Which agent can cause a phase II depolarizing block when used repeatedly for neuromuscular blockade reversal or maintenance?

Which agent can cause a phase II depolarizing block when used repeatedly for neuromuscular blockade reversal or maintenance?

• A. Rocuronium
• B. Vecuronium
• C. Succinylcholine
• D. Atracurium

Answer: (C)

Phase II depolarizing block arises when a depolarizing neuromuscular blocker, like succinylcholine, is used repeatedly or given for a prolonged period. Normally succinylcholine causes a brief Phase I block by continuously depolarizing the end-plate, which prevents further transmission until the drug wears off. If exposure is extended or dosing is repeated, the end-plate becomes desensitized and the membrane can repolarize while still being pharmacologically unresponsive to acetylcholine. This desensitized state produces a block that resembles a nondepolarizing blockade: reduced response to acetylcholine, slower recovery, and increased difficulty distinguishing from other nondepolarizing blocks. The important point is that this phase II block only happens with a depolarizing agent like succinylcholine after repeated or prolonged use, whereas the nondepolarizing agents do not generate a phase II depolarizing block. In practice, recognizing this pattern is crucial because continuing succinylcholine can worsen the block, necessitating supportive care and allowing time for recovery rather than relying on reversal strategies aimed at nondepolarizing blockers.

Phase II depolarizing block arises when a depolarizing neuromuscular blocker, like succinylcholine, is used repeatedly or given for a prolonged period. Normally succinylcholine causes a brief Phase I block by continuously depolarizing the end-plate, which prevents further transmission until the drug wears off. If exposure is extended or dosing is repeated, the end-plate becomes desensitized and the membrane can repolarize while still being pharmacologically unresponsive to acetylcholine. This desensitized state produces a block that resembles a nondepolarizing blockade: reduced response to acetylcholine, slower recovery, and increased difficulty distinguishing from other nondepolarizing blocks. The important point is that this phase II block only happens with a depolarizing agent like succinylcholine after repeated or prolonged use, whereas the nondepolarizing agents do not generate a phase II depolarizing block. In practice, recognizing this pattern is crucial because continuing succinylcholine can worsen the block, necessitating supportive care and allowing time for recovery rather than relying on reversal strategies aimed at nondepolarizing blockers.