Local Anesthetics Flashcards
How do local anesthetics work?
They bind in open Na-Channels, causing slowed rate of depolarization, reduced amplitude, increases threshold potential. Does not change resting potential.
–Prevent propagation of the AP–
Why do local anesthetics selectively bind to C-fibers and noriceptive fibers?
In the case of an injury, the pain fibers are firing more rapidly, thus the channels are open more frequently allowing the anesthetic to get into the channels.
What is the order of sensory that are affected with local anesthetics?
First: Pain, Cold, Warmth
Later: Touch, Deep pressure, and Motor
What kind of neurons are most sensitive to local anesthetic?
- smallest diameter and unmyelinated
C-fibers and B-fibers
Why are vasoconstrictors used with local anesthetics?
They restrict blood flow away from the site of injection to prevent systemic effects of the anesthetic and keeps more drugs locally where they were injected.
How does pH play a role in local anesthetic effectiveness?
The drugs have two forms B and BH+, the B form can penetrate the membrane and then the BH+ form is the one that binds in the channel.
-Wounds typically have lower pH allowing more to penetrate the neurons.-
What are common systemic effects if local anesthetics get into the blood stream?
CNS- stimulation first, then progresses to depression
CV- decreases contractility, BP, and rate of conduction, eventually leading to coma/CV depression.
What are the two methods of metabolism of local anesthetics?
Ester Anesthetics = inactivated by esterases in the plasma
Amide Anesthetics = inactivated/metabolized in liver
–Caution with individuals with liver disease-
Which local anesthetic has both anesthetic properties and vasoconstriction effects?
Cocaine. (Ester-based)
What is the most common use for cocaine use as an anesthetic?
Typically used in upper respiratory tract and nasal surgeries where both properties are useful.
Which local anesthetic has low potency, slow onset, and short duration?
Procaine (ester-based). Less commonly used now.
Which ester anesthetic is common used for spinal anesthesia that has long action?
Tetracaine - commonly used in topical and ophthalmic solutions.
Which local anesthetic is primarily used topically and is bought OTC?
Benzocaine (ester)
What is the most widely used local anesthetic?
Lidocaine (amide-class)
How does Lidocaine compare to Procaine?
Faster, longer action, more potent than procaine.
–Typically used with epinephrine for higher dose–
Also Lidocaine is metabolized in the liver.
