Flashcards in Exam #01b - Local Anesthetics Deck (22):
At what location on the nerve pathway do LA's work?
at the primary afferent neuron
LA would penetrate all of the following except:
A) smaller axons before larger axons
B) myelinated axons before nonmyelinated axons
C) outer nerves before inner nerves in large mixed nerves
D) rapidly-firing axons before resting axons
E) axons far from the site of injection before axons at the site of injection?
The unionized LA drug is able to penetrate the cell membrane. However, the ionized LA drug is the only way it has activity. Why is LA drug ionized inside the neuron cell?
There is a lower pH inside the neuron and therefore the LA drug gets ionized
All of the following regarding LA's is true except:
A) Most LA are esters
B) Most LA are amides
C) Most LA are weak bases
D) LA are partly lipid soluble, partly water-soluble
E) all the above are true
The effectiveness of a LA is a function of what?
Why would more LA be required for same effectiveness when injecting into site of inflammation?
Site of inflammation/infection is more acidic with a lower pH. This shifts the equilibrium towards formation of ionized LA drug which results in less penetration, which is why you'd need to administer more LA for the same effect
List the Ester LA's in order of shortest duration to longest (3)?
List the Amide LA's in order of shortest duration to longest (2)?
What (3) criteria is the clinical selection of LA's based on?
What enzyme metabolizes ester LA's?
plasma cholinesterase (LA's are not penetrating synapse so AChE is NOT metabolizing ester LA's
What enzyme metabolizes amide LA's?
liver microsomal enzymes (CYP450) - potential D/D interactions
Would liver disease increase or decrease the T1/2 of ester LA's?
Neither, since ester LA's are metabolized by plasma cholinesterases. Liver disease would INCREASE T1/2 of amide LA's since amide LA's are metabolized by CYP enzymes
Which LA type would be a better choice for a patient with liver disease?
ester type LA
What effect on T1/2 of amide LA's would decreased hepatic blood flow cause?
T1/2 would increase
How are LA's primarily excreted?
How can you reduce respiratory depression caused by LA's in brain stem when injecting into spinal cord?
Inject low on the spinal cord. There isn't much fluid movement in the CSF so not much drug would reach the brain stem
Name (8) adverse effects seen with CNS toxicity caused by LA's (being absorbed systemically aka into blood stream)?
7. respiratory depression
How are LA usually dispensed?
as an acidic salt solution (highly water soluble and stable)
How do LA slow the propagation of nerve impulses?
By reducing the rate of rise of the AP and the rate of repolarization
This term is defined as the exposure time required by an anesthetic in order for it to exert its action?
What critical length would smaller nerve fibers have?
Proportionally smaller critical length