Local anesthetics work by reversibly blocking sodium channels in nerve cell membranes, preventing the transmission of nerve impulses and sensation in a localized area. The three main classes are ester anesthetics like procaine, amide anesthetics like lidocaine, and ether/ketone anesthetics like pramocaine. Amide anesthetics have a faster onset and longer duration than esters. Local anesthetics work topically on mucous membranes or can be injected for nerve blocks. The mechanism involves blocking sodium channels from the inside of nerve cells. Overdoses can cause CNS and cardiac side effects.

1. LOCAL ANESTHESIA

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

7. No Sensation
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.

18. Thank you