434
P A R T 4
Drugs acting on the central and peripheral nervous systems
stimulation and muscle contraction, muscle
paralysis
, or
loss of muscle function, occurs.
■■
The nerves and muscles communicate at the
neuromuscular junction (NMJ).
■■
Acetylcholine (ACh) acts as the neurotransmitter at
the NMJ.
■■
NMJ blockers interfere with muscle function.
NEUROMUSCULAR JUNCTION–BLOCKING
AGENTS
Drugs that affect theNMJ can be divided into two groups.
One group, the
non-depolarising NMJs
, includes those
agents that act as antagonists to ACh at the NMJ and
prevent depolarisation of muscle cells. The other group,
the
depolarising NMJs
(of which there is one drug), act
KEY POINTS
as an ACh agonist at the junction, causing stimulation
of the muscle cell and staying on the receptor site, pre-
venting it from repolarising, which results in muscle
paralysis with the muscle in a constant, contracted state.
Both of these types of drugs are used to cause paralysis
for the performance of surgical procedures, endoscopic
diagnostic procedures or facilitation of mechanical ven-
tilation. Table 28.1 lists these drugs, their preferred uses
and potential problems. Box 28.1 highlights informa-
tion about using NMJ blockers with various age groups
(see also the Critical thinking scenario for care related
to an elderly person receiving an NMJ).
N
on
-
depolarising
NMJ
blockers
The first non-depolarising NMJ blocker to be discovered
was curare, a poison used on the tips of arrows or spears
by hunters to paralyse their game. Animals died when
their respiratory muscles became paralysed. Because
the poison was destroyed by the cooking process or by
TABLE 28.1
DRUGS IN FOCUS Neuromuscular junction blockers
Drug name
Preferred uses
Special considerations
Non-depolarising neuromuscular junction blockers
atracurium (Tracrium)
Mechanical ventilation; long duration of action;
surgical procedures
Has no effect on pain perception or
consciousness; do not use before
induction of anaesthesia; bradycardia is
more common with this drug; reduce
dose in renal failure
cisatracurium (Nimbex)
Intermediate action; used for surgical
procedures and to facilitate intubation
No known effect on pain perception or
consciousness; contains benzyl alcohol,
avoid use in neonates
mivacurium (Mivacron)
Short duration; mechanical ventilation and
tracheal intubation
No effect on pain perception or
consciousness
pancuronium (generic)
Surgical procedures; mechanical ventilation
Vagalytic effect, associated with increased
heart rate; long-term use for mechanical
ventilation, monitor for prolonged adverse
effects
rocuronium (Esmeron)
Rapid onset; preferred for rapid intubation;
short outpatient surgical procedures
No known effect on pain perception or
consciousness; may be associated with
pulmonary hypertension; use caution
with hepatic impairment
vecuronium (Norcuron,
Vecure)
Short surgical procedures; intubation;
mechanical ventilation
May contain benzyl alcohol; avoid use
in neonates, can cause fatalities in
premature infants; monitor with long-
term use during ventilation; if response
does not occur with first twitch test,
discontinue, may be associated with
permanent muscle damage
Depolarising neuromuscular junction blocker
suxamethonium (generic)
Surgical procedures; intubation; mechanical
ventilation
May cause myalgia secondary to muscle
contraction; associated with increased
intraocular pressure; increased
intragastric pressure, which may cause
vomiting; more likely to cause malignant
hyperthermia
