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
A 70 kg athlete is taken for surgery, due to unavailability of vecuronium, succinylcholine is given repeatedly (>640mg). He now is unable to take breath and his lower limbs are paralyzed. What will be cause? 
Select and explain. 
A. Phase II block, B. Succinylcholine causes muscle paralysis due to fasciculation, C. Hidden muscle dystrophy, D. Pseudo cholinesterase deficiency
A: Phase II block
Answer: A: Phase II block 
Explanation: Prolonged apnea due to repeated dosing with succinylcholine is due to it entering phase 2 block. Phase I depolarizing block is preceded by muscle fasciculation. During paial neuromuscular block, phase I depolarizing block is characterised by: No fade during repetitive stimulation (tetanic or TOF) No post tetanic facilitation (potentiation) Rapid hydrolysis by butyrylcholinesterase (plasma cholinesterase) terminates phase I depolarizing blockade of succinylcholine. Phase II block resembles non depolarizing block, is characterised by: Fade during repetitive stimulation (tetanic or TOF) Post tetanic facilitation (potentiation) Phase II block can be antagonized by administering a cholinesterase inhibitor like neostigmine.