The adverse effects of competitive neuromuscular blockers are generally similar although they differ in their propensity to cause histamine release and cardiovascular effects. Histamine release and associated cardiovascular effects appear to be rare with the aminosteroidal blockers.
Competitive neuromuscular blockers with vagolytic activity may produce tachycardia and a rise in blood pressure. The use of blockers which lack an effect on the vagus may result in bradycardia during anaesthesia due to the effects of other drugs employed or as a result of vagal stimulation. Reduction in blood pressure with compensatory tachycardia may occur with some competitive neuromuscular blockers due in part to sympathetic ganglion blockade or the release of histamine.
Reduction in gastrointestinal motility and tone may occur as a result of ganglionic blockade.
Histamine release may also lead to wheal-and-flare effects at the site of injection, flushing, occasionally bronchospasm, and rarely anaphylactoid reactions.
Malignant hyperthermia has been associated rarely with competitive neuromuscular blockers.
In overdosage, there is prolonged apnoea due to paralysis of the intercostal muscles and diaphragm, with cardiovascular collapse and the effects of histamine release.