lec 4: local anesthetics

what are desirable properties of anesthetics

1. rapid onset

2. adqeuate duration of action

3. reversible blockage of nerve impulse generation & conduction

4. minimal side effects

5. minimal local tissue damage

what is the structural features of the hydrophobic aromatic ring

an essential for anesthetic activity

it increases potency and duration of action

it increases toxicity

structural features of linkage site ester

unstable

rapid hydrolization by pseudocholinesterase

topical ocular

structural features of linkage site amides

stable

metabolized by liver amidases

injectables

structural features of hydrophilic ionizable amine

enhances water solubility and stability in solution

weak bases, pKa between 8 and 9

only non-ionized form readily crosses the cell membrane

how does ligand gated ion channel work

needs a neurotransmitter to bind to the receptor for it to open

how does mechanically gated channel work

needs pressure to open

how does voltage gated channel work

needs a voltage to open

what channel is always open

sodium potassium pump

what form of the hydrophilic ionizable amine can cross the nerve cell membrane

non-ionized

benzoic acid

cocaine

para-aminobenozic acid

tetracaine

oxybuprocaine

procaine

meta-aminobenzoic acid

proparacaine

types of esters

benzoic acid, para-aminobenzoic acid, meta-aminobenzoic acid

how can you tell the difference between an ester & an amide?

amide has two i’s :)

which is a stronger topical ester anesthetic

tetracaine

benozinate = proparacaine

which is a stronger topical ester anethetic

tetracaine

benozinate

proparacaine

what topical ester anesthetic destroys the epithelium more

tetracaine

benoxinate = proparacaine

what diameter is more sensitive to anesthesia

small diameter

which nerve diameter takes longer to recover

small diameter

what size diameter is less sensitive, takes a while to work, and recovers the quickest

large diameter nerve

unmyelinated or mylenated take a longer time to anesthesize

unmyelinated take longer to anesthetize bc they have a lot of Na+

what is the order of blockage from easiest to anesthesize to hardest to anesthesize

1. autonomic

2. pain

3. temp

4. touch

5. deep pressure

6. motor

is the order of recovery the same as order of anesthetics?

no, it is in opposite order

why does lidocaine have a shorter duration than mepivacaine

bc it causes more vasodilation

what does vasodilation mean more of

elimination

how do you counter vasodilation

vasoconstriction

topical ester onset & duration

onset: 0.5 min

duration: ¼ of an hour

lidocaine onset & duration

onset: 4-6 min

duration: 2/3 - 1 hour

mepivacaine onset & duration

onset: 3-5 min

duration: 2-3 hours

etidocaine onset & duration

onset: 3-5 min

duration: 5-10 hours

bupivacaine onset & duration

onset: 5-10 min

duration: 4-12 hours

what is lidocaine often combined with

phenylephrine or epinephrine

what are the advantages of combining a vasoconstricter like phenylephrine or epinephrine to lidocaine

1. reduces anesthetic absorption by circulatory system

2. reduces anesthetic metabolism

3. sustain local anesthetic effect (lasts twice as long)

4. reduces bleeding at injection site

what are some risks of combining lidocaine with vasoconstricters

local necrosis (esp if injected)

AVOID DIGITS, NOSE, PENIS, AND TOES (extremities)

what are some of the non-surgical procedure benefits of using anesthetics

decreases the burn of other topicals

increases absorption of other topical drugs bc it destroys the epithelium

decrease tear & blink reflex so you can remove a foreign body

goldmann tonometry

gonioscopy

pachymetry (to check corneal thickness)

schirmers test

ultrasonography

ERG

contact lens fitting & adaptation

corneal foreign body or abrasion evaluation

dilation & irrigation of lacrimal canal

punctal plug insertion

forced ductions

what are some of the minor procedure benefits of using anesthetics

foreign body removal

corneal puncture

suture removal

meibomian gland expression

culture or biopsy

corneal epithelial debridement with tetracaine (in PRK)

what are some adverse effects of using topical anesthetics

destroyed epithelium

corneal edema (overestimates IOP)

red eye

burning, stinging, and lacrimation

contact dermatitis

delayed wound healing (prolonged use)

rare: seizures, CNS depression

which anesthetic is more prone to hypersensitivity

esters>amides

what are some contraindications of esters

if someone is allergic

if someone has a cholinesterase deficiency

hyperthyroidism

cardiac disease

asthma

does cardiac suppression relate to cocaine

no

what activity does cocaine have that is unique from the other anesthetics

it has sympathetic activity which causes dilation

adverse effects of topical cocaine (ocularly)

lose ur cornea

dilation

lid retraction

adverse effects of topical cocaine (systemically)

excitement, convulsions, rapid heart rate, nausea, and delirium

what should you NOT use with cocaine

TCADS, MAO inhibitors, decongestants: epinephrine & phenylephrine, & anti-hypertensive meds

what are contraindications to cocaine

HTN

what is sometimes used in place instead of “caine” bc someone is allergic

antihistamines & salines (injectables)

antihistamines (topically)

how do you know if someone is abusing a topical anesthetic

they have smth that looks painful but they dont feel pain