Influence of infusion systems on pharmacokinetic parameters of tobramycin in newborn infants

The objective of this study was to assess the impact of intravenous infusion systems on the pharmacokinetic parameters of tobramycin in newborn infants. Thirty infants (gestational age 28-38 weeks; birth weight 0.8-3.5 kg; postnatal age 4-10 days) with presumed or proven gram-negative infection were studied. Tobramycin (2.5 mg/kg) was administered every 12 h over 0.5 h using two of four infusion systems at similar flow rates in a crossover fashion: syringe pump (auto syringe) versus either IVAC-y site, IVAC-flashball or IMED-y site. Blood samples were collected at 0.5 h after the end of infusion to determine the peak and prior to the dose to determine the trough serum concentration. Peak and time to achieve peak were different for IVAC-y versus auto syringe; the mean peak was 2 micrograms/ml higher and the time to achieve peak was 2 h shorter with auto syringe than IVAC (p less than 0.02). The apparent distribution volume of tobramycin was 1.02 +/- 0.68 with IVAC-y and 0.65 +/- 0.22 l/kg with auto syringe (p less than 0.05). The elimination half-life was 10.4 +/- 6.9 h with IVAC-y and 6.6 +/- 2.3 h with auto syringe (p less than 0.05); other systems and parameters were not different. These data demonstrate that the type of infusion system can markedly influence the estimation of certain pharmacokinetic parameters of tobramycin in newborn infants.