A 70-kg young athlete was planned for surgery. During anaesthesia, vecuronium was not available, so repeated doses of succinylcholine was given intermittently up to 640 mg. During recovery, patient was not able to spontaneously respire and move limbs. What is the cause?

Ans. (B) Phase II blockade(Ref: Wiley 7/384-586, Lee 12/223)Succinylcholine produces a characteristic depolarizing block that is associated with absence of fade in response to train-of-four and titanic stimulation, the absence of post-tetanic facilitation and increased block in the presence of anticholinesterase drugs. The type of block may change into a non-depolarizing type following prolonged administration of the drug (phase II block). Transition from a depolarizing to phase II block is gradual and usually occurs after administration of 7-10 mg/kg of succinylcholine.