436
P A R T 4
Drugs acting on the central and peripheral nervous systems
imbalance,
which could affect membrane stability and
subsequent muscular function
; some respiratory condi-
tions
that could be made worse by the histamine release
associated with some of these agents
; and breastfeeding
because of the potential for adverse effects on the baby.
Adverse effects
The adverse effects related to the use of non-depolarising
NMJ blockers are associated with the paralysis of
muscles. Profound and prolonged muscle paralysis is
always possible, and people must be supported until they
are able to resume voluntary and involuntary muscle
movement. When the respiratory muscles are para-
lysed, depressed respiration, bronchospasm and apnoea
are anticipated adverse effects. These agents are never
used without an anaesthetist present who can provide
assisted ventilatory measures and deliver oxygen under
positive pressure. Intubation is an anticipated procedure
with these drugs.
The histamine release associated with many of
the depolarising NMJ blockers can cause respiratory
obstruction with wheezing and bronchospasm. Hypoten-
sion and cardiac arrhythmias may occur in individuals
Motor nerve
terminal
Neuron (presynaptic cell)
Blood vessel
Skeletal muscle fibre
(postsynaptic cell)
Synaptic vessicles
containing acetylcholine
Acetyl CoA +
Choline (from diet)
Enzyme
Acetic acid
+ Choline
ACh
Suxamethonium
binds with ACh site
causing stimulation
and muscle contraction
Nicotinic or
cholinergic
receptor
Non-depolarising NMJ blockers
occupy ACh receptor site
preventing ACh from
stimulating site
Junction folds with
acetylcholine on top
Acetylcholinesterase
(eliminates free ACh
from synaptic cleft)
Ca
+
Release of acetylcholine
into synaptic cleft
FIGURE 28.2
Sites of action of the NMJ blockers.
