10. Local Anaesthetics

Question 1

Local anaesthetics

Answer 1

-substances reversibly produce blockade of sensitive neurons in certain part of body
-local analgesics - blocks perception of pain in certain part of the body

Question 2

mechanism of action of LA

Answer 2

-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

Question 3

PK of LA

Answer 3

-absorption and distribution influence duration of effect and toxicity of LA
-absorption from administration site depends on blood perfusion

Question 4

How are LA classified ?

Answer 4

• Esters
  -Amides

Question 5

PK of ester LAs

Answer 5

short bio half life
lower protein binding
metabolised by plasma esterases

Question 6

pk of amide LAs

Answer 6

strong plasma protein binding
metabolised in the liver

Question 7

what are the factors influencing effects of LA

Answer 7

-physical-chemical properties
-type of neuronal fibres (vegetative, sensitive (hot, cold, pain),motor fibres(

Question 8

what are the adverse effects of LA

Answer 8

-cardiovascular toxicity
-allergy
-neurotoxicity
-methemoglobinaemia

Question 9

cardiovascular toxicity involves

Answer 9

-bupivacaine- most cardiotoxic
-bradycardia
-vasodilation, hypotension, syncope
-cardiovascular collapse

Question 10

what is the therapy for cv toxicity?

Answer 10

cardiopulmonary support + sympathomimmetic therapy with adrenaline and atropine, lipid emulsions

Question 11

methemoglobinaemia

Answer 11

mostly in prilocaine -due to its metabolites
therapy: iv. methylene blue 1% +o2

Question 12

allergy

Answer 12

mostly with ESTERS - caused by their metabolites
-exanthem, edema, asthma attack, anaphylaxis

Question 13

what are some other adverse effects of LA

Answer 13

injury of nerve during administration
malignant hyperthermia

Question 14

what are the vasoconstringent adverse effects

Answer 14

ischemia/necrosis
tachycardia, palpitation
increased BP
arrythmia
do not co administer with MAO inhibitors

Question 15

what are the ester local anaesthetics ?

Answer 15

-procaine
-benzocaine
-tetracaine
-cocaine
-oxybuprocaine

Question 16

what are the amide local anaesthetics

Answer 16

Mesocaine
articaine
mepivacaine
bupivacaine
ropivacaine
-prilocaine
cinchocaine

Question 17

procaine

Answer 17

slow onset of action
short duration of effect
poorly absorbbed from skin and mucosa

Question 18

tetracaine

Answer 18

highly potent but with high toxicity
only used for topical anaesthesia

Question 19

benzocaine

Answer 19

only for topical anaesthesia
oral use for sore throat

Question 20

cocaine

Answer 20

first known LA
comes from the coca plant
vasoconstrictor effect , highly addictive
only for surface anaesthesia

Question 21

mesocaine

Answer 21

two drugs sold under the brand name
LIDOCAINE- fast onset and intermediate duration
TRIMECAINE-long onset , intermediate duration

Question 22

Articaine

Answer 22

fast onset long effect
used in dentistry - ADRENALINE REQUIRED

Question 23

Mepivacaine

Answer 23

vasoconstrictor- no need for adrenaline
used in dentistry

Question 24

Bupivacaine

Answer 24

CARDIOTOXIC
-local and infiltration anesthesia
-continual infusion to epidural space to treat acute pain

Question 25

Ropivacaine

Answer 25

-all types of anesthesia EXCEPT SUBARACHNOID never into a liquor space

Question 26

Prilocaine

Answer 26

surface anaesthesia (EMLA) spinal anaesthesia for short surgical procedures AE : METHAEMOGLOBINEMIA

Question 27

cinchocaine

Answer 27

topical anaesthesia HIGHLY TOXIC

Question 28

procaine

Answer 28

oldest synthetic LA slow onset slow duration infiltration and conduction anaesthesia

Question 29

benzocaine

Answer 29

topical anaesthesia fir ear, throat , oral cavity

Question 30

tetracaine

Answer 30

fast onset topical anaesthesia of oral cavity and throat HIGHLY SYSTEMIC TOXICITY

Question 31

what are the types of LA

Answer 31

-topical surface anaesthesia -infiltration anaesthesia -conduction anaesthesia

Question 32

Topical surface anaesthesia

Answer 32

transdermal penetration of LA in the form of solutionn, spray, gel -used on mucosa, cornea , oesophagus , GUT catheterisation -EMLA

Question 33

EMLA -eutectic mix of LA

Answer 33

-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

Question 34

Infiltration anaesthesia

Answer 34

subcutaneous, submucosal, intramuscular, intraarticular -blocks nerve conduction near site of admin -used in minor procedures, dentists

Question 35

Conduction anaesthesia involves ?

Answer 35

-peripheral nerve block -regional anaesthesia -central conduction anaesthesia

Question 36

Peripheral nerve block- conduction anaesthesia

Answer 36

-blocks nerve trunks and individual nerves

Question 37

Regional anaesthesia -conduction anaesthesia

Answer 37

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

Question 38

Central conduction anaesthesia

Answer 38

-epidural -subarachnoid

Question 39

epidural ->central conduction anaesthesia

Answer 39

-perioperative and obstetric anaesthesia -requires stopping anticoagulants and antiplatelet agents

Question 40

subarachnoid -> central conduction anaesthesia

Answer 40

-intrathecal admin of LA into interveertebral space