local anesthetics Flashcards
local anesthetics chemical structure
lipophilic group (aromatic ring) + intermediate chain + ionizable group (tertiary amine)
chemical properties of local anesthetics
ester links = prone to hydrolysis - shorter duration of action
cationic form = most active at receptor site
uncharged = penetrates biological membranes
importance of ester links in local anesthetics
prone to hydrolysis
importance of cationic form of local anesthetics
most active
importance of uncharged form of local anesthetics
penetrates biological membranes
how to enhance/lengthen duration of local anesthetics
vasocontrictors are given = usually EPI
dec systemic absorption by dec blood flow
dec systemic toxic effects
EPI in spinal anesthesia
acts at alpha 2 = inhibit substance P
cocaine as vasoconstrictor in local anesthetic
constricts BV by potentiating action of NE = preventing its own absorption
what metabolizes ester linked anesthetics
tissue and plasma esterases: pseudocholinesterase
what metabolizes/degrades amide linked local anesthetics
liver microsomal cytochrome p450
MOA of local anesthetic
block VG sodium channels
bind to receptors near intracellular end of channel - block it
stop AP
liposolubility vs toxicity in local anesthetics
greater liposolubility = grater toxicity
pKa vs speed of onset
closer pKa to body pH, faster the onset
procaine
short acting
chloroprocaine
short acting
lidocaine
intermediate acting
mepivacaine
intermediate acting
prilocaine
intermediate acting
tetracaine
long acting
bupivacaine
long acting
etidocaine
long acting
ropivacaine
long acting
local anesthetic toxicity of CNS
restless, tremor = clonic convulsions
respiratory failure
premedication with benzo provides prophylaxis against seizures
local anesthetic toxicity of CV
depress pacemaker activity, contractility
arteriolar dilation - hypotension
**cocaine can cause vasoconstriction and hypertension and arrhtymias
(bupivacaine is more cardiotoxic than others)
toxicity in blood
prilocaine large doses == accumulate o-toluidine
o-toluidine = oxidizing agent capable of forming methemoglobin
toxicity allergic reactions
ester types metabolize to PABA (p-aminobenzoic acid derivatives)
important for people allergic to PABA
BUT amides dont metabolize to PABA = no allergic reaction
esters vs amides
esters = have 1 "i" amides = have 2"i"'s
esters = be careful of PABA allergy
local anesthetic interactions
procaine -> PABA = inhibits action of sulfonamides
avoid in pt taking sulfonamides
