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Chapter: Clinical Anesthesiology: Clinical Pharmacology: Neuromuscular Blocking Agents

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Nondepolarizing Muscle Relaxants: Pancuronium

Pancuronium consists of a steroid ring on which two modified ACh molecules are positioned (a bisquater-nary relaxant).

PANCURONIUM

Physical Structure

Pancuronium consists of a steroid ring on which two modified ACh molecules are positioned (a bisquater-nary relaxant). The steroid ring serves as a “spacer” between the two quaternary amines. Pancuroniumresembles ACh enough to bind (but not activate) the nicotinic ACh receptor.

Metabolism & Excretion

Pancuronium is metabolized (deacetylated) by the liver to a limited degree. Its metabolic products have some neuromuscular blocking activity. Excretion is primarily renal (40%), although some of the drug is cleared by the bile (10%). Not surprisingly, elimina-tion of pancuronium is slowed and neuromuscular blockade is prolonged by renal failure. Patients with cirrhosis may require a larger initial dose due to an increased volume of distribution but have reduced maintenance requirements because of a decreased rate of plasma clearance.

Dosage

A dose of 0.08–0.12 mg/kg of pancuronium pro-vides adequate relaxation for intubation in 2–3 min. Intraoperative relaxation is achieved by administer-ing 0.04 mg/kg initially followed every 20–40 min by 0.01 mg/kg.Children may require moderately larger doses of pancuronium. Pancuronium is available as a solu-tion of 1 or 2 mg/mL and is stored at 2–8°C but may be stable for up to 6 months at normal room temperature.

Side Eects & Clinical Considerations

1.Hypertension and Tachycardia

Th ese  cardiovascular  effects  are  causedby the combination of vagal blockade andsympathetic stimulation. The latter is due to a combination of ganglionic stimulation, catechol-amine release from adrenergic nerve endings, and decreased catecholamine reuptake. Large bolus doses of pancuronium should be given with cau-tion to patients in whom an increased heart rate would be particularly detrimental (eg, coronary artery disease, hypertrophic cardiomyopathy, aor-tic stenosis).

B. Arrhythmias

Increased atrioventricular conduction and catechol-amine release increase the likelihood of ventricular arrhythmias in predisposed individuals. The com-bination of pancuronium, tricyclic antidepressants,and halothane has been reported to be particularly arrhythmogenic.

C. Allergic Reactions

Patients who are hypersensitive to bromides may exhibit allergic reactions to pancuronium (pan-curonium bromide).

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