Local anesthetics work by reversibly blocking voltage-gated sodium channels in nerve fibers, preventing the generation and propagation of action potentials. They are classified based on chemical structure as esters or amides and differ in potency, duration, and metabolism. Common local anesthetics administered by injection include lidocaine, bupivacaine, and procaine. They provide surface, infiltration, nerve block, and regional anesthesia and are used for procedures like wound suturing, dental work, and childbirth with minimal side effects when dosed properly. Factors like dosage, site of administration, pH, and addition of vasoconstrictors influence their effects.

2. Drugs that cause reversible block of nerve conduction
producing transient localized anesthesia without
significantly affecting consciousness.

3. According to their chemical structure:
 Esters:
Cocanie, Procaine, Benzocaine & Tetracaine
 Amides:
Lidocanie (xylocaine, ligocaine), Prilocaiine,
Mepivacaine & Dibucaine.

4. According to their solubility & therapeutic
application:
- Soluble Local anesthetics suitable for
injection: Procaine HCl, Lidocaine HCl
- Soluble Local anesthetics used only topically
on the eye: Cocaine HCl
- Local anesthetics of low solubility used as
powders & ointments: Benzocaine

5. According to their potency
 LA with weak potency & short duration(30-60
min)
Examples: Procaine
Chloroprocaine
 LA with moderate potency and intermediate
duration (1 - 3 hrs)
Examples: Lidocaine (xylocaine)
Prilocaine.
 LA with high potency and long duration(3 – 6 hrs)
Examples: Tetracaine
Bupivacaine

6. Mechanism of action:
local anesthesia blocks voltage dependent sodium
channels from inside the nerve fiber. → prevention
of sodium permeability into the nerves →
membrane stabilization → ↓ impulse generation and
propagation
At alkaline tissue pH= 7.4 They are Unionized
molecules → pass easily through membrane lipid
of nerve fiber → reach cytoplasm ( ionized +
unionized)→ the ionized form bind to Na+
channels blocking Na+ influx prevent initiation
of AP

7. Mechanism of action:

8. Action
Local anesthetic action
 Small fibers before large
 Demylinated before mylinated fiber
 Sympathetic & pain → temperature →
touch& pressure → motor fibers
 Recovery → reverse direction.
Addition of adrenaline→ vasoconstriction→
↓absorption of LA →↓spread →↑duration&
↓toxicity

9. Metabolism :
Esters are fastly metabolized by plasma
and tissues esterases. Thus , they have short
duration. They are metabolized to PABA
(cause allergy in some individuals).
Amides are metabolized slowly by liver
microsomal enzymes. Thus , they have
longer duration

10. Methods of administration and uses
 Surface anesthesia: Direct application of the drug on
accessible surface as skin or mucous membrane
LA with short or intermediate duration are used for this
purpose.
Dosage forms:
Powder , Solutions (spray) , Creams or Ointments.
Benoxinate ( ester LA) used in ophthalmology for corneal
anesthesia because :
 No mydriasis.
 No corneal injury.
Benzocaine used in form of powder or cream on skin
wounds or ulcer, because it is insoluble produces less
systemic toxicity

11. Methods of administration and uses (cont.)
 Infiltration anesthesia: They are injected directly
into the tissue by S.C injection e.g wound
suturing & cysts removal , Circumcisions .
 Nerve block anesthesia:
The anesthetic in injected close to the
appropriate nerve trunks or peripheral nerve at a
site proximal to where anesthesia is desired. e.g.
dental anesthesia

12. Methods of administration and uses (cont.)
 Sympathetic block: It is injected around
sympathetic ganglion.
 Para vertebral block: injected around spinal roots
as they emerge from the paravertebral foramina.
 Caudal anesthesia: injected in sacral canal.

13. Methods of administration and uses (cont.)
 Spinal anesthesia: LA injected in the subarachnoid
space in
the lumbar region.
 Epidural anesthesia Anesthetics injected in epidural
space
Uses
 abdominal, pelvic and lower limbs surgery in
patients unsuitable for general anesthesia.
 Epidural anesthesia is frequently used for painless
childbirth.
Some local anesthetic used for Treatment of cardiac
dysrhythmia e.g. Lidocaine

14. Side effects
The side effects of LA are usually minimum , because they are
applied Locally. They are combined with a vasoconstrictors
such as adrenaline to decrease systemic absorption. But
some side effects may occur due to :High dose is administered
OR They are injected (mistakenly ) into blood vessels
LA Side effects are
 Restlessness, headache &convulsions followed by respiratory
depression
 hypotension and bradycardia
 Hypersensitivity reaction (with ester type)
 Mucosal irritation (cocaine, dibuacine).
Side effects are more with local anesthetic that are potent and
have long duration

15. Influencing Factors
Dosage, high dose cause:
 Fast onset
 Longer duration.
 Increase risk of side effects.
Site of administration : high vascularity cause:
 Short duration.
 High risk of side effects.
Lipid solubility of LA: more lipid soluble more effective.
Infections/ inflammations cause:
- low pH
decrease action : LA are bases thus at low pH they
become more ionized . This will reduce their
penetrations across membranes this reduces
their effects.
- Vasodilation
This Increases absorption to blood and increase risk
of side effects and reduce duration of LA.

16. (LA- Influencing Factors (cont.
Type of solution : Alkalinization of LA solution :
 Less painful.
 Increases non ionization (uncharged)
 Increases diffusion through nerve
 Increases effects.
 Produce fast onset.
Addition of vasoconstrictor ( epinephrine) will:
 Decreases vascular absorption.
 Increases duration.
 Decreases risk of side effects.
 Contraindicated when LA injected around
end arteries ( fingers, toes, ear lobes, nose)
may lead to ischemia and gangrene

17. Other Methods of producing local
anesthesia
Application of cold:
Cooling decreases excitability and conductivity of
nerve
Ischemia to tissues:
by depriving any tissue from its blood supply e.g. by
tourniquet.
Paralysis of sensory nerve endings or fibers with drugs:
Astringents may lead to local anesthesia by
precipitating nerve proteins e.g. ethyl alcohol injected
perineurally in trigeminal neuralgia

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