New skeletal muscle relaxants.

In a little over 10 years, six new muscle relaxants have been introduced in clinical practice. The first two, intermediate-duration vecuronium and atracurium, were outstanding drugs and clearly an advance over the earlier, longer-acting drugs. With their introduction, the phenomenon of "recurarization" largely disappeared. The next two, long-acting doxacurium and pipecuronium, were relics of an earlier era and have made little clinical impact. Mivacurium created a new class, the short-acting nondepolarizing relaxant, and caused succinylcholine to be reclassified as an ultra-short-acting drug. However, mivacurium has neither the rapid onset nor the ultra-short duration of succinylcholine. Rocuronium is the first nondepolarizing relaxant with an onset approaching that of succinylcholine. It is likely that we will see the introduction of at least two more drugs, Org 9487 and 51W89, by the end of this decade, and the goal of developing a nondepolarizing relaxant that is a complete replacement for succinylcholine may not be too far in the future.