There is considerable variability and unpredictability in the duration of action of non-depolarizing muscle relaxants in the neonate. Continual organ maturation during the neonatal period leads to changes in metabolism and clearance of the non-depolarizing agents. Vecuronium is considered an intermediate-acting muscle relaxant in children and adults; however, in infants younger than 1 year of age, vecuronium is considered a long-acting muscle relaxant. In fact, its duration of action is approximately twice that observed in children because of liver immaturity. In addition, infants have less muscle mass. The recommended dose of vecuronium is 0.1 to 0.15 mg/kg with an onset time of 90 seconds and duration of action of 60 to 90 minutes in the neonate. The drug undergoes primarily hepatic metabolism with production of active metabolites that are dependent on renal excretion.
According a study of 49 children done by Kalli and Meretoja, duration in infants les than one year of age was 1.7 to 2.9 times longer than older patients.
I Kalli, O A Meretoja Duration of action of vecuronium in infants and children anaesthetized without potent inhalation agents. Acta Anaesthesiol Scand: 1989, 33(1);29-33