Phase II block given by which drug-

Ans. is 'a' i.e., Succinylcholine o Under certain conditions depolarizing agents produce dual mechanism of neuromuscular blockade which cand be divided into two phasesPhase I blocko Rapid in onseto Result from persistant depolarization of muscle end plate - Typical mechanism of action of depolarizing blocker.o Has classical features of depolarization block,o Block is not antagonized by anticholinesterases (neostigmine).Phase II block (Dual block)o Slow in onseto Results from desensitization of receptor to ACh - Ach can not act on Nm receptors (similar to competitive blocker).o Resembles block produced by competitive blockers - Therefore, has characteristics similar to non-depolarizing (competitive) block.o Block is partially reversed by anticholinesterases (Neostigmine).In man, normally, only phase I block is seen - typical depolarizing block.Phase II block is seen when fluorinated anaesthetics have been given or when SCh is injected in high dose.SCh also produces phase II block in patients with atypical or deficient pseudocholinesterase.