McKenna's Pharmacology for Nursing, 2e

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P A R T 4  Drugs acting on the central and peripheral nervous systems

Neuron (presynaptic cell)

Motor nerve terminal

Skeletal muscle fibre (postsynaptic cell)

Blood vessel

Acetyl CoA + Choline (from diet) Enzyme

Acetic acid + Choline

Synaptic vessicles containing acetylcholine

ACh

Release of acetylcholine into synaptic cleft

Acetylcholinesterase (eliminates free ACh from synaptic cleft)

Ca +

Junction folds with acetylcholine on top

Non-depolarising NMJ blockers occupy ACh receptor site preventing ACh from stimulating site

Nicotinic or cholinergic receptor

Suxamethonium binds with ACh site causing stimulation and muscle contraction

FIGURE 28.2  Sites of action of the NMJ blockers.

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