The ideal neuromuscular blocking (NMB) drug would be rapid in onset, have a predictable offset, be nontoxic, lack deleterious cardiovascular or autonomic effects, undergo a defined means of metabolism and excretion preferably independent of end-organ function, and be inexpensive. Many of these characteristics are found in clinically available drugs like cisatracurium.

To briefly review, neuromuscular blockade occurs via one of two different pharmacologic modes. Drugs that act as a prolonged agonist at the nicotinic acetylcholine (nACh) receptor are called depolarizing agents (e.g., succinylcholine). Succinylcholine attaches to each of the alpha subunits of the nACh receptor and mimics the action of acetylcholine, thus depolarizing the postjunctional membrane. Neuromuscular blockade develops because a depolarized postjunctional membrane cannot respond to subsequent release of acetylcholine.

A second group of WMB agents that bind noncovalently and competitively to nACh receptors and inhibit neuromuscular transmission are called nondepolarizing NMB drugs. In high doses, these drugs may act by blocking the ion receptor channels. Occupation of as many as 70% of the nACh receptors does not produce evidence of neuromuscular blockade. Neuromuscular transmission, however, fails when 80% to 90% of the receptors are blocked.

Nondepolarizing NMB drugs may be classified on the basis of their structure and duration of action. Clinically available nondepolarizing drugs can be grouped into two basic structural categories. The benzylisoquinolinium drugs (atracurium, cisatracurium, mivacurium, tubocurarine) tend to be potent (and therefore slower in onset) NMB drugs that are eliminated by the kidneys or by Hofmann elimination and may trigger histamine release. Conversely, the aminosteroid compounds (pancuronium, vecuronium, rocuronium) are less potent, have a faster onset of action, are eliminated by the liver with active metabolites, and lack significant histamine release or autonomic interactions.

NMB drugs also may be classified as short (succhinylcholine, mivacurium), intermediate (atracurium, cisatracurium, vecuronium,
rocuronium), or long-acting (tubocurarine, pancuronium) on the basis of their duration of action.