P H R M A C O L O G Y - NOTE 8 - Local Anesthesia

نسألكم الدعاء|

25

LOCAL ANESHESIA

weak Potency & short Duration

Procaine Chloroprocaine

moderate Potency & intermediate Duration

Lidocaine (Xylocaine)

Mepivacaine

Prilocaine

high Potency & long Duration

Tetracaine

Bupivacaine

Etidocaine

Ropivacaine

LA

Esters

Amide

•produce local loss of sensation without loss of consciousness

•Procaine

•Chloroprocaine

•Tetracaine

•Benzocaine

•Benoxinate

•Lidocaine (Xylocaine)

•Mepivacaine

•Bupivacaine

•Etidocaine

P H R M A C O L O G Y - NOTE 8 - Local Anesthesia

نسألكم الدعاء|

26

DRUG PHARMACOKINETIC ACTION USES SIDE EFFECT

Wea

k P

ote

ncy

&

sho

rt d

ura

tio

n

Procaine Administration

Local injection.

Local application ( solution, powder or cream)

Absorption

NOT desirable because: It duration. It systemic side effects.

Metabolism

Easter, fastly metabolized by tissues & plasma esterase.

Into PABA (cause allergy). Short duration.

Amides, slowly metabolized by liver microsomal enzymes.

Longer duration. .

Mechanism of action

LA block nerve conduction (initiation & propagation of AP) by: Binding to Na

+ channels &

prevent Na+ permeability.

Action

LA are lipid soluble / weak base.

At pH= 7.4, o they are UNIONIZED molecule. o They pass lipid membrane.

When reach the cytoplasm, o They become (ionized +

unionized). o The IONIZED molecules:

Bind to Na+

channels. Block Na

+ influx.

Prevent AP.

The action are susceptible for (small diameter / unmylinated) fibers more than (large diameter / mylinated) fibers.

1) Surface anesthesia: o on Skin (wound & ulcer) o on MM (mouth or nose). o in Ophthalmology (corneal A). o powder, solution creams or ointment

are used. 2) Infiltration anesthesia.

o as in (wound suturing, cyst removal). 3) Individual nerve block anesthesia.

o as in Dental anesthesia. 4) Spinal Epidural anesthesia.

o as in surgery of (LL, abd, pelvis, rectum).

5) Treatment of cardiac dysrhythmia.

Usually minimum, because:

o Applied locally. o Combinewd with

vasoconstrictors. 1) Hypotension. 2) Bradicardia. 3) CNS:

Tinnitus. Lightheadness. Headache. Convulsion.

4) Allergy (in ester type).

Side effects occur due to: o High dose. o Injected into BV.

They are potent & have long duration.

Chloroprocaine

Mo

der

ate

Po

ten

cy

& In

term

edia

te

du

rati

on

Lidocaine (Xylocaine)

Mepivacaine

Prilocaine

Hig

h P

oten

cy &

lo

ng d

ura

tion

Tetracaine 1) Infiltration anesthesia. o as in (wound suturing, cyst removal).

2) Individual nerve block anesthesia. o as in Dental anesthesia.

3) Spinal Epidural anesthesia. o as in surgery of (LL, abd, pelvis,

rectum). 4) Treatment of cardiac dysrhythmia.

Bupivacaine

Etidocaine

Ropivacaine

Benoxinate It is ester LA. In ophthalmology for corneal A because : NO mydriasis. NO corneal injury.

Benzocaine Used as powder or cream.

Because it is insoluble, it produces less systemic toxicity.

Surface anesthesia on Skin (wound & ulcer)

INFLUENCING FACTORS

IF Advantage Disadvantage

1 Dosage High Fast onset / long duration side effect

2 Site BV side effect / Short duration

3 Lipid solubility LS effect

4 Infection/ inflammation

pH action / ionized /effect

Vaso-dilation

absorb / side effect/ duration

5 Type of solution Alkali Less painful / fast onset / non-ionized / action / effect

6 + vasoconstrictors duration/ absorb /side effect