LOCAL ANESTHETICS

local anesthetic image

 

LOCAL ANESTHETICS

Definition

Local anesthetics are drug which on topical application /injection cause “reversible loss of sensory perception on specially in restricted area “
Block degeneration and conduction of nerve impulse of all part where they come in contact without causing any structural damage

Pharmacology of local anesthetics

There are two type of anesthetics used in treatment as follows

Surface anesthetics and injectable anesthetics

Injectable anesthetics

They used for induction and maintainace of state called unconsciousness

Generally used i.v. route for administration

Faster less pain full

Surface anesthetics

It produce by topical application of surface anesthetics

On set of action and duration depend on site of administration

CLASSIFICATION OF SURFACE ANESTHETICS

A) Injectable anesthetics

Low potent,short duration	Ex.procaine,chloroprocaine
Middle potent &duration	Lignocaine,prilocaine
High potent,long duration	Tetracaine,(bupiv,ropiv,dibu)acaine

B) Surface anesthetics

soluble	Cocaine,lignocaine,tetracaine, benoxicaine
insoluble	Benzocaine,oxethazine

Chemistry of local anesthetics

Two type of linkage occur in local anesthetics as follows

 Ester linked
 Amide linked

 Amide linked

More intense loner lasting anesthetics
Rarely cause sensitivity
Example–lignocaine,bupivacaine,dibucaine,prilocaine,ropivocaine

 Ester linked

Less intense and short duration
Cause high risk of sensitivity and rarely used in infiltration or nerve block
Example –procaine,chloroprocaine,cocaine,tetracaine,benzocaine

 Mode of action of local anesthetics

1)They block nerve conduction by decresing entry of Na⁺ ion during up store action of potential(A.P.)
2)As concentration of local anesthesia increased rate of rise of A.P.

3)All nerve fibers are sensitive to LAs, but due to a combination of diameter and myelination, fibers have different sensitivities to LA blockade, termed differential blockade. Type B fibers (sympathetic tone) are the most sensitive followed by type C (pain), type A delta (temperature), type A gamma (proprioception), type A beta (sensory touch and pressure), and type A alpha (motor). Although type B fibers are thicker than type C fibers, they are myelinated, thus are blocked before the unmyelinated, thin C fiber