Neuromuscular blockers in surgery and intensive care, Part 2.

The historical development, pharmacology, pharmacodynamics, pharmacokinetics, clinical applications, pharmacologic basis for selection, adverse effects, and cost of neuromuscular blockers (NMBs) are discussed. The first NMB to be used was tubocurarine. During neurotransmission, acetylcholine is synthesized, stored in vesicles at the neuromuscular junction, released into the synapse, and bound to nicotinic receptors in the muscle end plate. For muscle contraction to occur, the impulse generated in a neuron's cell body must create an action potential that is chemically transmitted across the synapse. The postsynaptic nicotinic receptor at the neuromuscular junction is the major site of action of depolarizing and nondepolarizing NMBs. All NMBs have the potential for cross-reactivity at other nicotinic and muscarinic sites. Drug interactions most commonly occur between NMBs and inhalation anesthetics, certain antimicrobials, calcium-channel blockers, and anticholinesterases. When selecting an NMB, an agent's onset and duration of action must be considered. NMBs can be used on a short-term or long-term basis. Apart from cost, the choice of an NMB is made on the basis of its adverse-reaction profile, pharmacokinetics, and indications for use. Monitoring tools, their use, the rationale for their use, and the interpretation of the results they provide are unique. The patterns of peripheral nerve stimulation vary and elicit different characteristics of nondepolarizing neuromuscular blockade. The effectiveness of reversal agents is proportional to the degree of blockade. The mechanism of action of anticholinesterases involves inhibition of acetylcholinesterase. The expensive NMBs should be conserved for use in surgery, while the cheaper, long-acting [corrected] agents should be used in the intensive care unit. An understanding of the pharmacology, pharmacodynamics, and pharmacokinetics of NMBs will help health care providers gain expertise in the selection and use of these agents.