Pharmacology for Dentistry

112 Section 2/ Drugs Acting on CNS

can also produce release of histamine and
can cause bronchospasm and increase other
body secretions.

d-Tubocurarine is not absorbed orally
and after intravascular administration, it is
widely distributed in tissue. As it does not
cross blood brain barrier it has no effect on
CNS.

Adverse effects include hypoxia, respi-
ratory paralysis, decreased blood pressure,
bronchospasm etc.

d-Tubocurarine is not used now due to
its prominent histamine releasing and
ganglionic blocking effect.

PANCURONIUM

Pancuronium is a synthetic steroidal
compounds and approximately five times
potent than d-tubocurarine. Vecuronium is
congener of pancuronium with short dura-
tion of action.

Atracurium is bisquarternary competi-
tive blocker similar to pancuronium in prop-
erties and duration of action.

SUCCINYLCHOLINE

It is a quarternary ammonium compound
with a structure similar to acetylcholine (De-
tails are discussed in chapter ‘Cholinergic
agents’).

Therapeutic uses

• As a adjuvant to general anaesthesia
  (specially in major surgical procedures
  e.g. abdominal and thoracic surgery,
  orthopaedic procedures, intubation etc).


• Succinylcholine is used for surgical
  procedure of brief duration (endotra-

cheal intubation, bronchoscopy,

esophagoscopy, laryngoscopy etc).

• Succinylcholine is used to avoid con-
  vulsion and coma from electroconvul-
  sive therapy.


• In the treatment of tetanus and emer-
  gency of epilepsy (status epilepticus).


• As a diagnostic tool for myasthenia
  gravis.

CENTRALLY ACTING MUSCLE RELAXANTS

These agents reduce skeletal muscle tone by

a selective action on cerebrospinal axis

without affecting consciousness.

Mephenesin was the first drug used as

muscle relaxant but due to its serious side

effects e.g. haemolysis, hypotension and

thrombophlebitis, it is not clinically used

now.

CHLORZOXAZONE

It is mephenesin related skeletal muscle

relaxant. After oral administration, it is

rapidly and completely absorbed. It is

metabolized in liver and excreted in urine

primarily as the glucuronide. Adverse

reactions include gastric irritation, nausea,

lethargy, headache.

It is used in painful skeletal muscle

spasm and is used in combination with

paracetamol and diclofenac.

METHOCARBAMOL

It causes skeletal muscle relaxation by

preferential blockade of polysynaptic spinal

reflexes.

It is rapidly absorbed from the GI tract,

metabolised in the liver and excreted in