Local Anaesthetics 117impulses thereby affecting local anaesthetic
action.
Pharmacokinetics
Lignocaine is completely absorbed
following parenteral administration, its rate
of absorption depending upon various
factors such as site of administration and the
presence or absence of vasoconstrictor agent.
Lignocaine is metabolised rapidly by the
liver and metabolites and unchanged drug
are excreted by the kidneys. Approximately
90% of lignocaine administered is excreted
in the form of various metabolites and less
than 10% is excreted unchanged.
The elimination half-life of lignocaine
following an intravenous bolus injection is
1.5 to 2.0 hours.
Adverse Effects
CNS manifestations are excitatory and/
or depressant and may be characterised by
light-headedness, nervousness, apprehen-
sion, euphoria, confusion, dizziness, drowsi-
ness, tinnitus, blurred or double vision,
vomiting, sensation of heat, cold or numb-
ness, twitching, tremors, convulsions, un-
consciousness, respiratory depression.
Drowsiness following the administration
of lignocaine is usually an early sign of a high
blood level of the drug and may occur as a
consequence of rapid absorption.
Cardiovascular manifestations are usu-
ally depressant and are characterised by
bradycardia, hypotension and cardiovascu-
lar collapse, which may lead to cardiac ar-
rest.
Allergic reactions are characterised by
cutaneous lesions, urticaria, edema or
anaphylactoid reactions may occur as a result
of sensitivity to local anaesthetic agent.
Indications
Lignocaine injections are indicated for
production of local or regional anaesthesia
by infiltration techniques such as percutane-
ous injection, peripheral nerve block, spinal
or subarachnoid block.
Lignocaine (2%) with adrenaline
(1:80,000) is mostly used local anaesthetic in
dentistry which produces good soft tissue
and pulpal anaesthesia and also reduces post
extraction bleeding. The pulpal anaesthesia
is obtained within 2-3 minutes after injection
and lasts for about on hour.BENZOCAINE
It is a local anaesthetic belonging to the
ester group. It inhibits conduction of nerve
impulses from sensory nerves. This action
is a result of alteration of cell membrane
permeability to ions. It is poorly absorbed
from the intact epidermis.
Benzocaine has been termed by the FDA
as ‘one of the most widely used and safest
external analgesic and that the incidence of
sensitivity of benzocaine is quite low’. It’s male
genital desensitizing product has been termed
as premature ejaculation remedy. Benzocaine
when applied on the penis aids in temporarily
slowing the onset of ejaculation.DIBUCAINE
It is another local anaesthetic with longer
action but most toxic. It is used for surface
anaesthesia.BUPIVACAINE
It is a potent and long acting local
anaesthetic used for spinal, infiltration,
epidural anaesthesia and nerve block.
Side effects include cardiac arrest,
cardiac arrhythmias and respiratory failure.