AUTONOMIC DRUGS

AUTONOMIC DRUGS

LEARNING OBJECTIVES

  • Identify the major components and functional organization of the autonomic nervous system (ANS)

  • 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 also 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

SIGNIFICANCE FOR DENTAL HYGIENISTS

  • Familiarity with ANS drugs is essential due to:

    • Certain ANS drugs being used in dental procedures.

    • Effects on vasoconstriction and salivary flow.

    • Oral adverse reactions caused by some ANS drugs.

    • Similar effects from other drug groups, including antidepressants and antipsychotics.

AUTONOMIC NERVOUS SYSTEM REVIEW

  • The ANS controls automatic, involuntary responses essential for regulating:

    • Blood pressure

    • Heart rate

    • Gastrointestinal (GI) motility

    • Salivation

    • Bronchial/smooth muscle tone

  • Communicates using specific neurotransmitters, which are chemicals that transmit messages across synapses, and a variety of receptors that help in message reception.

ANATOMY OF THE ANS

  • Two Main Divisions:

    1. Sympathetic Autonomic Nervous System (SANS):

    • Function: Fight or Flight

    • Mnemonic: S = Stress

    1. Parasympathetic Autonomic Nervous System (PANS):

    • Function: Rest and Digest

    • Mnemonic: P = Peace (or you cook in a pan)

FUNCTIONAL RESPONSES

  • Sympathetic Response (SANS):

    • Fight or Flight – Stress response

    • Increases blood pressure (vasoconstriction)

    • Increases heart rate

    • Increases oxygen delivery to muscles

    • Decreases blood flow to GI system

    • Dilation of bronchioles

    • Dilation of pupils (mydriasis)

    • Decreases salivary flow

  • Parasympathetic Response (PANS):

    • Rest and Digest – Peaceful functions

    • Decreases blood pressure

    • Decreases heart rate

    • Increases peristalsis and GI motility

    • Constriction of bronchioles

    • Constriction of pupils (miosis)

    • Increases salivary flow

STRUCTURE OF THE ANS

  • Both SANS & PANS consist of:

    • Afferent (sensory) fibers: Monitor conditions and send information to the CNS.

    • Central integrating areas: Coordinate incoming information.

    • Efferent (peripheral) motor preganglionic fibers: Carry commands from the CNS to the periphery.

    • Postganglionic motor fibers: Relay commands to effector organs.

TYPICAL EFFERENT NERVOUS SYSTEM FUNCTIONING

  • The preganglionic fiber originates in the brain, synapses with the postganglionic fiber, and releases neurotransmitters to send messages to effector organs.

DIFFERENCES IN EFFERENT NERVES

SANS:

  • Short preganglionic fibers

  • Long postganglionic fibers

  • Stimulation of SANS leads to adrenal medulla release of epinephrine and small amounts of norepinephrine

PANS:

  • Long preganglionic fibers

  • Short postganglionic fibers

NEUROTRANSMITTERS IN THE ANS

  • Neurotransmitters are crucial for communication between nerves or from nerves to effector tissues. They are released into the synaptic cleft and interact with specific receptors.

  • Classification:

    • Cholinergic Nerves: Release acetylcholine (ACh). Also stimulated by nicotine (termed nicotinic).

    • SANS Preganglionic Neurotransmitter: Acetylcholine

    • SANS Postganglionic Neurotransmitter: Norepinephrine

    • PANS Preganglionic Neurotransmitter: Acetylcholine

    • PANS Postganglionic Neurotransmitter: Acetylcholine (also known as cholinergic). It responds to muscarine, termed muscarinic (PANS).

REVIEW OF TERMS

  • Cholinergic: A drug acting at locations where acetylcholine is released.

  • Adrenergic: A drug acting at locations where norepinephrine is released.

  • Parasympatho-: Prefix for a drug acting where the PANS acts.

  • Sympatho-: Prefix for a drug acting where the SANS acts.

  • -mimetic: Suffix indicating a drug that mimics or acts like the neurotransmitter (agonist).

  • -lytic or –blocker: Suffix indicating a drug that blocks the neurotransmitter (antagonist).

PANS DRUG CLASSES

  1. Cholinergic (Parasympathomimetic) Agents:

    • Mimic PANS responses:

      • Reduce heart rate, lower blood pressure, increase motility, and induce miosis (pupil constriction)

      • Example agents:

      • Pilocarpine (Salagen): Used for xerostomia.

      • Cevimeline (Evoxac): Also used for xerostomia.

  2. Anticholinergic (Parasympatholytic) Agents:

    • Opposite action of PANS:

      • Induce mydriasis (pupil dilation), decrease secretions, and reduce GI motility.

    • Common agents include Atropine (for pre-op salivary flow reduction), Ipratropium (for COPD), Scopolamine (for motion sickness), and Loperamide (Imodium for diarrhea).

CHOLINERGIC AGENTS

  • Uses: Xerostomia, urinary retention, glaucoma, Alzheimer's disease.

  • Adverse Effects:

    • Large doses may induce SLUD: Salivation, Lacrimation, Urination, Defecation.

  • Contraindications:

    • Asthma: Causes bronchoconstriction.

    • Peptic Ulcer: Increases GI secretions.

    • Cardiac Disease: Lowers heart rate.

    • Obstructions: Increases motility.

ANTICHOLINERGIC AGENTS

  • Action: Block ACh receptors and induce effects opposite to PANS.

  • Adverse Effects: Hints using ABCD:

    • A: Anticholinergic agents

    • B: Blurred vision or bladder retention

    • C: Constipation

    • D: Dry mouth

  • Contraindications:

    • Glaucoma: Can cause acute rise in intraocular pressure.

    • Prostatic hypertrophy: Benign enlargement of prostate.

    • Obstructions: Intestinal or Urinary.

    • Cardiovascular diseases: Risk of tachycardia.

PANS STIMULATION DEMYSTIFIED

  • Mechanism:

    • ACh is released from preganglionic nerve into synapse, stimulating postganglionic receptors, which subsequently triggers additional ACh release causing dilation of blood vessels supplying salivary glands and increasing salivation.

  • Clinical Note: Increased salivation may be undesirable during oral surgical procedures. Pre-operative autonomic drugs can be utilized to mitigate this (e.g., anticholinergic agents).

SYMPATHETIC NERVOUS SYSTEM (SANS) DETAILS

  • Adrenergic Receptors:

    • α-receptors: Govern vasoconstriction, found in skin and skeletal muscle.

    • β-receptors:

    • β1-receptors: Increase heart rate and contraction strength.

    • β2-receptors: Relax smooth muscles in bronchioles for bronchodilation.

CLASSES OF SYMPATHETIC DRUGS

  1. Adrenergic (Sympathomimetic) Agents:

    • Role in treating anaphylaxis, asthma, and as vasoconstrictors to control bleeding.

  2. Adrenergic Blocking Agents:

    • Block various adrenergic receptors; may classify as α-blockers and β-blockers.

TYPES OF ADRENERGIC (SYMPATHOMIMETIC) DRUGS

  • Bronchodilators (e.g., Albuterol, Levalbuterol, and Salmeterol) target β2 receptors, treating asthma and COPD.

  • Vasopressors: Help in raising blood pressure and managing shock.

  • Examples of Vasopressors:

    • Epinephrine (local anesthetic adjunct)

    • Dopamine (shock treatment)

    • Ephedrine and Pseudoephedrine (cold medications)

  • Cardiac Stimulators: Stimulate, restore heartbeat in emergencies (e.g., Epinephrine).

OTHER COMMON ADRENERGIC AGENTS

  • ADHD Treatments: Ritalin, Adderall.

  • Behavioral Disorders: Clonidine.

  • Stimulants: Cocaine, Methamphetamine, with noted side effects of oral mucosal irritation due to administration methods, not the drugs.

  • Contraindications to Epinephrine: Should not be used in patients who abuse cocaine/methamphetamine.

ADVERSE EFFECTS OF ADRENERGIC AGENTS

  • Side Effects Include:

    • CNS disturbances: Anxiety, fear, tension, headache, tremor

    • Cardiac arrhythmias leading to cerebral hemorrhage.

  • Caution: Not recommended for patients with Angina, uncontrolled hypertension, or hyperthyroidism due to risk of exacerbating condition.

ADRENERGIC BLOCKING AGENTS

  • α-Adrenergic Blocking Agents: Increase blood flow, treat Raynaud’s syndrome.

  • β-Adrenergic Blocking Agents: Mainly for treating cardiac conditions; side effects may include non-selective β-blockers triggering bronchoconstriction (e.g., Propranolol). Specific β-blockers target heart and blood vessels without affecting the lungs (e.g., Atenolol, Metoprolol).

  • Combination Agents:

    • Labetalol: Both α- and β-blocking action, effective in treating hypertension with minimal reflex tachycardia.

BOARD ALERTS

  • Differentiate between Beta Blockers, Diuretics, and other hypertension medications as knowledge for exams and practical applications.