERVOUS SYSTEM MEDICATIONS

Adrenergic Medications Review

SNS Receptors, Responses, and Adverse Effects

  • Receptor: Alpha 1

    • Organs Affected: Blood vessels in skin, viscera & mucosa, eyes (pupils), penis, bladder

    • Stimulation/Activation Effects:

    • Vasoconstriction

    • Mydriasis (dilated pupils)

    • Ejaculation

    • Sphincter contraction

    • Common Adverse Effects:

    • Hypertension

    • Necrosis to local tissues (IV route) = Vesicant

    • Bradycardia

  • Receptor: Alpha 2

    • Organs Affected: Presynaptic nerve terminals

    • Stimulation/Activation Effect: Inhibits norepinephrine (NE) release

    • Common Adverse Effects: Typically less adverse effects

  • Receptor: Beta 1

    • Organs Affected: Heart, kidneys

    • Stimulation/Activation Effects:

    • Increased heart rate (HR)

    • Increased contractility

    • Increased conduction through AV node

    • Release of renin

    • Common Adverse Effects:

    • Tachycardia & dysrhythmias

    • Angina (chest pain)

  • Receptor: Beta 2

    • Organs Affected: Arterioles of heart, lung, skeletal muscle, bronchi (lungs), uterus, liver

    • Stimulation/Activation Effects:

    • Vasodilation

    • Bronchodilation

    • Relaxation of smooth muscle

    • Breaks down glycogen, thus increasing glucose in blood

    • Enhanced contraction in skeletal muscle

    • Common Adverse Effects:

    • Hyperglycemia

    • Tremors

ADR NERGIC ANTAGONISTS/SYMPATHOLYTICS

Beta-Adrenergic Antagonists (First Generation)

  • Drug Names: Propranolol (Inderal)

  • Mechanism of Action:

    • Blocks primarily beta 1 and also beta 2 receptors

  • Therapeutic Effects (Indication):

    • Beta 1:

    • Reduces HR, force of contraction, and conduction through AV node (for cardiovascular diseases such as hypertension [HTN], dysrhythmias, myocardial infarction [MI], angina)

    • Reduces renin secretion by kidneys

    • Beta 2:

    • Causes bronchoconstriction, vasoconstriction, reduced glycogenolysis

  • Pharmacokinetics / Pharmacodynamics:

    • Highly lipid soluble

    • Extensive first-pass metabolism; food may delay absorption

  • Side / Adverse Effects:

    • Bradycardia

    • Hypotension

    • Reduced cardiac output

    • Fatigue

    • Heart block

    • Bronchospasm (must identify patients who cannot receive this medication)

    • Hypoglycemia (must identify patients who cannot receive this medication)

    • Depression (rare but affecting CNS)

  • Drug Interactions:

    • Calcium Channel Blockers may increase cardiac effects

  • Route(s):

    • Oral (PO) (Extended Release [ER], Extended-Release [XL], Immediate Release [IR]), Intravenous (IV)

  • Other Considerations:

    • Assess HR before administration (suspend if HR < 60)

    • What are the consequences if a patient suddenly stops this medication?

    • Is this selective or non-selective?

Beta 1 Antagonists (Second Generation)

  • Drug Names: Atenolol, Metoprolol (Lopressor)

  • Mechanism of Action:

    • Blocks beta 1 receptors

  • Therapeutic Effects (Indication):

    • Reduces HR, force of contraction, and conduction through AV node (for cardiovascular diseases such as HTN, congestive heart failure [CHF], MI, angina)

    • Reduces renin secretion by kidneys

  • Pharmacokinetics / Pharmacodynamics:

    • Metoprolol: Highly lipid soluble

  • Side / Adverse Effects:

    • Bradycardia

    • Reduced cardiac output

    • Heart block

  • Drug Interactions:

    • None specified

  • Route(s):

    • Oral (PO), Intravenous (IV)

  • Other Considerations:

    • Assess HR before administration (suspend if HR < 60)

    • Contraindicated in patients with bradycardia, AV block; caution needed in heart failure

    • What occurs if the medication is suddenly stopped → rebound excitation effect

    • No selective beta 2 blocker… no rationale for intentionally causing bronchoconstriction

    • Considered to be “cardioselective”

Adrenergic Antagonists (Third Generation)

  • Drug Names: Labetalol (Trandate)

  • Mechanism of Action:

    • Blocks alpha 1 and beta 1 receptors

  • Therapeutic Effects (Indication):

    • Alpha 1:

    • Causes vasodilation (for hypertension)

    • Beta 1:

    • Reduces HR, force of contraction, and conduction through AV node (for cardiovascular diseases such as HTN, dysrhythmias, MI, angina)

    • Reduces renin secretion by kidneys

  • Pharmacokinetics / Pharmacodynamics:

  • Side / Adverse Effects:

    • Bradycardia

    • Reduced cardiac output

    • Heart block

    • Orthostatic hypotension

  • Drug Interactions:

    • None specified

  • Route(s):

    • Oral (PO), Intravenous (IV)

  • Other Considerations:

    • Assess HR before administration (suspend if HR < ??)

    • Contraindicated in patients with bradycardia, AV block; caution needed in heart failure

    • What happens if this medication is suddenly stopped → rebound excitation effect

    • Still classified as a “beta-blocker”

Alpha-Adrenergic Antagonists

  • Drug Names: Prazosin (Minipress)

  • Mechanism of Action:

    • Blocks alpha 1 receptors

  • Therapeutic Effects (Indication):

    • Decreases BP by dilating arterioles/inhibiting vasoconstriction (for hypertension)

    • Relaxes smooth muscle of bladder neck (for benign prostatic hyperplasia)

  • Pharmacokinetics:

  • Side / Adverse Effects:

    • Orthostatic hypotension

    • Reflex tachycardia

    • Nasal congestion

    • Fainting after first dose (requires patient education)

    • May inhibit ejaculation leading to erectile dysfunction

  • Drug Interactions:

    • None specified

  • Route(s):

    • Oral (PO)

  • Other Considerations:

    • Check BP before administration