This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
A patient in ICU seemed to be very aggressive and restless. He is pulling out all the i.v lines. Duty doctor administered a muscle relaxant which has a fast onset of action and asked the nurse to sta iv fluids. Which among the following muscle relaxant has the fastest onset of action? 
Select and explain. 
A. Vecuronium, B. Rocuronium, C. Mevacuronium, D. Atracuronium
B: Rocuronium
Answer: B: Rocuronium 
Explanation: Rocuronium is a monoquaternary steroid analogue of vecuronium was designed to provide a rapid onset of action. Rocuronium is the fastest acting nondepolarizing muscle relaxant. Rocuronium (at a dose of 0.9-1.2 mg/kg) has an onset of action that approaches succinylcholine (60-90 s), making it a suitable alternative for rapid-sequence induction. Rocuronium is less potent than most other steroidal muscle relaxants (potency appears to be inversely related to speed of onset). Because rocuronium does not have active metabolites, it may be a better choice than vecuronium for prolonged infusions. Its duration of action is not significantly affected by renal disease, but it is modestly prolonged by severe hepatic failure and pregnancy. Ref: Morgan, Jr. G.E., Mikhail M.S., Murray M.J. (2006). Chapter 9. Neuromuscular Blocking Agents. In G.E. Morgan, Jr., M.S. Mikhail, M.J. Murray (Eds), Clinical Anesthesiology, 4e.