Transcript
4
Local Anesthetics
Educational Objectives
After reading this chapter, the reader should be able to:
1. Discuss the mechanism of action of local anesthetics.
2. Classify local anesthetics used in dentistry.
3. Describe adverse effects of local anesthetics.
4. Describe the signs and symptoms of anesthetic toxicity.
5. Discuss the use of vasoconstrictors in medically compromised patients.
Lecture Outline
I. Local Anesthetics
A. History of use (e.g., lidocaine, used for cardiac arrhythmias [ventricular tachycardia]).
B. Chemical properties.
1. Amide bond.
2. Ester bond.
C. Mechanism of action.
1. Block sodium channels in neurons.
2. Nerve membrane.
a. Site of action.
D. Tissue inflammation decreases pH, makes less effective.
E. Metabolism and excretion.
1. Amides.
a. Metabolized in liver by cytochrome enzymes.
b. Excreted by the kidneys.
2. Esters almost completely hydrolyzed in the plasma by pseudocholinesterase, thus small concentrations found as the parent compound in the urine.
II. Local Anesthetic Agents
A. Amides.
1. Lidocaine.
2. Mepivicaine.
a. Half-life about 5 hours.
b. Metabolites stay in body for 30 hours.
3. Prilocaine.
a. Methemoglobinemia
4. Articaine.
5. Etidiocaine.
B. Esters.
1. Benzocaine.
2. Cocaine.
3. Tetracaine.
III. Topical Anesthetics
A. Benzocaine.
B. Lidocaine.
1. Gel
2. DentiPatch.
C. Lidocaine 2.5%/prilocaine 2.5%.
1. Oraqix Periodontal Gel.
2. Contraindicated with congenital or idiopathic methemoglobinemia.
IV. Vasoconstrictors
A. Epinephrine.
1. Constricts blood vessels in area.
2. Extends duration of action of anesthetic.
3. Stimulates a- and ß2-receptors.
4. Maximum safety doses in health and cardiac patients.
5. Cardiac effects; no effects in healthy individuals.
6. Precautions/contraindications in some patients; preservatives in epi cartridges.
B. Levonordefrin.
1. Half as potent vasoconstrictor.
2. Fewer cardiac effects but more toxic effects, contraindicated in patients taking psychotropic drugs.
V. Toxicity of Local Anesthetics
A. Allergic reactions.
B. Effects on central nervous system.
C. Blood disorders.
VI. Selection of Local Anesthetic
A. Onset of action.
B. Duration of action.
VII. Calculation of Maximum Amount
VIII. Special Populations
A. Children; problem with overdosing.
B. Pregnancy; local anesthetics and vasoconstrictors can be safely administered to pregnant or nursing patients.
C. Older adults; no significant differences in response to local anesthetics in older adults.
IX. Selection of Needle and Syringe
A. Aspirating syringe.
B. Type of needle.
X. Dental Management of Medically Compromised Patients
A. Cocaine.
B. Heart conditions.
C. Tricyclic antidepressants.
D. Diabetes mellitus.
E. Thyroid disorder.
XI. Dental management of patients taking certain drugs
A. Cocaine
B. Tricyclic antidepressants
XII. Clinical CalculationsTeaching Tips
1. Impress upon the students the difficulty in obtaining anesthesia in patients with local infections.
2. Explain to the students that there are many types of local anesthetic products with different onsets and durations of action. Thus, selection of the appropriate anesthetic is important and is determined by many factors, including the duration of the dental procedure.
3. Impress upon students that the use of vasoconstrictors in certain medically compromised patients taking medications must be carefully evaluated before using.
4. Stress the importance of obtaining a thorough medical/drug (including herbals) history from a patient before a local anesthetic is administered.
5. Stress the importance of doing mathematical calculations for the amount of local anesthetic used and recording the amount in the treatment record.
Factoids
1. The first local anesthetic used in dentistry was cocaine, introduced for use in 1884. Cocaine was used until Novocaine was developed as a nonadditive anesthetic by Alfred Einkorn, a German chemist, in 1905.
2. Eugenol, extracted from the plant eugenia, is the chemical extract found in cloves and produces a numbing effect. It is put into dental cavity preparations for temporary relief of pain.
3. As of 2005, most if not all dental cartridges contain 1.7 ml of solution. According to the manufacturers there is a range of 1.7–1.8 ml.
Discussion Questions
1. Discuss the classification of local anesthetics and the various anesthetics in each class.
2. Discuss the mechanism of action of local anesthetics.
3. Discuss the differences between a local anesthetic and topical anesthetic (including systemic absorption).
4. Explain the role of epinephrine in causing hypertensive problems in patients using noncardiac selective beta blockers.
5. Discuss the various aspects of dental management of the medically compromised patient regarding the use of local anesthetics.
Classroom Activities 1. Assign each student a local anesthetic to report on. Reports should include classification of anesthetic, route of administration, contraindications, precautions, dosage, and side effects. Allow students to share information with the class or post on a discussion board.
2. Review package inserts from the companies that produce the various local anesthetics (e.g., Cook-Waite). May print out from Web sites.
3. Arrange for students to go to the lab and adminster local anesthetics on typodonts and then discuss their experiences with the class.
4. Divide students into small groups and have each group develop a plan to administer a local anesthetic to a nonmedically compromised patient. Include the maximum amount of epinephrine that should be used. Have time for the entire class to discuss.
5. Divide students into small groups and have each group develop a plan to administer a local anesthetic to a medically compromised patient (e.g., hypertensive patient taking a nonselective beta-blocker, tricyclic antidepressants, cocaine user). Include the maximum amount of epinephrine that should be used. Allow time for the entire class to discuss.
Multimedia Found in the PowerPoint Lecture OutlineAnimations
1. Cocaine mechanism of action.
© 2013 by Education, Inc.
Weinberg, Instructor’s Resource Manual for Oral Pharmacology for the Dental Hygienist, 2nd Edition
