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Rocuronium onset and potency — FRCA Primary MCQ

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ModeratePharmacologyRocuronium onset and potencyFRCA Primary

A 42-year-old patient requires rapid sequence induction and rocuronium is selected rather than vecuronium. Both drugs are aminosteroid non-depolarising neuromuscular blockers. Which of the following is correct regarding rocuronium?

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Correct answer: D — It has a higher potency, requiring a smaller intubating dose

Rocuronium has a faster onset than vecuronium largely because its lower potency requires a larger dose, increasing the concentration gradient to the neuromuscular junction. The tempting misconception is that higher potency gives faster onset; in neuromuscular blockers, the opposite relationship is often seen. Rocuronium is not metabolised by plasma cholinesterase and phase II block is a suxamethonium phenomenon. This is the Bowman principle in a clinical setting.

Reference: RCoA Primary FRCA Syllabus 2026; Peck, Hill & Williams Pharmacology for Anaesthesia