neuromuscular blocking agent, a chemical substance that interferes locally with the transmission or reception of impulses from motor nerves to skeletal muscles. Nondepolarizing agents such as metocurine, pancuronium, and tubocurarine competitively block the transmitter action of acetylcholine at the motor end plate. Depolarizing blocking agents such as succinylcholine chloride also compete with acetylcholine for cholinergic receptors of the motor end plate but work by first activating the receptor and then blocking its ability to be reset for subsequent stimulation. Neuromuscular blocking agents are used to induce muscle relaxation in anesthesia, endotracheal intubation, and electroshock therapy and as adjuncts in the treatment of tetanus, encephalitis, and poliomyelitis. Neuromuscular blocking drugs can cause bronchospasm, hyperthermia, hypotension, or respiratory paralysis and are used with caution, especially in patients with myasthenia gravis or with renal, hepatic, or pulmonary impairment and in elderly and debilitated individuals. During surgery, it is important to recognize that these agents prevent muscle movement but do not block the sensation of pain. See also muscle relaxant.
