WHAT IS REALLY NEW ABOUT THE NEW RELAXANTS?

Abstract

SUMMARY The use of neuromuscular blocking agents is well established in the practice of anesthesia. Until recently, when the only muscle relaxants that were available had a long duration of action, a particular muscle relaxant was chosen so that its side effects would have the minimal adverse effect clinically. With the development of newer muscle relaxants, the cardiovascular side effects have been minimized and the pharmacodynamic profile of this class of drugs has been broadened. Structural changes in the steroidal class of compounds have yielded a long-acting muscle relaxant that is not vagolytic, and structural changes in the benzylisoquinolinium compounds have yielded a long-acting compound that does not cause histamine release. Decreasing the potency of the steroidal compounds has led to the development of rocuronium, which has a faster onset of action than other nondepolarizing muscle relaxants. Finally, the hydrolysis of mivacurium by plasma cholinesterases renders it shorter acting than other nondepolarizing muscle relaxants. The most striking aspect of these new muscle relaxants is that characteristics that could previously be broadly assigned on the basis of underlying structure, such as vagolytic-steroidal compounds, histamine-release benzylisoquinoliniums and metabolism by plasma cholinesterase-depolarizing muscle relaxants, seem to no longer apply. It is now known which structural changes in each class of compounds are required to minimize cardiovascular side effects. Further modifications of potency and metabolism may yet yield compounds that are faster in onset and have a shorter duration of action. However, the addition of rocuronium and mivacurium to the clinical armamentarium and the knowledge of the nuances of their clinical use will allow for timely endotracheal intubation and lack of residual neuromuscular block at the termination of anesthesia and surgery.