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Candocuronium Iodide (also formerly known as chandonium) is a nondepolarizing rapid onset short duration steroid structured neuromusclar blocking agent that never made it. It's specifically called an azasteroid, and an azasteroid means it has the steroid structure, but you can see there's that one double bond near the bottom. Azasteroids have those double bonds in them.
It could have done so well, but nope, it speeds up the heart, just like pancuronium. The effects are no better or worse than pancuronium's effects on the heart, so it apparently wasn't worth further testing. It is possible, then, that if candocuronium had been discovered first, pancuronium as we know it may not exist, or its eventual existence would have been delayed, because the scientists would have figured, "Well, pancuronium's effects on the heart are no better or worse than candocuronium," instead of the other way around. Sometimes I wonder that with vecuronium and pancuronium too, since vecuronium has minimal cardiovascular effects. If vecuronium had been created first, would researchers have even bothered with pancuronium after learning about its vagolytic effects and longer duration? Something to think about :)