This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuromuscular Blocker, Subject name: Anaesthesia
Which of the following drug causes pain on injection:- 
Select and explain. 
A. Rocuronium, B. Vacuronium, C. Rapocuronium, D. Atracurium
A: Rocuronium
Answer: A: Rocuronium 
Explanation: Rocuronium causes pain on injection, like propofol. Unlike propofol however it is given after patient is induced. Pain associated with injection of rocuronium is commonand can be very distressing. Tracheal intubation with rocuronium using the 'timing principle'. the described pain is a 'burning' in nature and occurred immediately on administration. We do not know the exact mechanism for the pain, although the immediate onset rapid precurarization technique using rocuronium probably reflects a direct irritant effect and not an indirect effect on the kinin cascade.