Alfentanil-induced rigidity in newborn infants.

The authors evaluated whether alfentanil could be given before treatment procedures in critically ill mechanically ventilated neonates without adverse effects. Alfentanil (mean dose 11.7 micrograms/kg, range 9-15) was given intravenously to 20 mechanically ventilated critically ill newborn infants (mean birth weight 2510 g, range 1490-3990) during the first 3 days of life before treatment procedures. Heart rate, arterial blood pressure, transcutaneous partial pressure of O2, respiratory rate, and general activity were observed continuously from 10 min before the administration of alfentanil until 1 h after it. Plasma alfentanil concentrations were measured in 15 subjects. The pharmacokinetics of alfentanil varied greatly among the subjects. The hemodynamic changes were not clinically significant, and the most important side effect was muscle rigidity. Nine infants had mild or moderate rigidity, which had little or no effect on ventilation. Four infants had severe rigidity and jerking comparable to convulsive activity, transiently impairing ventilation and oxygenation for approximately 5-10 min. Increased inspired oxygen and increased pressure by manual ventilation were needed to prevent hypoxemia. Electroencephalographic recordings for three infants during alfentanil administration showed no evidence of increased seizure activity. We conclude that alfentanil should not be used for newborn infants without simultaneous muscle relaxation because of the danger of rigidity.