Local anesthetics are drugs that reversibly block sensation, especially pain, in a localized area without loss of consciousness or control of vital functions. They can be administered topically, via injection, or infiltration. The ideal local anesthetic has rapid onset, sufficient duration, is potent, stable in solutions, and does not interfere with tissue healing or cause toxicity. Common techniques for local anesthesia include infiltration, field block, nerve block, spinal anesthesia, epidural anesthesia, and intravenous regional anesthesia. Proper administration and monitoring can prevent potential toxic effects on the central nervous system and cardiovascular system.

1. Local Anaesthetic drugs
By
Dr. Manoj Kumar
Assistant Professor
Department of Pharmacology
Adesh Medical College & Hospital Ambala Can’t

2. Local Anaesthesia
 Local anaesthetics are drugs which reversible loss
of sensation (Sensory) especially of pain in a local area
 Without loss of
consciousness
 Without loss of
control of vital functions
 Topical/Injection/
Infiltration

3. Ideal Local Anaesthetic
• Reversible action.
• Non-irritant.
• No allergic reaction.
• No systemic toxicity.
• Rapid onset of action.
• Sufficient duration of action.
• Potent.
• Stable in solutions.
• Not interfere with healing of tissue.
• Have a vasoconstrictor action.
• Not expensive

4. Some Clinical Examples of their Use
• Topically: Nasal mucosa and wound margins
• Infiltration: Vicinity of peripheral nerve endings
and major nerve trunks
• Epidural or Subarachnoid spaces:
surrounding spinal nerves
• Regional anesthesia: Intravenous injection
in arm or leg (Bier block)

5. Local Vs General Anaesthesia
General Local
Site of action CNS Peripheral nerves
Area Whole body Restricted areas
Consciousness Lost Unaltered
Preferential use Major surgery Minor surgery
Possible Not possible
Use in non-coperative
patients
Poor health patient
Risky Safer
Care for vital functions Essential Not needed

6. Classification
 Injectable
 Low Potency, Short Duration
 Procaine, Chloroprocaine
 Intermediate Potency and Duration
 Lignocaine, Prilocaine
 High Potency, long Duration
 Tetracaine, Bupivacaine, Ropivacaine, Dibucaine
 Surface Anaesthetic
 Soluble: Cocaine, Lignocaine, Tetracaine, Benoxinate
 Insoluble: Benzocaine, Butamben, Oxethazaine

7. Ester Linked Amide linked
 Cocaine, Procaine,
Chloroprocaine, Tetracaine
 – Short acting
 – Metabolized by plasma
esterase
 – Can be used in poor liver
function
 – Hypersensitivity - ↑
 Lignocaine, Bupivacaine,
Prilocaine, Ropivacaine
 – Longer acting
 – Metabolized by liver
enzymes
 – Avoided in poor liver
function
 – Hypersensitivity - ↓
Classification - II

8. Mechanism Of Action
 Prevent generation and conduction of Nerve impulses by acting at the cell
membrane:
 Decrease the entry of Na+ ions during action potential.
 Increase in LA conc. decreases the maximum depolarization causing slowing
of conduction.
 Finally depolarization fails to
reach threshold potential.

9. Mechanism Of Action

10. Factors Influencing Action of LA
 Lipid Solubility
 Lipid solubility helps in nerve penetration, faster action
 Non ionized form can easily cross nerve membrane
 pH
 Lower pKa (7.6 – 7.8) – faster acting (lidocaine,
mepivacaine)
 Higher pKa (8.1 – 8.9) – slower acting (procaine,
tetracaine, bupivacaine)

11. Factors Influencing Action of LA
 Vasoconstrictors (Adrenaline, Phenylephrine)
 Systemic Side effects
 Areas with terminal arteries (Fingers, Toe, Nose,
Penis) - Hypoxic injury - Tissue Necrosis and May
Produce gangrene
 Felypressin (Vasopressin Analogue) - Used as
vasoconstrictor in CV Dz Patients

12. Factors Influencing Action of LA
Inflammation
 Acidic environment
 Ionized LA, decreased Penetration
Alkalization
 Hasten onset of nerve block
 Limited increase in unionized form
 precipitation of LA

13. Pharmacodynamics
 Functions lost by LA (Local effects)
 Pain perception
 Temperature
 Touch sensation
 Skeletal muscle tone
 Proprioception

14. Local effects
 Sensory > Motor
 Nonmyelinated > Myelinated
 Small fibres > Large fibres
 Autonomic fibres > Somatic Fibres

15. CNS
 Lignocaine causes -Euphoria,
 Dysphoria,
 Muscle twitches
 LA causes stimulation by – Restlessness, tremors,
Convulsions
 Respiratory depression in high doses
 Respiratory failure - death

16. CVS
 ↓ Automaticity, Excitability, Conductivity,
Contractility.
 ↑ Effective refractory period
 Prolonged QTc interval
 Ventricular Tachycardia, Ventricular Fibrillation
 ↓ in Blood Pressure
 Cocaine ↑ Blood pressure

17. Smooth Muscle
 ↓ contraction of bowel
 Relaxation of vascular and bronchial smooth muscle
Sympathetic System
 Blockade – Spinal, Epidural anaesthesia, local
infiltration in peritoneal cavity
Neuromuscular Junction
 Block the ion channel of acetylcholine receptors at
higher concentration.
 Block NMJ, Inhibit ganglionic transmission

18. Pharmacokinetics
 Surface anesthetics from mucus membrane and
abraded skin.
 Depends on Blood flow to the area, total dose and
specific drug characteristics
Widely distributed in the body: (lipophilic)
 Enters brain, heart, liver and kidney
 Followed by muscle and other viscera

19. Pharmacokinetics
 Ester linked LA – inactivated by hydrolysis by
plasma esterases, cholinesterase
 Spinal anaesthesia – absorbed into systemic
circulation
 Amide linked LA – Degraded in liver by CYP450
 Use restricted in Liver disease

20. Pharmacokinetics
 Amide linked LA – bind with α1 acid glycoprotein
 α1 acid glycoprotein (↑) – MI, Trauma, Cancer,
Smoking
 α1 acid glycoprotein (↓) – Oral Contraceptive Pill
 Termination of action depends on rate of absorption
and elimination

21. Toxicity
 CNS
 Dizziness, sedation,
 Metallic confusion and disorientation.
 Higher doses
 Anxiety, Drowsiness, Lightheadedness, Restlessness
 Visual and auditory disturbances, Nystagmus
 Muscle tremors, Respiratory depression, convulsions
 Death due to respiratory failure

22. Toxicity
 CVS
 decrease force of contraction,
 Hypotension,
 Bradycardia,
 Cardiac Dysrhythmia
 Excitability and conduction velocity,
 Cardiac arrest.

23. Toxicity
 Hypersensitivity
 Esters> Amides
 Skin rashes
 Allergic dermatitis
 Asthmatic attack
 Anaphylaxis

24. Prevention of Toxicity
 Proper History, Allergy Testing
 4 hour fasting, Premedication
 Avoid in Hepatic and cardiac disease
 Administration at Proper site
 Wait for development of effect
 Look for signs of toxicity
 Observation post operatively

25. Drug Onset
Maximum Dose
(with Epinephrine)
Duration
(with Epinephrine)
Lidocaine 10-20min 4.5 mg/kg (7 mg/kg) 120 min (240 min)
Mepivacaine 10-20min 5 mg/kg (7 mg/kg) 180 min (300 min)
Bupivacaine 15-30min 2.5 mg/kg (3 mg/kg) 360-720 hour (8 h)
Procaine Rapid 8 mg/kg (10 mg/kg) 45 min (90 min)
Chloroprocaine Rapid 10 mg/kg (15 mg/kg) 30 min (90 min)
Etidocaine 10-20min 2.5 mg/kg (4 mg/kg) 360-720min (8 h)
Prilocaine 10-20min 5 mg/kg (7.5 mg/kg) 180-300min (360 min)
Tetracaine 20-30min 1.5 mg/kg (2.5 mg/kg) 300-600min (10 h)

26. Cocaine
 Natural alkaloid produces euphoria and drugs
dependence.
 Medical use limited to surface or topical anesthesia
 Avoid with adrenaline
 A toxic action on heart may induce rapid and lethal
cardiac failure
 Not used presently

27. Procaine
 Topically ineffective
 Used for infiltration because of low potency and short
duration
 Most commonly used for spinal anesthesia
 Produces significant vasodilatation.
 Adrenaline used to prolong effect
 Systemic toxicity negligible
because rapidly destroyed in plasma
 Procaine penicillin

28. Lignocaine
 Effective by all routes.
 Faster onset (3 Vs 15 min), more intense, longer lasting
 Good alternative for those allergic to ester type
 Quicker CNS effects than others
 Overdose (muscle twitching, cardiac arrhythmia, fall in
BP, coma and respiratory arrest)
 Ant arrhythmic
 Available as Injections, topical
solution, jelly and ointment etc

29. Eutectic Lignocaine/Prilocaine
 Eutectic Mixture – Lowering of melting point of two
solids when they are mixed
 Lignocaine+Prilocaine at 25 OC in equal proportion
 Oil is emulsified in water to form a cream
 Occlusive dressing prior to procedure
 IV Canulation, Superficial Procedure
 Up to 5mm
 last for 1-2 hour

30. Benzocaine, Butamben
 Low aqueous solubility – Not absorbed from
mucosa or broken skin
 Long lasting anaesthesia without systemic toxicity
 Lozenges for stomatitis, Sore throat
 Dusting powder/ointment on wounds/ Ulcerated
surfaces
 Suppositories for anorectal lesions
 PABA derivative

31. Techniques
 Surface Anaesthesia
 Mucous membranes and abraded skin
 Nose, mouth, bronchial tree, oesophagus
 Cornea and urinary tracts
 Lignocaine, Tetracaine

32. Infiltration Anaesthesia
 Injection of LA directly into tissues
 Superficial - skin
 Deeper structure including intra- abdominal organs.
 Amides are preferred
 Should not be injected into tissues supplied by end
arteries
 Dose required is more
 Chances of Systemic Toxicity

33. Field Block
 Injection of LA subcutaneously
 Anaesthesia starts 2-3 cm distal to site of injection
 All nerves coming to the field are blocked
 Dose required is less, Prolonged duration
 Use dental procedures,
Forearm, anterior abdominal
wall, scalp and lower extremity.

34. Nerve Block
 LA injected around individual Nerve/ Plexus. Not in
the Nerve
 Sensory and motor block distal to site of injection
 Block depends on Proximity, Conc. and Volume of
LA
 Degree of ionization and Time
 Trigeminal nerve blocks (face)
 tooth extraction, operations on eye, abdominal
wall, trauma to ribs.

35. Spinal Anaesthesia
 injected in to the subarachnoid space
 between L2-3 or L3-4
 Site of action – nerve root in the spinal cord.
 Level of anaesthesia –
vol. & speed of injection;
specific gravity of drug soln.
 Posture of patient
-sympathetic > motor

36. Spinal Anaesthesia cont..
 Uses – lower limbs, pelvis, lower abdomen,
prostatectomy fracture setting and obstetric
procedures
 Adverse effects
 Headache, hypotension, bradycardia and respiratory
depression, cauda equina syndrome and nausea-
vomiting
 Drugs - Lidocaine, Tetracaine

37. Contraindications to spinal anaesthesia
 Hypotension and hypovolemia.
 Uncooperative or mentally ill patients.
 Infants and children—control of level is difficult.
 Bleeding diathesis.
 Raised intracranial pressure.
 Vertebral abnormalities e.g. kyphosis, lordosis, etc.
 Sepsis at injection site.

38. Epidural Anaesthesia
 Site- nerve roots or lumber, thoracic or cervical region
 Catheters are used for continuous infusion
 Used like spinal and painless childbirth in women.
 Side effect Headache, hypotension, bradycardia and
respiratory depression,
cauda equina syndrome
and nausea-vomiting
 Lidocaine, bupivacaine,
Ropivacaine

39. Intravenous regional anaesthesia (Intravascular
infiltration anaesthesia
 Injection of LA in a vein of a tourniquet occluded
limb
 Drug diffuses from the peripheral vascular bed to
nonvascular tissues including nerve endings.
 Used for the upper limb and for orthopedic
procedures.

40. Regional anaesthesia (IV)
 Regional anesthesia is the use of local anesthetics to
block sensations of pain from a large area of the
body, such as an arm or leg or the abdomen.
 Regional anesthesia allows a procedure to be done
on a region of the body without unconscious.