5 Flumazenil 是下列何種麻醉藥物的拮抗劑（Antagonist）？

 Ketamine  Midazolam  Propofol  Thiopental

B

AZENIL ZOLAM

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6 有關非去極性肌肉鬆弛劑（Non-depolarizing muscle relaxants）的藥理特性，何者錯誤？

低體溫（Hypothermia）延長其作用時間

呼吸性酸中毒（Respiratory acidosis）強化其阻斷效果

低血鈣（Hypocalcemia）強化其阻斷效果

病人合併使用吸入性麻醉劑將增加對該藥物之需求劑量

D

Non-depolarizing blocking agents

A neuromuscular nondepolarizing agent is a form of neuromuscular blocker which do not depolarize the motor end plate.^[8]

The quaternary ammonium muscle relaxants belong to this class.

Mind Map showing a summary ofNeuromuscular nondepolarizing agent

Below are some of the more common agents that act as competitive antagonists against acetylcholine at the site of postsynaptic acetylcholine receptors.

Tubocurarine, found in curare of the South American plant Pareira, Chonodendron tomentosum, is the prototypical non-depolarizing neuromuscular blocker. It has a slow onset (>5 min) and a long duration of action (1–2 hours). Side effects include hypotension, which is partially explained by its effect of increasing histamine release, avasodilator,^[9] as well as its effect of blocking autonomic ganglia.^[10] It is excreted in the urine.

This drug needs to block about 70-80% of the Ach receptors for neuromuscular conduction to fail, and hence, for effective blockade to occur. At this stage, end-plate potentials (EPPs) can still be detected, but are too small the reach the threshold potential needed for activation of muscle fiber contraction.

Depolarizing blocking agents

A neuromuscular depolarizing agent is a form of neuromuscular blocker which depolarize the motor end plate.^[12]

An example is succinylcholine.

Mind Map showing a summary ofNeuromuscular depolarizing agent

Depolarizing blocking agents work by depolarizing the plasma membrane of the muscle fiber, similar toacetylcholine. However, these agents are more resistant to degradation by acetylcholinesterase, the enzyme responsible for degrading acetylcholine, and can thus more persistently depolarize the muscle fibers. This differs from acetylcholine, which is rapidly degraded and only transiently depolarizes the muscle.

Comparison of drugs

The main difference is in the reversal of these two types of neuromuscular-blocking drugs.

• Non-depolarizing blockers are reversed by acetylcholinesterase inhibitor drugs since they are competitive antagonists at the ACh receptor so can be reversed by increases in ACh.
• The depolarizing blockers already have ACh-like actions, so these agents will have prolonged effect under the influence of acetylcholinesterase inhibitors. The administration of depolarizing blockers will initially exhibit fasciculations (a sudden twitch just before paralysis occurs). This is due to the depolarization of the muscle. Also, post-operative pain is associated with depolarizing blockers.

The tetanic fade is the failure of muscles to maintain a fused tetany at sufficiently-high frequencies of electrical stimulation.

• Non-depolarizing blockers will have this effect on patients, probably by an effect on presynaptic receptors.^[13]
• Depolarizing blockers will not.

This discrepancy is diagnostically useful in case of intoxication of an unknown neuromuscular-blocking drug.