Flashcards in Pharmacology - Local Anesthetics - Vandana Sharma Deck (21):
In dealing with anesthetics, potency correlates to:
The onset of action of an anesthetic depends on what factors?
The more lipid soluble, the faster the onset of the drug
The duration of action of an anesthetic depends on:
binding to alpha-1-acid glycoprotein
What is the MOA of local anesthetics?
LA bind reversibly to the intracellular portion of the Na channel and inactivate the channel. The threshold for excitation therefore increases, impulse conduction slows, etc.
Short-acting ester local anesthetics are inherently safer w/r/t systemic toxicity due to their clearance by:
What is a potential complication of continuous spinal catheters infusing lidocaine in order to permit repetitive dosing to facilitate adequate anesthesia?
Cauda equina syndrome - severe back pain with motor and sensory deficit, loss of bowel and ladder control
An example of local neural toxicity from LA
What is TNS?
Transient Neurological Syndrome
transient pain or dysthesia linked to the use of lidocaine for spinal anesthesia, can be severe
Can occur with lidocaine, procaine, mepivicaine
Why are many people allergic to anesthetics containing esters?
para-aminobenzoic acid (PABA) metabolites are known allergens (methylparaben is the preservative that metabolizes to PABA)
What is the order of nerve depolarization?
1. Resting membrane potential
2. Stimulus --> threshold --> voltage-gated Na channels open
3. Voltage-gated K channels open --> depolarization
4. At peak, voltage-gated Na channels close
5. Repolarization phase --> K channels close
What is preemptive analgesia?
The nerve block is performed prior to the incision.
LAs all have a similar structure: the aromatic ring, the intermediate linkage, and the terminal amine. What is the function of the aromatic ring?
Aromatic ring = lipophilic portion = greater lipid solubility (correlates to high potency)
LAs all have a similar structure: the aromatic ring, the intermediate linkage, and the terminal amine. What is the function of the intermediate linkage?
The intermediate linkage determines the biodegradation and elimination of the drug
LAs all have a similar structure: the aromatic ring, the intermediate linkage, and the terminal amine. What is the function of the terminal amine?
The terminal amine tail is able to accept a proton and can go from tertiary to quarternary with a positive charge (weak base)
pKa = pH - log ([H]/[HA])
when base and acid concentration are equal, log 1=0
and pKa = pH
What is pKa?
The pH at which 50% of the molecule exists in ionized form and 50% in non-ionized form
What is the effect is there is a big difference between the pH of the blood and the pKa of the anesthetic agent?
Creates more ionized and less lipid soluble (and less potent) drug
T/F: Smaller nerves and myelinated nerves get blocked earlier than larger and unmyelinated nerves.
Can transient neurologic syndrome occur after administration of Bupivicaine or Clorprocaine?
More common in lidocaine (and others)
What is the cardiac toxicity associated with local anesthetic use?
Much higher doses than CNS toxicity;
Na channel blockade --> depression of myocardial contractility and reduced refractory period
**All local anesthetics except cocaine and ropivicaine are vasodilators which can lead to cardiac arrest
What anesthetic has the highest cardiac toxicity potential?