What was the first injectable LA?
What was the first topical locan anesthetic agent?
List the prototype injectable LA.
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Identify which vasoconstrictor is used in each formulation
- lidocaine and xylocaine: epinephrine
- mepivacaine (carbocaine): levonordefrine
- articaine (septocaine): epinepherine
- Prilocaine (citanest): epinepherine
- Bupivacaine (marcaine): epinepherine
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
Which LAs are associated with methemoglobinemia?
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
Which is the safest topical LA? Which is the most widely used?
- benzocaine is the safest
- benzocaine and lidocaine are the most widely used
Which topical anesthetics are associated with methemoglobinemia?
- combination products
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
Which drug reverses seizures from an LA overdose?
Im or IV diazepam (valium)
List the concentrations of vasoconstrictors available, and identify a situation in which each would be selected.
- 1:200,000: cardiovascular disease
List drug/vasoconstrictor interactions.
They reduce blood flow by contracting smooth muscle, and slow the rate of removal of LA
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
Define the 'cardiac' dose of vasoconstrictor
.04 mg, one cartridge of LA with epinepherine 1:50,000
Which LA is indicated for use during pregnancy?
low concentration lidocaine 2% with epinepherine 1:100,000
Identify how amides and esters are metabolized.
- ester - hydrolysis catalyzed by plasma chlinesterase
- amides -