Local anesthetics Flashcards
What is the definition of a local anesthetic?
Any substance that produces a reversible nerve blockade.
What are the two major types of local anesthetics?
Amides and esters
Drugs with two i’s in the name are _____. Drugs with one i are _____.
amides - two i’s
esters - one i
Where in the body are esters metabolized? By what enzymes?
In the blood by plasma or pseudocholinesterase
What is the half life of an ester LA?
minutes
Degradation of ester LA’s forms _____. Is the metabolite toxic? Can people be allergic to this?
PABA is toxic and a possible allergen.
Where are amide LAs metabolized? By what enzymes?
In liver by CYP450
What is the half life of an amide LA?
Hours
Does renal disease affect LA dosing?
Nope
Does pregnancy affect LA metabolism?
Yes, metabolism is slowed (half life increases)
Are sepsis, malignany, and cardiac ischemia significant clinically in dosing LAs?
Nope
What is the mechanism of action of local anethetics?
They bind to receptors inside Na+ channels and decrease the rate of rise of the action potential so the depolarization threshold is not reached.
What is the most important factor in onset of action of a LA? Explain.
pKa must be close to physiological pH so that the drug can dissociate from the protonated form to cross the cell membrane, then reassociate with a proton inside the cell to enter the sodium channel and bind the receptor.
Are LAs weak acids or weak bases?
weak bases
What is the most important factor in the potency of a LA?
Lipid solubility. More lipid solubility = greater potency.
What is the most important factor in the duration of action of a LA?
Protein binding. More protein binding = longer duration
Name the three major clinical effects of LAs in their correct order.
- Sympathetic block
- Sensory block
- Motor block
Which is more easily blocked: myelinated or non-myelinated nerves?
Myelinated
What are the signs of systemic LA toxicity in the correct order?
1st - light-headedness and numb tongue and lips
2nd - respiratory arrest
Last - cardiovascular depression
How is systemic LA toxicity treated?
Lipid infusion to pull lipid soluble drug out of cells and into the “lipid sink” in the blood.
Are pregnant women more susceptible to systemic toxic effects of LAs?
Yeah
What is a major side effect of benzocaine and prilocaine (local anesthetics)?
They can oxidize Hb –> metHb
True or false: Local anesthetics cause the reversible interruption of afferent and efferent neural conduction.
True
