Chapter 5 Autonomic Drugs

Autonomic Pharmacology Autonomic Nervous System This system is divided into two separate systems. These systems are called the parasympathetic nervous system and the sympathetic nervous system. These systems often produce opposite effects. Drugs in this group are designed to either enhance or mimic the autonomic nervous system or to block the effects of the neurotransmitters at their receptor sites. 2

Autonomic Nervous System Parasympathetic Nervous System This system is concerned with the conservation of the body processes. Its main neurotransmitter is acetylcholine. Its receptors are muscarinic, nicotinic, and the somatic-skeletal muscles. 3

Autonomic Nervous System Sympathetic Nervous System This nervous system is designed to cope with emergency situations. This is commonly known as the “fright or flight” response. Its neurotransmitters are epinephrine and norepinephrine. Its receptors are the α and β receptors. 4

Autonomic Pharmacology Cholinergic or Parasympathomimetic Drugs These drugs are classified as either direct or indirect acting agents. Direct acting drugs act directly on the parasympathetic receptors. Indirect acting drugs work by either of two methods. They can cause the release of the neurotransmitter which then goes to the receptor site or they inhibit the enzyme cholinesterase. 5

Autonomic Pharmacology Cholinergic Pharmacology Cardiovascular Direct effects include negative chronotropic and inotropic actions. Relaxation of smooth muscles causes a decrease in total peripheral resistance. Indirect effects include increased heart rate and cardiac output. The resulting effect depends upon the dose used. Usually, the patient experiences bradycardia and a decrease in blood pressure and cardiac output. 6

Autonomic Pharmacology Cholinergic Pharmacology Gastrointestinal These drugs excite the smooth muscle of the gastrointestinal tract and cause an increase in activity, motility, and secretion. Eye These drugs cause miosis and cycloplegia. They cause a decrease in intraocular pressure. 7

Autonomic Pharmacology Adverse Reactions Adverse reactions are an extension of the drugs’ pharmacologic effects. They include: Salivation Lacrimation Urination Defecation Paralysis Overdose 8

Cholinergic Pharmacology Contraindications The contraindications and relative cautions are a result of the drug’s pharmacologic and adverse effects. They include: Bronchial asthma Hyperthyroidism Gastrointestinal or urinary tract obstruction Myasthenia gravis treated with neostigmine Peptic ulcer disease Severe cardiac disease 9

Cholinergic Drugs 10

Anticholinergic Drugs These drugs prevent the action of acetylcholine at postganglionic parasympathetic endings. Acetylcholine is released but its receptor site is completely blocked by anticholinergic drugs. These drugs only block muscarinic receptors. 11

Anticholinergic Drugs Pharmacology Central Nervous System Depending on the dose, these drugs can cause stimulation or depression. Exocrine Glands They reduce the flow and volume of secretions in the respiratory, gastrointestinal, and genitourinary tracts. 12

Anticholinergic Drugs Pharmacology Smooth Muscle Relax smooth muscles in the respiratory and gastrointestinal tracts. They delay gastric emptying and decrease esophageal and gastric emptying. These drugs also cause bronchial dilation. Eye These drugs cause mydriasis and cycloplegia. 13

Anticholinergic Drugs Pharmacology Cardiovascular With large doses, these drugs produce vagal blocking which results in tachycardia. Bradycardia can occur with low doses. 14

Anticholinergic Drugs Adverse Reactions The adverse reactions are an extension of the drugs’ pharmacologic effects. They include: Xerostomia Constipation Urinary retention Blurred vision Hyperpyrexia Hallucinations Photophobia Tachycardia 15

Anticholinergic Drugs Contraindications Contraindications are usually due to the drugs’ pharmacologic and adverse effects. They include: Glaucoma Prostatic hypertrophy Intestinal or urinary obstruction or retention Cardiovascular disease 16

Anticholinergic Drugs Uses Preoperative Medication They inhibit salivary and bronchial secretions. They block the vagal slowing of the heart that can occur with general anesthesia. Gastrointestinal Disorders They decrease gastrointestinal motility and can be used to treat ulcers, diarrhea, and hypermotility. 17

Anticholinergic Drugs Uses Ophthalmologic Examinations Topical use can cause mydriasis which causes a full visualization of the retina. Cycloplegia relaxes the lens so that proper prescriptions for glasses can be determined. Parkinson Disease They reduce the tremors and rigidity associated with Parkinson and drug-induced Parkinson disease. 18

Anticholinergic Drugs Uses Motion Sickness These drugs are used to treat or prevent motion sickness because of their central nervous system depressant action. Dentistry These drugs are used to create a dry, oral field. 19

Adrenergic Drugs Adrenergic drugs can be classified as having direct action, indirect action, or mixed action. These drugs stimulate α and β receptors throughout the body. Drugs with direct action (epinephrine, norepinephrine, isoproterenol) produce their effect by directly stimulating the receptor site. Drugs with indirect action (amphetamine) release endogenous norepinephrine which then stimulates the receptor. Drugs with mixed action (ephedrine) either directly stimulate the receptor or release endogenous norepinephrine. 20

Adrenergic Drugs Pharmacology Central Nervous System (CNS) These drugs produce CNS excitation or alertness. Higher doses produce anxiety, apprehension, restlessness, and tremors. Cardiovascular System These drugs increase the force and rate of contraction of the heart. Blood pressure is also increased. Total peripheral resistance is also increased. 21

Adrenergic Drugs Pharmacology Eye Respiratory System Metabolic Effects These drugs lower intraocular pressure and can cause mydriasis. Respiratory System These drugs cause a relaxation of bronchiole smooth muscles. Metabolic Effects Increased glycogenolysis from β-receptor stimulation causes hyperglycemia. Salivary Glands These drugs produce vasoconstriction of the salivary glands which leads to decreased salivary flow which results in xerostomia. 22

Adrenergic Drugs Adverse Reactions The adverse reactions associated with these drugs are an extension of the drugs’ pharmacologic effects. They include: Anxiety Tremors Tachycardia Increased blood pressure Arrhythmias 23

Adrenergic Drugs Uses Vasoconstriction Cardiac Effects These drugs are used in dentistry because of their vasoconstrictive actions on blood vessels. They are added to local anesthetics because they prolong the action of the local anesthetic, reduce the risk for systemic toxicity, and help to create a dry field. Cardiac Effects These drugs are used to raise blood pressure and to treat cardiac arrest. 24

Adrenergic Drugs Uses Bronchodilation These drugs are used to treat asthma, emphysema, and allergic reaction. Central Nervous System Stimulation These medications are used for the treatment of attention deficit hyperactivity disorder, narcolepsy, and as diet aids. 25

Adrenergic Blocking Drugs These drugs competitively inhibit α and β receptor sites. One group of drugs is specific for α receptors. One group of drugs is specific for both β1 and β2 receptors. One group is specific for β2 receptors. One group is specific for both α and β receptors. 26

Antiadrenergic Drugs Pharmacology Uses These drugs reduce sympathetic tone in the blood vessels and decrease total peripheral resistance. This results in a reduction in blood pressure. Uses These drugs are used to treat hypertension, peripheral vascular disease (i.e., Raynaud syndrome) and benign prostatic hypertrophy. 27