Local anesthetics work by reversibly blocking nerve conduction without damaging neurons. They are commonly used in ophthalmology for foreign body removal, tonometry, contact lens fitting, and diagnostic procedures. The two main types are esters (like cocaine and procaine) and amides (like lidocaine and bupivacaine). Amides are metabolized in the liver while esters are metabolized by pseudocholinesterase. Topical anesthetics like tetracaine and proparacaine are often used, as well as infiltration with lidocaine or bupivacaine. Adverse effects can include cardiovascular and central nervous system issues, but local anesthetics are generally safe when used properly.

1. LOCAL ANAESTHETICS
OPTOM FASLU MUHAMMED

2. • LA are agents which produce reversible block
of nerve conduction without any structural
damage to the neuron concerned and without
any loss of consciousness.
• local anesthetics are used to block all
sensation in the part supplied by the nerve.

3. • Most local anesthetic agents consist of a
lipophilic group (eg, an aromatic ring)
connected by an intermediate chain via an
ester or amide to an ionizable group (eg, a
tertiary amine)

4. CLASSIFICATION
• ESTER TYPE
-COCAINE, TETRACAINE, PROCAINE,
BENZOCAINE etc .
 AMIDE TYPE
-LIDOCAINE, BUPIVACAINE, PRILOCAINE,
DIBUCAINE etc.

5. MECHANISM OF ACTION
 Sensory information passes along nerve fibers via
electrical impulse, or action potential.
 When nerve is at rest , the interior has a negative
charge.
 An action potential is generated by the influx of Na
ions in to the interior of the nerve, giving it a positive
charge-Depolarization
 The nerve fiber is returned to its resting potential by
efflux of k ions- repolarization.
 The action potential is then generated along the axon
by successive depolarization & repolarization of
adjacent regions.

6. • The primary mechanism of action of local
anesthetics is blockade of voltage-gated
sodium channels .
• Bind to receptors near the intracellular
end of the voltage gated Na channels.
• This reduce the permeability of cell
membrane to Na ions , so action
potential is not generated.

7. USES
• FOREIGN BODY REMOVAL
• A drop of LA will make location & removal of
the offending object very much easier.
• TONOMETRY
• Topical anesthesia is essential for the
assessment of IOP
• CONTACT LENS FITTING- eye impressions for
the constriction of scleral lenses
• Certain diagnostic procedures: LA are used
before a schirmer test of lacrimal function.

8. Commonly used local anesthetics in
ophthalmic practice.
• Lidocaine- -1-4%
• Bupivacaine-0.25-0.75%
• Etidocaine-1-1.5%
• Prilocaine-1-2%
• Mepivacaine-1-2%
• Hexylcaine-1-2%
• Proparacaine-0.75%
• Tetracaine-0.5%

9. Common topical anesthetics.
Lignocaine-2-4%
Tetracaine-0.5%
Proparacaine-0.75%
Common regional anesthetics
Lignocaine-1-2%
Bupivacaine-0.5%
Hexylcaine-1-2%

10. Pharmacokinetics
ABSORPTION
Systemic absorption of injected local anesthetic
from the site of administration is determined
by several factors, including dosage, site of
injection, drug-tissue binding, local blood flow
• Application of a local anesthetic to a highly
vascular area such as the tracheal mucosa or
the tissue surrounding intercostal nerves
results in more rapid absorption

11. DISTRIBUTION
• The amide local anesthetics are widely
distributed after intravenous bolus
administration.
• After an initial rapid distribution phase, which
consists of uptake into highly perfused organs
such as the brain, liver, kidney, and heart, a
slower distribution phase occurs with uptake
into moderately well-perfused tissues, such as
muscle and the gastrointestinal tract.

12. METABOLISM AND EXCRETION
• The local anesthetics are converted in the liver
(amide type) or in plasma (ester type) to more
water-soluble metabolites and then excreted
in the urine.
• Ester type LA is metabolized by
pseudocholinesterase and amide type by
hepatic microsomal enzymes and enzyme
amidase.

13. SIDE EFFECTS
• Cardiovascular
-depression of heart, bradycardia, hypotension,
cardiac arrhythmias etc.
 CNS
-rapid absorption produce restlessness, tremor,
convulsions.
 Anaphylactic reaction
-common with ester type.
-causes asthma, dermatitis, skin rash etc.

14. • Corneal change
-very rarely reversible corneal change may occur.

15. ROUTES OF APPLICATION
• SURFACE ANAESTHESIA
-Most popular method in ophthalmology.
-lignocaine 4% is used .
INFILTRATION ANESTHESIA
 Nerve endings are anaesthetized by direct
exposure to drug.
 Drug is infiltrated subcutaneously
Procaine [2%] and lignocaine [2%] used.

16. NERVE BLOCK ANAESTHESIA
Drug is injected very close to nerve eg; brachial
plexus.
SPINAL ANAESTHESIA
Drug is injected to the subarachnoid spaces.
Eg; procaine and lignocaine.
EPIDURAL ANAESTHESIA
Drug is injected outside the dura.

17. Commonly used drug with LA
 Adrenaline –to prolong the effect of LA and to
reduce the toxicity by reducing absorption
from local area.
 Hyaluronidase-enzyme which cause
depolymerization of hyaluronic acid and
increase the permeability of injected fluid.

18. TETRACAINE [Amethocaine]
 Topical anaesthetic [0.5%] in ophthalmic
practice.
 Onset of action is 30 minutes.
 Side effects-stinging sensation, punctate ,drug
allergy.

19. PROPARACAINE
Topical anaesthetic. [0.75%]
Onset of action-30 sec
COCAINE
First local anaesthetic obtained from leaves of
plant Erythroxylon Coca.
It is no more in use nowadays because of its
corneal toxicity, addicting nature etc.

20. PROCAINE
• First synthetic local anaesthetic
• Used as a small area infiltration and spinal
anaesthetic.
• It is poorly absorbed from mucous membrane-
so no topical use.
• 2% injection is the usual preparation.

21. LIGNOCAINE
 Most commonly used LA
 In ophthalmology 4% [topical] and 2%
[infiltration] solutions are commonly used.
 It has quick onset of action and high degree of
penetration.
 The drug is recommended for topical, nerve
block, infiltration and epidural injection and
for dental analgesia.
 It may cause drowsiness.

22. BUPIVACAINE
• Onset of action is slow
• A 0.75% solution produce anaesthesia and
akinesia for 8-12 hours.
• In ophthalmic practice, usually a combination
of 2% lignocaine,0.75% bupivacaine and 7.5
TRU of hyaluronidase is used for periocular
injection, and surgery of any kind may be
performed on such type of anaesthetized eye.