Cis-atracurium is preferred over atracurium, because:

Ans. (B) It causes less release of histamine(Ref: Miller's 7th/e p869)Both atracurium and cis-atracurium are non-depolarizing neuromuscular blockers.Both of these are intermediate acting agents (both have same duration of action).Both of these agents are cardiostableAtracurium has faster onset of action as compared to cis-atracurium.Both are eliminated by Hoffman's elimination. Atracurium is also metabolized by liver to some extent and result in production of a metabolite laudanosine that can cause CNS toxicity including seizures. On the other hand cis-atracurium is almost completely eliminated by Hoffman's elimination and produce negligible laudanosine.Major advantage of cis-atracurium over atracurium is that the former do not release histamine.Note: Only cis-atracurium and doxacurium are the drugs in this category (whose name ends with curium) that do not release histamine.