& IT’S ACTION

Local anesthetic solution

Prepared by Dr. Fatima Abdhamed Yaffai

Local anesthesia

Local anesthesia has been defined as

a loss of sensation in a circumscribed area of the body caused by a depression of

excitation in nerve endings or an inhibition of conduction process in peripheral nerves.

Local anesthetic: produce loss of sensation to pain in a specific area of the body without the

loss of consciousness

Solution contained

within a dental cartridge

1. Local anesthetic solution

2. Vasopressor

3. Sodium chloride

4. Distilled water.

Action of local anesthetic

The concept

They prevent both the generation and the

conduction of a nerve impulse.

It sets up a chemical roadblock between

the source of impulse (e.g. the scalpel incision in soft tissues) and the

brain.

Physiology of the peripheral nerves.

The function of a nerve is to carry messages from one part of the body to another. These

messages, in the form of electrical action potentials,

are called impulses.

Action potentials are transient membrane depolarization that result from a brief increase in

the permeability of the membrane to sodium, and usually also from a delayed

increase in the permeability to potassium.

Mode and site of action of local anesthetics

The nerve membrane is the

site at which local anesthetic

agents exert their

pharmacological actions.

The primary action of local anesthetic in producing a conduction block is to decease the permeability of the ion

channels to sodium ions (N+)

• All local anesthetics are amphipathic,

• Local anesthetics without a hydrophilic part are not suited for injection but are good

topical anesthetics.

• The nature of the linkage is important in defining several properties of the local anesthetic, including the basic mode of

biotransformation.

Local anesthetic are availabe as salts for clinical use. Within the solution it exists simultaneously as

1.Uncharged molecules (RN) also called the base and

2. positively charged molecules (RNH+), called the cation.

RNH+ RN + H+

The uncharged, lipid-soluble, free base form (RN) of the anesthetic is

responsible for diffusion through the nerve sheath.

In the presence of a high concentration of hydrogen ions (low pH) the equilibrium shifts to the left and most of the anesthetic solution

exists in cationic form.

RNH+ > RN + H+

As hydrogen ion concentration decreases (higher pH), the equilibrium shifts toward

the free base form. RNH+ < RN + H+

Local anesthetics

Esters

Esters of benzoic

acid

ButacaineCocaine

BenzocaineHedylcainePiperocaineTetracaine.

Esters of para-aminobenzoic

acid

ChloroprocaineProcaine

propoxycaine

Amides

ArticaineBupivacaineDibucaineEtidocaineLidocaine

Mepivacaineprilocaine

Quinoline

centbucridine

the doses of local anesthetic drugs are presented in terms of milligrams of drug

per unit of body weight, mg/kg.

Maximum dose for an individual is usually between 70mg to 500mgThe amount of dose also varied based on the type of solution used and the presence of vasoconstrictor

Example:---For adult whose weight is 150lbs and up, maximum dose Articaine and lidocaine is about 500mg---For children, the dosage reduced to about 1/3 to ½ depending on their weight.

.