Pharmacokinetics of Ampicillin in the Newborn Infant

Abstract

Ampicillin was injected into three newborn infants by continuous iv infusion at a constant rate, and levels in serum were studied during and after the infusion. The serum level initially rose rapidly, then rose more slowly and, .for practical purposes, reached a plateau after infusion for 6 hr (23.5 and 14.2 mg/ml, respectively, in two infants receiving ampicillin at a rate of 100 mg/kg per 24 hr and 7.8 mg/ml in an infant receiving 50 mg/kg per 24 hr). After the infusion was terminated at 6 hr, the level of ampicillin in serum fell exponentially; the biological half-lives were estimated to be 113, 166, and 123 min in the three infants (average, 134 min). The mean value for ..the rate constant of elimination during infusion among the three infants was 0.0138, which was greater than the mean value of 0.0053 found after cessation of the infusion.