7.4: Nondepolarizing (Competitive) Neuromuscular Blockers: Pharmacological Actions
Nondepolarizing neuromuscular blockers prevent the membrane depolarization of muscle cells and inhibit muscle contraction. These are usually administered with anesthetics to achieve complete muscle relaxation. Upon administration, these drugs first block the small, rapidly contracting muscles of the face and hands, followed by the larger muscles of the trunk and the intercostal muscles. The diaphragm is the last muscle to be affected.
Although all competitive neuromuscular blockers are designed to produce desirable pharmacological actions, they can also have adverse effects mediated by histamine or autonomic receptors. Drugs like tubocurarine and atracurium lead to histamine release into the systemic circulation. Histamine can cause a fall in blood pressure or hypotension. Pancuronium increases the heart rate and cardiac output. The release of larger doses of histamine can block autonomic ganglions, which affects cardiovascular functions, increasing the heart rate and blood pressure. Bradycardia occurs initially, followed by tachycardia. Prolonged administration of drugs like succinylcholine can result in cardiac arrhythmias and even cardiac arrest in some patients. Other patients may experience flushing, bronchospasm, and increased respiratory secretions.
