Local Anesthetics

Local anesthetic

Blocks peripheral nerve conduction and all sensation; generally does not result in loss of consciousness

Topical use of local anesthetic

Relieves pain from insect bites, minor burns, skin irritation, sore throat, and minor eye/ear/nose/throat/dental procedures

Parenteral use of local anesthetic

Involves injection near peripheral nerve endings (perineural infiltration), near major nerve trunks (bier blocks), or into epidural/ subarachnoid spaces

Bier block

Intravenous local anesthetic technique where drug is injected distally while limb circulation is isolated proximally

cocaine

_____ was first used by in 1884 for ophthalmic surgery

Weak base

Local anesthetics are weak _____ provided as salts (usually HCl)

slower

The greater the pKa, the greater the ratio of to Cationic to unionized form → ___ onset

unionized

The form of local anesthetic passes through the membrane

cationic

The _____ form binds the sodium channel from the inside and blocks it

Sodium

Blocks ____ channels → increases excitation threshold → blocks conduction

low pH

the effect of _____ on a local anesthetic pushes reaction toward ionic form that can’t pass membrane → reduced effect

Active

Sodium channel must open to allow entry of R3-NH+; the more____ the nerve, the more rapidly block develops

Small Fiber diameter, Firing frequency, longer action potential,

What are three factors that make nerves more susceptible to local aesthetics

Sensory (pain) fibers

Are thin, have high rates, and action potential durations

Esters, Amides

_____ are quickly inactivated by plasma & tissue esterase; ____are more stable and metabolized by liver

cardiac depression, hypotension

May cause ______ (due to Na+ current inhibition) and ______ (due to smooth muscle relaxation & SNS inhibition)

vasoconstriction

Cocaine causes ____________ instead of vasodilation

sleepiness, lightheadedness, restlessness, auditory disturbances, shivering, convulsions, and CNS depression

What are some unwanted effects on the CNS?

Vasoconstrictor addition

is added to limit systemic absorption, increase local concentration, and counteract anesthetic-induced

Local anesthetics contain an aromatic ring, ester or amide linkage, and a basic side chain

What are the chemical components of a local anesthetic

amino

Unlike other local anesthetics, benzocaine lacks an _____ group

Access to receptor

Limited by the state of the sodium channel