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Local Anesthetics
Dr. Myers
29
Pharmacology
Graduate
03/01/2012

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Term
Fct of local anesthetics
Definition

Block nerve conduction when applied at appropriate concentrations.

Block voltage dependent Na channel and therefore inward Na flow in order to block action potential.

Term

Local anesthetic mechanism of action

****he wants us to know this****

Definition
Cationic form interacts with open Na channels on the inner surface of the axonal membrane (must cross axonal membrane in order to be effective). This causes a dose dependent decrease in impulse conduction. 
Term
In general smaller nerve fibers are ____ susceptible than larger, heavily myelinated fibers
Definition

More

Type B and C fibers: * Postganglionic sympathetic, dorsal root pain fibers and preganglionic autonomic are much more effected than

Type A: delta (pain/temp), gamma (mm spindles), beta (touch and pressure), alpha (proprioception, motor).

With alpha being the least affected

Term
Which form of local anesthetics can cross axonal membrane
Definition
Non-ionized form
Term
Mode of transport of local anesthetics
Definition
Local anesthetics are weak bases, the are injected as ionized drug, they become a free base prior to crossing the membrane. Once in the membrane they convert to the ionized form which binds to the sodium channel. 
Term
Types of local anesthetics
Definition

Esters (procaine)

Amides (lidocaine)

Term
Common structure of all local anesthetics
Definition

Aromatic ring

Teritary amine

Alkyl chain

Term
Determinants of Blockade of local anesthetics
Definition

Potency (dependent on lipid solubility, the more lipid soluble the better effect)

Duration (protein binding capacity)

Onset

Effect on blood vessels

Term
Potency of bupivacaine and etidocaine compared to procaine
Definition

B: 10* more potent

E: 40* more potent

Term
Bupivacaine has a _____ degree of protein binding than procaine and thus a _____ duration of block
Definition

higher

longer

Term
Factors that increase local anesthetic binding protein
Definition
Trauma, surgery, tobacco smoking, chronic inflammation, chronic pain, uremia, CANCER
Term
Factors that decrease local anesthetic protein binding
Definition
Pregnancy, OCP, newborn status
Term
The _____ the pKa (the pH at which 50% of the agent exists in the ionic and 50% in the non-ionic form) the _____ basic the local anesthetic and the _____ it will be to get into membrane--> _______ onset
Definition

Higher

More

Harder

Longer

pka is generally between 7.7-9 (which is higher than the body)

Term
Vasodilation _____ the duration of action of local anesthetic and ______ the onset time. Which local anesthetic is not a vasodilator?
Definition

Decreases

Prolongs

Cocaine

Term
Determinants of toxicity
Definition
Plasma and blood concentrations, total concentration, free concentration (determined by protein binding and ionization, the ionized form is toxic to CNS), lipid solubility, site of injection
Term

Most common vasoconstrictors added to local anesthetics

Adverse effects of adding these

Definition

Epinephrine, ephedrine, phenylephrine

HTN, tachycardia, cardiac arrhythmia, ischemia

 

Term
Anesthetic cardiac toxicity
Definition
Decreased HR--> decreased CO--> ectopic foci--> MI or possibly fatal arrhythmia
Term
Why are bupivacaine and etidocaine so toxic to the heart?
Definition
Specific binding to cardiac conduction system
Term
Side effect of Prilocaine
Definition

Methemoglobinemia

 

Prilocaine oxidizes ferrous Hgb--> Ferric making it harder to transport Oxygen

Lead to a cyanotic color that in most cases is benign. 

DO NOT GIVE PRILOCAINE TO NEWBORNS

Term
All local anesthetic have a _____ therapeutic index
Definition

Narrow

At high concentration they are toxic to nerve cells and to tissue

Term
The majority of allergies to anesthetics are _____ agents
Definition
Ester
Term
Allergy to lidocaine
Definition
Rare, related to methylparaben (added as preservative)
Term
Metabolism of ester anesthetics
Definition
Hydrolyzed by cholinesterases in plasma--> short half life.
Term
Metabolism of amide anesthetics
Definition

Liver: N-dealkylation and hydrolysis

 

Decreased in patients with liver disease or decreased hepatic flow

Term
Resting nerves are ______ sensitive to local anesthetics
Definition
Less. They have closed Na channels. The nerve must open the channel for local anesthetic to work
Term
Use of local anesthetics
Definition

Surface anesthesia

Infiltration

Field Block

Nerve Block

IV regional

Spinal

Epidural: Bupivacaine, Mepivacaine

Term
Ester Local anesthetics
Definition
Procaine, Cocaine, Tetracaine, chloroprocaine, benzocaine
Term
Amide local anesthetics
Definition
Lidocaine, mepivacaine, bupivaciane, prilocaine, etidocaine, dubicaine, ropivacaine
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