Autonomic Drugs Study Guide

AUTONOMIC DRUGS

CHAPTER 4

LEARNING OBJECTIVES

  • Identify the major components and functional organization of the autonomic nervous system.
  • Discuss the major neurotransmitters in the sympathetic autonomic nervous system and the importance of receptors.
  • Discuss the pharmacologic effects, adverse reactions, contraindications, and dental considerations of cholinergic agents, which act on the parasympathetic nervous system.
  • Discuss the pharmacologic effects, adverse reactions, contraindications, and dental considerations of anticholinergic agents, which act on the parasympathetic nervous system.
  • Discuss the pharmacologic effects, adverse reactions, contraindications, and dental considerations of adrenergic agents and list several specific adrenergic agents.
  • Explain the workings of adrenergic blocking agents and neuromuscular blocking agents.

WHY DOES A DENTAL HYGIENIST NEED TO BE FAMILIAR WITH THE AUTONOMIC NERVOUS SYSTEM DRUGS?

  • Certain ANS drugs are used in dentistry.
  • Vasoconstrictors increase salivary flow.
  • Some ANS drugs produce oral adverse reactions, for example:
    • Anticholinergic drugs cause xerostomia.
  • Members of other drug groups have effects similar to those of the ANS drugs:
    • Antidepressants
    • Antipsychotics

AUTONOMIC NERVOUS SYSTEM REVIEW

  • Controls automatic, involuntary responses.
  • Responsible for regulating:
    • Blood pressure
    • Heart rate
    • GI Motility
    • Salivation
    • Bronchial/smooth muscle tone.
  • Requires specific neurotransmitters, which are chemicals released to send messages, and a variety of receptors.

ANATOMY OF THE AUTONOMIC NERVOUS SYSTEM

Two Divisions:

  1. Sympathetic Autonomic Nervous System (SANS)
    • Fight or Flight
    • Think S = Stress!
  2. Parasympathetic Autonomic Nervous System (PANS)
    • Rest and Digest
    • Think P = Peace or you cook in a pan!

AUTONOMIC NERVOUS SYSTEM RESPONSES

Sympathetic Response (SANS) vs. Parasympathetic Response (PANS)

  • Sympathetic (SANS - Fight or Flight – Stress):

    • Increases Blood Pressure (vasoconstriction)
    • Increases Heart Rate
    • Increases Oxygen to muscles
    • Reduces Blood flow to the GI system, decreasing peristalsis.
    • Dilates bronchioles
    • Dilates pupils (mydriasis)
    • Decreases Salivary flow

  • Parasympathetic (PANS - Rest and Digest - Peace):

    • Decreases Blood Pressure
    • Decreases Heart Rate
    • Increases Blood flow to GI system, increasing peristalsis.
    • Constricts bronchioles
    • Constricts pupils (miosis)
    • Increases Salivary flow

  • Agent Classifications:

    • Adrenergic agents / sympathomimetics: Think Adrenaline
    • Cholinergic agents / parasympathomimetics: Think Colon

COMPONENTS OF THE AUTONOMIC NERVOUS SYSTEM

  • Both PANS & SANS consist of:
    • Afferent (sensory) fibers: What’s happening?
    • Central integrating areas: Coordinate the information!
    • Efferent (peripheral) motor preganglionic fibers: This is what’s happening – e.g., Heart is beating too slow.
    • Postganglionic motor fibers: Heart, begin beating!

TYPICAL EFFERENT NERVE - FIG. 4.1 PG. 32

  • The preganglionic fiber originates in the brain.
  • It ends at the synapse, where the neurotransmitter carries the message to the postganglionic fiber.
  • The postganglionic fiber releases a neurotransmitter to relay the message to an effector organ.

EFFERENT NERVE DIFFERENCES

SANS

  • Short preganglionic fibers.
  • Long postganglionic fibers.
  • Stimulation of the SANS results in adrenal medulla releasing epinephrine & small amounts of norepinephrine into circulation.
  • BOARD ALERT

PANS

  • Long preganglionic fibers.
  • Short postganglionic fibers.

NEUROTRANSMITTERS

  • Carry messages and facilitate communication between nerves or nerves and effector tissues by releasing chemical neurotransmitters across the synaptic cleft.
  • Released to interact with the receptor, usually found on the postsynaptic fiber and the effector organ.
  • Can also be present on the presynaptic membrane.

NEUROTRANSMITTERS BETWEEN PREGANGLIONIC AND POSTGANGLIONIC NERVES

  • SANS
    • Preganglionic neurotransmitter: Acetylcholine (ACh)
    • Postganglionic fiber: Norepinephrine (NE)
  • PANS
    • Preganglionic neurotransmitter: Acetylcholine (ACh)
    • Postganglionic fiber: Acetylcholine (ACh)

TERMINOLOGY REVIEW

  • Cholinergic: a drug that acts where ACh is released
  • Adrenergic: a drug that acts where NE is released
  • Parasympatho-: prefix for drugs that act where PANS acts
  • Sympatho-: prefix for drugs that act where SANS acts
  • -mimetic: suffix indicating a drug that "mimes" or acts like the neurotransmitter (agonist)
  • -lytic or -blocker: suffix indicating a drug that blocks the neurotransmitter (antagonist)

PANS CLASSES OF DRUGS

Cholinergic (Parasympathomimetic) Agents

  • Mimic the PANS effects:
    • Bradycardia
    • Decreased blood pressure
    • Increased motility
    • Miosis (pupil constriction)
    • Decreased intraocular pressure

Anticholinergic (Parasympatholytic) Agents

  • Act opposite of PANS:
    • Block ACh receptors
    • Mydriasis (dilation of pupil)
    • Decreased secretions and GI motility

CHOLINERGIC (PARASYMPATHOMIMETIC) AGENTS

  • Use: treat xerostomia, urinary retention, glaucoma, & Alzheimer’s
  • Large doses cause SLUD: Salivation, Lacrimation, Urination, Defecation
  • Examples:
    • Pilocarpine (Salagen) – treats xerostomia
    • Cevimeline (Evoxac) – treats xerostomia

Contraindications for Cholinergic Agents

  • Asthma: Causes bronchoconstriction
  • Peptic Ulcer: Increases GI secretions
  • Cardiac Disease: Decreases heart rate
  • GI/Urinary Obstruction: Increases GI motility

ANTICHOLINERGIC (PARASYMPATHOLYTIC) AGENTS

  • Act opposite of PANS; block ACh receptors
  • Effects include:
    • Mydriasis (dilation of pupil)
    • Decreased secretions
    • Decreased GI motility
    • Helpful Hint: Think ABCD
    • A = Anticholinergic agents
    • B = Blurred vision or Bladder retention
    • C = Constipation
    • D = Dry mouth
  • Examples:
    • Atropine: used pre-operatively to reduce salivary flow in dental procedures
    • Ipratropium: COPD treatment; relaxes smooth muscle in the respiratory system
    • Scopolamine: for motion sickness prevention
    • Loperamide (Imodium): used to treat diarrhea

Contraindications for Anticholinergic Agents

  • Glaucoma: Can cause an acute rise in intraocular pressure
  • Prostatic Hypertrophy: benign enlargement of the prostate
  • Intestinal or Urinary Obstruction or Retention
  • Cardiovascular Disease: may cause tachycardia

PANS (Parasympathetic) Stimulation

  • Acetylcholine released from the preganglionic nerve into the synapse is received by receptors of the postganglionic nerve.
  • Action potential carries the message, leading to Acetylcholine release from postganglionic nerve.
  • Causes blood vessels supplying salivary glands to dilate, increasing salivation.
  • Note: Increased salivation is undesirable during oral surgery, so an autonomic drug may be given pre-surgery to decrease salivation.

SYMPATHETIC AUTONOMIC NERVOUS SYSTEM

Adrenergic Receptors

  • α-Receptors:

    • Stimulation results in smooth-muscle vasoconstriction; located in skin & skeletal muscle.
    • Drugs blocking this action are α-adrenergic blocking agents.

  • β-Receptors:

    • β1 receptors increase rate and strength of heart contractions.
    • β2 receptors relax smooth muscle of bronchioles (bronchodilation).
    • Mnemonic: 1 Heart & 2 Lungs.

SANS DRUG CLASSES

Adrenergic (Sympathomimetic) Agents

  • Important in treating anaphylaxis & asthma; added to local anesthetic solutions to prolong their action.

Adrenergic Blocking Agents

  • Can block adrenergic receptors: α-receptors (α-blockers) and β-receptors (β-blockers).

TYPES OF ADRENERGIC (SYMPATHOMIMETIC) DRUGS

  • Bronchodilators: Target β2 receptors; treat Asthma, COPD, Emphysema, & Bronchitis.

    • Examples:
    • Albuterol (Ventolin, ProAir, Proventil)
    • Levalbuterol (Xopenex)
    • Salmeterol (Serevent)
    • Note: Candidiasis can occur from asthma inhaler use.

  • Vasopressors: Contract smooth muscle in blood vessels, leading to vasoconstriction and increased blood pressure; used to treat shock and bleeding.

    • Used as nasal decongestants to treat colds by constricting swollen nasal mucous membranes.

EXAMPLES OF VASOPRESSORS

  • Epinephrine: Used in local anesthetics to maintain medication at the site of administration.

  • Dopamine: Used in the treatment of shock and hypotension.

  • Ephedrine and Pseudoephedrine: Used in cold medications.

  • Cardiac Stimulators: Used to stimulate and restore heartbeat in emergencies.

    • Example: Epinephrine.

OTHER COMMON ADRENERGIC (SYMPATHOMIMETIC) AGENTS

  • Ritalin/Adderall: Treatment for ADHD.
  • Clonidine (Catapres, Kapvay): Can be used for behavioral disorders.
  • Cocaine and Methamphetamine: Can lead to rampant caries and burned mucosal surfaces.
    • BOARD ALERT: Oral mucosal irritation stems from the method of administration, not the drug itself.
    • BOARD ALERT: Avoid using Epinephrine in cocaine or methamphetamine abusers.

ADVERSE EFFECTS OF ADRENERGIC AGENTS

  • CNS Disturbances: Anxiety, fear, tension, headache, tremor.
  • Cardiac Arrhythmias: Can lead to cerebral hemorrhage.
  • BOARD ALERT: Adrenergic drugs should not be used in patients with angina, uncontrolled hypertension, and uncontrolled hyperthyroidism.
  • Note: The body is not designed to maintain prolonged Fight or Flight response.

ADRENERGIC BLOCKING AGENTS

α-Adrenergic Blocking Agents

  • Increase blood flow and treat Raynaud’s syndrome (poor circulation).

β-Adrenergic Blocking Agents

  • Used mainly for cardiac conditions, including:
    • Hypertension
    • Cardiac arrhythmias
    • Heart failure
    • Post heart attack
    • Angina pectoris
  • May have off-label uses.
  • Typically end in -olol.
β-ADRENERGIC BLOCKING AGENTS
Non-specific (Nonselective)
  • Decrease heart rate and lower blood pressure, but may cause bronchoconstriction.
    • Example: Propranolol (Inderal).
Specific (Selective)
  • More active on the heart and blood vessels than on the lungs; reduce heart rate and blood pressure but do not induce bronchoconstriction; lead to fewer side effects.
    • Examples:
    • Atenolol (Tenormin)
    • Metoprolol (Lopressor)

α- AND β-BLOCKING AGENTS

  • Labetalol (Normodyne, Trandate):
    • Combines α- and β-blocking action.
    • Selective α- and nonselective β-blocker used for hypertension, producing a reduction in blood pressure without reflex tachycardia.

BOARD ALERT!

  • Be prepared to differentiate Beta Blockers from diuretics and other medications used in the treatment of hypertension.