Local anesthesia Mechanism Of Action as well as types
1. LOCAL ANESTHESIA
By :
Suman Bhattarai(ROLL NO :50)
Sujan Thapa Magar (ROLL NO :49)
Sujan Rai (ROLL NO :48)
B.V.Sc & A.H
Agriculture and Forestry University
2. Local Anesthesia
Drugs that are used to produce reversible loss of
sensation in a circumscribed area(restricted) of the
body
Caused by depression of excitation in nerve endings
or an inhibition of the conduction process in
peripheral nerves and in every type of nerve fibres i.e.
Sensory,motor or autonomic
No Structural damage to the neurons
3. Desirable Properties Of Local Anesthesia
Should not be irritating
Should not cause any permanent alteration of
nerve structure
Its systemic toxicity should be low
Time of onset of anesthesia should be short
Should have high potency so that low
concentration should be used
Should be free from producing allergic reactions
Should be stable in solution and relatively undergo
biotransformation in the body
4. MECHANISM OF ACTION
• Local Anesthetic receptors are located
in Na+ channel of axonal membrane
• Receptors Consists of 2 gates
1) Activation gate or ‘m’ gate
2) Inactivation gate or ‘h’ gate
Note: Action of ‘h’ gate is responsible for
blocking of Na+ channels
5. MECHANISM OF ACTION
Local Anesthesia – Weak bases , Present in Unionized form
Enter into cell membrane of Neuron
Block Voltage gated Na+ channels by physically
plugging the transmembrane pore from inside
No entry of Na+ ions into cell
No depolarisation
6. No depolarisation
No generation of action potential
No generation of impulse to CNS
No conduction of nerve impulse
Critical threshold potential required for impulse
transmission (-45mA) is not achieved
MECHANISM OF ACTION
8. Classification
Based on nature of the carbony- containing linkage group in
their structure, LA can be classified into
1) ESTER LOCAL ANESTHETICS
e.g. Procaine , Benzocaine , Tetracaine
2) AMIDE LOCAL ANESTHETICS
e.g. Lidocaine , Prilocaine
3) ETHER OR KETONE LOCAL ANESTHETICS
e.g Pramocaine , Dyclonine
9. 1) ESTER LOCAL ANESTHETICS
Procaine
• first synthetic local anesthetic introduced in 1905
• is an ester of diethylaminoethanol and paraamino benzoic
acid(PABA)
Pharmacological Effects
a) Local Action :
• Rapidly effective when injected locally
• When injected around mixed nerve , causes
anesthesia of skin and paralysis of voluntary muscle
supplied by the nerve
• Reduces the release of acetylcholine from motor nerve endings
10. • Local effects : Loss of pain, tempertature and touch,
vasodilation, and loss of motor power
b) Systemic actions
• CNS : Normal dose : rapidly inactivated in the plasma
and has little apparent CNS effects
High dose : CNS stimulation like restless , tremors
and convulsions
• Cardiovascular system :
Normal doses : No significant
effect on heart
High doses : Myocardial depressant activity and can
decrease automaticity, excitability, contractility, conductivity, and
increase refractory period
11. Pharmacokinetics :
Not effective due to its poor penetration through GI
mucosa and high first pass effect
parenterally injection → has delayed onset of action ( 5-10
min) and short duration of action ( 25-30 min )
[ causes vasodilation → results in rapid absorption and
biotransformation ]
after absorption → rapidly hydrolysed by plasma
cholinesterase and by esterase in liver → inactive
metabolites PABA and diethylaminoethanol → excreted by
the kidneys into the urine.
Metabolism : Hydrolysis by plasma esterases to PABA
Route of elimination : With normal kidney function, the
drug is excreted rapidly by tubular excretion.
Half life : 7.7 minutes
12. Side effects :
Low local and systemic toxicity
High doses may produce restlessness, tremors, and
convulsions followed by CNS depression
Cardiovascular toxicity includes hypotension,
bradycardia, arrthymias, and possible cardiac arrest
Contraindications & Precautions
Should not be used in patients suffering from
cardiac disease or those hypersensitive to it
Vasoconstrictor shouldnot be added to procaine
when used for nerve block of extremities ( e.g. tail,
toes, ears, penis, e.t.c )
13. Drug interaction :
Procaine should not be used with sulphonamides as it
decreases antimicrobial activity of sulphonamides by enhancing
availability of PABA
Clinical Uses :
Used mainly for nerve block anesthesia
Doses :
Dogs and cats : 2-5 ml of 2 % solution
Large animals : 5-10 ml of 4% solution
14. LIDOCAINE :
Is an aminoethlyamide and is the prototypical members of
amide group of local anesthetics
Pharmacological effects :
Most properties similar to procaine but produces more prompt,
more intense, long lasting, and more extensive anesthesia
Rapid onset of action ( blocks conduction within 3 minutes )
Duration of action : 45 min ( without epinephrine )
: 90 min ( with epinephrine )
Pharmacokinetics :
Not effective orally as it has high 1st pass effect
After absorption, is dealkylated in the liver by mixed function
oxidases ( MFOs ) → monoethylglycine and glycine xylidide
which retain local anesthetic activity
15. These active metabolites biotransformed further before
excretion in urine
Elimination half life : 90-120 min
Side Effects :
Same effects as procaine
Unlike procaine, early central effects are Drowsiness, dizziness,
and tinnitus
Overdosage causes muscle twitching, convulsions, cardiac
arrthymias, fall in blood pressure, coma & respiratory
depression and arrest
Contraindications and precautions :
Contraindicated in patients with known hypersensitivity to
amide type local anesthetic
16. Most widely used local anesthetic for infiltration, regional,
nerve block, epidural and also topical anesthesia
Clinical Uses
Use of epinephrine is contraindicated with lidocaine, if it is
used in treatment of ventricular arrthymias
For epidural injection (2 % soln) :
Dogs and Cats : 0.2 ml/kg
Sheep : 3-4 ml
Cattle : 5-6 ml
Doses
17. Pramocaine :
Ether or ketone local anesthetic
Used primarily on skin or mucous membrane as a
topical anesthetic
HCL salt form of pramocaine is water soluble and
hence more easily absorbed into skin
Used to relieve pain or itching caused by conditions
such as sunburn or minor burns, insect bites, poison,
minor cuts and scratches.