[PHARMA] LOCAL ANESTHETICS Flashcards
Local anesthetic definition
a drug that induces reversible loss of sensation without inducing loss consciousness or sleep
esters example
procaine
short acting LA
procaine (0.5-1h)
intermediate acting LA
lidocaine (2h)
long acting LA
bupivacaine (3h)
esters are hydrolyzed by
plasma pseudocholine esterases
amide are metabolized by
liver
PABA derivatives & liable to allergy
ester LA
liable to induce systemic toxicity
amide LA
amides duration of action is prolonged in case of
liver disease
reduced hepatic BF as in heart disease
esters duration of action
short
amides duration of action
long
duration of action is prolonged in esters by
genetic plasma pseudo choline esterase deficiency
LA mechanism of action
bind to receptors on inner surface of Na channel & block them=>block action potential
neurons sensitive to LA
Small neurons (pain,temp, autonomic nerves)
rapid firing nerves (sensory nerves)
motor neurons are only affected by LA in case of
higher LA concentration
pKA of LA
7.7-9
pH of LA is
basic, they’re weak bases
LA solubility can be increased by
preparing them as acid salts
forms of LA
ionized
unionized
which form of LA can cross nerve membrane
unionized
relation between PPB and LA
proportional
LA with highest percentage of PPB and therefore longer duration of action
Bupivacaine (95%)
relationship between lipid solubility and potency
proportional
lipid solubility affects
potency
the more the lipid content the ____the potency
potency
pKa affects
speed of onset
the lower the pKA the ____the onset of action
faster
affect of pKa
the lower the pKa the more unionized forms there is= faster onset
lidocaine pKa
7.9
bupivacaine pKa
8.1
which drug has a higher percentage of unionized forms: Lidocaine or Bupivacaine
Lidocaine
affect of extracellular pH
the more acidic the ECF pH, the less the unionized forms available= less crossing=less anesthesia
factors increasing extracellular acidity
infections or lidocaine Hcl repeated injection
how can extracellular acidity be decreased
adding NaHCO3
affect of vasoconstrictors
prolong action of LA
decrease absorption–>
↑duration & ↓systemic toxicity
LAs affect on BV
induce VD–>↑ absorption–> termination of effect–>↑risk of toxicity
adverse effects & toxicity
~CNS=
-sleepiness, numbness, metallic taste (low)
-tremors, convulsions, resp depression, coma,death (high conc)
~Neurotoxicity
~CVS: HypoTN, Bradycardia
~allergy (esters)
~↑BP & arrhythmias with VC added to LA
neurotoxicity can happen due to
high conc of LA injected close to nerve trunk/spinal cord
side effect of high dose Bupivacaine
extremely cardiotoxic
drug interaction b/w LA x propanolol
↓hepatic BF= impairs lidocaine clearance= toxicity
drug interaction b/w
LA x adrenaline x Propanolol
dangerous rise in BP
due to unopposed alpha action
drug interaction b/w
LA x adrenaline x TCAs
hypertensive crisis
DOC in surface anesthesia
lidocaine
surface anesthesia is used in
minor surgery
infiltration anesthesia is used in
minor surgery
nerve block anesthesia is used in
dentistry & surgery
spinal anesthesia site of injection
subarachnoid space below L2
spinal anesthesia is used in
abdomen surgery
pelvis, leg surgery when GA is CI
anesthesia injected close to nerve trunks
nerve trunk
anesthesia applied to skin, mucous membranes of nose, mouth, cornea as solution/jelly/cream
surface anesthesia
anesthesia injected SC & submucosal to reach nerve branches
infiltration
IV regional anesthesia procedure
double cuff is applied & inflated above arterial BP
LA is injected after elevation to drain venous the system
side effects of spinal aesthesia
headache
hypoTN
spinal root injury
infection
hypoTN as a result of spinal anesthesia is due to
sympathetic nerve block
headache as a result of spinal anesthesia is due to
CSF leakage & traction
CSF leakage & traction in spinal anesthesia can be avoided by
pencil point needles
anesthesia injected outside the dura to block the spinal roots
epidural anesthesia
epidural anesthesia is used in
painless labor
