Vecuronium is pancuronium minus a quaternary methyl group (a monoquaternary relaxant). This minor structural change beneficially alters side effects without affecting potency.
Vecuronium is metabolized to a small extent by the liver. It depends primarily on biliary excretion and secondarily (25%) on renal excretion. Although it is a satisfactory drug for patients with renal failure, its duration of action is somewhat prolonged. Vecuroni-um’s brief duration of action is explained by its shorter elimination half-life and more rapid clearance compared with pancuronium. Long-term administration of vecuronium to patients inintensive care units has resulted in prolonged neuro-muscular blockade (up to several days), possibly from accumulation of its active 3-hydroxy metabo-lite, changing drug clearance, and in some patients, leading to the development of a polyneuropathy. Risk factors seem to include female gender, renal failure, long-term or high-dose corticosteroid ther-apy, and sepsis. Thus, these patients must be closely monitored, and the dose of vecuronium carefully titrated. Long-term relaxant administration and the subsequent prolonged lack of ACh binding at the postsynaptic nicotinic ACh receptors may mimic a chronic denervation state and cause lasting receptor dysfunction and paralysis. Tolerance to nondepolar-izing muscle relaxants can also develop after long-term use. Fortunately, the use of unnecessary paralysis has greatly declined in critical care units.
Vecuronium is equipotent with pancuronium, and the intubating dose is 0.08–0.12 mg/kg. A dose of 0.04 mg/kg initially followed by increments of 0.01 mg/kg every 15–20 min provides intraop-erative relaxation. Alternatively, an infusion of 1–2 mcg/kg/min produces good maintenance of relaxation.
Age does not affect initial dose requirements, although subsequent doses are required less fre-quently in neonates and infants. Women seem to be approximately 30% more sensitive than men to vecuronium, as evidenced by a greater degree of blockade and longer duration of action (this has also been seen with pancuronium and rocuronium). The cause for this sensitivity may be related to gender-related differences in fat and muscle mass, protein binding, volume of distribu-tion, or metabolic activity. The duration of action of vecuronium may be further prolonged in post-partum patients due to alterations in hepatic blood flow or liver uptake.
Even at doses of 0.28 mg/kg, vecuronium is devoid of significant cardiovascular effects. Potentiation of opioid-induced bradycardia may be observed in some patients.
Although it is dependent on biliary excretion, the duration of action of vecuronium is usually not significantly prolonged in patients with cirrho-sis unless doses greater than 0.15 mg/kg are given. Vecuronium requirements are reduced during the anhepatic phase of liver transplantation.
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