ADVERSE-EFFECTS OF NEUROMUSCULAR BLOCKERS AND THEIR ANTAGONISTS

Among all the drugs used for general anaesthesia, neuromuscular blocke rs appear to play a prominent role in the incidence of severe adverse reactions. Tt now seems likely that most serious adverse drug reaction s occurring during anaesthesia are immunological in type. The frequenc y of life-threatening anaphylactic or anaphylactoid reactions occurrin g during anaesthesia has been estimated to be between 1 in 1000 and 1 in 25000 anaesthetic procedures. with the neuromuscular blockers being in involved in 80% of cases. The mortality from such serious reaction s is reported to be in the range of 3.4 ro 6%. The highly immunogenic drug, suxamethonium chloride (succinylcholine), was found to be the mo st hazardous agent. Drug-specific immunoglobulin E antibodies to suxam ethonium chloride and other neuromuscular blockers have been demonstra ted. This sensitivity to neuromuscular blockers seems to be a long-las ting phenomenon. During anaesthesia, the clinical features of an aller gic reaction are often masked. Tachycardia and circulatory collapse ma y be the only signs of an allergic reaction, and they are easily misdi agnosed. Bronchospasm is reported to be present in about 40% of cases. Successful management of these patients includes stabilisation during the acute reaction and avoidance of future reactions. The latter is b ased on the identification of the causative drug and potentially cross -reacting compounds. The use of suxamethonium chloride is associated w ith many other adverse effects, such as fasciculations, myalgia, potas sium release, changes in the heart fate, increases in intragastric and intraocular pressures. and malignant hyperthermia. Because of the dan gers of hyperkalaemic cardiac arrest after suxamethonium chloride admi nistration in children with unrecognised muscular dystrophy, there hav e now been moves to limit the use of this drug in children. Although n euromuscular blockers ar designed tu specifically block nicotinic chol inergic receptors at the neuromuscular junction: many bind to muscarin ic cholinergic receptors on ganglia and smooth muscle, and alter paras ympathetically mediated heart rate and airway calibre, Most benzylisoq uinolinium muscle relaxants call induce histamine release. especially when they are administered rapidly, which can lead to disturbances of cardiovascular function. In addition, nondepolarising neuromuscular bl ockers have been implicated in causing,generalised weakness following their ion term administration to patients on an intensive care unit. T he problem with these adverse drug reactions is their unpredictable na ture. Therefore, prompt recognition with appropriate therapy call help to improve the outcome.