Background: The bactericidal efficacy of aminoglycosides is directly related to maximum serum concentrations, particularly the initial one. Therefore, several groups have recommended an aminoglycoside loading dose. Our goal was to develop a simplified dosage regimen for preterm infants which would result in therapeutic maximum serum concentrations early in the course of therapy. Methods: Open, noncomparative study during November 2000 to April 2001. The modified netilmicin-dosing protocol included a loading dose of 5 mg/kg in the first week of life, followed by a maintenance regimen of 3.5 mg/kg every 24 h. After the first week of life the corresponding doses were 6 (loading) and 5 mg/kg (maintenance). A peak level was measured 30 min after the second dose, and a trough level immediately before the third dose. Results: Thirty-five very low birthweight infants (mean birthweight 876 ± 170, range 536–1,385 g; mean gestational age 26 ± 1.8, range 23–30 weeks) who had 46 episodes of netilmicin treatment were included in the analysis. Mean netilmicin peak and trough values were 15.9 ± 3.7 (range 8.9–28.9) and 3.4 ± 1.3 (range 1.0–7.8) µmol/l, respectively. Ninety-one percent of all peak levels were within the targeted range of ≧10 µmol/l. Eleven trough values (24%) were ≧4 µmol/l: in 7 instances netilmicin was administered within the first week of life, 5 of these patients had concomitant indomethacin treatment. Only 1 of the 35 neonates had a rise in serum creatinine of ≧0.5 mg/dl during netilmicin therapy. Hearing evaluations were performed in 25 of the 29 surviving infants at discharge home, all of which gave normal results. Conclusions: The new netilmicin-dosing protocol yielded therapeutic maximum serum concentrations in 91% of cases after the second dose. However, a significant number of very low birthweight infants had elevated trough levels, particularly when netilmicin was administered in the first week of life with concomitant indomethacin treatment. We speculate that a longer interval between the loading dose and the first maintenance dose would result in fewer elevated trough levels with a similarly high number of therapeutic peak levels.

Keywords:
Netilmicin, Very low birthweight, Preterm infant, Loading dose, netilmicin
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© 2003 S. Karger AG, Basel
2003
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