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What was the first injectable LA?
procaine (novocaine)
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What was the first topical locan anesthetic agent?
cocaine
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List the prototype injectable LA.
lidocaine
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Describe features of the 2 forms of LAs and identify examples of drugs in each category.
- Topical or injectable
- Topical only: benzocaine
- Topical or injectable: lidocaine, tetracaine, prilocaine
- Injectable only: mepivacaine, bupivacaine
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List 2 main classes of LA agents, identify agents in each class.
- Esters and Amides
- Esters: cocaine, procaine, tetracaine, benzocaine, butacaine, butamben
- Amides: lidocaine, mepivacaine, prilocaine, bupivacaine, articaine
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Explain the site of local anesthesia action and the significance of nodes of Ranvier.
- sodium channels on the axoplasmic side of the membrane
- the nodes of Ranvier are where LA agents enter the axoplasm of heavily mylenated nerves
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Explain the mechanism of action of an LA agent.
they prevent impulse transmission (propogation of action potentials) by blocking individual sodium channels in neuronal membranes
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describe pharmacokinetics of topical agents and injectable agents.
- topical agents cross the mucosal membrane by simple diffusion of the nonionized form and are rapidly absorbed
- injectable agents are put directly into or adjacent to the tissue being treated, or into or around peripheral nerve trunks (infiltration or nerve block)
- both types are eliminated from their site of activation by passive diffusion along the concentration gradient and absorbed into systemic circulation, they are then metabolised and excreted by the liver
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Identify factors that affect absorption in topical LA application
- the pH of the environment
- the presence or absence of a vasoconstrictor
- chemical characteristics of the agent
- vascularity of area
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describe two techniques for administering injectable LAs, and discuss features of each
- Infiltration anesthesia - injection of LA directly into or adjacent to the tissue to be treated (intrapulpal or intraligamental)
- Nerve Block anesthesia - injection of LA into or around peripheral nerve trunks or nerve plexuses
- Nerve block provides anesthesia to a greater area for a longer amount of time
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What are the purposes of adding a vasoconstrictor to an LA?
- controlling tissue bleeding in the local area
- prolong duration
- delay systemic absorption of the LA, thereby reducing risk of toxicity
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Describe the roles of the base and cation forms of LA agents. Which form promotes access to the site of action? Which form is in the cartridge?
- The base allows the LA to penetrate biologic barriers and ultimately the nerve sheath to reach the receptor site, it then leaves the extracellular area
- then the cation form molecules re-equilibriate and the newly created lipophilic molecules diffuse through the cell membrane, the cationic form has affinity for the internal receptor sites and blocks the impulse
- water-soluble salts with hydrochloric acid is in the cartridge the charged cation and uncharged base elements are in the cartridge
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Describe factors that affect absorption of an injectable LA.
- the pH of the environment - the more acidic the less that will be absorbed
- chemical characteristics of LA
- vascularity of area
- presence or absence of vasoconstrictor
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Describe alteration of effects from apical abscess?
because the environment has a more acidic pH, the equilibrium shifts to the water-soluble cationic form. Also, inflammation causes ilation of blood vessels, which causes LA molecules to leave the area faster
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Identify LA agents that have intermediate and long durations of action
- Long: bupivicaine
- Intermediate: lidocaine hydrochloride, mepivacaine hydrochloride, prilocaine hydrochloride, articaine hydrochloride (septocaine)
- Short: procaine
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Describe the contents of the LA cartridge and the purpose for each component. Which produces the salt form?
- sterile water - vehicle
- sodium chloride - isotonicity
- hydrogen chloride - adjust pH
- LA agent - 1.8 mL
- hydrochloric acid produces salt form
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Discuss what occurs when the metabisulfite is added to an LA formulation
It is an antioxidizing agent used in formulations containing vasoconstrictors to minimize oxidation of the vasoconstrictor
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Identify which vasoconstrictor is used in each formulation
- lidocaine and xylocaine: epinephrine
- mepivacaine (carbocaine): levonordefrine
- articaine (septocaine): epinepherine
- Prilocaine (citanest): epinepherine
- Bupivacaine (marcaine): epinepherine
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Identify LAs used for primary, secondary, and tertiary lines of treatment. Which is the agent of choice?
- Primary: lidocaine, mepivacaine, prilocaine, articaine
- Secondary: bupivacaine
- Tertiary: procaine
- agent of choice is lidocaine
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Which LAs are associated with methemoglobinemia?
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List topical agents and their doseforms. Which doseform has the least margin of safety?
- benzocaine - gel, liquid, spray, cotton applicator
- lidocaine - srapy, ointment, solution, patch
- combination products - liquid, spray, gel, solution
- the spray has the least margin of safety
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Which is the safest topical LA? Which is the most widely used?
- benzocaine is the safest
- benzocaine and lidocaine are the most widely used
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Which topical anesthetics are associated with methemoglobinemia?
- benzocaine
- combination products
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Describe the adverse events associated with the use of LAs and how they can be avoided.
- Tachyphylaxis - if repeated administration of LA is required before procedure is over, give next dose before nerve function is allowed to return
- Toxic reactions - do not give more LA then the recommended dose, use an LA with a vasoconstrictor, use aspirating technique, inject slowly
- methemoglobinemia - be aware if pt is susceptible
- CNS reactions - don't give too high a dose
- Cardiovascular reactions - try not to inject into vasculature, don't use to high a dose
- Sympathetic nervous system reactions - monitor vitals, dose
- Vasoconstrictor safety - don't use them on pts who've used cocaine, and use low doses if they have cardiovascular problems
- allergic reactions - if allergic to ester, use amide, asthma pts be careful
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Which drug reverses seizures from an LA overdose?
Im or IV diazepam (valium)
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List the concentrations of vasoconstrictors available, and identify a situation in which each would be selected.
- Epinephrine
- 1:50,000:
- 1:100,000:
- 1:200,000: cardiovascular disease
- Levonordefrin:
- 1:20,000:
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List drug/vasoconstrictor interactions.
They reduce blood flow by contracting smooth muscle, and slow the rate of removal of LA
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Identify the medical conditions that pose a risk when using a vasoconstrictor, and describe the management solution
- high BP
- cardiovascular disease
- unstable angina perctoris
- decompensated heart failure
- severe valvular disease
- symptomatic ventricular arrhythmias
- supraventricular arrhythmias
- uncontrolled hyperthyroidism
- limit vasoconstrictor use to no more than .04 mg which is one cartridge of LA w/ epi 1:50,000
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Define the 'cardiac' dose of vasoconstrictor
.04 mg, one cartridge of LA with epinepherine 1:50,000
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Which LA is indicated for use during pregnancy?
low concentration lidocaine 2% with epinepherine 1:100,000
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Identify how amides and esters are metabolized.
- ester - hydrolysis catalyzed by plasma chlinesterase
- amides -
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