Pharmacology for Dentistry

116 Section 2/ Drugs Acting on CNS

Local anaesthetics block both the
generation and conduction of the nerve
impulse.

Pharmacological Actions

Action on CNS: Local anaesthetics
stimulate CNS and produce restlessness,
tremor, mental confusion, convulsion. In
toxic doses, it causes respiratory depression,
coma and death. Cocaine is a powerful
stimulant while procaine and other agents
produce less CNS stimulant effect.

Action on CVS: Local anaesthetics are
myocardial depressant and decrease heart
rate and amplitude of myocardial
contraction. In high doses, they produce
changes in the ECG and may precipitate
ventricular fibrillation. Bupivacaine is more
cardiotoxic and can produce ventricular
tachycardia or fibrillation.

Local anaesthetics also produce decrease
in blood pressure which may be due to
sympathetic blockade. Only cocaine has the
property to raise the BP due to its
sympathomimetic property.

Pharmacokinetics

Local anaesthetics are readily absorbed
through mucous membranes and damaged
skin. These are weak bases and at tissue pH
diffuse through the connective tissue and
cellular membranes to reach the nerve fibres
where ionization can occur. Amide type
local anaesthetics (lignocaine, bupivacaine)
are metabolised in the liver and in some
cases the kidneys. These are considerably
protein bound. For certain procedures the
duration of action is prolonged by adding

adrenaline 1 in 2,00,000. In dentistry, where

the total dose is small higher concentration

such as 1 in 80,000 may be used.

Adverse Effects

CNS side effects include dizziness,

mental confusion, tremors, twitching,

visual disturbances, convulsion and

respiratory depression. CVS toxicity

includes hypotension, cardiac arrhythmias

and bradycardia. Other side effects include

allergic dermatitis, asthma, anaphylactic

shock etc.

Therapeutic Uses

Local anaesthetics are used for

• Surface anaesthesia.


• Spinal anaesthesia.


• Infiltration anaesthesia.


• Nerve block or conduction block and


• For systemic use in the treatment of
  cardiac arrhythmias (Details are given
  in chapter ‘Antiarrhythmic agents’).


• Dental anaesthesia—The total
  amount of local anaesthetics injected
  is much smaller (20-80 mg of
  lignocaine) than that used for othr
  purpose. Lignocaine (2%) with
  adrenaline (1:80,000) is the standard
  local anaesthetic preparation used in
  dentistry which produces good soft
  tissue and pulpal anaesthasia and
  also reduce postextraction bleeding.

LIGNOCAINE

Mechanism of Action

Lignocaine stabilizes the neuronal

membrane by inhibiting ionic fluxes

required for initiation and conduction of