Somatic NS Drugs: Local Anesthetics Flashcards
structure of LA
amphipathic - hydrophilic/hydrophobic
hydrophobic - (benzene) determines ability to cross membrane
hydrophilic (amine) influences drug solubility + ability to interact with receptor (Na) /enter cell
amide/ester = metabolic rate/duration of drug
oil: water partition coefficient
a high partition coefficient = increased potency of LA
most LA are weak bases why
LA cross membrane most efficiently in unionized form
ionized form = hight affinity for drug-receptor
use dependance of LA is mostly greatly enhanced when
high pKa
extracellular pH > pKa
how do LA work
- sodium channel antagonist
- reversibly bind to Na channel
- block influx of Na into axon during AP
=block propagation of action potential to CNS
duration of LA = due to shift of many Na channels > inactive state
sensitivity to LA is
inversely proportional to nerve fibre diameter + degree of myelination
small nerve fibers (myelinated):
- easy penetration of drug
- afferent sensory neurons (more pain stimulus - use dependence - more LA)
large fibers (myelinated): - big clusters - extra barrier to get through
coadministration of what increases the duration of an LA
vasoconstrictor (E)
uses of LA
- surface anesthesia - BENZOCAINE + LIDOCAINE
- infiltration anesthesia - drug injected into tissues - biopsies
- intravenous anesthesia - limb surgery
- nerve block anesthesia - dental surgery
- spinal anesthesia - abdomen
- epidural anesthesia - block childbirth pain
why is lidocaine used instead of benzocaine
ionizable - longer duration
benzocaine - penetrates well/doesn’t bind well = shorter duration
side effect of LA
- bradycardia
- myocardial depression
- hypotension
- respiratory depression
- urinary retention
BUPIVACAINE - s isomer
metabolism of LA
ester-linked LA hydrolyzed + inactivated by BChE
amide-linked LA metabolized by liver enzymes in N-alkylation reactions = longer plasma half lives
drug half life
time required for drug conc to reach half of its maximum level in body
newer LA
PRILOCAINE: - methemoglobinemia
ARTICAINE: rapid onset/short duration = dental process
heredity methemoglobinemia
higher levels of Fe3+ in blood due to lack of enzyme that converts to Fe2+
