Local anesthetics

1. Drug used in Mechanical
Ventilation
Dr. S. Parasuraman
Associate Professor,
Faculty of Pharmacy,
AIMST University, Malaysia.

2. Content
• Part II - Medications used for local and general
anaesthesia

3. Local anesthetics

4. Local anesthetics
• Local anesthetics provide a reversible regional loss of
sensation. They reduce pain and thereby facilitate
surgical procedures. Local anesthetics block nerve
conduction of sensory impulses and in higher
concentrations block motor impulses from the
periphery to the CNS.
• Sodium ion is required for an action potential that are
blocked to prevent the transient increase in
permeability of the nerve membrane to Na+.

5. Comparative features of general and local
anaesthesia

6. Classification of local anesthetics

7. Mechanism of local anesthetic action

8. Mechanism of local anesthetic action
• The local anesthetics block nerve conduction by
decreasing the entry of Na+ ions during upstroke of
action potential. As the concentration of the local
anesthetics is increased, the rate of rise of action
potential and maximum depolarization decreases
causing slowing of conduction.

9. Delivery techniques of local anesthetics
• The techniques include topical administration,
infiltration, perineural, and neuraxial (spinal, epidural,
or caudal) blocks.
– Regional anesthesia
– Surface anesthesia
– Infiltration anesthesia
– Field block
– Nerve block
– Spinal anesthesia
– Epidural anesthesia

10. Pharmacological properties of local anesthetics

11. Local anesthetics – actions
• All local anesthetics cause vasodilation, which leads to a
rapid diffusion away from the site of action and short
duration when these drugs are administered alone.
• By adding the vasoconstrictor epinephrine, the rate of local
anesthetic absorption and diffusion is decreased. This
minimizes systemic toxicity and increases the duration of
action.
• However, epinephrine should not be coadministered for
nerve block in extremities such as fingers and toes as
vasoconstriction of end arteries may lead to ischemia and
necrosis. It should be used with caution in patients with
thyrotoxicosis or cardiovascular disease and in labor.
Hepatic function does not affect the duration of action of
local anesthesia.

12. Local anesthetics – systemic actions
• Central nervous system:
• All local anesthetics are capable of producing a
sequence of stimulation followed by depression.
• Cocaine is a powerful CNS stimulant causing in
sequence euphoria—excitement—mental confusion—
restlessness— tremor and twitching of muscles—
convulsions—unconsciousness—respiratory
depression— death, in a dose-dependent manner.

13. Local anesthetics – systemic actions
• Cardiovascular system:
• Local anesthetics are cardiac depressants, but no
Significant effects are observed at conventional doses.
• At high doses (2–3 times the doses producing CNS
effects) or on inadvertent i.v. injection, they decrease
automaticity, excitability, contractility, conductivity and
prolong effective refractory period (ERP).

14. Local anesthetics – systemic actions
• Blood vessels:
• Local anesthetics tend to produce fall in BP.
• This is primarily due to sympathetic blockade, but high
concentrations, as obtained locally at the site of
injection, do cause direct relaxation of arteriolar
smooth muscle.

15. Local anesthetics
Onset, potency, and duration of action
• The onset of action of local anesthetics is influenced
by several factors including tissue pH, nerve
morphology, concentration, pKa, and lipid solubility of
the drug.
• Local anesthetics with a lower pKa have a quicker
onset.

16. Local anesthetics
Onset, potency, and duration of action

17. Local anesthetics – Allergic reactions (topical)
• Patient reports of allergic reactions to local anesthetics
are fairly common, but often times reported
“allergies” are actually side effects from the
coadministered epinephrine.
• Systemic toxic effect: Toxic blood levels of a local
anesthetic may be due to repeated injections or could
result from a single inadvertent IV injection.

18. Sites and uses of surface anaesthesia

19. Local anaesthetics used for spinal and epidural
anaesthesia and continuous epidural analgesia

20. Thank you