Pharmacology PPT

2. Local Anesthetics

3. Definition (LAs)
drugs which upon topical application or local injection
causes reversible loss of sensory perception, esp. pain
on a restricted area of body.
By blockade of generation and conduction of nerve impulse
at neuron where they come in contact.
Loss depends upon type of nerve

4. Comparative features of general and
local anaesthesia
FEATURES GENERAL ANAESTHETIA LOCAL ANAESTHESIA
Site of action CNS Peripheral nerves
Area of body involved Whole body Restricted area
Care of vital functions Essential Usually not needed
Physiological trespass High Low
Poor health patient Risky Safer
Use in non-cooperative
patient
Possible Not possible
Major surgery Preferred Cannot be used
Minor surgery Not preferred Preferred

5. CLASSIFICATION
LOCAL ANAESTHETICS
CLINICAL
INJECTABLE SURFACE
CHEMICAL
ESTERS AMIDES
Low potency,
short duration
Procaine
Chloroprocaine
Intermediate potency,
duration
Lidocaine,
Prilocaine
High potency,
long acting
Tetracaine
Bupivacaine
Ropivacaine
dibucaine
Cocaine
Lidocaine
Tetracaine
benzocaine
Cocaine
Procaine
Chloroprocaine
Tetracaine
benzocaine
Lidocaine
Bupivacaine
Prilocaine
Dibucaine
ropivacaine
Esters - one “ i “ Amides - two “ i “

6. Advantages of amides over esters
Not hydrolyses by plasma esterases
More intense and longer action
Rarely cause hypersensitivity

7. VG Na+2 channel
Na+
- - - - - - -
+ + + + + + + - - - - - - - - - - - - - - - - - - - - - -
+ + + + + + + + + + + + + + + + + + + + + + +
Na+
- - - - - - - - -
+ + + + + + + + + +
m
m
h
Impulse arise,
stimulus
Resting (closed)
active (open)
inactive (closed)
Mechanism of action

8. Na+
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
m
m
Impulse arise,
stimulus
h
LA prolongs inactivation state of channel
(LA blocks Na+ channel)
Mechanism of action

9. Mechanism of action LAs
Block voltage gated Na+ channels
No entry of Na+ ions in to cell (neuron)
No depolarization
No generation of action potential
No generation and conduction of impulse to CNS
Local Anaesthesia

10. Pharmacological actions
Local Systemic
Order of block
Nerve fibres
C→ B → A
System
Autonomic→ sensory → motor
Sensory
Pain→ Temp → Touch→ pressure
Fibres that are blocked first; last to recover
LAs are less effective in inflamed tissues
LAs + vasoconstrictor (eg. Adrenaline 1:50000 to 1: 200000)
Prolongs duration of action of LAs
Reduces the systemic toxicity of LAs
Provide bloodless field for surgery
Increase chances of local tissue edema, necrosis, delayed wound healing
May rise BP and promote arrhythmias (Systemic toxicity of adrenaline)
CNS
Stimulation followed by depression
CVS-
cardiac depressant
LAa may induces arrythmias
Bupivacaine is more cardiotoxic
Lignocaine is used in arrhythmias
Blood vessels
Fall in BP due to vasodialtion and
cardiac depression

11. ADRs
Local Systemic
Systemic toxicity depends upon entry of
drug in to circulation
CNS-
Stimulation followed by depression
CVS-
Bradycardia, arrhythmias, hypotension,
collapse
Hypersensitivity – more with esters
Injection site Pain, necrosis, delay
wound healing
Vasoconstrictor should not used at
regions with end arteries like hand,
feet, fingers, toes, penis, pinna

12. Methods OR Techniques of LA
Surface anaesthesia
Infiltration anaesthesia
Conduction block
Spinal anaesthesia
Epidural anaesthsia
Ointment, Drops, spray, jelly
Infiltration under skin to block nerve endings
LAs injected around nerve trunk
Field block
Nerve block
LAs injected in subarachnoid space
LAs injected in dural space

14. Thanks