10. Local Anaesthetics Flashcards
Local anaesthetics
-substances reversibly produce blockade of sensitive neurons in certain part of body
-local analgesics - blocks perception of pain in certain part of the body
mechanism of action of LA
-gradual block of Na+ voltage gated channels in neurons -> decrease or block of axonal conduction in neurons
-drug must penetrate neuron to evoke its effect
PK of LA
-absorption and distribution influence duration of effect and toxicity of LA
-absorption from administration site depends on blood perfusion
How are LA classified ?
- Esters
-Amides
PK of ester LAs
short bio half life
lower protein binding
metabolised by plasma esterases
pk of amide LAs
strong plasma protein binding
metabolised in the liver
what are the factors influencing effects of LA
-physical-chemical properties
-type of neuronal fibres (vegetative, sensitive (hot, cold, pain),motor fibres(
what are the adverse effects of LA
-cardiovascular toxicity
-allergy
-neurotoxicity
-methemoglobinaemia
cardiovascular toxicity involves
-bupivacaine- most cardiotoxic
-bradycardia
-vasodilation, hypotension, syncope
-cardiovascular collapse
what is the therapy for cv toxicity?
cardiopulmonary support + sympathomimmetic therapy with adrenaline and atropine, lipid emulsions
methemoglobinaemia
mostly in prilocaine -due to its metabolites
therapy: iv. methylene blue 1% +o2
allergy
mostly with ESTERS - caused by their metabolites
-exanthem, edema, asthma attack, anaphylaxis
what are some other adverse effects of LA
injury of nerve during administration
malignant hyperthermia
what are the vasoconstringent adverse effects
ischemia/necrosis
tachycardia, palpitation
increased BP
arrythmia
do not co administer with MAO inhibitors
what are the ester local anaesthetics ?
-procaine
-benzocaine
-tetracaine
-cocaine
-oxybuprocaine
what are the amide local anaesthetics
Mesocaine
articaine
mepivacaine
bupivacaine
ropivacaine
-prilocaine
cinchocaine
procaine
slow onset of action
short duration of effect
poorly absorbbed from skin and mucosa
tetracaine
highly potent but with high toxicity
only used for topical anaesthesia
benzocaine
only for topical anaesthesia
oral use for sore throat
cocaine
first known LA
comes from the coca plant
vasoconstrictor effect , highly addictive
only for surface anaesthesia
mesocaine
two drugs sold under the brand name
LIDOCAINE- fast onset and intermediate duration
TRIMECAINE-long onset , intermediate duration
Articaine
fast onset long effect
used in dentistry - ADRENALINE REQUIRED
Mepivacaine
vasoconstrictor- no need for adrenaline
used in dentistry
Bupivacaine
CARDIOTOXIC
-local and infiltration anesthesia
-continual infusion to epidural space to treat acute pain
Ropivacaine
-all types of anesthesia EXCEPT SUBARACHNOID
never into a liquor space
Prilocaine
surface anaesthesia (EMLA)
spinal anaesthesia for short surgical procedures
AE : METHAEMOGLOBINEMIA
cinchocaine
topical anaesthesia
HIGHLY TOXIC
procaine
oldest synthetic LA
slow onset slow duration
infiltration and conduction anaesthesia
benzocaine
topical anaesthesia fir ear, throat , oral cavity
tetracaine
fast onset
topical anaesthesia of oral cavity and throat
HIGHLY SYSTEMIC TOXICITY
what are the types of LA
-topical surface anaesthesia
-infiltration anaesthesia
-conduction anaesthesia
Topical surface anaesthesia
transdermal penetration of LA in the form of solutionn, spray, gel
-used on mucosa, cornea , oesophagus , GUT catheterisation
-EMLA
EMLA -eutectic mix of LA
-EMLA- lidocaine and prilocaine (euctectic mixture of LA)
-used on intact skin, in peds procedures
melts better has a better absorption compared to a single LA
Infiltration anaesthesia
subcutaneous, submucosal, intramuscular, intraarticular
-blocks nerve conduction near site of admin
-used in minor procedures, dentists
Conduction anaesthesia involves ?
-peripheral nerve block
-regional anaesthesia
-central conduction anaesthesia
Peripheral nerve block- conduction anaesthesia
-blocks nerve trunks and individual nerves
Regional anaesthesia -conduction anaesthesia
IV regional anaesthesia (Bier block)
-common- TRIMECAINE or LIDOCAINE -quick onset and quick inhibition of motor functions
-no toxic LA !! NO BUPIVACAINE
-requires exsanguination of limbs so only short procedures
Central conduction anaesthesia
-epidural
-subarachnoid
epidural ->central conduction anaesthesia
-perioperative and obstetric anaesthesia
-requires stopping anticoagulants and antiplatelet agents
subarachnoid -> central conduction anaesthesia
-intrathecal admin of LA into interveertebral space
