Local Anesthetics Flashcards
what are the three main parts of the molecule? which determines pKa? which determines mode of degradation?
Aromatic, intermediate, amine; amine; intermediate
exception to the terminal amino group rule
benzocaine
how do bulky alkyl substitutions chance action? How does this alter the therapeutic index?
enhance potency and duration by increasing hydrophobicity. No change
hederson haselbalch equation
log([BH+]/[B])=pKa-pH
what effect does raising external pH have on conc and block?
it increases axoplasmic conc and enhances block
what effect does inflammation have on block
acidifies the external environment, decreasing the block
are Na or K currents more strongly blocked?
Na. This is what produces the anesthesia
Use-dependent block
repetitive depolaization enhances Na channel block
frequency-dependent block
increase in frequency of repetitive activity enhances use-dependent block
state-dependence
channel changes states, drug interacts in open state
name two dz states in which use-dependent block is especially effective
seizure and arrythmia
potential dependent block
LA have higher affinity for inactivated state. works well in damaged tissues where membranes are slightly depolarized
differential block
different fibers differ in their sensitivity to anesthetics. small pain and temp first, large motor last
How does fiber size affect block? myelination? location of fibers w/in bundle?
smaller=more sensitive; less sensitive; outside are blocked first
metabolism of ester-type
hydrolyzed by pseudocholinesterase (produced in Liver). produce PABA, making sulfonamide AB’s less effective
metabolism of amide-type
P450 in liver.
how is ester metabolized in spine
absorbed into bloodsteam, no pseudocholinesterase in spine
why are ester anesthetics preferred during delivery?
quicly hydrolyzed by cholinesterase and doesnt reach fetus
IV regional anesthesia
introduced into circulation following tourniquet
Which are short-acting anesthetics
ester-type: procaine and chloroprocaine
LAST
local anesthetic systemic toxicity; due to excessive blood conc, esp amide type
toxic effects of LA
seizures, CV depression and drop in BP
LAST tx
IV intralipid
methemoglobinemia
oxidizing LAs convert heme so it cant carry O2. Cyanosis in absence of resp or cardio problems. Give Methylene Blue
Tetrodotoxin
blocks Na channels from outside. No K channel effect
