During induction of anaesthesia, a patient receives an intravenous dose of succinylcholine for intubation. Within seconds, brief visible twitches appear across the chest and abdominal wall, followed by flaccidity. The initial fasciculations are explained by which property of the drug?
- A It competitively displaces acetylcholine from the junctional folds, triggering asynchronous firing
- B It inhibits acetylcholinesterase transiently, flooding the synaptic cleft with transmitter
- C As a nicotinic agonist it initially depolarizes the end plate, firing muscle fibres before desensitization sets in ✓
- D It opens chloride channels on the sarcolemma, provoking repetitive discharge
Correct answer: C. As a nicotinic agonist it initially depolarizes the end plate, firing muscle fibres before desensitization sets in
Explanation
Succinylcholine is a depolarizing neuromuscular blocker. It first acts as a nicotinic receptor agonist, depolarizing every end plate simultaneously and producing transient asynchronous fasciculations, then maintains the channel open until desensitization produces phase I block. Because its action mimics rather than opposes acetylcholine, cholinesterase inhibitors prolong this block, the opposite of their effect on competitive agents like tubocurarine.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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Written and medically reviewed by the StethoPrep medical team.