.

1. Local
Anesthetics
(LAs)
Dr Gauri Sr Shrestha,
IOM, TU

2. Local anesthetics (LAs)
1. Local anesthetics are chemical agents that reversibly block the transmission of
nerve impulses along sensory fibers.
2. Weak amphiphilic bases (amine) on one side and lipophilic aromatic residue on the
other side joined by ester or amide.
• Ester linked anesthetic: cocaine, procaine, chloroprocaine, tetracaine,
benzocaine
• Amide linked anesthetic: lidocaine, bupivacaine, dibucaine, prilocaine,
ropivacaine
3. Mechanism of action
• Block nerve conduction by decreasing the entry of Na+ ions-related action
potential.
• Reduce the release of acetylcholine from the motor nerve endings.
• Stabilising the neuronal membranes * Commonly used in ophthalmic practice

3. Comparison of amide- and ester-linked LAs
(Self-Reading)
Features Amide-linked LAs Ester-linked LAs
Stability to heat Highly stable (can be autoclaved) Less stable
Storage Long time Short time
Level of
anaesthesia
Intense and long duration Low and short duration, rarely
used for anaesthesia
Hypersensitivity Rare and no cross-sensitivity High
Plasma binding Readily binding weakly binding
Level of
hydrolysis
Poor hydrolysis with plasma esterase
(para-aminobenzoic acid, PABA).
Degrade only in liver by dealkylation
and hydrolysis
rapidly hydrolyzed by plasma
pseudo-cholinesterase in plasma
membrane and esterase in liver

4. Comparison of general and local anesthesia
(self-reading)
Characteristics General Anesthesia Local Anesthesia
Site of action Central Nervous System (CNS) Peripheral nerves
Area Whole body Restricted area
Consciousness Lost Unaltered
Care of vital function Essential Usually not needed
Poor health patient Risky Safe
Major surgery Preferred not adequate
Minor surgery Unnecessary preferred

5. Effect of anaesthesia on tissues
CNS stimulation
(inhibition of
inhibitory neurons)
followed by
depression.
Cardiac depression,
cardiac arrhythmia
and cardiac
fibrillation (e.g.
Bupivacaine).
Blood vessels:
vasodilatation
(Bupivacaine > lidocaine
> prilocaine).
* Commonly used in ophthalmic practice

6. Adverse effect of anaesthesia on tissues
• CNS toxicity: dizziness, mental confusion, disorientation, shivering,
convulsion, respiratory arrest
• Central Vascular System (CVS): bradycardia, cardiac fibrillation,
hypotension, cardia arrhythmias, vascular collapse, vasodilatation
• Local: delay wound healing, rashes, angioedema, contact dermatitis,
asthma, anaphylaxis
• Eye: chemosis, toxic keratopathy,
• Eye injection (retrobulbar, peribulbar, sub-tenon): globe perforation,
haemorrhage, optic nerve damage, muscle palsy

7. Figure.
Schematic of
several ocular
drug
administration
routes
https://link.springer.com/article/10.1007/s00210-022-02287-3

8. Classification
Injectable LA
• Low potent and acting
for short-duration
• Procaine,
chloroprocaine
• Intermediate potent and
acting intermediate
duration
• prilocaine
• Highly potent and acting
long duration
• bupivacaine
Surface LA
• soluble
• Cocaine
• Insoluble
• Benxocaine,
oxethazaine,
butylaminobenz
oate
* Commonly used in ophthalmic practice
Both injectable and
surface LA
• Intermediate potent,
acting intermediate
duration, soluble
• Lidocaine
(xylocaine)
• Highly potent, acting
long duration, soluble
• Tetracaine

9. Ocular anesthesia
Name Strength Single
dose
Onset of
anaesthesia
Duration of
anaesthesia
Remarks
Tetracaine HCL 0.5, 1.0,
2.0
Yes 2 – 3 mins 15 – 20 mins Toxic to corneal epithelium,
Delay corneal wound healing,
least comfortable
Oxybuprocaine
(Benoxinate) HCL
0.4 Yes 2 – 3 mins 15 mins Less irritation and stinging,
most comfortable LA, than
tetracaine, Less SPKs
Proparacaine HCL 0.5 Yes 2 – 3 mins 15 – 20 mins Toxic to corneal epithelium,
Delay corneal wound healing

10. Ocular anesthesia
Name Strength Single
dose
Onset of
anaesthesia
Duration of
anaesthesia
Remarks
Lidocaine
HCL
2.0, 4.0 Yes 2 – 3 mins 15 – 30 mins Universal anaesthetic, Better tissue
diffusion, an antiarrhythmic agent,
metabolised in liver, less allergic
reaction,
Bupivacain
e HCL
0.5 Yes > 10 mins 75 – 90 mins Ideal for ophthalmic surgery, most
potent of all amide anaesthetics,
cardiotoxic, liver metabolise, IV
injection may cause seizure,
vasoconstrictor has less effect on
prolonging its anaesthetic effect

11. Table. Anaesthetic agents and maximum
recommended doses (systemic administration)
Anaesthetic
agents
Maximum anaesthetic per dose
Lidocaine 4.5 mg/kg
(not to exceed 300 mg total)
Lidocaine +
Epinephrine
7 mg/kg
(not to exceed 500 mg total)
Bupivacaine 2.5 mg/kg
(not to exceed 175 mg per dose, with a maximum 24-hour dose of 400 mg)
Bupivacaine +
Epinephrine
3 mg/kg
(not to exceed 225 mg per dose, with a maximum 24-hour dose of 400 mg)

12. Indication for ocular anesthesia
Ophthalmic surgical procedures
• Intraocular surgery. e.g., cataract,
Retina
• Periocular surgery. e.g., pterygium,
conjunctival cysts, chalazion, strabismus
• Oculoplastic and lacrimal surgery.
e.g., ptosis, entropion, ectropion, DCR
• Intraocular FB removal
Ophthalmic and optometric non-
surgical procedures
• Ocular surface FB removal
• Contact tonometry. e.g., Goldman
applanation tonometry, Schiotz
tonometry
• Hard CL fitting
• Diagnostic procedures. e.g., Schirmer
test II
• Lacrimal procedures. e.g., dilation,
irrigation, insertion of punctal plug
• Reduce reflex lacrimation for eye
examination

13. Contraindications
• Allergy to anaesthetic
• Open globe
• Local infection
• Distorted anatomy (traumatic, post-surgical, or due to underlying
disease)
• Bleeding or clotting disorders
• Poor patient cooperation and refusal

14. Adding a vasoconstrictor (alpha-adrenergic
agonist) to a local anaesthetic
• To increase the duration of anaesthetic effect
• To decrease the risk of systemic overdose-related toxicity of the drug.
• Increased the concentration of local anaesthetics at receptor sites.
• Dose: Adrenaline (1:50,000 – 1:200,000)

15. Further reading
• 1. https://www.ncbi.nlm.nih.gov/books/NBK574554/

16. Thank you