McKenna's Pharmacology for Nursing, 2e

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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.

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

KEY POINTS

■■ 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

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 No known effect on pain perception or consciousness; contains benzyl alcohol, avoid use in neonates Vagalytic effect, associated with increased heart rate; long-term use for mechanical ventilation, monitor for prolonged adverse effects No known effect on pain perception or consciousness; may be associated with pulmonary hypertension; use caution with hepatic impairment 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 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 No effect on pain perception or consciousness

cisatracurium (Nimbex)

Intermediate action; used for surgical procedures and to facilitate intubation

mivacurium (Mivacron)

Short duration; mechanical ventilation and tracheal intubation Surgical procedures; mechanical ventilation

pancuronium (generic)

rocuronium (Esmeron)

Rapid onset; preferred for rapid intubation; short outpatient surgical procedures

vecuronium (Norcuron, Vecure)

Short surgical procedures; intubation; mechanical ventilation

Depolarising neuromuscular junction blocker suxamethonium (generic)

Surgical procedures; intubation; mechanical ventilation