Local Anesthesia

local anesthsia

loss of sensation or motor function in a local or circumscribed area

what are local anesthetics used for?

temporary released of localized pain in dentistry and minor surgical procedures as well as a state of non resistance in the case of spinal anesthesia

topical local anesthetics are used for...

relief of pain and itching caused minor burns, bites, allergic responses, hemorrhoids, and for procedures such as endoscopy, sigmoidoscopy, intubation etc

Local anesthetics block...

conductions by decreasing or preventing the influx of sodium during the propagation of an action potential

Local anesthetic action is due to...

direct interaction with the voltage gated Na+ channels

site of interaction

inside surface of the membrane

what is the first local anesthetic and the lead compounds that are in current use?

cocaine

When is cocaine still used?

surgical procedures of the head and neck

Why is cocaine no longer used in opthalmology?

corneal sloughing due to vasoconstriction

How is cocaine used?

topical application only

Concentrations of cocaine used

1-4% dependent on the area

What kind of local anesthetic is cocaine?

benzoic acid ester type

What advantage does cocaine have ?

it causes vasoconstriction in the area thus prolonging its duration of action

How does cocaine cause vasoconstriction?

a2 blockade which increases NE concentration in the synapse and increases vascular tone

why is cocaine abused?

a2 blockade causes CNS stimulation

How do we use other local anesthetics to mimic cocaine action?

used in combination with epinephrine to cause vasoconstriction

What should cocaine not be used in combination with?

epinephrine due to the possibility of additive increase in BP and HR

Hexylcaine

topical local benzoic acid ester type local anesthetic

what is hexylcaine used for?

on the skin and nerve block and spinal anesthesia

What can topical use of Hexylcaine cause?

irritation to mucus membranes such as the eye

Benzocaine

PABA ester topical local anesthetic

How is benzocaine used?

topically only but is not effective on intact skin

Where is benzocaine effective?

mucous membrane and injured skin

what are some common uses of benzocaine ?

- minor burns

- hemorrhoids

- severe sunburn

- psoriasis

- pruritus

Why can't benzocaine be inject?

it is insoluble in water

what is would be required to form a salt with benzocaine? why?

strongly acidic solution because the NH2 is a weak base

What is the major risk with benzocaine ?

possible allergic response due to p-aminobenzoic acid. Some individuals because sensitive and this sensitivity carries over other local anesthetics that contain PABA

Procaine, Novocain

local anesthetic PABA ester type

How is procaine used? why?

injection only because it is not effective topically due to high polarity

What is procaine the primary use in?

dental practice

Procaine onset

slow

Procaine duration

short

Procaine can be...

co-administered with epinephrine to increase duration by causing vasoconstriction which decreases blood flow and decreased the diffusion of the compound from the site

Choroprocaine, Nesacaine

local anesthetic PABA ester type

what is choroprocaine related to? How?

ortho chloro analogue of procaine

what does the ortho position chlorine on choroprocaine do?

makes it more lipophilic

Choroprocaine onset

fast (lipiphilic)

Choroporcaine duration

short due to rapid hydrolysis of EWG chlorine

When comparing Choroprocaine and Procaine which one lasts longer and why?

ester hydrolysis is 4X faster in choroprocaine

What is Choroprocaine used for?

systemic use due to rapid hydrolysis but it can be used for one limb if you cut off blood flow

Tetracaine Pontocaine

PABA ester type local anesthetic

Tetracaine relationship to chlorprocaine

more lipophilic due to the n-butyl group on aromatic amine

Tetracaine onset

fast

Tetrcaine duration

long 8-10x more potent, 2-3x longer duration than procaine

Important structural characteristic of tetracaine

nBuNH in the para position donates electrons to carbonyl decreasing the rate of hydrolysis and increasing duration of action

Tetracaine use

injection and topical

What is a major concern with Tetracaine?

some systemic toxicity due to slow rate of hydrolysis

Proparacaine Alcaine , Opthaine

local anesthetic PABA ester type

Proparacaine is used....

topically only for eyes

Can proparacaine be used systemically?

no

why can proparacaine not be used systemically?

m-NH2 makes it too toxic for systemic use

Dibucaine Nupercainal, Nupercaine

local anesthetic non-PABA

Dibucaine is used....

topically and injected

Topical Dibucaine potency

15-20X more than procaine

Injected Dibucaine potency

most potent of all long acting locals

What makes Dibucaine so potent?

the amide is resistant to hydrolysis

what is an issue with Dibucaine?

can cause transient liver abnormalities

what is special about Dibucaine?

can be considered a member of the ester type or lidocaine type

Isogramine

lead lidocaine type local anesthetic found in a reed that camels would not eat

Lidocaine (Xylocaine)

local anesthetic

Lidocaine free base

topical use skin only

Lidocaine salt

topical in the ear, nose, and throat and injection

Lidocaine potency

2x more than procaine

Lidocaine duration of action

longer due to decreased hydrolysis

Lidocaine toxicity

little more than procaine

Where is lidocaine metabolized?

little in the plasma but primarily in the liver

Lidocaine can be used in....

patients who are sensitive to PABA

Who may have a toxic reaction to lidocaine?

individuals who are genetically deficient in choline esterases or who have been exposed to cholinesterase inhibitors use amide type

who should NOT receive an amide type?

patients with liver disease, use ester type

Lidocaine is also used for what?

arrhythmias, the MOA is the same as for local anesthesia in that the compound decreases conduction of the nerve but in this case in the heart

Etidocaine (Duranest)

local anesthetic Lidocaine type

Etidocaine when compared to Lidocaine

greater potency and duration of action due to increased lipophilic nature

what is etidocaine used for?

same as for lidocaine

Mepivacaine (Carbocaine, Arestocaine)

lidocaine type of local anesthetics

what route is Mepivacine administered?

injection

Mepivacaine potency

same as Lidocaine

Mepivacaine duration of action

slightly longer than lidocaine

What is mepivacaine used for?

Epidural

Bupivacaine (Marcaine, Duocaine)

lidocaine type local anesthetic

Bupivacaine duration of action

long, 2-3X that of lidocaine

Bupivacaine potency

6X that of procaine

What is special about Bupivacaine ?

produces a motor nerve blockade which can be useful

Bupivaine uses

good for epidurals preferred for abdominal surgeries

Prilocaine (Citanest)

lidocaine type local anesthetic

Prilocaine duration of action

intermediate between lidocaine and mepivacaine

Prilocaine uses

injection for infiltration and topically for dentistry

When Prilocaine is used for injection for infiltration (directly into tissue) it...

tends to be irritating

When Prilocaine is hydrolyzed ....

Methemogloniemia can occur due to the oxidation of 2 methyl aniline produced from metabolism to 2-methyl nitrosobenzyne which oxidized Fe++ in hemoglobin to Fe+++ (cannot carry oxygen)

Methemogloniemia

a condition where an abnormal amount of methemoglobin, a form of hemoglobin, is present in the blood

Why does Methemogloniemia not occur with the other lidocaines?

thier 2,6dimemthyl anilin is resistant to these oxidations

Pramoxine

ether type local anesthetic

What is pramoxine used for??

- topical for throat, hemorrhoids, and skin- sigmoidoscopy, endotracheal intubation, does not abolish gag reflex

Pramoxine cannot be used ...

in nose, eyes, or injection because it is too irritating

Dyclonine

ketone type local anesthetic

Dyclonine is typically used for what?

- topically for throat, rectum, and skin

- sore throat lozenges

Dyclonine cannot be used in.......

injection, it is too irritating because the ketone cannot be hydrolyzed

Toxic side effects of local anesthetics are

CNS and cardiovascular in nature

CNS adverse effects of local anesthetics

- excitatory and/or depressant

- nervousness

- dizziness

- blurred vision

- tremor

- followed by drowsiness

- merge into unconsciousness and respiratory depression

Cardiovascular reactions of local anesthetics

- depressant

- hypotension

- myocardial depression

- bradycardia

- possible cardiac arrest